Centos6のApacheはリモートクライアントアクセスを許可します。ただし、iptablesを無効にしない限り、サーバーは発信アクセス（例ping google.com：sshなど）を許可しません。
iptablesが発信アクセスをブロックするのはなぜですか。これを防ぐにはどうすればよいですか？
[Michael@vps2 ~]$ ping google.com
^C
[Michael@vps2 ~]$ ping localhost
PING localhost.localdomain (127.0.0.1) 56(84) bytes of data.
64 bytes from localhost.localdomain (127.0.0.1): icmp_seq=1 ttl=64 time=0.019 ms
^C
--- localhost.localdomain ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 789ms
rtt min/avg/max/mdev = 0.019/0.019/0.019/0.000 ms
[Michael@vps2 ~]$ sudo /etc/init.d/iptables status
Table: mangle
Chain PREROUTING (policy ACCEPT)
num target prot opt source destination
Chain INPUT (policy ACCEPT)
num target prot opt source destination
Chain FORWARD (policy ACCEPT)
num target prot opt source destination
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
Chain POSTROUTING (policy ACCEPT)
num target prot opt source destination
Table: filter
Chain INPUT (policy DROP)
num target prot opt source destination
1 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:22
2 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:80
3 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:443
4 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:1443
5 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:10000
6 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
7 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:1337
8 DROP all -- 0.0.0.0/0 0.0.0.0/0
Chain FORWARD (policy DROP)
num target prot opt source destination
Chain OUTPUT (policy ACCEPT)
num target prot opt source destination
[Michael@vps2 ~]$ sudo iptables -L -v
Chain INPUT (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
380 41335 ACCEPT tcp -- any any anywhere anywhere tcp dpt:ssh
0 0 ACCEPT tcp -- any any anywhere anywhere tcp dpt:http
0 0 ACCEPT tcp -- any any anywhere anywhere tcp dpt:https
0 0 ACCEPT tcp -- any any anywhere anywhere tcp dpt:ies-lm
0 0 ACCEPT tcp -- any any anywhere anywhere tcp dpt:ndmp
2 168 ACCEPT all -- lo any anywhere anywhere
0 0 ACCEPT tcp -- any any anywhere anywhere tcp dpt:menandmice-dns
23 1208 DROP all -- any any anywhere anywhere
Chain FORWARD (policy DROP 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 352 packets, 55019 bytes)
pkts bytes target prot opt in out source destination
[Michael@vps2 ~]$ sudo /etc/init.d/iptables stop
iptables: Setting chains to policy ACCEPT: mangle filter [ OK ]
iptables: Flushing firewall rules: [ OK ]
iptables: Unloading modules: [ OK ]
[Michael@vps2 ~]$ ping google.com
PING google.com (172.217.4.110) 56(84) bytes of data.
64 bytes from ord36s04-in-f110.1e100.net (172.217.4.110): icmp_seq=1 ttl=55 time=1.08 ms
64 bytes from ord36s04-in-f110.1e100.net (172.217.4.110): icmp_seq=2 ttl=55 time=1.00 ms
^C
--- google.com ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1209ms
rtt min/avg/max/mdev = 1.002/1.045/1.088/0.043 ms
[Michael@vps2 ~]$
ベストアンサー1
まず、関連して設定されたパケットを有効にする必要があります。ルールリストの一番上に配置します。
# iptables -I INPUT 1 -m state --state ESTABLISHED,RELATED -j ACCEPT
また、ICMPはTCPやUDPとは異なるプロトコルなので、明示的に許可する必要があります。私は通常ICMPを完全に受け入れます。 ICMPをブロックすると、断片化などの問題が発生する可能性があるためです。
# iptables -I INPUT 2 -p icmp -j ACCEPT
別の点：「すべて削除」ルールを追加する代わりに、チェーンのポリシーを変更できます。
# iptables -P INPUT DROP