This is a known "feature" of GRE tunnels. I think towards the end of
12.xT, there's a way around this, either an option for the GRE or
something to do with the ipip encapsulation. I know that the reference
is a big vague, but it's hard to find something on CCU that triggers
a match for every versions's reference manual.
George
> From: Adam Rothschild <asr@latency.net>
> To: cisco-nsp@puck.nether.net
> Subject: [nsp] GRE tunneling and MTU
>
> Hi,
>
> Most likely a lame question resulting from oversight on my end, but here
> goes:
>
> I have a GRE/IP tunnel between a 7206VXR [running 12.0(8)S] and a 2611
> [running 12.0(8)]. On the 7206, 'sh in' output is:
>
> MTU 1514 bytes, BW 10000 Kbit, DLY 500000 usec, rely 255/255, load 1/255
> Encapsulation TUNNEL, loopback not set
> Keepalive set (10 sec)
> ...
> Tunnel protocol/transport GRE/IP, key disabled, sequencing disabled
> Checksumming of packets enabled, fast tunneling enabled
>
> On the 2611:
>
> MTU 1472 bytes, BW 10000 Kbit, DLY 500000 usec, rely 255/255, load 1/255
> Encapsulation TUNNEL, loopback not set, keepalive set (10 sec)
> ...
> Tunnel protocol/transport GRE/IP, key disabled, sequencing disabled
> Checksumming of packets enabled, fast tunneling enabled
>
> MTU cannot be set on these tunnel interfaces. This discrepancy is causing
> bad transmission-related things to happen, as would be expected.
>
> Any advice/insight would be greatly appreciated.
>
> Thanks in advance,
> -adam
>
>
This archive was generated by hypermail 2b29 : Sun Aug 04 2002 - 04:12:09 EDT