Subject: Re: [Tsvwg] overlapping TCP segments during reassembly

From: David Borman <[email-masked]>
Date: Tue, 26 Aug 2003 15:39:40 -0500 (CDT)

> Date: Mon, 25 Aug 2003 18:56:48 -0700
> From: Murali Bashyam <[email-masked]>
> Subject: [Tsvwg] overlapping TCP segments during reassembly
...
> Is there any guidelines outlined by any TCP RFC's  for determining what
> data in the sequence space to keep and what to drop during TCP out of
> order packet reassembly when there are overlaps? The BSD code tries to
> trim the incoming segment when there is an overlap with a previous
> segment in sequence space, and trims the already queued segments when
> there is an overlap with succeeding segments in sequence space. I was
> curious abt the motivation behind this strategy.

In the BSD code, it is less work to trim from the front of an mbuf
chain than from the tail of an mbuf chain, so when the front overlaps
it's easier to trim the new segment, and when the tail overlaps it's
easier to trim the succeeding segments.  See m_adj() in uipc_mbuf.c.

			-David Borman

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