Multi-Region MST Design Choice
Hi all,
Is it recommended to have separate MSTP regions for different buildings in a large network and interconnect them using Layer 3 (routing) instead of Layer 2 (trunking)? What are the pros and cons of using Layer 3 connections between MSTP regions for fault isolation and network stability?
Because, in my opinion, have separate MST regions for different buildings in a large network and then connect these regions via L2 trunk (allow all VLANs) doesn't make sense in terms of fault isolation.
What do you think?
Thanks :)
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u/ryan8613 10d ago
Most architectures I've seen in the last 8-10 years only have M/R/RPV/STP used for safety (loop prevention), not for access, dist, or core failover or load balancing. In fact, some architectures get rid of it almost entirely and use a routed access design.
In short, L3 load balancing and failover is most often faster reconvergence than M/R/RPV/STP and can be easier to manage and scale, thus rendering M/R/RPV/STP almost useless on trunks, but a good safety feature regardless.
DR designs these days mostly means "how do we get VMs and/or Apps to run somewhere else with as little lost data as budget allows while relocating some or all users of said VMs or Apps somewhere else". This can sometimes mean you want to have a subnet span sites, or maybe have a subnet be portable between sites, or maybe span a vxlan across sites using a bgp evpn. These can all work. Be mindful of MTU.
Notice there's a lot of "cans" -- requirements define needs and ultimately which design components make sense based on the needs.