几个月前，我们曾经有一位系统管理员在我们的一台服务器上禁用了 ping 响应。但现在我们要重新启用 ping 响应。
我尝试检查 ping 是否已从配置中禁用。这些值设置为 0。
root@dumpty:/mnt/NAS# cat /proc/sys/net/ipv4/icmp_echo_ignore_broadcasts
0
root@dumpty:/mnt/NAS# cat /proc/sys/net/ipv4/icmp_echo_ignore_all
0
这是sysctl.conf：
root@dumpty:/mnt/NAS# cat /etc/sysctl.conf | grep icmp
#net.ipv4.icmp_echo_ignore_broadcasts = 1
#net.ipv4.icmp_ignore_bogus_error_responses = 1
net.ipv4.icmp_echo_ignore_broadcasts = 0
net.ipv4.icmp_echo_ignore_all = 0
ping 仍然无法正常工作。我知道服务器能够接收 ping，因为我可以看到其中的请求，tcpdump但看不到传出的响应，示例：
ping 的 tcpdump 捕获：
root@dumpty:/mnt/NAS# tcpdump -nni eth0 icmp
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
18:39:45.260686 IP 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 1, length 64
18:39:46.259975 IP 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 2, length 64
18:39:47.260289 IP 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 3, length 64
18:39:48.259971 IP 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 4, length 64
18:39:49.261652 IP 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 5, length 64
18:39:50.261956 IP 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 6, length 64
18:39:51.260058 IP 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 7, length 64
18:39:52.260309 IP 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 8, length 64
^C
8 packets captured
13 packets received by filter
0 packets dropped by kernel
我可能是错的，但这是我在网上找到的应该捕获传入数据包的命令：
root@dumpty:/mnt/NAS# tcpdump -nni eth0 -e icmp[icmptype] == 8
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
18:40:48.260108 00:10:db:ff:10:01 > bc:30:5b:da:51:a6, ethertype IPv4 (0x0800), length 98: 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 64, length 64
18:40:49.260064 00:10:db:ff:10:01 > bc:30:5b:da:51:a6, ethertype IPv4 (0x0800), length 98: 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 65, length 64
18:40:50.260119 00:10:db:ff:10:01 > bc:30:5b:da:51:a6, ethertype IPv4 (0x0800), length 98: 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 66, length 64
18:40:51.260092 00:10:db:ff:10:01 > bc:30:5b:da:51:a6, ethertype IPv4 (0x0800), length 98: 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 67, length 64
18:40:52.260285 00:10:db:ff:10:01 > bc:30:5b:da:51:a6, ethertype IPv4 (0x0800), length 98: 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 68, length 64
18:40:53.260465 00:10:db:ff:10:01 > bc:30:5b:da:51:a6, ethertype IPv4 (0x0800), length 98: 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 69, length 64
18:40:54.262405 00:10:db:ff:10:01 > bc:30:5b:da:51:a6, ethertype IPv4 (0x0800), length 98: 103.227.98.242 > SEVERIP: ICMP echo request, id 4799, seq 70, length 64
^C
7 packets captured
7 packets received by filter
0 packets dropped by kernel
这是传出的
root@dumpty:/mnt/NAS# tcpdump -nni eth0 -e icmp[icmptype] == 0
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on eth0, link-type EN10MB (Ethernet), capture size 65535 bytes
^C
0 packets captured
0 packets received by filter
0 packets dropped by kernel
我没有看到任何传出数据包，我还检查了 iptables 是否有任何阻止 icmp 的规则
root@dumpty:/mnt/NAS# sudo iptables -L INPUT | grep reject
REJECT tcp -- anywhere anywhere tcp dpt:9200 reject-with icmp-port-unreachable
REJECT tcp -- anywhere anywhere tcp dpt:httpflags: FIN,SYN,RST,ACK/SYN #conn src/32 > 15 reject-with tcp-reset
root@dumpty:/mnt/NAS# sudo iptables -L INPUT | grep icmp
REJECT tcp -- anywhere anywhere tcp dpt:9200 reject-with icmp-port-unreachable
root@dumpty:/mnt/NAS# sudo iptables -L INPUT | grep drop
root@dumpty:/mnt/NAS#
我们在端口 9200 上被拒绝，但我认为它不应该阻止所有端口？还有什么可以阻止我们的 ping 响应？我错过了任何其他配置吗？
我尽力调试，非常感谢任何帮助。
注意：我编辑了控制台的输出并将我们的服务器 IP 替换为SEVERIP
编辑：
添加 iptables OUTPUT 链
root@dumpty:/mnt/NAS# sudo iptables -L OUTPUT
Chain OUTPUT (policy ACCEPT)
target prot opt source destination
编辑2：
root@dumpty:/mnt/NAS# iptables -t nat -vnL
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain INPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
root@dumpty:/mnt/NAS# iptables -t raw -vnL
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain OUTPUT (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
root@dumpty:/mnt/NAS# iptables -t mangle -vnL
Chain PREROUTING (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain INPUT (policy ACCEPT 0 packets, 0 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 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination