iptables-extensions拓展模块

iptables-extensions

Section: iptables 1.4.18 (8)
Updated:
Index

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NAME

iptables-extensions --- list of extensions in the standard iptables distribution  

SYNOPSIS

ip6tables [ -m name [ module-options...]][ -j target-name [ target-options...]

iptables [-m name [module-options...]][-jtarget-name [target-options...] 

MATCH EXTENSIONS

iptables can use extended packet matching moduleswith the -m or --match options, followed by the matching module name; after these, variousextra command line options become available, depending on the specificmodule. You can specify multiple extended match modules in one line,and you can use the -h or --helpoptions after the module has been specified to receive help specificto that module. The extended match modules are evaluated in the orderthey are specified in the rule.

If the -p or --protocol was specified and if and only if anunknown option is encountered, iptables will try load a match module of thesame name as the protocol, to try making the option available. 

addrtype

This module matches packets based on their address type.Address types are used within the kernel networking stack and categorizeaddresses into various groups. The exact definition of that group depends on the specific layer three protocol.

The following address types are possible:

UNSPEC

an unspecified address (i.e. 0.0.0.0)

UNICAST

an unicast address

LOCAL

a local address

BROADCAST

a broadcast address

ANYCAST

an anycast packet

MULTICAST

a multicast address

BLACKHOLE

a blackhole address

UNREACHABLE

an unreachable address

PROHIBIT

a prohibited address

THROW

FIXME

NAT

FIXME

XRESOLVE

[ !] --src-type type

Matches if the source address is of given type

[ !] --dst-type type

Matches if the destination address is of given type

--limit-iface-in

The address type checking can be limited to the interface the packet is comingin. This option is only valid in the PREROUTING, INPUTand FORWARDchains. It cannot be specified with the --limit-iface-outoption.

--limit-iface-out

The address type checking can be limited to the interface the packet is goingout. This option is only valid in the POSTROUTING, OUTPUTand FORWARDchains. It cannot be specified with the --limit-iface-inoption.

 

ah (IPv6-specific)

This module matches the parameters in Authentication header of IPsec packets.

[ !] --ahspi spi[ : spi]

Matches SPI.

[ !] --ahlen length

Total length of this header in octets.

--ahres

Matches if the reserved field is filled with zero.

 

ah (IPv4-specific)

This module matches the SPIs in Authentication header of IPsec packets.

[ !] --ahspi spi[ : spi]

 

cluster

Allows you to deploy gateway and back-end load-sharing clusters without theneed of load-balancers.

This match requires that all the nodes see the same packets. Thus, the clustermatch decides if this node has to handle a packet given the following options:

--cluster-total-nodes num

Set number of total nodes in cluster.

[ !] --cluster-local-node num

Set the local node number ID.

[ !] --cluster-local-nodemask mask

Set the local node number ID mask. You can use this option insteadof --cluster-local-node.

--cluster-hash-seed value

Set seed value of the Jenkins hash.

Example:

iptables -A PREROUTING -t mangle -i eth1 -m cluster--cluster-total-nodes 2 --cluster-local-node 1--cluster-hash-seed 0xdeadbeef-j MARK --set-mark 0xffff

iptables -A PREROUTING -t mangle -i eth2 -m cluster--cluster-total-nodes 2 --cluster-local-node 1--cluster-hash-seed 0xdeadbeef-j MARK --set-mark 0xffff

iptables -A PREROUTING -t mangle -i eth1-m mark ! --mark 0xffff -j DROP

iptables -A PREROUTING -t mangle -i eth2-m mark ! --mark 0xffff -j DROP

And the following commands to make all nodes see the same packets:

ip maddr add 01:00:5e:00:01:01 dev eth1

ip maddr add 01:00:5e:00:01:02 dev eth2

arptables -A OUTPUT -o eth1 --h-length 6-j mangle --mangle-mac-s 01:00:5e:00:01:01

arptables -A INPUT -i eth1 --h-length 6--destination-mac 01:00:5e:00:01:01-j mangle --mangle-mac-d 00:zz:yy:xx:5a:27

arptables -A OUTPUT -o eth2 --h-length 6-j mangle --mangle-mac-s 01:00:5e:00:01:02

arptables -A INPUT -i eth2 --h-length 6--destination-mac 01:00:5e:00:01:02-j mangle --mangle-mac-d 00:zz:yy:xx:5a:27

In the case of TCP connections, pickup facility has to be disabledto avoid marking TCP ACK packets coming in the reply direction asvalid.

echo 0 > /proc/sys/net/netfilter/nf_conntrack_tcp_loose

 

trigger

原帖由 falcon_13 于 2007-5-11 19:02 发表于 1楼  
1。我想请教下，如何用iptables 做port trigger啊？
2。我在网上看到一条命令：
iptables -A FORWARD -o eth0 -j TRIGGER --trigger-type out --trigger-proto udp --trigger-match 3000 --trigger-relate 68 ...

你好，触发是对两类数据包的操作 utput 的包 和 input 的包。第一条命令主要是建立一个触发链表，此链表记录一些触发信息，以便后续操作。如你写的命令，对 output包 如果是udp协议，且目的端口是3000的话，那么就触发开启6880-6890端口，建立触发链表，记录信息主要有原ip，协议，触发端口（即3000），打开端口（即6880-6890）。对 input 包的处理，则在第二条命令中实现  iptables -t nat -A PREROUTING -j TRIGGER --trigger-type dnat 此命令会查找触发链表，如果是udp包，且目的端口在6880-6890内的话，就会进行dnat操作，默认ip是链表记录的原ip。

当然，链表有一个定时器，如果提供接口的话，可以修改此定时器的value

点击打开链接

comment

Allows you to add comments (up to 256 characters) to any rule.

--comment comment

Example:

iptables -A INPUT -i eth1 -m comment --comment "my local LAN"

 

connbytes

Match by how many bytes or packets a connection (or one of the twoflows constituting the connection) has transferred so far, or byaverage bytes per packet.

The counters are 64-bit and are thus not expected to overflow ;)

The primary use is to detect long-lived downloads and mark them to bescheduled using a lower priority band in traffic control.

The transferred bytes per connection can also be viewed through`conntrack -L` and accessed via ctnetlink.

NOTE that for connections which have no accounting information, the match willalways return false. The "net.netfilter.nf_conntrack_acct" sysctl flag controlswhethernew connections will be byte/packet counted. Existing connectionflows will not be gaining/losing a/the accounting structure when be sysctl flagis flipped.

[ !] --connbytes from[ : to]

match packets from a connection whose packets/bytes/average packetsize is more than FROM and less than TO bytes/packets. if TO isomitted only FROM check is done. "!" is used to match packets notfalling in the range.

--connbytes-dir { original| reply| both}

which packets to consider

--connbytes-mode { packets| bytes| avgpkt}

whether to check the amount of packets, number of bytes transferred orthe average size (in bytes) of all packets received so far. Note thatwhen "both" is used together with "avgpkt", and data is going (mainly)only in one direction (for example HTTP), the average packet size willbe about half of the actual data packets.

Example:

iptables .. -m connbytes --connbytes 10000:100000 --connbytes-dir both --connbytes-mode bytes ...

 

connlimit

Allows you to restrict the number of parallel connections to a server perclient IP address (or client address block).

--connlimit-upto n

Match if the number of existing connections is below or equal n.

--connlimit-above n

Match if the number of existing connections is above n.

--connlimit-mask prefix_length

Group hosts using the prefix length. For IPv4, this must be a number between(including) 0 and 32. For IPv6, between 0 and 128. If not specified, themaximum prefix length for the applicable protocol is used.

--connlimit-saddr

Apply the limit onto the source group. This is the default if--connlimit-daddr is not specified.

--connlimit-daddr

Apply the limit onto the destination group.

Examples:

# allow 2 telnet connections per client host

iptables -A INPUT -p tcp --syn --dport 23 -m connlimit --connlimit-above 2 -j REJECT

# you can also match the other way around:

iptables -A INPUT -p tcp --syn --dport 23 -m connlimit --connlimit-upto 2 -j ACCEPT

# limit the number of parallel HTTP requests to 16 per class C sized source network (24 bit netmask)

iptables -p tcp --syn --dport 80 -m connlimit --connlimit-above 16--connlimit-mask 24 -j REJECT

# limit the number of parallel HTTP requests to 16 for the link local network

(ipv6)ip6tables -p tcp --syn --dport 80 -s fe80::/64 -m connlimit --connlimit-above16 --connlimit-mask 64 -j REJECT

# Limit the number of connections to a particular host:

ip6tables -p tcp --syn --dport 49152:65535 -d 2001:db8::1 -m connlimit--connlimit-above 100 -j REJECT

 

connmark

This module matches the netfilter mark field associated with a connection(which can be set using the CONNMARK target below).

[ !] --mark value[ / mask]

Matches packets in connections with the given mark value (if a mask isspecified, this is logically ANDed with the mark before the comparison).

 

conntrack

This module, when combined with connection tracking, allows access to theconnection tracking state for this packet/connection.

[ !] --ctstate statelist

statelist is a comma separated list of the connection states to match.Possible states are listed below.

[ !] --ctproto l4proto

Layer-4 protocol to match (by number or name)

[ !] --ctorigsrc address[ / mask]

[ !] --ctorigdst address[ / mask]

[ !] --ctreplsrc address[ / mask]

[ !] --ctrepldst address[ / mask]

Match against original/reply source/destination address

[ !] --ctorigsrcport port[ : port]

[ !] --ctorigdstport port[ : port]

[ !] --ctreplsrcport port[ : port]

[ !] --ctrepldstport port[ : port]

Match against original/reply source/destination port (TCP/UDP/etc.) or GRE key.Matching against port ranges is only supported in kernel versions above 2.6.38.

[ !] --ctstatus statelist

statuslist is a comma separated list of the connection statuses to match.Possible statuses are listed below.

[ !] --ctexpire time[ : time]

Match remaining lifetime in seconds against given value or range of values(inclusive)

--ctdir { ORIGINAL| REPLY}

Match packets that are flowing in the specified direction. If this flag is notspecified at all, matches packets in both directions.

States for --ctstate:

INVALID

The packet is associated with no known connection.

NEW

The packet has started a new connection, or otherwise associatedwith a connection which has not seen packets in both directions.

ESTABLISHED

The packet is associated with a connection which has seen packetsin both directions.

RELATED

The packet is starting a new connection, but is associated with anexisting connection, such as an FTP data transfer, or an ICMP error.

UNTRACKED

The packet is not tracked at all, which happens if you explicitly untrack itby using -j CT --notrack in the raw table.

SNAT

A virtual state, matching if the original source address differs from the replydestination.

DNAT

A virtual state, matching if the original destination differs from the replysource.

Statuses for --ctstatus:

NONE

None of the below.

