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Date:      Tue, 4 May 1999 14:43:43 +0100
From:      Tony Finch <fanf@demon.net>
To:        current@freebsd.org
Subject:   Re: NFS Patch #8 for current available - new TCP fixes
Message-ID:  <E10efU7-0004Iv-00@fanf.noc.demon.net>
In-Reply-To: <m2n.s.10cEKr-000C8D@chiark.greenend.org.uk>

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Matthew Dillon <dillon@apollo.backplane.com> wrote:
>
>    (fanfair!)

:-)

>    NFS attempts to realign packet buffers and trods all over the underlying
>    mbufs.  For TCP connections, several RPC's may be present in an mbuf 
>    chain.  The realignment of one of them may destroy the others.  This does
>    not occur with UDP because each UDP packet contains only a single rpc.
>
>    Packet buffers may be unaligned for a number of reasons.  The main reason
>    is due to the 14 byte MAC header on the ethernet frame.  This causes the
>    remainder of the packet - the ip payload - to NOT be 4-byte aligned.

We're planning to try replacing some Solaris web servers with FreeBSD
machines in the near future. The documents are on a read-only NFS
filestore connected to the web servers with CDDI. (Updates will stay
on a Sun box.) Are we going to have nfs_realign problems if we use TCP
in this situation or should we stick with UDP?

Tony.
-- 
f.a.n.finch   dot@dotat.at   fanf@demon.net
Arthur: "Oh, that sounds better, have you worked out the controls?"
Ford:   "No, we just stopped playing with them."


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