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Jonathan Cuthbert
Hi
I have two Border nodes Anyware and two fusion routers
i configure EBGP bentween two borders (Anywhere) and two fusion
i configure iBGP between the two border (Anywhere)
B1-->Fusion1 : EBGP
B2-->Fusion2 : EBGP
B1-->B2 : iBGP
when i loss the connection between B2 and Fusion router i check my routing table on B2 i see the default route 0.0.0.0 through the EDGE node with ISIS so in this stat i have my problem
but looks like in SDA it's mandatory (i'd be glad to be mistaken :0)
If I may answer your question with another question:
What do you think IBGP between redundant border nodes is "mandatory?"
Two of the most common questions or common misconceptions in SD-Access revolve around these two subjects:
- What kind of border node should I provision (Internal-Only, External-Only, and Anywhere)?
- Should I use IBGP between my redundant border nodes?
Interestingly, both of these questions came up in this post.
- What kind of border node should I provision (Internal-Only, External-Only, and Anywhere)?
I am currently recording some content for our YouTube channel that I hope will add additional clarity as an answer to this question. To sum things up here, +95% of deployments should use external-only Border Nodes.
Here is the diagram provided in the original question.
These should be external-only border nodes. Based on the information provided, they should not be anywhere border nodes. It's adding configuration (and thus potential complexity/interactions) that are unneeded.
Adding in even further, there should absolutely be crosslinks here. This topology is a square. Square topologies do not provide the resilience and failover and deterministic convergence needed in networks today. They should be avoided unless there is simply not enough fiber to make it possible. Saying another way: avoid them unless there is absolutely no other choice. I covered this heavily in the SD-Access CVD. "build triangles, not squares, to take advantage of equal-cost redundant paths for the best deterministic convergence."
2. Should I use IBGP between my redundant border nodes?
This is a question that is pretty large in scope to answer. There is no definitive yes and definitive no. It is all based on what the network is trying to accomplish along with the topology. I am working on answering this question in all the variations and permutations in a guide I am working on.
Bear in mind that when we are discussing IBGP, we are asking two questions:
- Should I use IBGP between my redundant border nodes (in the underlay)
- Should I use IBGP between my redundant border nodes (in the overlay)
It's insufficient to just answer one and not the other, as they both accomplish completely different things and neither are strictly due to SDA. The underlay question has to do with how to avoid using the IGP to 'heal' the BGP domain and the overlay question has to do with how to address VRFs continuity in BGP while providing deterministic failover and redundancy.
