[j-nsp] Does EX4200 support changing TCP-MSS on transit packets?

[Saku Ytti]

On (2014-02-24 12:47 +0200), Mark Tinka wrote:
 
> TCP MSS adjustments generally affect traffic terminating on 
> the switch itself.
> 
> Transit packets are affected by interface MTU.
> 
> If you're able to affect TCP MSS of transit traffic, I 
> certainly haven't yet heard about it (which is not to say it 
> doesn't exist).

I think you're mixing system level setting and interface level setting. When
configured in interface it indeed mangles transit packets. When in system
level it affects local when interface it affects transit.
IIRC JunOS does not support interface-level 'stateless' mangling, but will
only do it in FW via flows.

It's typically used to make tunneling optimal, instead of forcing TCP packet
to always be split into one large and one tiny packet over tunnel, you curb
MSS to maximum possible with tunnel over-head, essentially halving your PPS
and improving BPS due to less overhead.

There is no particular reason why Trio couldn't do this statelessly in
interface level. But I don't think EX has hardware smart enough to do this.

-- 
  ++ytti