MPLS TE over Inter-AS

Today we will talk about a special case of using MPLS TE tunnels over Inter-AS connection, but before showing up this idea and how it works out we need firstly to define the meanings of Inter-AS and MPLS TE Tunnels.

Inter-AS MPLS VPN is invented to maintain the continuity of VPN services across multiple service providers, mainly for customers who span world wide on different service providers. So technically it is achieved by  maintaining a connection between the service providers – ASBR routers – and exchange customers routes.

Now, lets define the MPLS TE Tunnels as these tunnels are very important and useful component to optimize the network resources and drive the traffic in planned paths. like in the below shown topology:
MPLS TE Tunnels


In the previous topology we just need to optimize the links utilization across our network by controlling the forwarded traffic from R1 to R6, so simply we just create a TE tunnel and specify the path statically – by using explicit path option and specify all the next hops – or dynamically – by making the tunnel chose the path depending on the IGP itself – to be like that: R3 then R4 then finally reach R6.

Without going in deep details, what if we have an Inter-AS connection and want to Traffic Engineer the traffic end-to-end in order to achieve the best of the best. So that we gonna have to know how to do that “MPLS TE over Inter-AS”, firstly enable the MPLS TE and RSVP on all devices that are in the path of the traffic in both Autonomous-Systems, yes it is the same start of creating Intera-area MPLS TE tunnel, also creating the tunnel itself is the same but the only restriction is no dynamic path option for this type of tunnels. So that we have to create an explicit path list with the next-address loose* option and specify the loopback of OUR ASBR and the ASBR of the next AS.

*loose option is to specify non-direct hop of the mentioned path.

After finishing we just have only one step is to enable the Inter-AS TE under the ASBR outside interface.

Enabling this option is by defining the interface as MPLS TE passive interface and defining neighbor’s parameters as follow:
1- nbr-te-id : The MPLS Traffic Engineering router ID of the neighbor.
2- nbr-igp-id: Define the IGP used by the other AS if OSPF or IS-IS and then define the ID itself of the neighbor “in-case of IS-IS the net address is the ID”.
3-  nbr-if-addr: The point-to-point interface between our ASBRs.

for example:

ASBR#show run int fa 1/0
Building configuration…

Current configuration : 260 bytes
interface FastEthernet1/0
ip address
speed auto
duplex auto
mpls traffic-eng tunnels
mpls traffic-eng passive-interface nbr-te-id nbr-if-addr nbr-igp-id isis 01.0000.0000.0002.00
ip rsvp bandwidth


Note: Tunnels are one way, for the MPLS TE tunnel it shouldn’t know the way to the Tail-End router as the ASBR will handle it, but if we created just one tunnel from A to B, B does not know how to return back to A so you have to create another Tunnel for the return traffic.

Try it and enjoy if you can 😉