3Com 4924 to 7906E single link trunk

[irobot8]

Hello

I'm not fantastic with networking, so bear with me :smileywink:

We have 2x 3Com 4924 access switches that all our servers are plugged in to.

These have a single 1000BASE-SX fiber link each (via expansion module) to a 7906E core switch - which does the inter-VLAN routing between server and workstation networks.

They are also linked together via a single 1000BASE-SX fiber link.  I realise this constitutes a physical loop (unless someone corrects me here), but suspect Spanning Tree Protocol is currently preventing multiple paths (STP is enabled on all inter-switch link ports).

I tried to incorporate an additional 4924 access switch into the setup (we're running out of ports!), with a single link to one of the other 4924s via the 1000BASE-SX expansion modules, but as soon as I did this - all servers lost their connection to the network!

I'd appreciate any advice on how to check the 4924s and 7906E core for possible STP port blocking, as a result of linking in this additional switch.  In addition, should STP be disabled on the link ports? (or is this only a requirement for split multi-link trunking?).

Many thanks in advance.

IR8