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Uplink Fast Not Working

lamav
Level 8
Level 8

Folks:

Heres the scenario:

I have 2 L2 access switches dual homed to 2 distros.

Im running pvst+, uplinkfast, and backbonefast.

Timers are: 15 FDelay and 20 MAge

For a given vlan, all trunk ports on the access and distros are forwarding except for 1 on the distro. This is normal, of course.

When I fail one of the forwarding trunk links, it takes 30 sec to for that port to start forwarding. In other word, uplinkfast isnt doing anything.

Any ideas?

30 Replies 30

royalblues
Level 10
Level 10

which switch is the core switch and where all have you enabled uplinkfast...

what are the switch models you are using

Narayan

I have the following on all 4 switches;

spanning-tree mode pvst

spanning-tree uplinkfast

spanning-tree backbonefast

timers are equal on all 4 switches.

Actually my post had a typo.. i wanted to know the root switch in your network.

Do you see a ALT/BLK port hen you do a sh spanning-tree vlan on the access switches..

Narayan

OK, here goes:

distro 1 is the secondary for vlan 127 and distro 2 is primary for vlan 127

the primary forwarding path is access 1 to distro 2 to access 2.

all ports on all switches are forwarding EXCEPT for the port on distro1 that faces access 2.

In th eevent of a failure of the primary path, THAT port on distro 1 that faces access 2 must go into a forwarding state. It is that port that is taking 30 seconds to go to forwarding, as if uplinkfast is not on.

IF I use rapid-pvst instead, that port goes to forwarding immediately after the failure of the primary path.

Draw it on a piece of paper so you can visualize what Im writing.

Spanning tree uplinkfast should not be configured on your distribution switches. Uplinkfast should only be configured on the access.

CHRI:

I removed uplinkfast from the distros and left it only on the access -- still no good. That port on the distro, which is blocked under normal conditions, is going through the listening and learning stages (when I do a sh spannibg-tree vlan 127) AND TAKING 30 SECS TO GO FORWARD.

Ideally your dist switches should be configured as primary root switch and secondary root switch respectively for your vlans.

Uplinkfast should be enabled on th eaccess switches which would make one link as the alternate link i.e block which can be seen with the show command i provided earlier.

Narayan

Sounds like Access_2 may be the root bridge for vlan 127. If it is why and can you make one of those distribution switches to be the root bridge for that vlan?

HTH

Sundar

Sundar:

No, access 2 is not the root bridge.

distro 2 is the root bridge for vlan 127. i configured it as such. I rigged the election, if you will.

Heres something interesting, though. The blocked port on distro 1 goes to forwarding immediately when I use rapid-pvst. But, if I configure pvst, plus uplinkfast and backbonefast, that same port takes 30 seconds.

Another interesting thing is the following: Isn't it true that the "alternate" port role is a rapid-pvst port role? That blocked port on distro 2 has an "ALTN" designation when I do a 'sh spanning-tree vlan 127' command, yet I dont have rapid-pvst configured. I did at one point, but I removed it using the spanning-tree mode rapid-pvst' command.

Do you have a direct link between the two distribution switches?

No, no connection at all between between distros.

Can you create a direction connection between the two distribution switches and advise what the outcome is?

Just want to reiterate what others stated before in this thread 'uplink fast' feature helps faster STP reconvergence in case of failure of primary uplink on Access switches. The key here is ACCESS switches. If you disconnect the primary uplink to distribution_2 from any one of the access switches then, with 'uplink fast' enabled on the access switch, the access switch should convert the blocked uplink port to distribution_1 as the primary uplink or root port.

HTH

Sundar

When you enable uplinkfast, you will see an ALT/BLK port. what i do not understand is if the Distro 2 is the core switch it should not have any block ports for the vlan.

All ports of the root switch are in the forwarding state.

can you post the details of sh spanning-tree vlan 127

Narayan

narayan:

Distro 2 does not have any blocked ports. Please re-read my posts.

Sundar:

An L2 connection or an L3 connection between distros?

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