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GRE, CEF and Traceroute

When I enabled CEF on my router (12.3(4)T3) and performing traceroute across GRE tunnels, it doesn't display the IP address of the GRE tunnel.

For example, without CEF enabled doing a traceroute from 172.16.1.3 to 172.18.1.3 will show the following:

1. 172.16.1.1

2. 172.17.1.1

3. 172.18.1.3

Hop 2 is the GRE tunnel.

If doing the same traceroute with CEF enabled, it will produce:

1.172.16.1.1

2.172.18.1.3

I need to know the middle-hop because there are 2 GRE tunnels for each destination and we need to absolutely know which tunnel it goes through (using PBR).

Thanks!

James

  • Other Network Infrastructure Subjects
1 REPLY
Silver

Re: GRE, CEF and Traceroute

This behaviour is because with CEF enabled the TTL is ignored and hence the 2nd hop is ignored. Please see the bug CSCdv04959 for details. The issue has been resolved in 12.3(6)

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