Microsoft Skype for Business Contact - Broken PMTUD

Fri Mar 17 01:45:19 UTC 2017

Hi Reuben,

I've responded offline.

Thanks,
Christian

-----Original Message-----
From: NANOG [mailto:nanog-bounces at nanog.org] On Behalf Of Reuben Farrelly via NANOG
Sent: Thursday, March 16, 2017 6:15 PM
To: nanog at nanog.org
Subject: Microsoft Skype for Business Contact - Broken PMTUD

Hi,

Can someone from Microsoft who manages the network for the Skype for Business please contact me to help resolve what I believe is a problem with the S4B network?

I am experiencing PMTUD issues whereby connections with an IPv4 TCP MSS above 1492 and an IPv6 TCP MSS of above 1432 do not function.  I can run a clean 1500 byte MTU on both IPv4 and IPv6 from the connection I am testing with.

External validation (thus ruling out my own link) from https://wand.net.nz/pmtud/ reports that the following URLs used by Lync/S4B are failing PMTUD:

meet.lync.com
webdir0b.online.lync.com

----------

tbit from 2001:df0:4:4000::1:115 to 2603:1047:0:a::12
  server-mss 1440, result: pmtud-fail
  app: http, url: https://meet.lync.com/
  [  0.010] TX SYN             64  seq = 0:0
  [  0.049] RX SYN/ACK         64  seq = 0:1
  [  0.049] TX                 60  seq = 1:1
  [  0.049] TX                373  seq = 1:1(313)
  [  0.097] RX               1500  seq = 1:314(1440)
  [  0.097] RX               1500  seq = 1441:314(1440)
  [  0.097] RX                868  seq = 2881:314(808)
  [  0.097] TX PTB           1280  mtu = 1280
  [  0.097] TX                 60  seq = 314:1
  [  0.399] RX               1500  seq = 1:314(1440)
  [  0.399] TX PTB           1280  mtu = 1280
  [  0.994] RX               1500  seq = 1:314(1440)
  [  0.994] TX PTB           1280  mtu = 1280
  [  2.197] RX               1500  seq = 1:314(1440)
  [  2.197] TX PTB           1280  mtu = 1280
  [  4.603] RX               1500  seq = 1:314(1440)
tbit from 130.217.250.115 to 52.113.65.78
  server-mss 1460, result: pmtud-fail
  app: http, url: https://meet.lync.com/
  [  0.009] TX SYN             44  seq = 0:0              c5c9
  [  0.152] RX SYN/ACK         44  seq = 0:1              56ef
  [  0.152] TX                 40  seq = 1:1              c5ca
  [  0.153] TX                353  seq = 1:1(313)         c5cb DF
  [  0.299] RX                808  seq = 2921:314(768)    56f7 DF
  [  0.299] RX               1500  seq = 1:314(1460)      56f5 DF
  [  0.299] RX               1500  seq = 1461:314(1460)   56f6 DF
  [  0.299] TX                 40  seq = 314:1            c5cc
  [  0.299] TX PTB             56  mtu = 1280
  [  0.763] RX               1500  seq = 1:314(1460)      5720 DF
  [  0.764] TX PTB             56  mtu = 1280
  [  1.592] RX               1500  seq = 1:314(1460)      5750 DF
  [  1.592] TX PTB             56  mtu = 1280
  [  3.232] RX               1500  seq = 1:314(1460)      57dc DF
  [  3.232] TX PTB             56  mtu = 1280
  [  6.514] RX               1500  seq = 1:314(1460)      5910 DF

---------

This is in the Asia Pacific region.

Thanks,
Reuben Farrelly