Re: [c-nsp] MTU and PMTUD
Saku Ytti via cisco-nsp <[email protected]>
| Newsgroups | gmane.network.nsp.cisco |
|---|---|
| Message-ID | <CAAeewD-VS_+nTF=0TX6MwGzDu5uwPWurCtSAxQ6JXx-PGNk7aA@mail.gmail.com> |
Hey Marcin, > XR without enabled PMTUD (default setting) means ~1240 bytes available > for TCP payload. > > That seems to be a bit small, did you perform any kind of performance > testing to see the difference between defaults and let's say 9000 for BGP? I am embarrassed to say, but I _just_ found out, like literally weeks ago, that Junos BGP TCP window is 16kB, I did also find hidden command (https://github.com/ytti/seeker-junos) to bump it up to 64kB. I am working with JNPR to have public documentation for the hidden command to improve supportability and optics. I am separately working on hopes of getting TCP window scaling. I know that we are limited by TCP window, as the BGP transfer speed is within 0.5% of theoretical max, and increasing 16kB to 64kB increases BGP transfer speed exactly 4 times, being still capped by TCP window. I think Cisco can go to 130k, but won't by default. Maybe after that issue is remedied I will review packet size. > I'm thinking about RRs in particular, higher MTU (9000 vs 1200) should > result in some performance benefit, at least from CPU point of view. I > haven't tested this though. I've seen Cisco presentations in the 90s and early 00s showing significant benefit from it. I have no idea how accurate it is today,nor why it would have made a difference in the past, like was the CPU interrupt rate constrained? > Agree. Thing is, PMTUD on XR is a global setting, so it does affect all > TCP based protocols. You can do 'tcp mss X' under neighbor stanza. -- ++ytti _______________________________________________ cisco-nsp mailing list [email protected] https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/