Ignoring Inbound I think depends on what type of packet it is.
A while back while experimenting with RFC 1483, one end of a circuit had a
MTU of 4470 (default ATM if memory serves...) and the other had 1500.
OSPF was configured across this circuit but an adjacency would not form.
When OSPF debugging was turned on it was cool that we actually got an
English type of answer on the lines of "MTU mismatch".
When the ATM interface was changed to 1500 the adjacency formed and routes
were propagated.
So another case of "it depends".
Kevin Wigle
----- Original Message -----
From: "EA Louie"
To:
Sent: Sunday, 16 September, 2001 08:26
Subject: Re: MTU Question [7:20096]
> > I am a little confused about how the MTU size
> > configured on an interface affects the transmission of
> > packets through that interface. My question is does it
> > affects packets received on the interface or packets
> > transmitted out of the interface?
>
> Great question. It definitely affects packets transmitted OUT of the
> interface - if the packet is larger than the interface ip mtu, the router
> fragments the packet using the configured interface MTU value. A
> demonstration of this is in GRE tunnel applications, which are by default
> 1478 bytes (as opposed to 1500), so that a 1500 byte packet gets
fragmented
> when traversing the tunnel.
>
> On an INBOUND packet, the MTU is ignored.
>
> Just to verify this, I ran a bunch of debugs that show outbound
> fragmentation, but inbound the packets are not fragmented, just forwarded
to
> the next interface.
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=20114&t=20096
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