EXPECTED

This is an expected connection (i.e. a conntrack helper set it up).

SEEN_REPLY

Conntrack has seen packets in both directions.

ASSURED

Conntrack entry should never be early-expired.

CONFIRMED

Connection is confirmed: originating packet has left box.

 

cpu

[ !] --cpu number

Match cpu handling this packet. cpus are numbered from 0 to NR_CPUS-1Can be used in combination with RPS (Remote Packet Steering) ormultiqueue NICs to spread network traffic on different queues.

Example:

iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 0 -j REDIRECT --to-port 8080

iptables -t nat -A PREROUTING -p tcp --dport 80 -m cpu --cpu 1 -j REDIRECT --to-port 8081

Available since Linux 2.6.36. 

dccp

[ !] --source-port, --sport port[ : port]

[ !] --destination-port, --dport port[ : port]

[ !] --dccp-types mask

Match when the DCCP packet type is one of 'mask'. 'mask' is a comma-separatedlist of packet types. Packet types are: REQUEST RESPONSE DATA ACK DATAACK CLOSEREQ CLOSE RESET SYNC SYNCACK INVALID.

[ !] --dccp-option number

Match if DCCP option set.

 

devgroup

Match device group of a packets incoming/outgoing interface.

[ !] --src-group name

Match device group of incoming device

[ !] --dst-group name

Match device group of outgoing device

 

dscp

This module matches the 6 bit DSCP field within the TOS field in theIP header. DSCP has superseded TOS within the IETF.

[ !] --dscp value

Match against a numeric (decimal or hex) value [0-63].

[ !] --dscp-class class

Match the DiffServ class. This value may be any of theBE, EF, AFxx or CSx classes. It will then be convertedinto its according numeric value.

 

dst (IPv6-specific)

This module matches the parameters in Destination Options header

[ !] --dst-len length

Total length of this header in octets.

--dst-opts type[ : length][ , type[ : length]...]

numeric type of option and the length of the option data in octets.

 

ecn

This allows you to match the ECN bits of the IPv4/IPv6 and TCP header. ECN is the Explicit Congestion Notification mechanism as specified in RFC3168

[ !] --ecn-tcp-cwr

This matches if the TCP ECN CWR (Congestion Window Received) bit is set.

[ !] --ecn-tcp-ece

This matches if the TCP ECN ECE (ECN Echo) bit is set.

[ !] --ecn-ip-ect num

This matches a particular IPv4/IPv6 ECT (ECN-Capable Transport). You have to specifya number between `0' and `3'.

 

esp

This module matches the SPIs in ESP header of IPsec packets.

[ !] --espspi spi[ : spi]

 

eui64 (IPv6-specific)

This module matches the EUI-64 part of a stateless autoconfigured IPv6 address.It compares the EUI-64 derived from the source MAC address in Ethernet framewith the lower 64 bits of the IPv6 source address. But "Universal/Local"bit is not compared. This module doesn't match other link layer frame, andis only valid in the PREROUTING, INPUTand FORWARDchains.  

frag (IPv6-specific)

This module matches the parameters in Fragment header.

[ !] --fragid id[ : id]

Matches the given Identification or range of it.

[ !] --fraglen length

This option cannot be used with kernel version 2.6.10 or later. The length ofFragment header is static and this option doesn't make sense.

--fragres

Matches if the reserved fields are filled with zero.

--fragfirst

Matches on the first fragment.

--fragmore

Matches if there are more fragments.

--fraglast

Matches if this is the last fragment.

 

hashlimit

hashlimit uses hash buckets to express a rate limiting match (like the limit match) for a group of connections using a single iptablesrule. Grouping can be done per-hostgroup (source and/or destination address)and/or per-port. It gives you the ability to express " N packets per timequantum per group" or " N bytes per seconds" (see below for some examples).

A hash limit option (--hashlimit-upto, --hashlimit-above) and--hashlimit-name are required.

--hashlimit-upto amount[ /second| /minute| /hour| /day]

Match if the rate is below or equal to amount/quantum. It is specified either asa number, with an optional time quantum suffix (the default is 3/hour), or as amountb/second (number of bytes per second).

--hashlimit-above amount[ /second| /minute| /hour| /day]

Match if the rate is above amount/quantum.

--hashlimit-burst amount

Maximum initial number of packets to match: this number gets recharged by oneevery time the limit specified above is not reached, up to this number; thedefault is 5. When byte-based rate matching is requested, this option specifiesthe amount of bytes that can exceed the given rate. This option should be usedwith caution -- if the entry expires, the burst value is reset too.

--hashlimit-mode { srcip| srcport| dstip| dstport} ,...

A comma-separated list of objects to take into consideration. If no--hashlimit-mode option is given, hashlimit acts like limit, but at theexpensive of doing the hash housekeeping.

--hashlimit-srcmask prefix

When --hashlimit-mode srcip is used, all source addresses encountered will begrouped according to the given prefix length and the so-created subnet will besubject to hashlimit. prefix must be between (inclusive) 0 and 32. Notethat --hashlimit-srcmask 0 is basically doing the same thing as not specifyingsrcip for --hashlimit-mode, but is technically more expensive.

--hashlimit-dstmask prefix

Like --hashlimit-srcmask, but for destination addresses.

--hashlimit-name foo

The name for the /proc/net/ipt_hashlimit/foo entry.

--hashlimit-htable-size buckets

The number of buckets of the hash table

--hashlimit-htable-max entries

Maximum entries in the hash.

--hashlimit-htable-expire msec

After how many milliseconds do hash entries expire.

--hashlimit-htable-gcinterval msec

How many milliseconds between garbage collection intervals.

Examples:

matching on source host

"1000 packets per second for every host in 192.168.0.0/16" =>-s 192.168.0.0/16 --hashlimit-mode srcip --hashlimit-upto 1000/sec

matching on source port

"100 packets per second for every service of 192.168.1.1" =>-s 192.168.1.1 --hashlimit-mode srcport --hashlimit-upto 100/sec

matching on subnet

"10000 packets per minute for every /28 subnet (groups of 8 addresses)in 10.0.0.0/8" =>-s 10.0.0.8 --hashlimit-mask 28 --hashlimit-upto 10000/min

matching bytes per second

"flows exceeding 512kbyte/s" =>--hashlimit-mode srcip,dstip,srcport,dstport --hashlimit-above 512kb/s

matching bytes per second

"hosts that exceed 512kbyte/s, but permit up to 1Megabytes without matching"--hashlimit-mode dstip --hashlimit-above 512kb/s --hashlimit-burst 1mb

 

hbh (IPv6-specific)

This module matches the parameters in Hop-by-Hop Options header

[ !] --hbh-len length

Total length of this header in octets.

--hbh-opts type[ : length][ , type[ : length]...]

numeric type of option and the length of the option data in octets.

 

helper

This module matches packets related to a specific conntrack-helper.

[ !] --helper string

Matches packets related to the specified conntrack-helper.

string can be "ftp" for packets related to a ftp-session on default port.For other ports append -portnr to the value, ie. "ftp-2121".

Same rules apply for other conntrack-helpers.

 

hl (IPv6-specific)

This module matches the Hop Limit field in the IPv6 header.

[ !] --hl-eq value

Matches if Hop Limit equals value.

--hl-lt value

Matches if Hop Limit is less than value.

--hl-gt value

Matches if Hop Limit is greater than value.

 

icmp (IPv4-specific)

This extension can be used if `--protocol icmp' is specified. Itprovides the following option:

[ !] --icmp-type { type[ / code]| typename}

This allows specification of the ICMP type, which can be a numericICMP type, type/code pair, or one of the ICMP type names shown by the command

 iptables -p icmp -h

 

icmp6 (IPv6-specific)

This extension can be used if `--protocol ipv6-icmp' or `--protocol icmpv6' isspecified. It provides the following option:

[ !] --icmpv6-type type[ / code]| typename

This allows specification of the ICMPv6 type, which can be a numericICMPv6 type, typeand code,or one of the ICMPv6 type names shown by the command

 ip6tables -p ipv6-icmp -h

 

iprange

This matches on a given arbitrary range of IP addresses.

[ !] --src-range from[ - to]

Match source IP in the specified range.

[ !] --dst-range from[ - to]

Match destination IP in the specified range.

 

ipv6header (IPv6-specific)

This module matches IPv6 extension headers and/or upper layer header.

--soft

Matches if the packet includes any of the headers specified with --header.

[ !] --header header[ , header...]

Matches the packet which EXACTLY includes all specified headers. The headersencapsulated with ESP header are out of scope.Possible header types can be:

hop| hop-by-hop

Hop-by-Hop Options header

dst

Destination Options header

route

Routing header

frag

Fragment header

auth

Authentication header

esp

Encapsulating Security Payload header

none

No Next header which matches 59 in the 'Next Header field' of IPv6 header orany IPv6 extension headers

proto

which matches any upper layer protocol header. A protocol name from/etc/protocols and numeric value also allowed. The number 255 is equivalent to proto.

 

ipvs

Match IPVS connection properties.

[ !] --ipvs

packet belongs to an IPVS connection

Any of the following options implies --ipvs (even negated)

[ !] --vproto protocol

VIP protocol to match; by number or name, e.g. "tcp"

[ !] --vaddr address[ / mask]

VIP address to match

[ !] --vport port

VIP port to match; by number or name, e.g. "http"

--vdir { ORIGINAL| REPLY}

flow direction of packet

[ !] --vmethod { GATE| IPIP| MASQ}

IPVS forwarding method used

[ !] --vportctl port

VIP port of the controlling connection to match, e.g. 21 for FTP

 

length

This module matches the length of the layer-3 payload (e.g. layer-4 packet)of a packet against a specific valueor range of values.

[ !] --length length[ : length]

 

limit

This module matches at a limited rate using a token bucket filter.A rule using this extension will match until this limit is reached.It can be used in combination with the LOGtarget to give limited logging, for example.

xt_limit has no negation support - you will have to use -m hashlimit !--hashlimitrate in this case whilst omitting --hashlimit-mode.

--limit rate[ /second| /minute| /hour| /day]

Maximum average matching rate: specified as a number, with an optional`/second', `/minute', `/hour', or `/day' suffix; the default is3/hour.

--limit-burst number

Maximum initial number of packets to match: this number getsrecharged by one every time the limit specified above is not reached,up to this number; the default is 5.

 

mac

[ !] --mac-source address

Match source MAC address. It must be of the form XX:XX:XX:XX:XX:XX.Note that this only makes sense for packets coming from an Ethernet deviceand entering the PREROUTING, FORWARDor INPUTchains.

 

mark

This module matches the netfilter mark field associated with a packet(which can be set using the MARKtarget below).

[ !] --mark value[ / mask]

Matches packets with the given unsigned mark value (if a mask isspecified, this is logically ANDed with the mask before thecomparison).

