From: ccie2be (ccie2be@nyc.rr.com)
Date: Wed Aug 10 2005 - 18:16:13 GMT-3
Shawn,
Yes, ospf requires the mtu to match to form an adjacency. However, you can
tell ospf to ignore mtu size or make sure the mtu's are the same.
On a 3550, there are 2 ways to change the mtu size:
a) change the system mtu which requires a reboot or
b) change the mtu per vlan - no reboot required, however, the vlan mtu
must less than or equal to the system mtu.
If allowed, I would always use a method that doesn't require a reboot.
HTH, Tim
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Shawn williams
Sent: Wednesday, August 10, 2005 5:03 PM
To: ccielab@groupstudy.com
Subject: OSPF Adjacency issue and MTU mismatch
I'm working with a Cisco 2501 and a Catalyst 3550.
I configured them both for OSPF area 0. I was not able to form an OSPF
adjacency between the two devices until I changed the ethernet MTU size on
the Catalyst 3550 from 1503 to 1500 to match the 2501.
Can someone explain what is happening here? I can pass data between the two
devices without adjusting the MTU size, but can't form an OSPF adjacency. Is
MTU size a parameter that must match like hello timers or does OSPF use the
maximum frame size when forming adjacencies?
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