[c-nsp] MTU issue on a GRE tunnel

[John Kougoulos]

>
> Config example. The remote end is the same.
>
> Tunnel73
> ip address yy.yy.yy.yy 255.255.255.252
> ip mtu 1476
> ip tcp adjust-mss 1460
> tunnel source xxxxx
> tunnel destination zzzzzzzzz
> tunnel path-mtu-discovery
>
>
> The two tunnel endpoints are ME3400s.  I expected that this
> configuration would reduce the quantity of fragmentations needed by the
> router but looks like "IP Input" was up to around 20%.  The user
> experience was bad since most web pages would fail to load.  I thought
> "ip tcp adjust-mss" would signal help signal the users OSs to act
> appropriately given the situation.
>

do fragments increase in "show ip traffic | in frag"? In any case, since 
you use ip mtu 1476, you should set the TCP MSS at 40 bytes lower (max 
1436 in your case)

Regards,
John