[46701] in North American Network Operators' Group
Re: packet reordering at exchange points
daemon@ATHENA.MIT.EDU (Richard A Steenbergen)
Mon Apr 8 17:46:41 2002
Date: Mon, 8 Apr 2002 17:45:34 -0400
From: Richard A Steenbergen <ras@e-gerbil.net>
To: Paul Vixie <paul@vix.com>
Cc: nanog@merit.edu
Message-ID: <20020408214534.GP523@overlord.e-gerbil.net>
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On Mon, Apr 08, 2002 at 02:18:52PM -0700, Paul Vixie wrote:
>
> > packet reordering at MAE East was extremely common a few years ago. Does
> > anyone have information whether this is still happening?
>
> more to the point, does anybody still care about packet reordering at
> exchange points? we (paix) go through significant effort to prevent it,
> and interswitch trunking with round robin would be a lot easier. are
> we chasing an urban legend here, or would reordering still cause pain?
Setup a freebsd system with a dummynet pipe, do a probability match on 50%
of the packets and send them through a pipe with a few more bytes of
queueing and 1ms more delay than the rest. Then test the performance of
TCP across that link.
There is a good paper on the subject that was published by ACM in
Janurary: http://citeseer.nj.nec.com/450712.html
So just how common is packet reordering today? Well I did a quick peak at
a few machines which I don't have any reason to believe are out of the
ordinary, and they all pretty much come out about the same:
32896155 packets received
9961197 acks (for 2309956346 bytes)
96322 duplicate acks
0 acks for unsent data
17328137 packets (2667939981 bytes) received in-sequence
10755 completely duplicate packets (1803069 bytes)
19 old duplicate packets
375 packets with some dup. data (38297 bytes duped)
53862 out-of-order packets (75435307 bytes)
0.3% of non-ACK packets by packet were received out of order, or 2.8% by
bytes.
--
Richard A Steenbergen <ras@e-gerbil.net> http://www.e-gerbil.net/ras
PGP Key ID: 0x138EA177 (67 29 D7 BC E8 18 3E DA B2 46 B3 D8 14 36 FE B6)
