R-PVST and single instance RSPT

[l.buschi]

Hello,

I need to connect cisco switches (2960S) to 3COM layer 3 modular switches.

3COM supports only SPT and RSPT on a single istance and not per vlan.

do you think I'll have  problems with spanning-tree convergence?

I'm obliged to have 3COM switches as spanning tree root (on vlan 1) what about spanning tree on all other vlans? I'd like to have spanning tree root for all vlan in the same switch as root switch for vlan 1.

Thanks a lot

Johnny

[dominic.caron]

Its ugly....

Can't you migrate to MST?

[lamav]

Johnny:

The  problem is that Cisco’s PVST+ uses a proprietary multicast destination  address when exchanging BPDUs during convergence that 3^rd party switches that adhere to the IEEE standards do not (except for a  few exceptions). That means that the two switches will converge on the  CST (vlan 1 by default) but on no other VLAN. This effects the proposal  and agreement semantics that rapid-STP and rapid-PVST+ use to create  uplink groups, which are needed for fast reconvergence during an uplink  failure (ie what Cisco calls Uplinkfast).

Here is a link to a white paper I wrote involving Dell switches, but it'sapplicable to 3Com also.

https://supportforums.cisco.com/docs/DOC-16177

[dominic.caron]

I agree with you, this is why I've asked if it was possible to migrate to MST. MST is a standard and is design to manage multiple vlan. It's supported on newer switch model but you have to check for the 3com. I've got a few old 3com switch and it's not supported so I've dicided to only have 1 vlan on each of those  but you might to be able to do this in your network. (I've got classroom, I dont need multiple vlan in that)