STP SWITCH

[PRAMOD_IND]

what are the issues when use multiple vlan in stp ?

[Georg Pauwen]

Hello,

what do you mean, MSTP ? Spanning tree loops ?

[balaji.bandi]

As long the Physical Links are not looped, there is no issue.

[PRAMOD_IND]

any other issue like cpu utilization or regarding VLANs

[paul driver · Accepted solution]

Hello

Any time a switch ( non root) sees a change ( port going into forwarding state or going down) it will incur a STP event thus it will notify the root switch via a TCN which will acknowledge that TCN via a TCA then notify the entire switching estate of this change with it own TCN's.

One good way to reduce such stp re-transmissions is to enable stp portfast on all your switch access-ports, doing so will negate these ports participating any TCN when the ports goes down or move into a forwarding state and can reduced the impact on the cpu/memory process of your switches

[Joseph W. Doherty]

Depends whether you're running a per-VLAN "flavor" of STP or not.

STP will consume switch CPU, so if running one STP instance per VLAN, and your have lots of VLANs, you might overtax the CPU resources of the switch. (NB: swtiches often have low end CPUs as the bulk of their data traffic is handled by dedicated/special hardware, i.e. ASICs.)

To avoid this, on Cisco switches (which default to per-VLAN STP), you might run MSTP with only one or a couple of STP instances.

Also in current switch environments, except for provider data centers, often you don't have massive numbers of VLANs and/or large L2 topologies, as many of today's topologies have L3 switches.