Problem statement
But R1 is not on the optimal path between R2 and R3! the packet does more hop the reach the destination even if R2 is directly connected to R3 in the vlan204 network…
Traffic from R2 must cross 123.0.0.0/24 network twice to reach PC-2 behind R3 which is another problem if we consider how NOT optimized is the usage of the network and ressources.
ICMP Redirect
Why in this case, the ip icmp redirect is not into play? R1 could hint R2 on a better gateway that is R3 to reach PC2 network… a show ip traffic shows in ICMP section that no redirects were issued at R1 level.
The show command confirms that NO redirects were sent (nor received)
We checked also the version of these routers to confirm they support this feature and that there’s no bug related to this feature.
We confirmed that the ip redirects are also enabled locally on the ip interfaces
and globally. Let’s note that the feature is named ip icmp redirect host and not router!
Let’s send a ping directly from R2 and enable a debug icmp
Now we check that a redirect messages was received from R1 for 23.0.0.1 and hints him to use the gateway R3 instead. The difference is that the traffic is generated within the same network the vlan204 network.
On R1 we check now using the show command that 3 redirects were sent (already received by R2 as checked with the previous debug command)
And nothing happens on R3 (the second gateway!) which is very important…
What is the most suitable option? Have R3 to send the ip redirect (to himself)? Or keep it by R1?
Even if R1 sends redirection messages, the the effective path PC1 packets take does not change
