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TCP Packet Size up to 64k on Edge Servers causes weird issues RRS feed

  • Question

  • Hello !

    i have a strange problem with 2 edge servers here! Short things about the OCS environment:

    2 Forests, 2 OCS Environments with both OCS 2007 R2 Standard Edition Servers, CWA Servers, Edge Servers. All Servers running Win2k3 R2, latest Updates and Hotfixes. All Hotfixes recommendet by the OCS BPA Analyzer.

    The thing is, there are sporadic errors in the intercompany communication like users cannot be invited into Video chats or errors like "The message was not delivered to xxx because there was no response from the server" when starting a text chat session. Mostly in those cases you just have to try it again or sometimes 3 times and than its working normaly. But this is very annoying to the users and i am searching for the error and a solution for quite a long time now. The trace and Snooper tool at least did not give me much information so i went a level down to Wireshark. And yes, i found some really strange behavior than.

    Both Edge Servers are sending TCP Packets with a size up to 64k ! About 10 percent of the packets sniffed are bigger than 1500 bytes and have a random size up to 64k. Due to the fact that Windows sets the do not fragment bit by default i am wondering why any of those packets can pass the firewall. Anyway, sometimes it happens that the Firewall do not accept those packets and send reset packets to just one!! of the edge servers. What remains is a half open TCP connection on one side witch causes the sporadic errors on both sides. The behavior of the firewall is, i would say, kind of normal, but the question is.

    Why are the Edge Servers sending packets witch are so unnormal in any way? And how can i solve this?

    What I tried so far:

    • - Set a fixed MTU-Size in the registry
    • - Set in the registry to allow fragmentation of packets (as workaround... did not work)
    • - Set the Ethernet interfaces to 100mbit (large packets normally are not defined in Fast Ethernet)
    • - Jumbo Frames are disabled by default on the NIC-Settings

    Nothing helped... anyone any idea? What wondering me the most is, i havent found anything similar in the internet. Am I the first experience this behavior? Cant believe that :o)

    Thank you and regards

    P. Cattide

    Tuesday, September 7, 2010 10:01 AM

All replies

  • I would recommend you contact MSFT PSS to raise the case maybe more helpful. 
    Best regards,
    Thursday, September 9, 2010 5:28 AM