PPPOE, MTU, and boom.

Thu Jul 19 05:11:41 UTC 2001

> This section describes possibly unexpected behavior that are resolved
> in Release 12.2(2)XH.
>
> CSCds69577
>
> Starting with Release 12.2(2)XH, you can resolve this problem by
> changing the value of the maximum segment size (MSS) contained
> in the MTU to 1492 or less. Use the following IOS command:
>
> ip tcp adjust-mss mss
>
> where mss is 1492 or less.

Post-mortem: this seems to work. Hoever, mss is 1460 or less, assuming mtu
is 1492.

dsl1.ahr(config-if)#ip tcp adjust-mss ?
  <500-1460>  Maximum segment size in bytes

Key (which took me a moment to figure out): the mss MUST be AT LEAST 32
bytes or more less than MTU; for a while, I had MTU set to 1400 on the
aggregation side, and didn't realise it, and this didn't work. As soon as
I upped the MTU to 1492, all started working, including all broken sites
and quicken.