From: ccie2be (ccie2be@nyc.rr.com)
Date: Sat Nov 15 2003 - 15:35:18 GMT-3
Thanks for getting back to me on this. However, I was more concerned with
the fact that by default, the MTU size on the Cat 3550 is different than the
default MTU size on Cisco routers. I was aware that the MTU size on OSPF
neighbors need to match for an adjacency to form as the link you provided
proved. However, the example, in the link shows that on one router the MTU
size had been manually changed from it's default setting.
In the originial question, there was a problem because the default MTU on
the Cat is different than the default MTU size on the router.
This leads to the obvious question of why the Cat 3550 has a different
default MTU size than Cisco routers?
Another question is what other potential problems lay in wait because of
this different default MTU size?
I would think that if Cisco decided to have a different default MTU size on
the Cat 3550 compared with it's routers, there's probably a reason for that
and since this will cause problems, at least with OSPF, this difference
would be well documented. Furthermore, I would expect that Cisco would
highlight those features and functions that depended on the MTU size
matching between the Cat 3550 and routers, since those features won't work
if the MTU size isn't manually changed.
Form a lab point of view, I just think it would be good to have a list of
those features/functions that require the MTU size to be manually changed so
that if something isn't working one would know to wonder if this problem is
a result of a MTU mismatch.
----- Original Message -----
From: <matijevi@bellsouth.net>
To: "ccie2be" <ccie2be@nyc.rr.com>; "seonghui" <seonghui@vads.com>; "'Silvio
Nunes'" <silvio_98@hotmail.com>; <ccielab@groupstudy.com>
Sent: Saturday, November 15, 2003 12:55 PM
Subject: Re: OSPF - MTU mismatch
> Hello CCIE2be,
> This is documented on Cisco's web site, I also believe it is documented in
> Doyle vol1 book. This problem has also been discussed before on
Groupstudy,
> search the archives and I am sure you can find it. Here is the link on
> cisco's website:
>
http://www.cisco.com/en/US/tech/tk365/tk480/technologies_tech_note09186a0080093f0d.shtml
> Sincerely,
> Matijevic
> ----- Original Message -----
> From: "ccie2be" <ccie2be@nyc.rr.com>
> To: "seonghui" <seonghui@vads.com>; "'Silvio Nunes'"
> <silvio_98@hotmail.com>; <ccielab@groupstudy.com>
> Sent: Saturday, November 15, 2003 12:37 PM
> Subject: Re: OSPF - MTU mismatch
>
>
> > I've checked the 3550 documentation and didn't see anything regarding
the
> > need to change MTU for OSPF or any other routing protocol for
adjacencies
> to
> > properly form. Is this problem specific MTU size documented anywhere or
> is
> > this something that you had best just know.
> >
> > Thanks
> >
> > ----- Original Message -----
> > From: "seonghui" <seonghui@vads.com>
> > To: "'Silvio Nunes'" <silvio_98@hotmail.com>; <ccielab@groupstudy.com>
> > Sent: Saturday, November 15, 2003 11:24 AM
> > Subject: RE: OSPF - MTU mismatch
> >
> >
> > > global command --> system MTU 1500
> > >
> > > follow by a reload
> > >
> > > -----Original Message-----
> > > From: nobody@groupstudy.com [mailto:nobody@groupstudy.com]On Behalf Of
> > > Silvio Nunes
> > > Sent: Saturday, November 15, 2003 11:06 PM
> > > To: ccielab@groupstudy.com
> > > Subject: OSPF - MTU mismatch
> > >
> > >
> > > Group,
> > >
> > > When I try to establish an relationship between Interface Vlan1 (Cat
> 3550)
> > > and Ethernet0 (R1) in OSPF, the relationship can not be form because
the
> > MTU
> > > is different:
> > > Interface Vlan1 - MTU Size 1504 bytes
> > > Ethernet 0 - MTU Size 1500 butes
> > >
> > > When I put the command IP OSPF IGNORE-MTU for each interface,
everything
> > > works fine.
> > >
> > > Is there another way to do the same thing ?
> > >
> > > Considering that there is not the command MTU xx for interface Vlan..
> > >
> > > Regards,
> > >
> > > _________________________________________________________________
> > > MSN Messenger: converse com os seus amigos online.
> > > http://messenger.msn.com.br
> > >
> > >
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