From: marvin greenlee (marvin@ccbootcamp.com)
Date: Mon Apr 11 2005 - 23:06:48 GMT-3
If a system MTU change on the router requires a reboot in order to take
effect, don't you think the MTU change would be able to survive a reboot?
Look at the flash before and after a MTU change.
**** Before changing ****
3550_B#show flash
Directory of flash:/
2 -rwx 4203904 Jan 1 1970 09:27:03 +00:00
c3550-i5q3l2-mz.121-20.EA1
a.bin
3 -rwx 976 Mar 6 1993 00:49:18 +00:00 vlan.dat
5 -rwx 0 Mar 25 1993 07:14:00 +00:00 system_env_vars
6 -rwx 5 Mar 1 1993 06:31:15 +00:00 private-config.text
7 -rwx 3191 Mar 1 1993 06:31:15 +00:00 config.text
8 -rwx 16 Mar 25 1993 07:14:00 +00:00 env_vars
15998976 bytes total (11788288 bytes free)
**** Set the clock, and change MTU ****
3550_B#clock set 12:00:00 11 April 2005
3550_B#conf t
Enter configuration commands, one per line. End with CNTL/Z.
3550_B(config)#system mtu 1505
**** After changing ****
3550_B#show flash
Directory of flash:/
2 -rwx 4203904 Jan 1 1970 09:27:03 +00:00
c3550-i5q3l2-mz.121-20.EA1
a.bin
3 -rwx 976 Mar 6 1993 00:49:18 +00:00 vlan.dat
4 -rwx 16 Apr 11 2005 12:00:16 +00:00 env_vars
6 -rwx 5 Mar 1 1993 06:31:15 +00:00 private-config.text
7 -rwx 3191 Mar 1 1993 06:31:15 +00:00 config.text
8 -rwx 0 Apr 11 2005 12:00:16 +00:00 system_env_vars
Marvin Greenlee, CCIE#12237, CCSI# 30483
Network Learning Inc
marvin@ccbootcamp.com
www.ccbootcamp.com (Cisco Training)
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Matt
Mullen
Sent: Monday, April 11, 2005 5:22 PM
To: James Ventre
Cc: Group Study
Subject: Re: system MTU and OSPF [bcc][faked-from]
Importance: Low
James,
Yes, I did have 802.1Q tunneling configured on interface f0/20.
According to the doc CD for 802.1Q tunneling the system MTU is 1500 by
default and you must manually set it to 1504 with the 'system mtu'
command. I didn't configure the 'system mtu' command however. One
possibility I just thought of was that maybe someone on the rack
before me set the system mtu to 1504 and the switch wasn't rebooted.
Thanks,
Matt
On Apr 11, 2005 7:03 PM, James Ventre <messageboard@ventrefamily.com> wrote:
> >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
> >
> >_______________________________________________________________________
> >Subscription information may be found at:
> >http://www.groupstudy.com/list/CCIELab.html
>
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
This archive was generated by hypermail 2.1.4 : Tue May 03 2005 - 07:54:56 GMT-3