 

mh (IPv6-specific)

This extension is loaded if `--protocol ipv6-mh' or `--protocol mh' isspecified. It provides the following option:

[ !] --mh-type type[ : type]

This allows specification of the Mobility Header(MH) type, which can bea numeric MH type, typeor one of the MH type names shown by the command

 ip6tables -p mh -h

 

multiport

This module matches a set of source or destination ports. Up to 15ports can be specified. A port range (port:port) counts as twoports. It can only be used in conjunction with -p tcpor -p udp.

[ !] --source-ports, --sports port[ , port| , port : port]...

Match if the source port is one of the given ports. The flag --sportsis a convenient alias for this option. Multiple ports or port ranges areseparated using a comma, and a port range is specified using a colon. 53,1024:65535 would therefore match ports 53 and all from 1024 through65535.

[ !] --destination-ports, --dports port[ , port| , port : port]...

Match if the destination port is one of the given ports. The flag --dportsis a convenient alias for this option.

[ !] --ports port[ , port| , port : port]...

Match if either the source or destination ports are equal to one ofthe given ports.

 

nfacct

The nfacct match provides the extended accounting infrastructure for iptables.You have to use this match together with the standalone user-space utility nfacct.

The only option available for this match is the following:

--nfacct-name name

This allows you to specify the existing object name that will be use foraccounting the traffic that this rule-set is matching.

To use this extension, you have to create an accounting object:

nfacct add http-traffic

Then, you have to attach it to the accounting object via iptables:

iptables -I INPUT -p tcp --sport 80 -m nfacct --nfacct-name http-traffic

iptables -I OUTPUT -p tcp --dport 80 -m nfacct --nfacct-name http-traffic

Then, you can check for the amount of traffic that the rules match:

nfacct get http-traffic

{ pkts = 00000000000000000156, bytes = 00000000000000151786 } = http-traffic;

You can obtainnfacctfrom http://www.netfilter.org or, alternatively, from the git.netfilter.orgrepository. 

osf

The osf module does passive operating system fingerprinting. This modulescompares some data (Window Size, MSS, options and their order, TTL, DF,and others) from packets with the SYN bit set.

[ !] --genre string

Match an operating system genre by using a passive fingerprinting.

--ttl level

Do additional TTL checks on the packet to determine the operating system. level can be one of the following values:

•

0 - True IP address and fingerprint TTL comparison. This generally works forLANs.

•

1 - Check if the IP header's TTL is less than the fingerprint one. Works forglobally-routable addresses.

•

2 - Do not compare the TTL at all.

--log level

Log determined genres into dmesg even if they do not match the desired one. level can be one of the following values:

•

0 - Log all matched or unknown signatures

•

1 - Log only the first one

•

2 - Log all known matched signatures

You may find something like this in syslog:

Windows [2000:SP3:Windows XP Pro SP1, 2000 SP3]: 11.22.33.55:4024 ->11.22.33.44:139 hops=3 Linux [2.5-2.6:] : 1.2.3.4:42624 -> 1.2.3.5:22 hops=4

OS fingerprints are loadable using the nfnl_osf program. To loadfingerprints from a file, use:

nfnl_osf -f /usr/share/xtables/pf.os

To remove them again,

nfnl_osf -f /usr/share/xtables/pf.os -d

The fingerprint database can be downlaoded fromhttp://www.openbsd.org/cgi-bin/cvsweb/src/etc/pf.os . 

owner

This module attempts to match various characteristics of the packet creator,for locally generated packets. This match is only valid in the OUTPUT andPOSTROUTING chains. Forwarded packets do not have any socket associated withthem. Packets from kernel threads do have a socket, but usually no owner.

[ !] --uid-owner username

[ !] --uid-owner userid[ - userid]

Matches if the packet socket's file structure (if it has one) is owned by thegiven user. You may also specify a numerical UID, or an UID range.

[ !] --gid-owner groupname

[ !] --gid-owner groupid[ - groupid]

Matches if the packet socket's file structure is owned by the given group.You may also specify a numerical GID, or a GID range.

[ !] --socket-exists

Matches if the packet is associated with a socket.

 

physdev

This module matches on the bridge port input and output devices enslavedto a bridge device. This module is a part of the infrastructure that enablesa transparent bridging IP firewall and is only useful for kernel versionsabove version 2.5.44.

[ !] --physdev-in name

Name of a bridge port via which a packet is received (only forpackets entering the INPUT, FORWARDand PREROUTINGchains). If the interface name ends in a "+", then anyinterface which begins with this name will match. If the packet didn't arrivethrough a bridge device, this packet won't match this option, unless '!' is used.

[ !] --physdev-out name

Name of a bridge port via which a packet is going to be sent (for packetsentering the FORWARD, OUTPUTand POSTROUTINGchains). If the interface name ends in a "+", then anyinterface which begins with this name will match. Note that in the nat and mangleOUTPUTchains one cannot match on the bridge output port, however one can in the filter OUTPUTchain. If the packet won't leave by a bridge device or if it is yet unknown whatthe output device will be, then the packet won't match this option,unless '!' is used.

[ !] --physdev-is-in

Matches if the packet has entered through a bridge interface.

[ !] --physdev-is-out

Matches if the packet will leave through a bridge interface.

[ !] --physdev-is-bridged

Matches if the packet is being bridged and therefore is not being routed.This is only useful in the FORWARD and POSTROUTING chains.

 

pkttype

This module matches the link-layer packet type.

[ !] --pkt-type { unicast| broadcast| multicast}

 

policy

This modules matches the policy used by IPsec for handling a packet.

--dir { in| out}

Used to select whether to match the policy used for decapsulation or thepolicy that will be used for encapsulation. inis valid in the PREROUTING, INPUT and FORWARDchains, outis valid in the POSTROUTING, OUTPUT and FORWARDchains.

--pol { none| ipsec}

Matches if the packet is subject to IPsec processing. --pol nonecannot be combined with --strict.

--strict

Selects whether to match the exact policy or match if any rule ofthe policy matches the given policy.

For each policy element that is to be described, one can use one or more ofthe following options. When--strict is in effect, at least one must beused per element.

[ !] --reqid id

Matches the reqid of the policy rule. The reqid can be specified with setkeyusing unique:idas level.

[ !] --spi spi

Matches the SPI of the SA.

[ !] --proto { ah| esp| ipcomp}

Matches the encapsulation protocol.

[ !] --mode { tunnel| transport}

Matches the encapsulation mode.

[ !] --tunnel-src addr[ / mask]

Matches the source end-point address of a tunnel mode SA.Only valid with --mode tunnel.

[ !] --tunnel-dst addr[ / mask]

Matches the destination end-point address of a tunnel mode SA.Only valid with --mode tunnel.

--next

Start the next element in the policy specification. Can only be used with --strict.

 

quota

Implements network quotas by decrementing a byte counter with eachpacket. The condition matches until the byte counter reaches zero. Behavioris reversed with negation (i.e. the condition does not match until thebyte counter reaches zero).

[ !] --quota bytes

The quota in bytes.

 

rateest

The rate estimator can match on estimated rates as collected by the RATEESTtarget. It supports matching on absolute bps/pps values, comparing two rateestimators and matching on the difference between two rate estimators.

For a better understanding of the available options, these are all possiblecombinations:

•

rateest operator rateest-bps

•

rateest operator rateest-pps

•

( rateest minus rateest-bps1) operator rateest-bps2

•

( rateest minus rateest-pps1) operator rateest-pps2

•

rateest1 operator rateest2 rateest-bps(without rate!)

•

rateest1 operator rateest2 rateest-pps(without rate!)

•

( rateest1 minus rateest-bps1) operator( rateest2 minus rateest-bps2)

•

( rateest1 minus rateest-pps1) operator( rateest2 minus rateest-pps2)

--rateest-delta

For each estimator (either absolute or relative mode), calculate the differencebetween the estimator-determined flow rate and the static value chosen with theBPS/PPS options. If the flow rate is higher than the specified BPS/PPS, 0 willbe used instead of a negative value. In other words, "max(0, rateest#_rate -rateest#_bps)" is used.

[ !] --rateest-lt

Match if rate is less than given rate/estimator.

[ !] --rateest-gt

Match if rate is greater than given rate/estimator.

[ !] --rateest-eq

Match if rate is equal to given rate/estimator.

In the so-called "absolute mode", only one rate estimator is used and comparedagainst a static value, while in "relative mode", two rate estimators arecompared against another.

--rateest name

Name of the one rate estimator for absolute mode.

--rateest1 name

--rateest2 name

The names of the two rate estimators for relative mode.

--rateest-bps [ value]

--rateest-pps [ value]

--rateest-bps1 [ value]

--rateest-bps2 [ value]

--rateest-pps1 [ value]

--rateest-pps2 [ value]

Compare the estimator(s) by bytes or packets per second, and compare againstthe chosen value. See the above bullet list for which option is to be used inwhich case. A unit suffix may be used - available ones are: bit, [kmgt]bit,[KMGT]ibit, Bps, [KMGT]Bps, [KMGT]iBps.

Example: This is what can be used to route outgoing data connections from anFTP server over two lines based on the available bandwidth at the time the dataconnection was started:

# Estimate outgoing rates

iptables -t mangle -A POSTROUTING -o eth0 -j RATEEST --rateest-name eth0--rateest-interval 250ms --rateest-ewma 0.5s

iptables -t mangle -A POSTROUTING -o ppp0 -j RATEEST --rateest-name ppp0--rateest-interval 250ms --rateest-ewma 0.5s

# Mark based on available bandwidth

iptables -t mangle -A balance -m conntrack --ctstate NEW -m helper --helper ftp-m rateest --rateest-delta --rateest1 eth0 --rateest-bps1 2.5mbit --rateest-gt--rateest2 ppp0 --rateest-bps2 2mbit -j CONNMARK --set-mark 1

iptables -t mangle -A balance -m conntrack --ctstate NEW -m helper --helper ftp-m rateest --rateest-delta --rateest1 ppp0 --rateest-bps1 2mbit --rateest-gt--rateest2 eth0 --rateest-bps2 2.5mbit -j CONNMARK --set-mark 2

iptables -t mangle -A balance -j CONNMARK --restore-mark 

realm (IPv4-specific)

This matches the routing realm. Routing realms are used in complex routingsetups involving dynamic routing protocols like BGP.

[ !] --realm value[ / mask]

Matches a given realm number (and optionally mask). If not a number, valuecan be a named realm from /etc/iproute2/rt_realms (mask can not be used inthat case).

 

recent

Allows you to dynamically create a list of IP addresses and then match againstthat list in a few different ways.

For example, you can create a "badguy" list out of people attempting to connectto port 139 on your firewall and then DROP all future packets from them withoutconsidering them.

