probably a noob question but any help is appreciated.

Question: What are the disadvantages of spanning L2 subnets across a WAN as opposed to a routed connection?

Background: I've got a client who's setting up a new link between their two office locations carrying separate traffic (essentially a new internal "tenant"). They have an MPLS link already, but are talking about spanning multiple L2 domains across the network (using VPLS or similar). For similar clients in the past we've always established a routed connection between the sites. There are no application-specific limitations that are driving the L2 connection, I think they're just not familiar with routing. My specific network knowledge is limited here but I'm sure L3 connectivity is better, so I'm not sure how to guide them towards a routed connection.

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    You also extend all the layer-2 problems, such as spanning tree failures and broadcast storms that can bring a site down. You are also at the mercy of layer-2 broadcasts crossing the WAN and wasting WAN bandwidth.
    – Ron Maupin
    Commented Jan 9, 2019 at 0:34

1 Answer 1


L2 bridging is not a good approach for a network extended over WAN. L2 protocols are ill-suited for bandwidth-limited and high-latency connections.

Bridging a gigabit network over something like 10 Mbit/s WAN (in extreme) requires very elaborate filtering. You won't want that.

You are correct, they will be much better off using a routed link over an L3 tunnel, especially with integrated encryption - the usual VPN.

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