What is the benefit of TLOC Extension?

[muthumohan]

Hello,

I do not understand the benefits of TLOC Extension. I does not seem to provide any more redundancy compared to two routers connecting to two separate transports. It only creates more IPSec tunnels and complicates the configuration.

Can anyone show me why would the customer go for TLCO extension and what benefit they get?

Thanks,

Mohan

[Torbjørn]

First thing that comes to mind is that both edges on a site must have TLOC of each color/be aware of each transport if you wish to use application pinning, or if you wish to use application-aware routing.

[MHM Cisco World]

Cisco SD-WAN TLOC Extension and VRRP - YouTube

this video is so so good to explain the TLOC extension. 

Thanks A Lot
MHM

[Gopinath_Pigili]

• TLOC extension is a feature that allows a WAN Edge router to communicate over the WAN transport connected to the adjacent WAN Edge router through a TLOC-extension interface
• TLOC-extension feature allows to  extending the WAN transports to both SD-WAN routers without requiring direct attachment to both service provider clouds.
• The feature is set up in a per-interface manner and provides transparent connectivity from one interface (called a TLOC extension interface) to a particular WAN transport. 

Best regards
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[muthumohan]

Thank you all for your responses. I understand what is TLOC Extension and how it works. But what I fail to understand is how is it improving the availability of a site against a transport failure or WANEdge failure. For example, if a WAN Edge fails, the transport attached to that WANEdge becomes unavailable too. Or if a transport fails, the router attached to that transport is of no use to the site, because the traffic will anyway exit the other router/transport. So, what benefit does TLOC extension bring to improve the availability of a site is my question. Thanks.

[Kanan Huseynli]

Hi,

you are correct, in in reality does not provide redundancy. Because if router A fails or WAN circuit which is terminated on router A fails, then router B also loses that WAN circuit (i.e TLOC).

The only benefit is, based on design you may not want to connect both routers to intermediate L2 device to avoid dependency on "perimeter L2 device". And you don't want the second ISP / SP link for the same WAN circuit for cost point of view (each port/ connection is separate connectivity, thus adds cost). CVD also describes similar things:

There are times when WAN Edge routers cannot be connected to each transport directly and only one WAN Edge router can be connected to a single transport.

Alternatively, a switch can be connected to each transport and the SD-WAN routers can connect to each transport through the connected switches. This is not usually recommended at a branch because it adds cost to the solution and results in having another device to manage.

https://www.cisco.com/c/en/us/td/docs/solutions/CVD/SDWAN/cisco-sdwan-design-guide.html

In this case, you may use TLOC extension to have two TLOCs and in case of one circuit fails you still have both routers on the overlay.

I just figured out, it can be case to have one border router with higher performance (routerA) and some additional features enabled on them. But another router (routerB) with pure routing functionality. You may have ingress and egress path primarily via routerA and when its circuit fails, it is still functions through routerB (which will just forward routerA packets to/from). And at worst case, if routerA is totally fails, you still have routerB for simple routing without additional functions.

[MHM Cisco World]

what point you confuse about ? 

Why tloc extension  ? The answer is COST

If you have two vedge and you need to give redundacy you need two circuits mpls and two circuits internet connect to both vedge.

With extension you need two circuits.

Mpls connect to vedge-1 and internet connect to vedge-2 and for redundacy we use extension.

That it.

MHM