--set, --rcheck, --update and--remove aremutually exclusive.

--name name

Specify the list to use for the commands. If no name is given then DEFAULT will be used.

[ !] --set

This will add the source address of the packet to the list. If the sourceaddress is already in the list, this will update the existing entry. This willalways return success (or failure if ! is passed in).

--rsource

Match/save the source address of each packet in the recent list table. Thisis the default.

--rdest

Match/save the destination address of each packet in the recent list table.

--masknetmask

Netmask that will be applied to this recent list.

[ !] --rcheck

Check if the source address of the packet is currently in the list.

[ !] --update

Like --rcheck, except it will update the "last seen" timestamp if itmatches.

[ !] --remove

Check if the source address of the packet is currently in the list and if sothat address will be removed from the list and the rule will return true. Ifthe address is not found, false is returned.

--seconds seconds

This option must be used in conjunction with one of --rcheck or --update. When used, this will narrow the match to only happen when theaddress is in the list and was seen within the last given number of seconds.

--reap

This option can only be used in conjunction with --seconds.When used, this will cause entries older than the last given number of secondsto be purged.

--hitcount hits

This option must be used in conjunction with one of --rcheck or --update. When used, this will narrow the match to only happen when theaddress is in the list and packets had been received greater than or equal tothe given value. This option may be used along with --seconds to createan even narrower match requiring a certain number of hits within a specifictime frame. The maximum value for the hitcount parameter is given by the"ip_pkt_list_tot" parameter of the xt_recent kernel module. Exceeding thisvalue on the command line will cause the rule to be rejected.

--rttl

This option may only be used in conjunction with one of --rcheck or --update. When used, this will narrow the match to only happen when theaddress is in the list and the TTL of the current packet matches that of thepacket which hit the --set rule. This may be useful if you have problemswith people faking their source address in order to DoS you via this module bydisallowing others access to your site by sending bogus packets to you.

Examples:

iptables -A FORWARD -m recent --name badguy --rcheck --seconds 60 -j DROP

iptables -A FORWARD -p tcp -i eth0 --dport 139 -m recent --name badguy --set -j DROP

Steve's ipt_recent website (http://snowman.net/projects/ipt_recent/) also hassome examples of usage.

/proc/net/xt_recent/* are the current lists of addresses and informationabout each entry of each list.

Each file in /proc/net/xt_recent/ can be read from to see the currentlist or written two using the following commands to modify the list:

echo + addr >/proc/net/xt_recent/DEFAULT

to add addr to the DEFAULT list

echo - addr >/proc/net/xt_recent/DEFAULT

to remove addr from the DEFAULT list

echo / >/proc/net/xt_recent/DEFAULT

to flush the DEFAULT list (remove all entries).

The module itself accepts parameters, defaults shown:

ip_list_tot= 100

Number of addresses remembered per table.

ip_pkt_list_tot= 20

Number of packets per address remembered.

ip_list_hash_size= 0

Hash table size. 0 means to calculate it based on ip_list_tot, default: 512.

ip_list_perms= 0644

Permissions for /proc/net/xt_recent/* files.

ip_list_uid= 0

Numerical UID for ownership of /proc/net/xt_recent/* files.

ip_list_gid= 0

Numerical GID for ownership of /proc/net/xt_recent/* files.

 

rpfilter

Performs a reverse path filter test on a packet.If a reply to the packet would be sent via the same interfacethat the packet arrived on, the packet will match.Note that, unlike the in-kernel rp_filter, packets protectedby IPSec are not treated specially. Combine this match withthe policy match if you want this.Also, packets arriving via the loopback interface are always permitted.This match can only be used in the PREROUTING chain of the raw or mangle table.

--loose

Used to specifiy that the reverse path filter test should matcheven if the selected output device is not the expected one.

--validmark

Also use the packets' nfmark value when performing the reverse path route lookup.

--accept-local

This will permit packets arriving from the network with a source address that is alsoassigned to the local machine.

--invert

This will invert the sense of the match. Instead of matching packets that passed thereverse path filter test, match those that have failed it.

Example to log and drop packets failing the reverse path filter test:

iptables -t raw -N RPFILTER

iptables -t raw -A RPFILTER -m rpfilter -j RETURN

iptables -t raw -A RPFILTER -m limit --limit 10/minute -j NFLOG --nflog-prefix "rpfilter drop"

iptables -t raw -A RPFILTER -j DROP

iptables -t raw -A PREROUTING -j RPFILTER

Example to drop failed packets, without logging:

iptables -t raw -A RPFILTER -m rpfilter --invert -j DROP 

rt (IPv6-specific)

Match on IPv6 routing header

[ !] --rt-type type

Match the type (numeric).

[ !] --rt-segsleft num[ : num]

Match the `segments left' field (range).

[ !] --rt-len length

Match the length of this header.

--rt-0-res

Match the reserved field, too (type=0)

--rt-0-addrs addr[ , addr...]

Match type=0 addresses (list).

--rt-0-not-strict

List of type=0 addresses is not a strict list.

 

sctp

[ !] --source-port, --sport port[ : port]

[ !] --destination-port, --dport port[ : port]

[ !] --chunk-types { all| any| only} chunktype[ : flags] [...]

The flag letter in upper case indicates that the flag is to match if set,in the lower case indicates to match if unset.

Chunk types: DATA INIT INIT_ACK SACK HEARTBEAT HEARTBEAT_ACK ABORT SHUTDOWN SHUTDOWN_ACK ERROR COOKIE_ECHO COOKIE_ACK ECN_ECNE ECN_CWR SHUTDOWN_COMPLETE ASCONF ASCONF_ACK FORWARD_TSN

chunk type available flags
DATA I U B E i u b e
ABORT T t
SHUTDOWN_COMPLETE T t

(lowercase means flag should be "off", uppercase means "on")

Examples:

iptables -A INPUT -p sctp --dport 80 -j DROP

iptables -A INPUT -p sctp --chunk-types any DATA,INIT -j DROP

iptables -A INPUT -p sctp --chunk-types any DATA:Be -j ACCEPT 

set

This module matches IP sets which can be defined by ipset(8).

[ !] --match-set setname flag[ , flag]...

where flags are the comma separated list of srcand/or dstspecifications and there can be no more than six of them. Hence the command

 iptables -A FORWARD -m set --match-set test src,dst

will match packets, for which (if the set type is ipportmap) the sourceaddress and destination port pair can be found in the specified set. Ifthe set type of the specified set is single dimension (for example ipmap),then the command will match packets for which the source address can befound in the specified set.

--return-nomatch

If the --return-nomatch option is specified and the set typesupports the nomatch flag, then the matching is reversed: a matchwith an element flagged with nomatch returns true, while amatch with a plain element returns false.

! --update-counters

If the --update-counters flag is negated, then the packet andbyte counters of the matching element in the set won't be updated. Defaultthe packet and byte counters are updated.

! --update-subcounters

If the --update-subcounters flag is negated, then the packet andbyte counters of the matching element in the member set of a list type ofset won't be updated. Default the packet and byte counters are updated.

[ !] --packets-eq value

If the packet is matched an element in the set, match only if thepacket counter of the element matches the given value too.

--packets-lt value

If the packet is matched an element in the set, match only if thepacket counter of the element is less than the given value as well.

--packets-gt value

If the packet is matched an element in the set, match only if thepacket counter of the element is greater than the given value as well.

[ !] -bytes-eq value

If the packet is matched an element in the set, match only if thebyte counter of the element matches the given value too.

--bytes-lt value

If the packet is matched an element in the set, match only if thebyte counter of the element is less than the given value as well.

--bytes-gt value

If the packet is matched an element in the set, match only if thebyte counter of the element is greater than the given value as well.

The packet and byte counters related options and flags are ignoredwhen the set was defined without counter support.

The option --match-set can be replaced by --set if that does not * with an option of other extensions.

Use of -m set requires that ipset kernel support is provided, which, forstandard kernels, is the case since Linux 2.6.39. 

socket

This matches if an open socket can be found by doing a socket lookup on thepacket.

--transparent

Ignore non-transparent sockets.

 

state

The "state" extension is a subset of the "conntrack" module."state" allows access to the connection tracking state for this packet.

[ !] --state state

Where state is a comma separated list of the connection states to match. Only asubset of the states unterstood by "conntrack" are recognized: INVALID, ESTABLISHED, NEW, RELATED or UNTRACKED. For theirdescription, see the "conntrack" heading in this manpage.

 

statistic

This module matches packets based on some statistic condition.It supports two distinct modes settable with the --modeoption.

Supported options:

--mode mode

Set the matching mode of the matching rule, supported modes are randomand nth.

[ !] --probability p

Set the probability for a packet to be randomly matched. It only works with the random mode. p must be within 0.0 and 1.0. The supportedgranularity is in 1/2147483648th increments.

[ !] --every n

Match one packet every nth packet. It works only with the nthmode (see also the --packetoption).

--packet p

Set the initial counter value (0 <= p <= n-1, default 0) for the nth mode.

 

string

This modules matches a given string by using some pattern matching strategy. It requires a linux kernel >= 2.6.14.

--algo { bm| kmp}

Select the pattern matching strategy. (bm = Boyer-Moore, kmp = Knuth-Pratt-Morris)

--from offset

Set the offset from which it starts looking for any matching. If not passed, default is 0.

--to offset

Set the offset up to which should be scanned. That is, byte offset-1(counting from 0) is the last one that is scanned.If not passed, default is the packet size.

[ !] --string pattern

Matches the given pattern.

[ !] --hex-string pattern

Matches the given pattern in hex notation.

 

tcp

These extensions can be used if `--protocol tcp' is specified. Itprovides the following options:

[ !] --source-port, --sport port[ : port]

Source port or port range specification. This can either be a servicename or a port number. An inclusive range can also be specified,using the format first : last.If the first port is omitted, "0" is assumed; if the last is omitted,"65535" is assumed.If the first port is greater than the second one they will be swapped.The flag --sportis a convenient alias for this option.

[ !] --destination-port, --dport port[ : port]

Destination port or port range specification. The flag --dportis a convenient alias for this option.

[ !] --tcp-flags mask comp

Match when the TCP flags are as specified. The first argument mask is theflags which we should examine, written as a comma-separated list, andthe second argument comp is a comma-separated list of flags which must beset. Flags are: SYN ACK FIN RST URG PSH ALL NONE.Hence the command

 iptables -A FORWARD -p tcp --tcp-flags SYN,ACK,FIN,RST SYN

will only match packets with the SYN flag set, and the ACK, FIN andRST flags unset.

[ !] --syn

Only match TCP packets with the SYN bit set and the ACK,RST and FIN bitscleared. Such packets are used to request TCP connection initiation;for example, blocking such packets coming in an interface will preventincoming TCP connections, but outgoing TCP connections will beunaffected.It is equivalent to --tcp-flags SYN,RST,ACK,FIN SYN.If the "!" flag precedes the "--syn", the sense of theoption is inverted.

