[lwip-devel] [bug #21492] TCP MSS can be larger than MTU

[Simon Goldschmidt]

URL:
  <http://savannah.nongnu.org/bugs/?21492>

                 Summary: TCP MSS can be larger than MTU
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: goldsimon
            Submitted on: Donnerstag 01.11.2007 um 16:08
                Category: TCP
                Severity: 3 - Normal
              Item Group: Feature Request
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: 

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Details:

This might currently not be a problem for most users, but (according to RFC
1122, chapter 4.2.2.6), the MSS should be the minimum of the received MSS
(option) and the 'MTU-minus-headersize'-(calculated)-MSS (effectivly MTU-20
for us).

I think this is very straightforward: since netif already holds the MTU, just
call ip_route on connection setup and calculate the "effective send MSS" based
on the netif's MTU.

This is also a precondition for effectively using path MTU discovery with
TCP.




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