Not strictly an OpenWRT question here, but I know that the knowledgable people here will help!
Am I right in thinking that it's OK to set up circular links between switches (that is to say, if I have 3 switches, connect A to B, B to C and C to A) so long as Spanning Tree Protocol is enabled?
In this scenario, it would create a fault tolerant situation where if the link from B to C failed, STP would automatically re-route packets via switch A (B to A to C)?
Does STP handle this all automatically?
STP is implemented in software kernel bridges, it's not part of hardware switches. So you'd need to set it up so any potential loop goes through a software bridge with STP enabled.
Yes, that is the exact scenario why STP was created. However, the failover functionality may not be as fast as you would expect.
Yup. I've actually explicitly disabled STP for a bunch of VPNs using tap bridges because STP causes significant initialization delays in just bringing the connection up.
Sure, but in terms of enabling it on an L2 managed switch.. this should be a no-brainer right?
Also this switch supports RSTP (Rapid STP) which I think is designed to make these delays significantly shorter.