[ !] --tcp-option number

Match if TCP option set.

 

tcpmss

This matches the TCP MSS (maximum segment size) field of the TCP header. You can only use this on TCP SYN or SYN/ACK packets, since the MSS is only negotiated during the TCP handshake at connection startup time.

[ !] --mss value[ : value]

Match a given TCP MSS value or range.

 

time

This matches if the packet arrival time/date is within a given range. Alloptions are optional, but are ANDed when specified. All times are interpretedas UTC by default.

--datestart YYYY[ - MM[ - DD[ T hh[ : mm[ : ss]]]]]

--datestop YYYY[ - MM[ - DD[ T hh[ : mm[ : ss]]]]]

Only match during the given time, which must be in ISO 8601 "T" notation.The possible time range is 1970-01-01T00:00:00 to 2038-01-19T04:17:07.

If --datestart or --datestop are not specified, it will default to 1970-01-01and 2038-01-19, respectively.

--timestart hh : mm[ : ss]

--timestop hh : mm[ : ss]

Only match during the given daytime. The possible time range is 00:00:00 to23:59:59. Leading zeroes are allowed (e.g. "06:03") and correctly interpretedas base-10.

[ !] --monthdays day[ , day...]

Only match on the given days of the month. Possible values are 1to 31. Note that specifying 31 will of course not matchon months which do not have a 31st day; the same goes for 28- or 29-dayFebruary.

[ !] --weekdays day[ , day...]

Only match on the given weekdays. Possible values are Mon, Tue, Wed, Thu, Fri, Sat, Sun, or values from 1to 7, respectively. You may also use two-character variants ( Mo, Tu, etc.).

--contiguous

When --timestop is smaller than --timestart value, matchthis as a single time period instead distinct intervals. See EXAMPLES.

--kerneltz

Use the kernel timezone instead of UTC to determine whether a packet meets thetime regulations.

About kernel timezones: Linux keeps the system time in UTC, and always does so.On boot, system time is initialized from a referential time source. Where thistime source has no timezone information, such as the x86 CMOS RTC, UTC will beassumed. If the time source is however not in UTC, userspace should provide thecorrect system time and timezone to the kernel once it has the information.

Local time is a feature on top of the (timezone independent) system time. Eachprocess has its own idea of local time, specified via the TZ environmentvariable. The kernel also has its own timezone offset variable. The TZuserspace environment variable specifies how the UTC-based system time isdisplayed, e.g. when you run date, or what you see on your desktop clock.The TZ string may resolve to different offsets at different dates, which iswhat enables the automatic time-jumping in userspace. when DST changes. Thekernel's timezone offset variable is used when it has to convert betweennon-UTC sources, such as FAT filesystems, to UTC (since the latter is what therest of the system uses).

The caveat with the kernel timezone is that Linux distributions may ignore toset the kernel timezone, and instead only set the system time. Even if aparticular distribution does set the timezone at boot, it is usually does notkeep the kernel timezone offset - which is what changes on DST - up to date.ntpd will not touch the kernel timezone, so running it will not resolve theissue. As such, one may encounter a timezone that is always +0000, or one thatis wrong half of the time of the year. As such,using --kerneltz is highlydiscouraged.

EXAMPLES. To match on weekends, use:

-m time --weekdays Sa,Su

Or, to match (once) on a national holiday block:

-m time --datestart 2007-12-24 --datestop 2007-12-27

Since the stop time is actually inclusive, you would need the following stoptime to not match the first second of the new day:

-m time --datestart 2007-01-01T17:00 --datestop 2007-01-01T23:59:59

During lunch hour:

-m time --timestart 12:30 --timestop 13:30

The fourth Friday in the month:

-m time --weekdays Fr --monthdays 22,23,24,25,26,27,28

(Note that this exploits a certain mathematical property. It is not possible tosay "fourth Thursday OR fourth Friday" in one rule. It is possible withmultiple rules, though.)

Matching across days might not do what is expected. For instance,

-m time --weekdays Mo --timestart 23:00 --timestop 01:00Will match Monday, for one hour from midnight to 1 a.m., and thenagain for another hour from 23:00 onwards. If this is unwanted, e.g. if youwould like 'match for two hours from Montay 23:00 onwards' you need to also specifythe --contiguous option in the example above.

 

tos

This module matches the 8-bit Type of Service field in the IPv4 header (i.e.including the "Precedence" bits) or the (also 8-bit) Priority field in the IPv6header.

[ !] --tos value[ / mask]

Matches packets with the given TOS mark value. If a mask is specified, it islogically ANDed with the TOS mark before the comparison.

[ !] --tos symbol

You can specify a symbolic name when using the tos match for IPv4. The list ofrecognized TOS names can be obtained by calling iptables with -m tos -h.Note that this implies a mask of 0x3F, i.e. all but the ECN bits.

 

ttl (IPv4-specific)

This module matches the time to live field in the IP header.

[ !] --ttl-eq ttl

Matches the given TTL value.

--ttl-gt ttl

Matches if TTL is greater than the given TTL value.

--ttl-lt ttl

Matches if TTL is less than the given TTL value.

 

u32

U32 tests whether quantities of up to 4 bytes extracted from a packet havespecified values. The specification of what to extract is general enough tofind data at given offsets from tcp headers or payloads.

[ !] --u32 tests

The argument amounts to a program in a small language described below.

tests := location "=" value | tests "&&" location "=" value

value := range | value "," range

range := number | number ":" number

a single number, n, is interpreted the same as n:n. n:m isinterpreted as the range of numbers>=n and <=m.

location := number | location operator number

operator := "&" | "<<" | ">>" | "@"

The operators &, <<, >> and&& mean the same as in C.The = is really a set membership operator and the value syntax describesa set. The@ operator is what allows moving to the next header and isdescribed further below.

There are currently some artificial implementation limits on the size of thetests:

*

no more than 10 of " =" (and 9 " &&"s) in the u32 argument

*

no more than 10 ranges (and 9 commas) per value

*

no more than 10 numbers (and 9 operators) per location

To describe the meaning of location, imagine the following machine thatinterprets it. There are three registers:

A is of type char *, initially the address of the IP header

B and C are unsigned 32 bit integers, initially zero

The instructions are:

number B = number;

C = (*(A+B)<<24) + (*(A+B+1)<<16) + (*(A+B+2)<<8) + *(A+B+3)

&number C = C & number

<< number C = C << number

>> number C = C >> number

@number A = A + C; then do the instruction number

Any access of memory outside [skb->data,skb->end] causes the match to fail.Otherwise the result of the computation is the final value of C.

Whitespace is allowed but not required in the tests. However, the charactersthat do occur there are likely to require shell quoting, so it is a good ideato enclose the arguments in quotes.

Example:

match IP packets with total length >= 256

The IP header contains a total length field in bytes 2-3.

--u32 " 0 & 0xFFFF = 0x100:0xFFFF"

read bytes 0-3

AND that with 0xFFFF (giving bytes 2-3), and test whether that is in the range[0x100:0xFFFF]

Example: (more realistic, hence more complicated)

match ICMP packets with icmp type 0

First test that it is an ICMP packet, true iff byte 9 (protocol) = 1

--u32 " 6 & 0xFF = 1 && ...

read bytes 6-9, use & to throw away bytes 6-8 and compare the result to1. Next test that it is not a fragment. (If so, it might be part of such apacket but we cannot always tell.) N.B.: This test is generally needed if youwant to match anything beyond the IP header. The last 6 bits of byte 6 and allof byte 7 are 0 iff this is a complete packet (not a fragment). Alternatively,you can allow first fragments by only testing the last 5 bits of byte 6.

 ...  4 & 0x3FFF = 0 && ...

Last test: the first byte past the IP header (the type) is 0. This is where wehave to use the @syntax. The length of the IP header (IHL) in 32 bit words isstored in the right half of byte 0 of the IP header itself.

 ...  0 >> 22 & 0x3C @ 0 >> 24 = 0"

The first 0 means read bytes 0-3, >>22 means shift that 22 bits to theright. Shifting 24 bits would give the first byte, so only 22 bits is fourtimes that plus a few more bits. &3C then eliminates the two extra bitson the right and the first four bits of the first byte. For instance, if IHL=5,then the IP header is 20 (4 x 5) bytes long. In this case, bytes 0-1 are (inbinary) xxxx0101 yyzzzzzz, >>22 gives the 10 bit value xxxx0101yy and &3C gives 010100. @ means to use this number as a new offset intothe packet, and read four bytes starting from there. This is the first 4 bytesof the ICMP payload, of which byte 0 is the ICMP type. Therefore, we simplyshift the value 24 to the right to throw out all but the first byte and comparethe result with 0.

Example:

TCP payload bytes 8-12 is any of 1, 2, 5 or 8

First we test that the packet is a tcp packet (similar to ICMP).

--u32 " 6 & 0xFF = 6 && ...

Next, test that it is not a fragment (same as above).

 ...  0 >> 22 & 0x3C @ 12 >> 26 & 0x3C @ 8 = 1,2,5,8"

0>>22&3C as above computes the number of bytes in the IP header. @makes this the new offset into the packet, which is the start of the TCPheader. The length of the TCP header (again in 32 bit words) is the left halfof byte 12 of the TCP header. The 12>>26&3C computes this length in bytes(similar to the IP header before). "@" makes this the new offset, which is thestart of the TCP payload. Finally, 8 reads bytes 8-12 of the payload and = checks whether the result is any of 1, 2, 5 or 8.

 

udp

These extensions can be used if `--protocol udp' is specified. Itprovides the following options:

[ !] --source-port, --sport port[ : port]

Source port or port range specification.See the description of the --source-portoption of the TCP extension for details.

[ !] --destination-port, --dport port[ : port]

Destination port or port range specification.See the description of the --destination-portoption of the TCP extension for details.

 

unclean (IPv4-specific)

This module takes no options, but attempts to match packets which seemmalformed or unusual. This is regarded as experimental.  

TARGET EXTENSIONS

iptables can use extended target modules: the following are includedin the standard distribution.  

AUDIT

This target allows to create audit records for packets hitting the target.It can be used to record accepted, dropped, and rejected packets. See auditd for additional details.

--type { accept| drop| reject}

Set type of audit record.

Example:

iptables -N AUDIT_DROP

iptables -A AUDIT_DROP -j AUDIT --type drop

iptables -A AUDIT_DROP -j DROP

 

CHECKSUM

This target allows to selectively work around broken/old applications.It can only be used in the mangle table.

--checksum-fill

Compute and fill in the checksum in a packet that lacks a checksum.This is particularly useful, if you need to work around old applicationssuch as dhcp clients, that do not work well with checksum offloads,but don't want to disable checksum offload in your device.

