On 6 mei 2008, at 23:48, Valdis.Kletnieks@vt.edu wrote:

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A more common approach is to rewrite the MSS option in all TCP SYNs with a smaller value so there won't be TCP segments large enough to trigger the problem. AFAIK, all boxes that do PPPoE do this.

And just the other day, you were saying:

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Very few people out there use an MTU significantly below 1500 bytes. A 1500-byte MTU will give you an _average_ packet size of ~1000 on long- lived TCP flows because there is one tiny ACK for every two full size data segments.

Right. Why is that noteworthy? I have a lot more to say about MTU issues in this draft about negotating MTUs between two hosts/routers on a subnet so jumboframes can be deployed without manual configuration: http://www.ietf.org/internet-drafts/draft-van-beijnum-multi-mtu-02.txt

Apparently, there's a *reason* why RFC1122, section 3.3.3 says:

It is generally desirable to avoid local fragmentation and to choose EMTU_S low enough to avoid fragmentation in any gateway along the path. In the absence of actual knowledge of the minimum MTU along the path, the IP layer SHOULD use EMTU_S <= 576 whenever the destination address is not on a connected network, and otherwise use the connected network's MTU.

Tell it to Microsoft and their ICMP-filtering friends...