SD-Access Design - 2-tier and 3-tier Border Node Connectivity

[MAP_2k]

Due to the amount of EN nodes in our environment we need to implement intermediate nodes but we are still short of a few ports on the intermediate node to connect all EN.

In the design can we connect EN to the Intermediate Nodes and have EN connect to the BN? So a mix of 2-tier & 3-tier connectivity to the BN, as shown in the picture below.

From my perspective I don't see a issue as long as everything is Layer 3 reachable, but maybe someone with more deployment expertise could share their thoughts. Thanks.

[Torbjørn · Accepted solution]

Creating the topology like this is not an issue. As long as you have the required redundancy for all nodes and everything is L3 reachable(preferrably LAN automated/fully routed) it is fine.

[Sylvain_Che]

We have deployed such environment and have no issue at all.

[M02@rt37]

Hello @MAP_2k 

Your proposed design is feasible as long as certain conditions are met...

The primary requirement is ensuring L3 reachability across the entire topology. Both edge nodes connected directly to the Bacbone Node and those connecting via an Intermediate Node must have reliable IP conectivity to the BN. 

Introducing an IN layer adds complexity to the network, and care must be taken to avoid creating L2 loops... While most designs at this level are fully L3, any residual L2 connections must be managed carefully. Alternatively, you can design a completely loop-free L3 topology by avoiding redundant Layer 2 links altogether.

Another consideration is the impact of an additional hop in the network. Intermediate Nodes add a slight increase in latency and could create bandwidth bottlenecks if not properly sized. Ensure that the IN has sufficient capacity to handle aggregated traffic from multiple EN nodes without introducing congestion, especially for bandwidth-intensive or latency-sensitive applications.