 

CLASSIFY

This module allows you to set the skb->priority value (and thus classify the packet into a specific CBQ class).

--set-class major : minor

Set the major and minor class value. The values are always interpreted ashexadecimal even if no 0x prefix is given.

 

CLUSTERIP (IPv4-specific)

This module allows you to configure a simple cluster of nodes that sharea certain IP and MAC address without an explicit load balancer in front ofthem. Connections are statically distributed between the nodes in thiscluster.

--new

Create a new ClusterIP. You always have to set this on the first rulefor a given ClusterIP.

--hashmode mode

Specify the hashing mode. Has to be one of sourceip, sourceip-sourceport, sourceip-sourceport-destport.

--clustermac mac

Specify the ClusterIP MAC address. Has to be a link-layer multicast address

--total-nodes num

Number of total nodes within this cluster.

--local-node num

Local node number within this cluster.

--hash-init rnd

Specify the random seed used for hash initialization.

 

CONNMARK

This module sets the netfilter mark value associated with a connection. Themark is 32 bits wide.

--set-xmark value[ / mask]

Zero out the bits given by mask and XOR value into the ctmark.

--save-mark [ --nfmask nfmask] [ --ctmask ctmask]

Copy the packet mark (nfmark) to the connection mark (ctmark) using the givenmasks. The new nfmark value is determined as follows:

ctmark = (ctmark & ~ctmask) ^ (nfmark & nfmask)

i.e. ctmask defines what bits to clear and nfmask what bits of thenfmark to XOR into the ctmark. ctmask and nfmask default to0xFFFFFFFF.

--restore-mark [ --nfmask nfmask] [ --ctmask ctmask]

Copy the connection mark (ctmark) to the packet mark (nfmark) using the givenmasks. The new ctmark value is determined as follows:

nfmark = (nfmark & ~ nfmask) ^ (ctmark & ctmask);

i.e. nfmask defines what bits to clear and ctmask what bits of thectmark to XOR into the nfmark. ctmask and nfmask default to0xFFFFFFFF.

--restore-mark is only valid in the mangle table.

The following mnemonics are available for --set-xmark:

--and-mark bits

Binary AND the ctmark with bits. (Mnemonic for --set-xmark0/ invbits, where invbits is the binary negation of bits.)

--or-mark bits

Binary OR the ctmark with bits. (Mnemonic for --set-xmark bits / bits.)

--xor-mark bits

Binary XOR the ctmark with bits. (Mnemonic for --set-xmark bits /0.)

--set-mark value[ / mask]

Set the connection mark. If a mask is specified then only those bits set in themask are modified.

--save-mark [ --mask mask]

Copy the nfmark to the ctmark. If a mask is specified, only those bits arecopied.

--restore-mark [ --mask mask]

Copy the ctmark to the nfmark. If a mask is specified, only those bits arecopied. This is only valid in the mangle table.

 

CONNSECMARK

This module copies security markings from packets to connections(if unlabeled), and from connections back to packets (also onlyif unlabeled). Typically used in conjunction with SECMARK, it isvalid in the securitytable (for backwards compatibility with older kernels, it is alsovalid in the mangletable).

--save

If the packet has a security marking, copy it to the connectionif the connection is not marked.

--restore

If the packet does not have a security marking, and the connectiondoes, copy the security marking from the connection to the packet.

 

CT

The CT target allows to set parameters for a packet or its associatedconnection. The target attaches a "template" connection tracking entry tothe packet, which is then used by the conntrack core when initializinga new ct entry. This target is thus only valid in the "raw" table.

--notrack

Disables connection tracking for this packet.

--helper name

Use the helper identified by name for the connection. This is moreflexible than loading the conntrack helper modules with preset ports.

--ctevents event[ ,...]

Only generate the specified conntrack events for this connection. Possibleevent types are: new, related, destroy, reply, assured, protoinfo, helper, mark (this refers tothe ctmark, not nfmark), natseqinfo, secmark (ctsecmark).

--expevents event[ ,...]

Only generate the specified expectation events for this connection.Possible event types are: new.

--zone id

Assign this packet to zone id and only have lookups done in that zone.By default, packets have zone 0.

--timeout name

Use the timeout policy identified by name for the connection. This isprovides more flexible timeout policy definition than global timeout valuesavailable at /proc/sys/net/netfilter/nf_conntrack_*_timeout_*.

 

DNAT

This target is only valid in the nattable, in the PREROUTINGand OUTPUTchains, and user-defined chains which are only called from thosechains. It specifies that the destination address of the packetshould be modified (and all future packets in this connection willalso be mangled), and rules should cease being examined. It takes thefollowing options:

--to-destination [ ipaddr[ - ipaddr]][ : port[ - port]]

which can specify a single new destination IP address, an inclusiverange of IP addresses. Optionally a port range,if the rule also specifies one of the following protocols: tcp, udp, dccp or sctp.If no port range is specified, then the destination port will never bemodified. If no IP address is specified then only the destination portwill be modified.In Kernels up to 2.6.10 you can add several --to-destination options. Forthose kernels, if you specify more than one destination address, either via anaddress range or multiple --to-destination options, a simple round-robin (oneafter another in cycle) load balancing takes place between these addresses.Later Kernels (>= 2.6.11-rc1) don't have the ability to NAT to multiple rangesanymore.

--random

If option --randomis used then port mapping will be randomized (kernel >= 2.6.22).

--persistent

Gives a client the same source-/destination-address for each connection.This supersedes the SAME target. Support for persistent mappings is availablefrom 2.6.29-rc2.

IPv6 support available since Linux kernels >= 3.7.

 

DSCP

This target allows to alter the value of the DSCP bits within the TOSheader of the IPv4 packet. As this manipulates a packet, it can onlybe used in the mangle table.

--set-dscp value

Set the DSCP field to a numerical value (can be decimal or hex)

--set-dscp-class class

Set the DSCP field to a DiffServ class.

 

ECN (IPv4-specific)

This target allows to selectively work around known ECN blackholes.It can only be used in the mangle table.

--ecn-tcp-remove

Remove all ECN bits from the TCP header. Of course, it can only be usedin conjunction with -p tcp.

 

HL (IPv6-specific)

This is used to modify the Hop Limit field in IPv6 header. The Hop Limit fieldis similar to what is known as TTL value in IPv4. Setting or incrementing theHop Limit field can potentially be very dangerous, so it should be avoided atany cost. This target is only valid in mangletable.

Don't ever set or increment the value on packets that leave your local network!

--hl-set value

Set the Hop Limit to `value'.

--hl-dec value

Decrement the Hop Limit `value' times.

--hl-inc value

Increment the Hop Limit `value' times.

 

HMARK

Like MARK, i.e. set the fwmark, but the mark is calculated from hashingpacket selector at choice. You have also to specify the mark range and,optionally, the offset to start from. ICMP error messages are inspectedand used to calculate the hashing.

Existing options are:

--hmark-tuple tuple

Possible tuple members are: srcmeaning source address (IPv4, IPv6 address), dstmeaning destination address (IPv4, IPv6 address), sportmeaning source port (TCP, UDP, UDPlite, SCTP, DCCP), dportmeaning destination port (TCP, UDP, UDPlite, SCTP, DCCP), spimeaning Security Parameter Index (AH, ESP), and ctmeaning the usage of the conntrack tuple instead of the packet selectors.

--hmark-mod value (must be > 0)

Modulus for hash calculation (to limit the range of possible marks)

--hmark-offset value

Offset to start marks from.

For advanced usage, instead of using --hmark-tuple, you can specify custom

prefixes and masks:

--hmark-src-prefix cidr

The source address mask in CIDR notation.

--hmark-dst-prefix cidr

The destination address mask in CIDR notation.

--hmark-sport-mask value

A 16 bit source port mask in hexadecimal.

--hmark-dport-mask value

A 16 bit destination port mask in hexadecimal.

--hmark-spi-mask value

A 32 bit field with spi mask.

--hmark-proto-mask value

An 8 bit field with layer 4 protocol number.

--hmark-rnd value

A 32 bit random custom value to feed hash calculation.

Examples:

iptables -t mangle -A PREROUTING -m conntrack --ctstate NEW
 -j HMARK --hmark-tuple ct,src,dst,proto --hmark-offset 10000--hmark-mod 10 --hmark-rnd 0xfeedcafe

iptables -t mangle -A PREROUTING -j HMARK --hmark-offset 10000--hmark-tuple src,dst,proto --hmark-mod 10 --hmark-rnd 0xdeafbeef 

IDLETIMER

This target can be used to identify when interfaces have been idle for acertain period of time. Timers are identified by labels and are created whena rule is set with a new label. The rules also take a timeout value (inseconds) as an option. If more than one rule uses the same timer label, thetimer will be restarted whenever any of the rules get a hit. One entry foreach timer is created in sysfs. This attribute contains the timer remainingfor the timer to expire. The attributes are located under the xt_idletimerclass:

/sys/class/xt_idletimer/timers/<label>

When the timer expires, the target module sends a sysfs notification to theuserspace, which can then decide what to do (eg. disconnect to save power).

--timeout amount

This is the time in seconds that will trigger the notification.

--label string

This is a unique identifier for the timer. The maximum length for thelabel string is 27 characters.

 

LED

This creates an LED-trigger that can then be attached to system indicatorlights, to blink or illuminate them when certain packets pass through thesystem. One example might be to light up an LED for a few minutes every timean SSH connection is made to the local machine. The following options controlthe trigger behavior:

--led-trigger-id name

This is the name given to the LED trigger. The actual name of the triggerwill be prefixed with "netfilter-".

--led-delay ms

This indicates how long (in milliseconds) the LED should be left illuminatedwhen a packet arrives before being switched off again. The default is 0(blink as fast as possible.) The special value inf can be given toleave the LED on permanently once activated. (In this case the trigger willneed to be manually detached and reattached to the LED device to switch itoff again.)

--led-always-blink

Always make the LED blink on packet arrival, even if the LED is already on.This allows notification of new packets even with long delay values (whichotherwise would result in a silent prolonging of the delay time.)

Example:

Create an LED trigger for incoming SSH traffic:

iptables -A INPUT -p tcp --dport 22 -j LED --led-trigger-id ssh

Then attach the new trigger to an LED:

echo netfilter-ssh >/sys/class/leds/ ledname/trigger

 

LOG (IPv6-specific)

Turn on kernel logging of matching packets. When this option is setfor a rule, the Linux kernel will print some information on allmatching packets (like most IPv6 IPv6-header fields) via the kernel log(where it can be read with dmesgor syslogd).This is a "non-terminating target", i.e. rule traversal continues atthe next rule. So if you want to LOG the packets you refuse, use twoseparate rules with the same matching criteria, first using target LOGthen DROP (or REJECT).

