From: James Ventre (messageboard@ventrefamily.com)
Date: Mon Apr 11 2005 - 21:03:33 GMT-3
>1) Why was the MTU of the switch appearing as 1504?
Do you have 802.1Q tunneling on? I'm not sure if it would increase it
by default, but that would require 4 extra bytes in the MTU.
James
Matt Mullen wrote:
>Hello group,
>
>I was working a lab scenario this past weekend where there were two
>routers, R6 and R5 both trying to form an OSPF adjacency to a 3550
>switch via a SVI (VLAN interface). The adjacencies were not coming
>up, and a 'debug ip ospf adj' showed me that there was an MTU
>mismatch between the routers and the 3550 switch. The switch had an
>MTU of 1504 while the routers had an MTU of 1500. To correct the
>problem, I set the MTU on the 3550 switch SVI to 1500.
>
>Today going back and checking my work against the solutions, the
>solutions show 'ip ospf mtu-ignore' being configured on the routers
>and on the SVI. So, this leads me to a couple of questions:
>
>1) Why was the MTU of the switch appearing as 1504? Is it possible
>that the switch automatically bumped the system mtu up to 1504 because
>I had previously configured 802.1Q tunneling? I thought you had to
>manually set the 'system mtu 1504' for this to happen, which I didn't
>do.
>
>2) Is there anything wrong with the solution I used to solve the
>problem? i.e. Would I get the points?
>
>TIA,
>
>Matt
>
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