jumbo frames

Richard A. Steenbergen ras at e-gerbil.net
Wed May 30 19:15:20 UTC 2001

On Tue, 29 May 2001, Dave Siegel wrote:

> I've seen a lot of discussion about why one would want to do Jumbo
> frames on your backbone...let's assume for the sake of argument that a
> customer requirement is to support 9000 bytes packets across your
> backbone, without fragmentation.
> Why not bump MTU up to 9000 on your backbone interfaces (assuming they
> support it)?
> What negative affects might this have on your network?
> a) performance delivering average packet sizes
> b) QoS
> c) buffer/pkt memory utilization
> d) other areas

Theoretically increasing the MTU anywhere you are not actually generating
packets should have no impact except to prevent unnecessary fragmentation.
But then again, theoretically IOS shouldn't get buggier with each release.

There will obviously be different packet handling techniques for the
larger packets, and I'm not aware of any performance or stability testing
that has been done for jumbo frames. I'm guessing the people who are
actively using them havn't been putting it in line rate mixed small and
large packets conditions.

Obviously anything extra and uncommon you try to do runs the risk of
setting off new bugs (even common stuff sets off new bugs). I can tell you
some of the drivers I have seen for PC gige cards (especially linux) badly
mangle jumbo frames and may not perform well.

Richard A Steenbergen <ras at 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)

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