[c-nsp] jumbo frames

[Gert Doering]

Hi,

On Sat, Mar 04, 2006 at 11:45:33AM -0500, Alex Rubenstein wrote:
> >They need to match the MTU of all hosts connected to the respective
> >VLAN.
> 
> In practive, should the MTU of the SVI be larger than that of the hosts on 
> the network, Stuff Works Right Most Of The Time (tm).

This is a clear example of something that will eventually come back, 
bite you in the behind, and everybody will wonder "what happened?  It
worked all the time, didn't it?".

This works fine, *as long* as nobody will ever send a packet towards
the L3 switch that's larger than the host MTU - which will be the
normal case if all "other" devices on "other" LANs are using the same
sized MTU.

Add some WAN links that come with a larger default MTU, and, say, an
IP tunnel terminating in a router connected to one of the WAN links 
and going to one of the hosts -> boom, doesn't work (but only for
large packets, "ping" works fine), and you'll spend hours to diagnose
that.

Such misconfigurations should better fail right away, but alas, they
don't.

gert
-- 
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Gert Doering - Munich, Germany                             gert at greenie.muc.de
fax: +49-89-35655025                        gert at net.informatik.tu-muenchen.de