iptables -nvL 查看防火墙是否关闭：如下代表防火墙没关闭。
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
4157 1985K RH-Firewall-1-INPUT all -- * * 0.0.0.0/0 0.0.0.0/0
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 RH-Firewall-1-INPUT all -- * * 0.0.0.0/0 0.0.0.0/0
Chain OUTPUT (policy ACCEPT 2338 packets, 1850K bytes)
pkts bytes target prot opt in out source destination
Chain RH-Firewall-1-INPUT (2 references)
pkts bytes target prot opt in out source destination
1521 1766K ACCEPT all -- lo * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT icmp -- * * 0.0.0.0/0 0.0.0.0/0 icmp type 255
0 0 ACCEPT esp -- * * 0.0.0.0/0 0.0.0.0/0
0 0 ACCEPT ah -- * * 0.0.0.0/0 0.0.0.0/0
34 5274 ACCEPT udp -- * * 0.0.0.0/0 224.0.0.251 udp dpt:5353
0 0 ACCEPT udp -- * * 0.0.0.0/0 0.0.0.0/0 udp dpt:631
0 0 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 tcp dpt:631
415 25587 ACCEPT all -- * * 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
1 52 ACCEPT tcp -- * * 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
2186 188K REJECT all -- * * 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
正常情况如下：
iptables -nvL
Chain INPUT (policy ACCEPT 770 packets, 52869 bytes)
pkts bytes target prot opt in out source destination
Chain FORWARD (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 737 packets, 108K bytes)
pkts bytes target prot opt in out source destination
[root@localhost ~]#