Can you use SFP stacking with trunking?
We have two Prosafe S3300-28x switches stacked using two SFP cables. These switches also have two 10Gig ports, which we would like to connect to a separate Prosafe XS708E 10Gig switch.
The idea being that all the 10Gig traffic happens across the 10Gig switch, but it still has access to the rest of the network via the trunked 10Gig connections.
Diagram:
Prosafe S3300-28X -----10Gig trunk 1-----
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SFP SFP Prosafe XS708E
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Prosafe S3300-28X -----10Gig trunk 2-----
Each 1Gig host has a connection to each S3300, and each 10Gig host has a connection to the 10Gig switch as well as two connections to the S3300 stack. Essentially, we are looking for complete redundancy on the 1Gig, not too fussed about the 10Gig, that's more of a nice-ty, but would still like it to work in case one of the S3300's dies.
The problem we have is that it appears as if the 10Gig trunk 2 (when plugged in) causes a loop in the network, and one of the trunks promptly gets disabled. What I want to know is how can I connect these three switches, with a trunk, to be a fail over?
Our thought was that the trunking should handle the looping, but it seems like it doesn't. Is there something else we should be doing instead of trunking?
Best Answer
What you are running into isn't a trunking problem. This behavior is what STP does in order to prevent loops. STP will create a loop-free layer-2 by sending BPDUs to determine the possible paths to the root bridge, and it selects one path and blocks the others.
If your switch stack is a true stack (appears to be a single switch), you should be able to use a LAG to fool STP into treating the two links as if they were one link. This will also balance traffic flows across the two links, and switch to the remaining link if one fails.
See the Reference Manual, page 117: