Re: [c-nsp] MTU and PMTUD
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 cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
Re: [c-nsp] MTU and PMTUD
We set the 'physical' MTU (In IOS-XR+Junos L2 but no CRC is in this humber) as high as it went when the decision was made. Today you can do I think 10k in Cisco8k and 16k in Juniper. We do not seet MPLS or IP MTUs separately in Core. On the edge you should always set L3 MTU, because you want to have the ability to add subinterfaces with large MTU, so physical MTU must be large, as change will affect all subinterfaces. This way you can later add big MTU subint, without affecting other subints. Thanks. Actually, I should have said "core-facing" interfaces in the edge :) 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'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. No, not at this time, our BGP transfer performance is limited by TCP window-size, so larger packets would not do anything for us. And LDP has a trivial amount of stable data so it doesn't matter. Agree. Thing is, PMTUD on XR is a global setting, so it does affect all TCP based protocols. ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
Re: [c-nsp] MTU and PMTUD
> Assuming typical MPLS network running L2VPNs and L3VPNs, how do you > configure MTU values for core interfaces? Do you set interface (L2) MTU, > MPLS MTU and IP MTU separately? We set the 'physical' MTU (In IOS-XR+Junos L2 but no CRC is in this humber) as high as it went when the decision was made. Today you can do I think 10k in Cisco8k and 16k in Juniper. We do not seet MPLS or IP MTUs separately in Core. On the edge you should always set L3 MTU, because you want to have the ability to add subinterfaces with large MTU, so physical MTU must be large, as change will affect all subinterfaces. This way you can later add big MTU subint, without affecting other subints. > Do you enable PMTUD for TCP based control plane protocols like BGP or LDP? No, not at this time, our BGP transfer performance is limited by TCP window-size, so larger packets would not do anything for us. And LDP has a trivial amount of stable data so it doesn't matter. -- ++ytti ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
[c-nsp] MTU and PMTUD
Hi all, Assuming typical MPLS network running L2VPNs and L3VPNs, how do you configure MTU values for core interfaces? Do you set interface (L2) MTU, MPLS MTU and IP MTU separately? Do you enable PMTUD for TCP based control plane protocols like BGP or LDP? Thanks! ___ cisco-nsp mailing list cisco-nsp@puck.nether.net https://puck.nether.net/mailman/listinfo/cisco-nsp archive at http://puck.nether.net/pipermail/cisco-nsp/
