One of a significant topic in sd-wan is TLOC extension. In this article, I want to teach how to implement and deploy transport redundancy called TLOC-Extension.
Usually vEdge routers connect to only one respective transport cloud.

But how about a transport failure?
One of the solutions for transport redundancy is TLOC Extension.
In TLOC extension, we connect our vEdge to its neighbor vEdge in the same site for transport redundancy, using two layer 3 link or one link with sub interface.
According to diagram, we have two vEdge routers, and each vEdge router connect to a separated transport cloud.
Now, if our vEdge 1 lost the connectivity to MPLS cloud, it can use other neighbor vEdge transport as backup or redundant. (metro cloud)
So second vEdge router takes over forwarding the traffic.

Let’s go to lab

Configuration

Here the interface configuration for Rome1 vEdge.

And the interface configuration for Rome2vEdgeshown here.

Based on topology, there is a csr router behind Rome1 vEdge. We have OSPF neighborship between them and OMP routes are redistributed into OSPF.

The result of redistribution OMP to OSPF shown in this picture.

Now we have connectivity between Rome-csr and Paris-csr.

TLOC configuration

In this picture, you can see the configuration for TLOC extension.

The red line is for TLOC extension from Rome2 to Rome1 mpls cloud. And the blue line is for Rome1 to Rome2 metro cloud.

So, if Rome2 lost connectivity to metro cloud, it will use Ge0/2 to reach Rome1 mpls cloud.

Verification Process

We are trying to show you the OMP route and IP route tables for Paris csr prefix, after TLOC extension configuration.

As we expected, we have two OMP route and two IP route for Paris csr loopback IP address.

We have a very useful command to check the tunnel statistics on vEdge route.

# show tunnel statistics

Here we want to test TLOC extension function. For this purpose, I want to shutdown Ge0/1 on Rome1 vEdge router.

After losing connection to mpls cloud we can use TLOC extension to reach metro cloud.

Here is the output of IP route table for Paris csr loopback prefix and output of show tunnel statistics.

TLOC extension – redundant only

In my previous picture, if you noticed the output of OMP route and IP route table for Paris csr loopback, we had two routes in our routing table.

If we want to use TLOC extension to metro cloud as REDUNDANT only on Rome1 vEdge , we can use a very cool command and make the TLOC extension ipsec tunnel as redundant only.

# last-resort-circuit

After issuing “last-resort-circuit” command, we have a new output for OMP route.

And now this is the output of Rome1 route table.

last-resort-circuit command has also very important effect on interface.

We practiced how to configure, deploy and how to verify TLOC extension.

I hope you enjoyed the article, waiting for your feedbacks.