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