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[lwip-devel] [patch #5834] Don't fragment flag


From: Frédéric Bernon
Subject: [lwip-devel] [patch #5834] Don't fragment flag
Date: Thu, 29 Mar 2007 15:18:15 +0000
User-agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; fr; rv:1.8.1.3) Gecko/20070309 Firefox/2.0.0.3

URL:
  <http://savannah.nongnu.org/patch/?5834>

                 Summary: Don't fragment flag
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: fbernon
            Submitted on: jeudi 29.03.2007 à 17:18
                Category: None
                Priority: 5 - Normal
                  Status: None
                 Privacy: Public
             Assigned to: fbernon
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any

    _______________________________________________________

Details:

In last March (March 22th 2006), a user tell us there was a problem with
ip.c: "IPH_OFFSET_SET(iphdr, htons(IP_DF))" is always called in ip_output_if
(even if you have enable IP_FRAG and IP_REASSEMBLY). This limitation is
really important, because if big packets are sent by a circuit with several
routers, where MTU is lower than the one lwIP use, packets are lost.

Kieran, you answer was :

"I'm not sure why it's like that in lwIP, but more generally you might set
this bit if you're doing path MTU discovery, and so believe you have chosen
an MTU that should not need fragmenting.  If you set this bit, and it turns
out the packet does need fragmenting, you'll get an ICMP message telling you
this from whoever drops the packet, and so you can update your MTU for future
packets."

I propose to remove that line, and in a second time, to propose a new
IP_DONTFRAGMENT option (for IPPROTO_IP level) for set/getsocketopt, if some
users need it...







    _______________________________________________________

Reply to this item at:

  <http://savannah.nongnu.org/patch/?5834>

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