SD-Access Design

[jeanciriacdorgelest]

Hello everyone

In the SD-Access Design with Layer 3 Routed Access I noticed that the access switches are interconnected to the distribution switches but not directly to each other.

So I'd like to know, since the routing decision is made directly at the access switches, why not interconnect them directly to each other in addition to interconnecting them to the distribution switches?

[andy!doesnt!like!uucp]

bc access-switches build VXLAN tunnels between themselves when traffic needs to be delivered between endpoints within SDA Site's arbitrary VN. otherwise traffic leaves SDA Site via BNs. Having distribution switches in the middle is the matter of underlay architecture (when BNs have not enough ports to interconnect to each access-switch or/& BNs throughput limitations).

[jeanciriacdorgelest]

I understand this principle well with VXLANs

But I'm just asking if it's possible to interconnect access switches
directly with links.

[andy!doesnt!like!uucp · Accepted solution]

theoretically u could build even full-mesh L3 fabric instead of IP CLOS, but what would be the purpose of this? what would be the benefit of paying for interswitch-links from single EN to each & every EN in the Fabric? imagine single fabric site with 20xENs. from each EN in there u would have to allocate 19xlinks to connect to other ENs (apart of links to BNs). basically DN's purpose is to make connectivity job in underlay instead. 

[jeanciriacdorgelest · Accepted solution]

Okay I understand. Thanks for this answer

Best regards