Hello,
Has anyone else here seen problems with microsoft/msn/hotmail/live.com sites not performing PMTUD correctly? We have, for a while now, had people on our network complain of poor microsoft.com reachability, and discovered we can work around the issue by changing MSS on all TCP SYN as they go out of our network.
I recently watched the whole conversation between msn.com and a host on our network (with the MSS rewrite disabled), and if I'm reading it right, we are following PMTUD protocol correctly by sending back ICMP type 3 code 4, but all Microsoft hosts seem to ignore this and continue to send packets back to our host with an MSS that is too large.
I hope I'm wrong and that it is we who are doing something stupid, but after cruising Google for a while, I found a multitude of other complaints from people connected to other ISPs specifically about not being able to reach Microsoft web sites. It seems crazy that MS could have PMTUD broken for so long with nobody ever raising a complaint to them directly, though, which makes me wonder if there is another answer here that I'm missing.
I sent the following message to a couple of addresses that I gleaned from ARIN WHOIS for the IP block in question and threw hostmaster in there just in case it went somewhere, but noc@microsoft.com appears to be defunct. I have yet to receive acknowledgment of receipt from the other address.
Are there any microsoft.com admins that hang out here that can comment on this or get in touch with me, or is there perhaps someone on here with connections to the Microsoft NOC?
(BTW, I stripped the referenced libpcap attachment off of this message to the list just so that I wouldn't accidentally incur the wrath of NANOG...if y'all want to see it, I'm happy to post it.)
Thanks,