Cisco SDA - Why does routed access layer design recommend using IS-IS

[yaddekolrt]

Currently studying for my CCNA and I am in the Software-Defined Access section. I saw that the recommended configuration includes the IS-IS underlay protocol. I started researching if other protocols were supported and others stated that it really doesn't matter and that I can use OSPF as well. However, I saw one mentioning that is better to use OSPF when the SDA is not going to scale to a very large amount.

So my question is, why is IS-IS recommended mostly when on large-scale SDA deployment compared to other underlay protocols like OSPF.

[Joseph W. Doherty]

My guess would be IS-IS has various extensions capabilities, that SD-WAN might take advantage of, that might be most useful in a large scale network.

[David Ruess]

Hello,

As far as I know the IS-IS is definitely used for the LAN automation but any IGP works.

You can check the Cisco Validated Design Guides here:

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

Noteable this section:

  LAN Automation for deployment—The configuration of the underlay can be orchestrated by using LAN Automation services in Cisco DNA Center. The LAN Automation feature is an alternative to manual underlay deployments for new networks and uses an IS-IS routed access design. Although there are many alternative routing protocols, the IS-IS routing protocol offers operational advantages such as neighbor establishment without IP protocol dependencies, peering capability using loopback addresses, and agnostic treatment of IPv4, IPv6, and non-IP traffic. Manual underlays are also supported and allow variations from the automated underlay deployment (for example, a different IGP could be chosen), though the underlay design principles still apply.

It doesn't mention specifically Small/Large networks. Can you provide the resource that mentions it and under what context?

-David