STP and Portfast

[PinkLips]

In a nutshell, I know what STP provides redundant links with loop avoidance. However I more interested in configuring it. I read the Cisco technotes and I'm still confused. If I have 3 switches: SwitchA (2950), SwitchB (5500), and SwitchC(6500). SwitchC is my core with 2 fiber trunk connections into SwitchB. One trunk is in blocking mode and the other is in forwarding mode. Now I want to plug SwitchA into SwitchB. If I connect a x-over cable from SwitchA to SwitchB (only one cat5 connection) would it cause a STP loop? Is there some other configuration I should do? Also my collegue and I are debating if you connect a switch to another switch, do you enable portfast on both ports or disable portfast? I was always under the impression that if the end device has portfast capability then it should be disabled on both ends.




Thanks,
Nicole

 

[BuckWeet]

No..

It is only a loop when there are 2 or more uplinks going into the same core network..


The fact that you hooked 2 connections between the 5500 and 6500, if STP wasn't turned on, that would have caused a loop..

But since STP was on, it sensed that and shut one of the ports down..


Then you throw the 2950 onto the 5500, that is still not a loop..


You could setup 2 connections betwen the 5500 and 6500, then a connetion between the 6500 and 2950, then another connnection between the 5500 and 2950.. That would still be a loop if STP wasn't enabled..


BuckWeet

 

[robertjo24]

It is usually not a good idea to enable portfast on any ports interconnecting switches, even if you do not ever anticipate creating a loop.
If you are utilizing STP for redundant connections between switches, you can enable "Uplink Fast" on the ports to cut down the time STP takes to decide which ports to block and unblock.

 

[PinkLips]

Isn't PORTFAST the same as UPLINK FAST?

Thanks,
Nicole

 

[vipergg]

No uplink fast and portfast are not the same . Go to cisco.com and search on both .

 

[robertjo24]

Portfast is like not having STP turned on.
Uplink fast speeds the time it takes to open up a blocked port in STP.