[afnog] afnog Digest, Vol 54, Issue 19

Frank A. Kuse franko at africaonline.com.gh
Mon Sep 22 15:06:01 UTC 2008


HI Scott,

I have set same MTU value on both interfaces. And on the FastEthernet
Interface, i have set an equivalent MPLS MTU value.

Cheers, 

Frank A. Kuse
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Today's Topics:

   1. Re:  Problem bringing up MPLS on disimilar interfaces
      (Scott Weeks)
   2. Re:  Problem bringing up MPLS on disimilar interfaces
      (Frank A. Kuse)
   3. Re:  Problem bringing up MPLS on disimilar interfaces (Mark Tinka)
   4. Re:  Problem bringing up MPLS on disimilar interfaces (Mark Tinka)


----------------------------------------------------------------------

Message: 1
Date: Fri, 19 Sep 2008 13:31:06 -0700
From: "Scott Weeks" <surfer at mauigateway.com>
Subject: Re: [afnog] Problem bringing up MPLS on disimilar interfaces
To: <afnog at afnog.org>
Message-ID: <20080919133106.79037BE6 at resin15.mta.everyone.net>
Content-Type: text/plain; charset="UTF-8"



------- franko at africaonline.com.gh wrote: -------------
From: "Frank A. Kuse" <franko at africaonline.com.gh>
 
I am having some trouble bringing up MPLS up on disimilar interfaces (
FastEthernet Interface and Gigabit interface both connecting to a cisco 3750
switch with Jumbo frames enabled) When i change the Gigabit interface to a
FastEthernet interface, the MPLS comes up.
I would like to know if it's possible to bring up MPLS up between two
disimilar interfaces.
--------------------------------------------------------



Have you checked the MTU on the router interfaces themselves?  It sounds
like a possible MTU mismatch.

scott







































----------------------------------
----------------------------------
----------------------------------



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Message: 2
Date: Sat, 20 Sep 2008 11:00:06 -0000
From: "Frank A. Kuse" <franko at africaonline.com.gh>
Subject: Re: [afnog] Problem bringing up MPLS on disimilar interfaces
To: "'Alfred Farrington II'" <alfred.farrington at gmail.com>
Cc: afnog at afnog.org
Message-ID: <20080920110001.51A41290E1A at av2.africaonline.com.gh>
Content-Type: text/plain; charset="us-ascii"

Hi Alfred,
 
I'm not getting any errors at all when i do a debug but my MPLS connection
are with Gigabit interface preference.
 
Thanks,
 

...................................................

Frank A. Kuse
Systems Administrator
Africa Online Ghana
Tel: +233 (21) 211 823 Ext: 273
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From: Alfred Farrington II [mailto:alfred.farrington at gmail.com] 
Sent: Friday, September 19, 2008 10:41 PM
To: franko at africaonline.com.gh
Subject: [afnog] Problem bringing up MPLS on disimilar interfaces


What do the logs say? Is your MPLS connection Gig?


>Hi All,
>
>I am having some trouble bringing up MPLS up on disimilar interfaces >(
>FastEthernet Interface and Gigabit interface both connecting to a >cisco
3750
>switch with Jumbo frames enabled)
>When i change the Gigabit interface to a FastEthernet interface, the >MPLS
>comes up.
>I would like to know if it's possible to bring up MPLS up between two
>disimilar interfaces.
>
>Thanks,
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Message: 3
Date: Sat, 20 Sep 2008 19:05:24 +0800
From: Mark Tinka <mtinka at globaltransit.net>
Subject: Re: [afnog] Problem bringing up MPLS on disimilar interfaces
To: surfer at mauigateway.com
Cc: afnog at afnog.org
Message-ID: <200809201905.31363.mtinka at globaltransit.net>
Content-Type: text/plain; charset="iso-8859-1"

On Saturday 20 September 2008 04:31:06 Scott Weeks wrote:

> Have you checked the MTU on the router interfaces
> themselves?  It sounds like a possible MTU mismatch.

Be careful when adjusting interface MTU parametres, as link 
state routing protocols such as OSPF and IS-IS require a 
common MTU value across links before adjacencies can be 
successfully established.

Not sure which routers you're using, but if it's Cisco, 
typically IOS requires that you flap the interface 
(shut/unshut) for any interface MTU changes to take effect 
(my experience in later code).

If it's Juniper, JunOS would implement the new MTU upon 
a 'commit' of the candidate configuration.

Keep this in mind to avoid melting your IGP domain.

side note: It is possible to implement an MTU value at the
           protocol level that would affect only said
	   protocol, while leaving any other protocols to
	   infer their working MTU value from the main interface
	   MTU setting.

  	   However, I'd recommend this be the exception than the
	   rule, depending on the existing complications of your
	   network that you're trying to get around. In otherwords,
	   it may add unnecessary complexity where it's not really
	   needed.

Cheers,

Mark.
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Message: 4
Date: Sat, 20 Sep 2008 19:54:33 +0800
From: Mark Tinka <mtinka at globaltransit.net>
Subject: Re: [afnog] Problem bringing up MPLS on disimilar interfaces
To: "Frank A. Kuse" <franko at africaonline.com.gh>
Cc: afnog at afnog.org
Message-ID: <200809201954.39391.mtinka at globaltransit.net>
Content-Type: text/plain; charset="utf-8"

On Saturday 20 September 2008 03:08:31 Frank A. Kuse wrote:

> I am having some trouble bringing up MPLS up on disimilar
> interfaces ( FastEthernet Interface and Gigabit interface
> both connecting to a cisco 3750 switch with Jumbo frames
> enabled)

Note that if these are Cisco routers, with the exception of 
the high-end kit (i.e., 7600, XR 12000, CRS-1), Cisco don't 
generally support baby giant or jumbo frames on their FE 
cards (although we are now seeing support for being able to 
change the MTU on FE interfaces on the 7200 for much more 
recent code).

> When i change the Gigabit interface to a FastEthernet
> interface, the MPLS comes up.

Could we see some of your configurations on both routers 
(I'm assuming these are Cisco)? If possible, can you send?

* sh run int <interface>
* sh int <interface>
* sh mpls interfaces
* sh mpls ldp neighbor

It'd be good to also look at your IGP configuration.

Recommend that you also have these commands by default in 
your global configuration:

* mpls label protocol ldp
* mpls ldp router-id Loopback0

> I would like to know if it's possible to bring up MPLS up
> between two disimilar interfaces.

It is possible - I've done it before.

Cheers,

Mark.
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