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Icmp request received but not responding

I installed 3 centos servers, configured server2 as a router between 192.168.1.0/24 and 30.0.0.0/24, but ping cannot go through

I tried ping 192.168.1.62 from server1, according to tcpdump on server3, the icmp request is accepted, but it does not generate icmp response.

23: 36: 06.436243 IP 30.0.0.2> 192.168.1.62: ICMP echo request, id 23570, seq 2838, length 64 23: 36: 07.436212 IP 30.0.0.2> 192.168.1.62: ICMP echo request, id 23570, seq 2839, length 64

server1: eth0 - 30.0.0.2

server2: eth0 - 192.168.1.61 eth0: 0 - 30.0.0.1

server3: eth0 - 192.168.1.62

route information on server1: 0.0.0.0 30.0.0.1

route information on server3: 30.0.0.0/24 192.168.1.61

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3 answers

I received ICMP packets but did not see them coming out. The problem is related to traffic passing through several interfaces, and filtering by return path is enabled by default ...

I first turned on a record of Martian sources:

echo 1 >/proc/sys/net/ipv4/conf/eth2/log_martians

Then there are several options for what to do with them ... I allow them to be processed freely:

 sysctl net.ipv4.conf.all.rp_filter=2

See http://lartc.org/howto/lartc.kernel.html for more information https://access.redhat.com/site/solutions/53031

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Run tcpdump with the -e flag and verify that the destination MAC address is correct.

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Check if you have problems with the receiver side firewall.

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Source: https://habr.com/ru/post/952844/

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