--log-level level

Level of logging, which can be (system-specific) numeric or a mnemonic.Possible values are (in decreasing order of priority): emerg, alert, crit, error, warning, notice, infoor debug.

--log-prefix prefix

Prefix log messages with the specified prefix; up to 29 letters long,and useful for distinguishing messages in the logs.

--log-tcp-sequence

Log TCP sequence numbers. This is a security risk if the log isreadable by users.

--log-tcp-options

Log options from the TCP packet header.

--log-ip-options

Log options from the IPv6 packet header.

--log-uid

Log the userid of the process which generated the packet.

 

LOG (IPv4-specific)

Turn on kernel logging of matching packets. When this option is setfor a rule, the Linux kernel will print some information on allmatching packets (like most IP header fields) via the kernel log(where it can be read with dmesgor syslogd).This is a "non-terminating target", i.e. rule traversal continues atthe next rule. So if you want to LOG the packets you refuse, use twoseparate rules with the same matching criteria, first using target LOGthen DROP (or REJECT).

--log-level level

Level of logging, which can be (system-specific) numeric or a mnemonic.Possible values are (in decreasing order of priority): emerg, alert, crit, error, warning, notice, infoor debug.

--log-prefix prefix

Prefix log messages with the specified prefix; up to 29 letters long,and useful for distinguishing messages in the logs.

--log-tcp-sequence

Log TCP sequence numbers. This is a security risk if the log isreadable by users.

--log-tcp-options

Log options from the TCP packet header.

--log-ip-options

Log options from the IP packet header.

--log-uid

Log the userid of the process which generated the packet.

 

MARK

This target is used to set the Netfilter mark value associated with the packet.It can, for example, be used in conjunction with routing based on fwmark (needsiproute2). If you plan on doing so, note that the mark needs to be set in thePREROUTING chain of the mangle table to affect routing.The mark field is 32 bits wide.

--set-xmark value[ / mask]

Zeroes out the bits given by mask and XORs value into the packetmark ("nfmark"). If mask is omitted, 0xFFFFFFFF is assumed.

--set-mark value[ / mask]

Zeroes out the bits given by mask and ORs value into the packetmark. If mask is omitted, 0xFFFFFFFF is assumed.

The following mnemonics are available:

--and-mark bits

Binary AND the nfmark with bits. (Mnemonic for --set-xmark0/ invbits, where invbits is the binary negation of bits.)

--or-mark bits

Binary OR the nfmark with bits. (Mnemonic for --set-xmark bits / bits.)

--xor-mark bits

Binary XOR the nfmark with bits. (Mnemonic for --set-xmark bits /0.)

 

MASQUERADE (IPv6-specific)

This target is only valid in the nattable, in the POSTROUTINGchain. It should only be used with dynamically assigned IPv6 (dialup)connections: if you have a static IP address, you should use the SNATtarget. Masquerading is equivalent to specifying a mapping to the IPaddress of the interface the packet is going out, but also has theeffect that connections are forgottenwhen the interface goes down. This is the correct behavior when thenext dialup is unlikely to have the same interface address (and henceany established connections are lost anyway).

--to-ports port[ - port]

This specifies a range of source ports to use, overriding the default SNATsource port-selection heuristics (see above). This is only validif the rule also specifies -p tcpor -p udp.

--random

Randomize source port mappingIf option --randomis used then port mapping will be randomized.

 

MASQUERADE (IPv4-specific)

This target is only valid in the nattable, in the POSTROUTINGchain. It should only be used with dynamically assigned IP (dialup)connections: if you have a static IP address, you should use the SNATtarget. Masquerading is equivalent to specifying a mapping to the IPaddress of the interface the packet is going out, but also has theeffect that connections are forgottenwhen the interface goes down. This is the correct behavior when thenext dialup is unlikely to have the same interface address (and henceany established connections are lost anyway).

--to-ports port[ - port]

This specifies a range of source ports to use, overriding the default SNATsource port-selection heuristics (see above). This is only validif the rule also specifies -p tcpor -p udp.

--random

Randomize source port mappingIf option --randomis used then port mapping will be randomized (kernel >= 2.6.21).

 

MIRROR (IPv4-specific)

This is an experimental demonstration target which inverts the sourceand destination fields in the IP header and retransmits the packet.It is only valid in the INPUT, FORWARDand PREROUTINGchains, and user-defined chains which are only called from thosechains. Note that the outgoing packets are NOTseen by any packet filtering chains, connection tracking or NAT, toavoid loops and other problems.  

NETMAP

This target allows you to statically map a whole network of addresses ontoanother network of addresses. It can only be used from rules in the nattable.

--to address[ / mask]

Network address to map to. The resulting address will be constructed in thefollowing way: All 'one' bits in the mask are filled in from the new `address'.All bits that are zero in the mask are filled in from the original address.

IPv6 support available since Linux kernels >= 3.7.

 

NFLOG

This target provides logging of matching packets. When this target isset for a rule, the Linux kernel will pass the packet to the loadedlogging backend to log the packet. This is usually used in combinationwith nfnetlink_log as logging backend, which will multicast the packetthrough a netlinksocket to the specified multicast group. One or more userspace processesmay subscribe to the group to receive the packets. Like LOG, this is anon-terminating target, i.e. rule traversal continues at the next rule.

--nflog-group nlgroup

The netlink group (0 - 2^16-1) to which packets are (only applicable fornfnetlink_log). The default value is 0.

--nflog-prefix prefix

A prefix string to include in the log message, up to 64 characterslong, useful for distinguishing messages in the logs.

--nflog-range size

The number of bytes to be copied to userspace (only applicable fornfnetlink_log). nfnetlink_log instances may specify their ownrange, this option overrides it.

--nflog-threshold size

Number of packets to queue inside the kernel before sending themto userspace (only applicable for nfnetlink_log). Higher valuesresult in less overhead per packet, but increase delay until thepackets reach userspace. The default value is 1.

 

NFQUEUE

This target is an extension of the QUEUE target. As opposed to QUEUE, it allowsyou to put a packet into any specific queue, identified by its 16-bit queuenumber.It can only be used with Kernel versions 2.6.14 or later, since it requiresthe nfnetlink_queuekernel support. The queue-balance option was added in Linux 2.6.31, queue-bypass in 2.6.39.

--queue-num value

This specifies the QUEUE number to use. Valid queue numbers are 0 to 65535. The default value is 0.

--queue-balance value : value

This specifies a range of queues to use. Packets are then balanced across the given queues.This is useful for multicore systems: start multiple instances of the userspace program onqueues x, x+1, .. x+n and use "--queue-balance x : x+n".Packets belonging to the same connection are put into the same nfqueue.

--queue-bypass

By default, if no userspace program is listening on an NFQUEUE, then all packets that are to be queuedare dropped. When this option is used, the NFQUEUE rule is silently bypassed instead. The packetwill move on to the next rule.

--queue-cpu-fanout

Available starting Linux kernel 3.10. When used together with --queue-balance this will use the CPU ID as an index to map packets tothe queues. The idea is that you can improve performance if there's a queueper CPU. This requires --queue-balance to be specified.

 

NOTRACK

This target disables connection tracking for all packets matching that rule.It is obsoleted by -j CT --notrack. Like CT, NOTRACK can only be used inthe raw table.  

RATEEST

The RATEEST target collects statistics, performs rate estimation calculationand saves the results for later evaluation using the rateest match.

--rateest-name name

Count matched packets into the pool referred to by name, which is freelychoosable.

--rateest-interval amount{ s| ms| us}

Rate measurement interval, in seconds, milliseconds or microseconds.

--rateest-ewmalog value

Rate measurement averaging time constant.

 

REDIRECT

This target is only valid in the nattable, in the PREROUTINGand OUTPUTchains, and user-defined chains which are only called from thosechains. It redirects the packet to the machine itself by changing thedestination IP to the primary address of the incoming interface(locally-generated packets are mapped to the localhost address,127.0.0.1 for IPv4 and ::1 for IPv6).

--to-ports port[ - port]

This specifies a destination port or range of ports to use: withoutthis, the destination port is never altered. This is only validif the rule also specifies one of the following protocols: tcp, udp, dccp or sctp.

--random

If option --randomis used then port mapping will be randomized (kernel >= 2.6.22).

IPv6 support available starting Linux kernels >= 3.7.

 

REJECT (IPv6-specific)

This is used to send back an error packet in response to the matchedpacket: otherwise it is equivalent to DROPso it is a terminating TARGET, ending rule traversal.This target is only valid in the INPUT, FORWARDand OUTPUTchains, and user-defined chains which are only called from thosechains. The following option controls the nature of the error packetreturned:

--reject-with type

The type given can be icmp6-no-route, no-route, icmp6-adm-prohibited, adm-prohibited, icmp6-addr-unreachable, addr-unreach, icmp6-port-unreachable or port-unreachwhich return the appropriate ICMPv6 error message ( port-unreach isthe default). Finally, the option tcp-resetcan be used on rules which only match the TCP protocol: this causes aTCP RST packet to be sent back. This is mainly useful for blocking ident(113/tcp) probes which frequently occur when sending mail to broken mailhosts (which won't accept your mail otherwise). tcp-resetcan only be used with kernel versions 2.6.14 or later.

 

REJECT (IPv4-specific)

This is used to send back an error packet in response to the matchedpacket: otherwise it is equivalent to DROPso it is a terminating TARGET, ending rule traversal.This target is only valid in the INPUT, FORWARDand OUTPUTchains, and user-defined chains which are only called from thosechains. The following option controls the nature of the error packetreturned:

--reject-with type

The type given can be icmp-net-unreachable, icmp-host-unreachable, icmp-port-unreachable, icmp-proto-unreachable, icmp-net-prohibited, icmp-host-prohibited or icmp-admin-prohibited (*)which return the appropriate ICMP error message ( port-unreachable isthe default). The option tcp-resetcan be used on rules which only match the TCP protocol: this causes aTCP RST packet to be sent back. This is mainly useful for blocking ident(113/tcp) probes which frequently occur when sending mail to broken mailhosts (which won't accept your mail otherwise).

(*) Using icmp-admin-prohibited with kernels that do not support it will result in a plain DROP instead of REJECT 

SAME (IPv4-specific)

Similar to SNAT/DNAT depending on chain: it takes a range of addresses(`--to 1.2.3.4-1.2.3.7') and gives a client the samesource-/destination-address for each connection.

N.B.: The DNAT target's --persistent option replaced the SAME target.

--to ipaddr[ - ipaddr]

Addresses to map source to. May be specified more than once formultiple ranges.

--nodst

Don't use the destination-ip in the calculations when selecting thenew source-ip

--random

Port mapping will be forcibly randomized to avoid attacks based on port prediction (kernel >= 2.6.21).

