[c-nsp] jumbo frames

[Gert Doering]

Hi,

On Sat, Mar 04, 2006 at 12:10:48AM -0600, Tim Winders wrote:
> MTU on SVI's?
> 
> Do you mean the VLAN interfaces on the 6500?
> 
> And what *should* happen with them?

They need to match the MTU of all hosts connected to the respective
VLAN.

Imagine a jumbo packet coming in "from the outside", and the router
forwarding it to an end host that can only handle MTU 1500 packets - the
packet will be lost.  If the SVI knows that the MTU in *this VLAN* is
only 1500, the router can fragment the packet, or send an ICMP fragmentation
required message back to the sender.

Unfortunately, at least on some 35xx switches (I don't remember the specific
model nor the IOS version - it was at a customer's site, and I no longer
have access to the devices), this does not seem to be possible - there
is only a global L3 MTU value, and it is automatically applied to ALL 
L3 interfaces.  Which sucks.

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