ICMPv4/v6 redirect pkt received but route table not updated?

Question

In FreeBSD/Linux, the ICMPv4/v6 Redirect pkt can be received by the OS, but the route table will not be changed accordingly?

I have enabled the necessary sysctl variables under /proc to accept the redirect pkt.

Any suggestion?

Answer 1

On Linux you can check the setting for eth0 with:

cat /proc/sys/net/ipv6/conf/eth0/accept_redirects

You can change the setting manually with:

echo 1 > /proc/sys/net/ipv6/conf/eth0/accept_redirects

or

echo 1 > /proc/sys/net/ipv6/conf/all/accept_redirects

If you want to change this permanently you can add the following to /etc/sysctl.conf:

net.ipv6.conf.all.accept_redirect = 1

I think redirects are accepted by default, so maybe they are turned of somewhere? It is possible that your /etc/sysctl.conf contains the line

net.ipv6.conf.all.accept_redirect = 0

If it does, just remove it or change it to ... = 1