I'm having the following strange issue since I've updated one of our routers to sles11sp1. On the below picture you can see the network architecture:

Router 1 - SLES11sp1
default gateway ISP Router public IP@
ip route add via dev eth0

Router 2 - SLES10sp2
default gateway
ip forwarding enabled

default gateway

default gateway

When PC1 pings PC2 all is fine.

When PC2 pings PC1, then several things happen:
the icmp request reaches PC1
PC1 sends icmp reply to its default gateway Router 1
Router 1 receives the reply, but doesn't forward it to Router 2, the reply gets lost somehow (can't see it anywhere in any log)
PC2 ping times out

If on PC1 I manually do route add via dev eth0 then all is fine, but this solution is not applicable in our case.

When Router 1 was SLES10sp2 all was fine. Since we updated Router 1 to SLES11sp1, we've got the above issue. I suspect some parameter changed for the kernel, but I can't find which one it is. Is there something wrong with this setup?

I've tried the TID 7007649 http://www.novell.com/support/kb/doc.php?id=7007649 but setting the rp_filter to 0 or to 2 on Router 1 and Router 2 didn't make any difference.

Any help will be greatly appreciated!