 

SECMARK

This is used to set the security mark value associated with thepacket for use by security subsystems such as SELinux. It isvalid in the securitytable (for backwards compatibility with older kernels, it is alsovalid in the mangletable). The mark is 32 bits wide.

--selctx security_context

 

SET

This module adds and/or deletes entries from IP sets which can be definedby ipset(8).

--add-set setname flag[ , flag...]

add the address(es)/port(s) of the packet to the set

--del-set setname flag[ , flag...]

delete the address(es)/port(s) of the packet from the set

where flag(s) are srcand/or dstspecifications and there can be no more than six of them.

--timeout value

when adding an entry, the timeout value to use instead of the defaultone from the set definition

--exist

when adding an entry if it already exists, reset the timeout valueto the specified one or to the default from the set definition

Use of -j SET requires that ipset kernel support is provided, which, forstandard kernels, is the case since Linux 2.6.39. 

SNAT

This target is only valid in the nattable, in the POSTROUTINGchain. It specifies that the source address of the packet should bemodified (and all future packets in this connection will also bemangled), and rules should cease being examined. It takes thefollowing options:

--to-source [ ipaddr[ - ipaddr]][ : port[ - port]]

which can specify a single new source IP address, an inclusive rangeof IP addresses. Optionally a port range,if the rule also specifies one of the following protocols: tcp, udp, dccp or sctp.If no port range is specified, then source ports below 512 will bemapped to other ports below 512: those between 512 and 1023 inclusivewill be mapped to ports below 1024, and other ports will be mapped to1024 or above. Where possible, no port alteration will occur.In Kernels up to 2.6.10, you can add several --to-source options. For thosekernels, if you specify more than one source address, either via an addressrange or multiple --to-source options, a simple round-robin (one after anotherin cycle) takes place between these addresses.Later Kernels (>= 2.6.11-rc1) don't have the ability to NAT to multiple rangesanymore.

--random

If option --randomis used then port mapping will be randomized (kernel >= 2.6.21).

--persistent

Gives a client the same source-/destination-address for each connection.This supersedes the SAME target. Support for persistent mappings is availablefrom 2.6.29-rc2.

IPv6 support available since Linux kernels >= 3.7.

 

TCPMSS

This target allows to alter the MSS value of TCP SYN packets, to controlthe maximum size for that connection (usually limiting it to youroutgoing interface's MTU minus 40 for IPv4 or 60 for IPv6, respectively).Of course, it can only be usedin conjunction with -p tcp.

This target is used to overcome criminally braindead ISPs or serverswhich block "ICMP Fragmentation Needed" or "ICMPv6 Packet Too Big"packets. The symptoms of thisproblem are that everything works fine from your Linuxfirewall/router, but machines behind it can never exchange largepackets:

1.

Web browsers connect, then hang with no data received.

2.

Small mail works fine, but large emails hang.

3.

ssh works fine, but scp hangs after initial handshaking.

Workaround: activate this option and add a rule to your firewallconfiguration like:

 iptables -t mangle -A FORWARD -p tcp --tcp-flags SYN,RST SYN
             -j TCPMSS --clamp-mss-to-pmtu

--set-mss value

Explicitly sets MSS option to specified value. If the MSS of the packet isalready lower than value, it will not be increased (from Linux2.6.25 onwards) to avoid more problems with hosts relying on a proper MSS.

--clamp-mss-to-pmtu

Automatically clamp MSS value to (path_MTU - 40 for IPv4; -60 for IPv6).This may not function as desired where asymmetric routes with differingpath MTU exist --- the kernel uses the path MTU which it would use to sendpackets from itself to the source and destination IP addresses. Prior toLinux 2.6.25, only the path MTU to the destination IP address wasconsidered by this option; subsequent kernels also consider the path MTUto the source IP address.

These options are mutually exclusive. 

TCPOPTSTRIP

This target will strip TCP options off a TCP packet. (It will actually replacethem by NO-OPs.) As such, you will need to add the -p tcp parameters.

--strip-options option[ , option...]

Strip the given option(s). The options may be specified by TCP option number orby symbolic name. The list of recognized options can be obtained by callingiptables with -j TCPOPTSTRIP -h.

 

TEE

The TEE target will clone a packet and redirect this clone to anothermachine on the local network segment. In other words, the nexthopmust be the target, or you will have to configure the nexthop to forward itfurther if so desired.

--gateway ipaddr

Send the cloned packet to the host reachable at the given IP address.Use of 0.0.0.0 (for IPv4 packets) or :: (IPv6) is invalid.

To forward all incoming traffic on eth0 to an Network Layer logging box:

-t mangle -A PREROUTING -i eth0 -j TEE --gateway 2001:db8::1 

TOS

This module sets the Type of Service field in the IPv4 header (including the"precedence" bits) or the Priority field in the IPv6 header. Note that TOSshares the same bits as DSCP and ECN. The TOS target is only valid in the mangle table.

--set-tos value[ / mask]

Zeroes out the bits given by mask (see NOTE below) and XORs valueinto the TOS/Priority field. If mask is omitted, 0xFF is assumed.

--set-tos symbol

You can specify a symbolic name when using the TOS target for IPv4. It impliesa mask of 0xFF (see NOTE below). The list of recognized TOS names can beobtained by calling iptables with -j TOS -h.

The following mnemonics are available:

--and-tos bits

Binary AND the TOS value with bits. (Mnemonic for --set-tos0/ invbits, where invbits is the binary negation of bits.See NOTE below.)

--or-tos bits

Binary OR the TOS value with bits. (Mnemonic for --set-tos bits / bits. See NOTE below.)

--xor-tos bits

Binary XOR the TOS value with bits. (Mnemonic for --set-tos bits /0. See NOTE below.)

NOTE: In Linux kernels up to and including 2.6.38, with the exception oflongterm releases 2.6.32 (>=.42), 2.6.33 (>=.15), and 2.6.35 (>=.14), there isa bug whereby IPv6 TOS mangling does not behave as documented and differs fromthe IPv4 version. The TOS mask indicates the bits one wants to zero out, so itneeds to be inverted before applying it to the original TOS field. However, theaformentioned kernels forgo the inversion which breaks --set-tos and itsmnemonics. 

TPROXY

This target is only valid in the mangle table, in the PREROUTINGchain and user-defined chains which are only called from this chain. Itredirects the packet to a local socket without changing the packet header inany way. It can also change the mark value which can then be used in advancedrouting rules.It takes three options:

--on-port port

This specifies a destination port to use. It is a required option, 0 means thenew destination port is the same as the original. This is only valid if therule also specifies -p tcp or -p udp.

--on-ip address

This specifies a destination address to use. By default the address is the IPaddress of the incoming interface. This is only valid if the rule alsospecifies -p tcp or -p udp.

--tproxy-mark value[ / mask]

Marks packets with the given value/mask. The fwmark value set here can be usedby advanced routing. (Required for transparent proxying to work: otherwisethese packets will get forwarded, which is probably not what you want.)

 

TRACE

This target marks packets so that the kernel will log every rule which match the packets as those traverse the tables, chains, rules.

A logging backend, such as ipt_LOG or nfnetlink_log, must be loaded for thisto be visible.The packets are logged with the string prefix:"TRACE: tablename:chainname:type:rulenum " where type can be "rule" for plain rule, "return" for implicit rule at the end of a user defined chain and "policy" for the policy of the built in chains.
It can only be used in therawtable. 

TTL (IPv4-specific)

This is used to modify the IPv4 TTL header field. The TTL field determineshow many hops (routers) a packet can traverse until it's time to live isexceeded.

Setting or incrementing the TTL field can potentially be very dangerous,so it should be avoided at any cost. This target is only valid inmangletable.

Don't ever set or increment the value on packets that leave your local network!

--ttl-set value

Set the TTL value to `value'.

--ttl-dec value

Decrement the TTL value `value' times.

--ttl-inc value

Increment the TTL value `value' times.

 

ULOG (IPv4-specific)

This target provides userspace logging of matching packets. When thistarget is set for a rule, the Linux kernel will multicast this packetthrough a netlinksocket. One or more userspace processes may then subscribe to various multicast groups and receive the packets.Like LOG, this is a "non-terminating target", i.e. rule traversalcontinues at the next rule.

--ulog-nlgroup nlgroup

This specifies the netlink group (1-32) to which the packet is sent.Default value is 1.

--ulog-prefix prefix

Prefix log messages with the specified prefix; up to 32 characterslong, and useful for distinguishing messages in the logs.

--ulog-cprange size

Number of bytes to be copied to userspace. A value of 0 always copiesthe entire packet, regardless of its size. Default is 0.

--ulog-qthreshold size

Number of packet to queue inside kernel. Setting this value to, e.g. 10accumulates ten packets inside the kernel and transmits them as onenetlink multipart message to userspace. Default is 1 (for backwardscompatibility).

---

 

Index

NAME

SYNOPSIS

MATCH EXTENSIONS

addrtype

ah (IPv6-specific)

ah (IPv4-specific)

cluster

comment

connbytes

connlimit

connmark

conntrack

cpu

dccp

devgroup

dscp

dst (IPv6-specific)

ecn

esp

eui64 (IPv6-specific)

frag (IPv6-specific)

hashlimit

hbh (IPv6-specific)

helper

hl (IPv6-specific)

icmp (IPv4-specific)

icmp6 (IPv6-specific)

iprange

ipv6header (IPv6-specific)

ipvs

length

limit

mac

mark

mh (IPv6-specific)

multiport

nfacct

osf

owner

physdev

pkttype

policy

quota

rateest

realm (IPv4-specific)

recent

rpfilter

rt (IPv6-specific)

sctp

set

socket

state

statistic

string

tcp

tcpmss

time

tos

ttl (IPv4-specific)

u32

udp

unclean (IPv4-specific)

TARGET EXTENSIONS

AUDIT

CHECKSUM

CLASSIFY

CLUSTERIP (IPv4-specific)

CONNMARK

CONNSECMARK

CT

DNAT

DSCP

ECN (IPv4-specific)

HL (IPv6-specific)

HMARK

IDLETIMER

LED

LOG (IPv6-specific)

LOG (IPv4-specific)

MARK

MASQUERADE (IPv6-specific)

MASQUERADE (IPv4-specific)

MIRROR (IPv4-specific)

NETMAP

NFLOG

NFQUEUE

NOTRACK

RATEEST

REDIRECT

REJECT (IPv6-specific)

REJECT (IPv4-specific)

SAME (IPv4-specific)

SECMARK

SET

SNAT

TCPMSS

TCPOPTSTRIP

TEE

TOS

TPROXY

TRACE

TTL (IPv4-specific)

ULOG (IPv4-specific)

---

This document was created by man2html,using the manual pages.
Time: 14:41:34 GMT, May 10, 2013