RE: System MTU question

Justin,

Did you configure QinQ tunneling during your switching section? If you didn't, it's most like left over from a previous lab, a wr er does not reset system mtu. Overconfiguration is not going to cost you points, only time and you need the MTU's to match for the adjacency to form. It's not IOS version specific, I just wasn't 100% of the syntax of the interface level command, I typically hit the question mark there to make sure :)

-ryan

-----Original Message-----
From: Justin Mitchell [mailto:jgmitchell_at_gmail.com]
Sent: Sunday, October 18, 2009 7:49 AM
To: Nadeem Rafi
Cc: Ryan West; Cisco certification
Subject: Re: System MTU question

Is it IOS version specific then? I'm reviewing the final configs for
the lab and I don't see either command being issued.

Justin G. Mitchell
http://www.google.com/profiles/jgmitchell

On Sun, Oct 18, 2009 at 6:45 AM, Nadeem Rafi <nrafia_at_gmail.com> wrote:
> yes Ryan... its correct. Its under interface.
>
> On Sun, Oct 18, 2009 at 2:38 PM, Ryan West <rwest_at_zyedge.com> wrote:
>>
>> Justin,
>>
>> That's normal, probably a left over system mtu from QinQ configuration.
>> You do have the option of setting of system mtu routing 1500 as a
>> workaround for the 3560 and above series. You can also tell the OSPF
>> process to ignore the MTU on a per-interface basis. Ip ospf mtu-ignore (I
>> think).
>>
>> -ryan
>>
>> -----Original Message-----
>> From: nobody_at_groupstudy.com [mailto:nobody_at_groupstudy.com] On Behalf Of
>> Justin Mitchell
>> Sent: Sunday, October 18, 2009 7:35 AM
>> To: Cisco certification
>> Subject: System MTU question
>>
>> I am working on an OSPF configuration and watching the console
>> messages long enough I get to see one neighbor go up and down with the
>> message:
>>
>> R3#
>> *Nov 7 21:13:10.955: %OSPF-5-ADJCHG: Process 1, Nbr 112.12.108.1 on
>> FastEthernet0/0 from EXSTART to DOWN, Neighbor Down: Too many
>> retransmissions
>> R3#
>> *Nov 7 21:14:10.955: %OSPF-5-ADJCHG: Process 1, Nbr 112.12.108.1 on
>> FastEthernet0/0 from DOWN to DOWN, Neighbor Down: Ignore timer expired
>>
>> So I issue "debug ip ospf ev" and get the notice the following:
>>
>> *Nov 7 21:11:12.815: OSPF: Rcv DBD from 112.12.108.1 on
>> FastEthernet0/0 seq 0x12A6 opt 0x52 flag 0x7 len 32 mtu 1504 state
>> EXSTART
>> *Nov 7 21:11:12.815: OSPF: Nbr 112.12.108.1 has larger interface MTU
>>
>> I changed to the switch causing the problem and set "system mtu 1500"
>> reloaded and then the adjacency forms without any problems.
>>
>> Is this normal? I usually don't set the MTU unless required for
>> overhead reasons.
>>
>> Justin G. Mitchell
>> http://www.google.com/profiles/jgmitchell
>>
>>
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Received on Sun Oct 18 2009 - 07:52:48 ART