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1430MTU, MRU, and MSS

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  • Eric A. Hall
    Nov 4, 1998
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      Question about PPP MTU/MRU sizes and how they affect the MSS being
      advertised in various implementations:

      RFC 793 states unequivocably that the local network's MRU should be used
      for the value that is advertised in the MSS:

      Maximum Segment Size Option Data: 16 bits

      If this option is present, then it communicates the maximum
      receive segment size at the TCP which sends this segment.

      However, many of the systems I've been testing don't seem to do this,
      instead choosing to advertise a (predetermined) fixed size that has no
      relation to the negotiated MRU. Also, some systems seem to use the MTU
      for the MSS, even though MRU should be the deciding factor since A) the
      spec says so, and B) anything larger would fragment.

      Does anybody have a good reason for not defining MSS based on MRU?

      Eric A. Hall ehall@...
      +1-650-685-0557 http://www.ehsco.com
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