Re: mpls doubts

After enabling mpls ldp sync --- you should consider the below caveat

As per CSCsu65189 caveat:

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Symptoms: If router is configured as follows:

router ospf 1
...
passive-interface Loopback0

And later LDP/IGP synchronization is enabled using the following commands:

Router(config)# router ospf 1
Router(config-router)# mpls ldp sync
Router(config-router)# ^Z

MPLS LDP/IGP synchronization will be allowed on interface loopback too.

Router# sh ip ospf mpls ldp in Loopback0 Process ID 1, Area 0 LDP is not
configured through LDP autoconfig LDP-IGP Synchronization : Required < ----
NOK Holddown timer is not configured Interface is up

If the clear ip ospf proc command is entered, LDP will keep the interface
down. Down interface is not included in the router LSA, therefore IP address
configured on loopback is not propagated. If some application like BGP or
LDP use the loopback IP address for the communication, application will go
down too.

Conditions: Occurs when interface configured as passive. Note: all interface
types configured as passive are affected, not only loopbacks.

Workaround: Do not configure passive loopback under OSPF. *Problem only
occurs during reconfiguration*.

The problem will not occur if LDP/IGP sync is already in place and:

 Router is reloaded with image with fix for CSCsk48227.

 Passive-interface command is removed/added.

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-FJ

On Fri, May 20, 2011 at 10:11 PM, Marko Milivojevic
<markom_at_ipexpert.com>wrote:

> > 1) what is ment by ldp - igp synchornisation . ? by default its disabled
> > ....what benifits i will get if i enable it ?
>
> I think it may be beneficial for you to take a look at this document here:
> http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/fsldpsyn.html
>
> If you have any doubts left after that, let's follow it up here.
>
> > 2) in the follwoing output outgoing actiion is Aggregate ...what does it
> > imply ? i have not done summarization any where ....
>
> It's an Aggregate label. In almost all cases, it indicates an MPLS
> VPN, but it doesn't have to be (in your case it is).
>
> > 3) why is it required that two PE must use loopback interface for BGP
> > sessions ? why it is required that these loopback must be /32 route ?
>
> It isn't required. However, if you are not using Loopbacks for
> peering, or you are not using /32 masks, you need to understand the
> implications. Not using /32 Loopback mask is kind of an issue with
> OSPF that you may need to address. If you're not using Loopbacks, you
> can use whatever interface you like, except the downstream interface
> to your PE peer. Take a look at this:
> http://blog.ipexpert.com/2010/05/31/next-hop-in-mpls-vpns/
>
> --
> Marko Milivojevic - CCIE #18427
> Senior Technical Instructor - IPexpert
>
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Received on Sat May 21 2011 - 16:30:39 ART