Adding one ISL will cause a loop?

[DrPepper1234]

Good morning to all, I'm here to ask a question...

I've got two MDS9513, each in a different building. They are connected via ISL port-channel.

Let's call them MDS1 and MDS2

MDS2 is connected also to a Nexus 5K (N5K1), via ISL port-channel as well, so connectivity from MDS1 to N5K1 is allowed through MDS2.

MDS1 <-> MDS2 <-> N5K1

Is it allowed to add one more ISL, directly from MDS1 to N5K1, without causing network problems?

If this would be an IP network, STP should be enabled in order to avoid loops.

Anyway I don't know how SAN behaves in such a case.

Thanks a lot.

[Walter Dey · Accepted solution]

Fibrechannel runs a routing protocol FSFP at the datalink layer; therefore no spanning tree.

However, the usual routing metrics apply, and you can check the routing table on each switch.

e.g. form MDS1 to N5k1 are 2 paths, one direct, the other 2 hops; if all are same speed, always the direct hop is used !

Walter.