[c-nsp] mtu size GRE tunnel

[Ben Steele]

If you are running a 1500 byte MTU path for your GRE tunnels take off 24 
bytes for your GRE encapsulation, ie try adding ip mtu 1476 into your 
tunnel interface, as long as there is no blocking of ICMP in the return 
path back to the host it should work.

Ben

Stefan Hegger wrote:
> Hi,
>
> hope you can help me to solve my problem. We are running some GSR's (cisco 
> 12008/GRP) with IOS Version 12.0(26)S6. We opened a GRE tunnel to another 
> location and have problems with the MTU size.
>
> It seems that the GSR's does not  return an ICMP message 
> indicating "fragmentation needed".
>
> When we decrease the MTU to 1400 on host, everything works fine.
>
> Best Stefan
>