not sure disabling spanning tree would be the way I'd go - first I'd make sure what flavor of spanning tree your running... PVST+ is the default mode for catalyst cisco - so first of all...are you running seperate vlans on your cisco device? if so, what is the root bridge for the instance of spanning tree on those ports? "show span vlan 10" or "show span vlan 10 detail" - set the priority on the cisco to be lower than that of the 450 "spanning-tree vlan 10 priority XXXX"
2nd - steer which port in that uplink set of ports you want forwarding...set the port priority - use "show span interface FastE 1/15 detail" to find the priority then decide which one you want to put in the forwarding state and use the interface level command "spann vlan 10 cost 18" ( the default port cost on 100M interfaces is 19 and for Gig interfaces its 4 so a metric lower than that and STP will choose the port with the lowest port cost to put in forward state)
- on the 450, once it know its not the root of that STP instance it will then decide which port will be the root port - 450 documentation should have something to show you how to set a priority on your 2 uplink ports...I'd think that would be enough to stop the fighting...
I've implemented 450s into an Extreme summit 250 environment with the redundant configuration your speaking of, and had port 5 and 6 wind up exhibiting strange behavior - the port 5 would go stupid but it would not switch packets over port 6, - there was weeks of wailing and gnashing of teeth until Avaya came out with a later load of 450 firmware, once we loaded it the problems went away and the links were stable - my advise is to make sure you have the latest firmware load on the 450
- I also got fooled by the CLI structure - coming from the cisco world I got used to having to be in interface mode to set speed duplex. but on the 450 you use the "set port negotiation 10/5 disable" from the default CLI prompt to set the port speed on the actual ports... 10/5 and 10/6. for awhile there, my ports for 100/half until I disccovered this little bit of minutia...
it's worth checking the speed duplex..."show port 10/5" from the default CLI prompt
not sure if any of this helps, and I hate to throw trash out here that doesn't apply to what your experiencing but you never know...I'd like to know what the fix is when you get it worked out - thanks for the post
I've also got a 450 in the lab and could scrounge up a catalyst switch if you need furthur help - I'm interested in finding out about this one..