[nsp] weird gre tunnel...

[Daniel Roesen]

On Mon, Apr 19, 2004 at 12:34:42AM -0400, James wrote:
> And I found out that when you turn OFF cef on the Cisco, the TTL problem
> with the gre tunnel immediately goes away, and the hidden hop in the
> traceroute now shows up as expected.. So it appears cef implementation
> on the IOS versions I tried (12.0.25S1 on 7500, 12.2(17a) on 2610) has a
> bug or anamolgy that causes it to not decrement the TTL on gre tunnels..

Yes, I've stumbled over the same problem here. IOS does not decrement
TTL when a packet is forwarded into a GRE tunnel if CEF is enabled on
the ingress interface. Observed on 12.2(17) mainline.

CSCea77189 ("Packet to be switched into a tunnel does not decrement
TTL") matches perfectly from the description of the problem,
but the affected versions do not match. :-)

There is another bug (CSCdv04959) for "TTL is not decreased while
switching packets coming from GRE tunnel".

Counting (be it interface counters, or TTL) is not one of Cisco's
strengths. :-P


Best regards,
Daniel