Set Redundancy Through Another WAN Edge using TLOC Extensions

This method becomes handy when there are 2 physical WAN Edges at a branch, each with a separate transport like in the following design. I am only going to explain the logic behind this and how it works, not going to make this a configuration guide.

In this example, cEdge2 is taken in to consideration. As you can see, cEdge2 has only one transport which is a MPLS connection. On the other hand, cEdge1 has another transport to Internet (Biz-Internet). Both has internal connection to Site-2 Core Switch but Gi3 interface of cEdge2 is configured with OSPF only to learn 192.168.22.0/24. So cEdge2 will only advertise 192.168.22.0/24 subnet to OMP via its transport MPLS.

Requirement is like the following..

Make a redundant path for 192.168.22.0/24 subnet through cEdge1 router which means utilize the Internet Link of cEdge1 to give redundancy to the MPLS traffic going through cEdge2.. In other words, 192.168.22.0/24 should be able to access from vEdge1 even after MPLS of cEdge2 is down even though it seems the only path.. 

This can be achieved by configuring a TLOC Extension interface on Gi2 interface of cEdge1.

To do that, following things are required to be done.

1. Gi1 of cEdge2 should be configured as a Tunnel Interface of Biz-Internet color.

2. A default route is needed in cEdge2 to reach controllers and biz-internet cloud; next-hop should be the Gi2 of cEdge1.

3. Gi2 of cEdge1 should be configured as a TLOC Extension Interface, a Non Tunnel Interface.

4. There must be a route from Internet to reach 10.12.12.0/30 subnet, the next-hop should be Gi1 interface of cEdge1 which is for the reverse traffic.

5. There should be NAT enabled on Gi1 interface of cEdge1.

To make the Gi2 Interface of cEdge1, navigate to Advanced in Interface Template of G2.

TLOC Extension field should be configured as "GigabitEthernet1" which specifies the interface it will forward the traffic to; from the TLOC Extension Interface.

NAT Configuration will be like the following in Interface Template of Gi1 of cEdge1.

Routes will be like the following from vEdge1;

Biz-Internet TLOC from 10.1.1.113 will be like the following in show omp tlocs output.

Let's check what will happen to the OMP routes when the MPLS link of cEdge2 is down..

It turned the transport in TLOC to biz-internet.

Notes:-

If the TLOC Extension's transport was not Internet, (a private transport); you may not need to configure NAT but will need to advertise the subnet of interlink to service provider etc though BGP or something for the reverse traffic.

If the inter-link is routed through L3 network, GRE tunnel should be configured, but only cEdges will support, vEdges need direct or L2 connectivity.

BFD session for biz-internet will be down while MPLS link is up, it will come up as soon as MPLS link is down.

Before:

After: