Wednesday, October 7, 2009

GRE Tunnel IP Facing Latency But Destination Address Doesn't

According to the customer, when he pings the GRE tunnel ip address a latency of 300-400ms is receiving but the latency of destination address of tunnel is 40ms. Really such a weird issue and ping outputs are phenomenal. During the analysis, we find backbone is having two equal cost path and destination based packet forwarding is configured. After running show ip cef exact route , we find that the packet forwading is occuring from the second path which is very less utilize and ist path is fully choked. But not able to check the same results with GRE ip address. There after, per packet based forwarding is configured and problem completely vanishes.
Does anyone know how to check the cef exact route for GRE tunnel address?

People who read this post also read :


Ivan Pepelnjak said...

My personal guess is that you can't. The CEF path selection code works on inside source/destination IP address, but since the destination is not in the main IP routing table, the "show ip cef ..." command cannot display meaningful data.

shivlu jain said...


Thanks for the comments. It means one cannot drill the exact RCA in this case because the problem disappears after configuring per packet based load sharing.

Harsh S said...

If the gre customer is configured under vrf, then probably "sh ip cef vrf XXX exact-route" may help.

Harsh S.

nancy john said...

thanks for sharing information really it is very useful

study abroad