[c-nsp] MTU and PMTUD

[Marcin Kurek]

> I did some benchmarking back in ~2008-2009 (with 12.2.31SB and 12.2SR,
> who still remembers that?), and we (Cisco) fixed numerous non optimized
> paths in the routing code. But that was over a decade ago, so I’ll
> limit bragging about it ;) There are two presentations, quoted from
> about that time I can find some references to, which show in general
> terms what improvements you can expect. XR code was however way
> more optimized right from the start, and specially over last 5 years
> there was a lot additional work done to optimize it.
>
> <SNIP>

Hi Lukasz,

Thanks for sharing this interesting information.

I've done a bit of testing and there is some performance gain, but not 
as much as I initially expected.

Still, 9k MTU is the right way to go, because as you pointed out, most 
networks run 9k in the core anyway.


Just to update this thread - I've consulted with TAC about the MSS 
"negotiation" where XR is passive.
It is a known issue, and currently, there is no way to fix it, because 
it would require complex changes to how TCP listening sockets are 
programmed.

However, as a workaround, we can configure the remote peer as passive to 
make sure that XR is always initiating the TCP connection.


Kind regards,
Marcin