MPLS auto-tunnel backup issue for MPLS L3 VPN !

Answered Question
May 14th, 2010

Hi All


When I using MPLS Auto-tunnel backup feature and running MPLS L3 VPN Services , I am unable to get the Lables over this tunnel for the BGP VPNv4 Peer as this tunnel is not enabled for MPLS by default.


I need to go and manually config this Tunnel Interface for MPLS to achieve that.


I was thinking is there a way to do it dynamically, the way we have it for auto-tunnel primary using this command


mpls traffic-eng auto-tunnel primary config mpls ip.


I am not seeing any such command for auto-tunnel backup.


Regards

Vaibhava Varma

Correct Answer by Olivier ARRIGHI about 6 years 9 months ago

Right, the rule is that the primary tunnel is never seen down, just encapsulated in the backup tunnel by adding one level of tag(thanks to rsvp), so no need of ldp running through this backup tunnel, as your primary tunnel is still alive,and taking care of your LDP lsp.

In the case of auto tunnel, as the primary tunnel is a one hop tunnel only you don't have any rsvp label stacked, as it is poped because of implicit-null behavior.However, you will notice the label added by rsvp when encapsulating the primary tunnel in the backup tunnel, so you will have the following labels from bottom to top of the stack when primary path broken : vpn label, ldp label(obtained over the rsvp tunnel),rsvp label(backup tunnel)




Also make sure Auto-tunnel is right for you as there are caveats, not very NSF friendly, and no control on your tunnel numbering, as a tunnel could have his name changed on a reboot for example.So not very cool for troubleshooting and monitoring.




olivier

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Olivier ARRIGHI Fri, 05/14/2010 - 12:00

Hi Vaibhava


mpls traffic-eng auto-tunnel primary config mpls ip. should be enough and enable ldp over the backup tunnel. It worked for me.


Are you sure your backup tunnel is up and running?


olivier

Vaibhava Varma Fri, 05/14/2010 - 15:41

Hi Olivier


Yes the backup tunnels are up and running but thet are not showing up as MPLS enabled and hence as a reason it seems to me that my MPLS L3 VPN Traffic would be breaking. Ok let me put this other way. What I mean to say is I am not seeing the Backup Tunnle Interfaces as MPLS Enabled and hence so in case the Primary Goes down the backup will not be able to carry MPLS L3 VN Trafic as the LSP will be broken via backup tunnel. I am having P-P Tunnels and not PE-PE.Hence P-P Backup Tunnel will not have MPLS Lable for the  BGP VPNv4 Remote Peer of PE Routers 



Regards

Vaibhava Varma

Vaibhava Varma Sat, 05/15/2010 - 09:30

Hi Olivier


I did some research on this and I have figured it out as you said it works fine even though the Backup Tunnels are not MPLS Enabled


In the event of Primary Tunnel Failover due to the protected path being down the Primary Tunnel itself is mapped to the already existing Backup Tunnel to the same Tailend. Since the Primary Tunnel is MPLS enabled and hence traffic is still flows smoothly. The MPLS forwarding table always shows the MPLS Labels for the BGP VPNv4 remote peer as learnt via Primary Tunnel (though labels are lost for a while and rebuilt). The backup tunnel does not actually carries the traffic but tells the Primary Tunnel to be rerouted across the Backup Tunnel Path.


Regards

Vaibhava Varma

Correct Answer
Olivier ARRIGHI Sat, 05/15/2010 - 09:49

Right, the rule is that the primary tunnel is never seen down, just encapsulated in the backup tunnel by adding one level of tag(thanks to rsvp), so no need of ldp running through this backup tunnel, as your primary tunnel is still alive,and taking care of your LDP lsp.

In the case of auto tunnel, as the primary tunnel is a one hop tunnel only you don't have any rsvp label stacked, as it is poped because of implicit-null behavior.However, you will notice the label added by rsvp when encapsulating the primary tunnel in the backup tunnel, so you will have the following labels from bottom to top of the stack when primary path broken : vpn label, ldp label(obtained over the rsvp tunnel),rsvp label(backup tunnel)




Also make sure Auto-tunnel is right for you as there are caveats, not very NSF friendly, and no control on your tunnel numbering, as a tunnel could have his name changed on a reboot for example.So not very cool for troubleshooting and monitoring.




olivier

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