ICMP Redirect Host(New addr: X.X.X.X)

I'm setting up a VPN on my linux server and I wanted to have firewall rules to control communication between clients so in my OpenVPN configuration I removed client-to-client so OpenVPN pass all of the traffic to the kernel.

Once I did this and did a ping from one client to another, I would get these ICMP Redirect messages but the ping would work.

$ ping 192.168.12.127
PING 192.168.12.127 (192.168.12.127): 56 data bytes
64 bytes from 192.168.12.127: icmp_seq=0 ttl=63 time=59.198 ms
92 bytes from 192.168.12.1: Redirect Host(New addr: 192.168.12.127)
Vr HL TOS  Len   ID Flg  off TTL Pro  cks      Src      Dst
 4  5  00 0054 b2ac   0 0000  3f  01 f1d7 192.168.12.128 192.168.12.127

64 bytes from 192.168.12.127: icmp_seq=1 ttl=63 time=54.229 ms
92 bytes from 192.168.12.1: Redirect Host(New addr: 192.168.12.127)
Vr HL TOS  Len   ID Flg  off TTL Pro  cks      Src      Dst
 4  5  00 0054 b854   0 0000  3f  01 ec2f 192.168.12.128  192.168.12.127

64 bytes from 192.168.12.127: icmp_seq=2 ttl=63 time=55.497 ms
64 bytes from 192.168.12.127: icmp_seq=3 ttl=63 time=54.718 ms

After a bit of Googling I found this forum post which mentions traffic that comes in from one interface and goes out the same interface on linux causes the redirects. I then found there's a sysctl that controls this behavour called net.ipv4.conf.all.send_redirects. So a quick sysctl net.ipv4.conf.all.send_redirects=0 and the redirects went away and all was right in the world.

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