Configuring RSTP in a mixed switch environment

[mike.butorac]

Hi,

Can someone point me in the right direction here? I am trying to determine the best way to configure spanning tree in a multiple vlan environment with Cisco switches (that only support PVST, and 3Com switches that do not support PVST.

Thanks.

[shah.chintan]

Hi mike,

PVST is Cisco proprietery and RSTP will give you advantage of fast converagance around 2 secs for STP but if you have number of vlans like 1000 vlans then you can go ahed with MSTP so one STP instance for ragne of vlan and that range you can design based on mangment vlan - 1 STP instance, Data vlans second. MSTP will reduce the CPU load also.

In you case 3 com and cisco two differnt vendor so i recommoned to go with either RSTP or MSTP based on my above input.

Thanks

Chintan

[mike.butorac]

Thanks. However the problem remains, I don't think you can turn off PVST. The cisco and 3com devices recognize each others RSTP, but using other vlans remains a problem. I only have a few so maybe there is no reason to worry, but if there is a preferred way to deal with this, I'd like to know.

Thanks,

Mike

[Francois Tallet]

Cisco supports 3 stp modes (more in CatOS): PVST (with -1- plain STP or -2- RSTP) and -3- MST.

-The two PVST modes are proprietary. They are still able to interoperate with standard STP though.Vlan 1 will run STP with the 3com's unique STP (I'm assuming that your 3com box is running standard STP). Other vlan PVST instances will run on the top of the 3com box, as if the 3com switch was a hub.

-If you run MST with absolutely no configuration on the cisco switches, it's a little bit as if you were running standard RSTP, with a single instance. This should interoperate with the 3com easily. The only constraint is that you will only have a single STP instance, which means a single topology in your network (that's what the IEEE standard for STP and RSTP provide). If you create several MST instances, you will be able to have several topologies at least on the cisco switches running MST.

If the 3com supports MST, then everything is of course much simpler as all the box then run the same standard;-)

Regards,

Francois