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Routing issue

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  • 1.  Routing issue

    Posted 05-25-2018 08:47



    Has anyone ever seen the following issue:


    We have successfully registered our first subscriber for testing and can complete the following from the CPE:


    Ping to URL: Success (Example.... ping www.google.co.uk)

    Ping to address: Success (example .... ping

    nslookup: Success

     Here are the issues:


    Open a browser and type the address into the address bar: Failure

    Connect to facebook: Success

    Connect to youtube: Success

    Connect to google and search: Success

    Click on link from search: Failure


    It's like some sites work and the majority do not. I have tested from both directions with regards to possibility of loops and there are none. Traceroutes are correct. There are no restrictions from an HTTP or HTTPS perspective (or facebook and youtube would not work). I have filters in place for SSH and other non related protocols.


    This is a strange issue I have not seen before. I am using a technicolour CPE.




  • 2.  RE: Routing issue
    Best Answer

    Posted 05-26-2018 04:42

    I've seen this behavior when there is an mtu or mss issue on the path before.  Check these from the cpe up.


  • 3.  RE: Routing issue

    Posted 05-26-2018 15:08


    In addition to what has been said, GOOG ignores the TCP MSS sent in client SYN and uses max 1470B packets.

    GOOG also advertises TCP MSS 1380B for self.

    AFAIK, it also uses max 1380B UDP packet size for QUICC (think Youtube video streaming).

    Akamai and Amazon do similar thing.

    So, find a knob on Your CPE to adjust TCP MSS down to at least 1400 B, then re-test and report back.




  • 4.  RE: Routing issue

    Posted 05-29-2018 01:05

    Hi all,


    Just got in from long weekend. Got a call yesterday stating that the user had adjusted their MTU to 1492 and it all worked. It was indeeed an MSS/MTU issue on the CPE. All is working perfectly.



  • 5.  RE: Routing issue

    Posted 05-29-2018 02:59

    Good news, too bad he didn't tell you before the long weekend you would have had a more relaxing time.