Using uplinkfast cost up with 3000 and priority up with 16384?

I've notices that when I enable uplink fast, the cost and Bridge priority go up:

SW2(config)#do sh spann
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address aabb.cc00.0b00
Cost 19
Port 67 (Port-channel12)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 32769 (priority 32768 sys-id-ext 1)
Address aabb.cc00.0c00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 15 sec

After enabling Uplinkfast:

SW2(config)#do sh spann
VLAN0001
Spanning tree enabled protocol ieee
Root ID Priority 32769
Address aabb.cc00.0b00
Cost 3019
Port 67 (Port-channel12)
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec

Bridge ID Priority 49153 (priority 49152 sys-id-ext 1)
Address aabb.cc00.0c00
Hello Time 2 sec Max Age 20 sec Forward Delay 15 sec
Aging Time 300 sec
Uplinkfast enabled

Based on what does the switch up the values of the cost with 3000 and the Bridge Priority with 16384?

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Comments

fredrikjj

The feature is not supposed to be used on transit switches. Increasing the cost like that reduces the risk of that happening.

FrankGuthrie

I was under the impression that you configure uplinkfast on all ports to the Root switch.... I guess this is not the way.

Hondabuff

Uplinkfast is used on wiring closet switches and only works if you have 2 links to the root switch. That way if the primary port goes down the blocked port comes up instantly without going through the spanning tree process.

FrankGuthrie

Hondabuff wrote: »

Uplinkfast is used on wiring closet switches and only works if you have 2 links to the root switch. That way if the primary port goes down the blocked port comes up instantly without going through the spanning tree process.

Does this means it's only used in the access layer going up to the root, or is this also used in the distribution layer?

Danielh22185

FrankGuthrie wrote: »

Does this means it's only used in the access layer going up to the root, or is this also used in the distribution layer?

Access uplinks. You should have routing going on between a well designed Distribution / Core layer. Also remember you root switches should be located within the distribution layer.

Hondabuff

Danielh22185 wrote: »

Access uplinks. You should have routing going on between a well designed Distribution / Core layer. Also remember you root switches should be located within the distribution layer.

Core switch should be manually set to be the root bridge unless your talking about a collapsed core. I would say unless you have redundant links going back to the dist/core then not even use uplink fast.

networker050184

You are usually going to go L3 from dist to core so no way to set root there. Unless you have some very good reason to span a VLAN across the core. Even then I'd tell you to figure a different way out.

Hondabuff

networker050184 wrote: »

You are usually going to go L3 from dist to core so no way to set root there. Unless you have some very good reason to span a VLAN across the core. Even then I'd tell you to figure a different way out.

Yep, That's why I mentioned a collapsed core. I have seen a lot of small businesses and schools setup this way. Enterprise model I agree with the Dist layer since STP is a L2 protocol.

Danielh22185

Hondabuff wrote: »

Yep, That's why I mentioned a collapsed core. I have seen a lot of small businesses and schools setup this way. Enterprise model I agree with the Dist layer since STP is a L2 protocol.

Well he specifically mentioned a core and distribution layer. So if you have two seperate core and distribution layers this is not a collapsed core concpet. So in a non-collapsed core design you DO NOT want to have a core switch the root. However in a collapsed core that brings the core layer down into the distribution layer to serve that dual function you would indeed end up having a core switch also hosting the root switch.