Tunnel in MPLS VPN L3

Unanswered Question
Apr 23rd, 2007

hi.. anybody know what and how tunnel is for in mpls actually? is it tunnel ipip or gre? how it change the way plain MPLS works? where and how the tunnel need to be configured and qos configured? tx friend..

I have this problem too.
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Harold Ritter Mon, 04/23/2007 - 18:48

I suppose you are referring to RSVP-TE Tunnels. This type of tunnel is not ip based bit rather MPLS based.

MPLS TE uses RSVP to set up an LSP between the head end router and the tail end router. This LSP is then used by the head end router to forward traffic destined to or behind the tail end router.

TE tunnels are configured on the head end router and are uni-directional in nature, so you generally want to have another tunnel configured in the reverse direction.

Hope this helps,

jemekeren Wed, 04/25/2007 - 00:40

tx a alot hritter. you said tunnel that exist at the head end and tailend. does it indicates that tunnel only used on pe to pe? and not used an pe to p? and what kind of tunnel is used? tunnel that used third stack label? tx for info...

Harold Ritter Wed, 04/25/2007 - 04:38

Jimmy,

Your tunnel can be between any two LSRs, ie. PE-PE, PE-P, P-P. My point was more that if you have a TE tunnel between two PEs then you don't need LDP to signal the end to end LSP between the ingress and egress PE.

On the other hand, if the LSP is between a PE and a P or a P and a P then you still need to use LDP to signal an end to end LSP between the ingress and egress PE. In this case you end up with a 3 label stack when the traffic flows over the TE tunnel (te tunnel label, IGP label and VPN label).

Hope this helps,

jemekeren Fri, 05/04/2007 - 21:50

yes..tx hritter. if "Te tunnel between two PEs" dont need LDP so what labels(stack) is used? is it te tunnel label + vpn label only? tx for attention.

mohammedmahmoud Fri, 05/04/2007 - 22:04

Hi Jimmy,

Basically every LSR must have the entire network topology which can be done only via using OSPF or ISIS (as they are the only IGPs that hold the entire topology) --> Accordingly OSPF or ISIS with MPLS TE extensions is needed.

OSPF and ISIS MPLS TE extensions can propagate available resources and constraints of all network links.

Either RSVP or CR-LDP can be used to create the TE tunnel and propagate the TE Labels in the control plane.

NOTE: Because RSVP with TE extensions takes care of the distribution of the MPLS labels,

you do not need to configure Label Distribution Protocol (LDP) on the interfaces. Therefore, the MPLS network does not strictly need to have mpls ip on the interfaces, if TE is deployed. However, if you do not deploy TE to carry all traffic from ingress LSRs to egress LSRs, you need LDP to avoid unlabeled traffic in the core network. MPLS VPN traffic, for instance, needs to be labeled at all times in the core network.

HTH, please do rate if it does help,

Mohammed Mahmoud.

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