uplink fast and backbone fast

Unanswered Question
Feb 18th, 2009

Hi all, Can anyone tell me how the above works in simple terms, when should I use each one? I know they should be used on trunk links, but what benefit will they give me?

also is there no such concept when using RSTP? As there is already an alternate port.

cheers

I have this problem too.
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Mohamed Sobair Wed, 02/18/2009 - 01:10

Hi,

The simple meaning as follows:

1- (Backbone fast): should be configured to Protect the root bridge. lets take an example:

consider you have 3 switches interconnected in a traingle setup. Switch (A) is the root for vlan1 , Switch(A) has 2 uplinks toward Switch(B) and (C), Switch (B) and (C) are also connected.

If the link from Switch A to Switch C fails, Switch C will claim to be the root for vlan 1 if it doesnt recieve 3 consecutive hellos from SwitchA, Switch B knows the root is still Switch A, Switch B then informs Switch C that a root Bridge is reachable via Switch B. This process could be avoided if (Backbone fast) configured on the root bridge. as soon as one of SwitchA links fails, it makes Sure No bridge will claim to be the root.

2- Uplink fast: This Protects the root Port. Consider the above example:

If Switch A link to Switch C fails the root port becomes the port connected to switchB, however, when the link is restored, the Switch immidiately return the root port to its previous status.

The RSTP enhance features includes:

A) Backup port

B) Alternat Port

The Backup port: is simply a backup port for the Deignated forwarding port connected to the same bridge.

The Alternate Port: is a port chosen to be alternat to the backup deignated port, if it fails on a differnet deignated bridge.

HTH

Mohamed

Tshi M Wed, 02/18/2009 - 04:41

To add to Mohamed comments:

Cisco recommends to use uplinkfast on access-layer switches while backbonefast can be used on all switches.

regards,

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