When to use portfast trunk?

[Cooky]

The option is to allow portfast, even when in trunk mode.
Wouldn't that potentially create a loop?

Or do you use it when connecting to a server that does trunk port? (VM or Blade)

 

[jlazzaro]

portfast on an end-station trunk is a valid reason, although i would run bpduguard as well.

i could see using it with router on a stick as well...

 

[jersiq]

Like jlazzaro said, use BPDUguard. We have crippled a 6500 with a 2600 (I think) by not having properly planned the network. Thankfully I was in Operations, not planning.

 

[spidey07]

Normally used when you're doing VOIP. Since the access port is trunking to the phone portfast trunk is used on the access port.

 

[jlazzaro]

i believe portfast is automatically enabled when you configure the voice vlan...checking now.

 

[mcmilljb]

The idea was that a host (PC, Desktop, Workstation, Server or any end-system) did not need to wait through the STP process. This was their solution to the problem. I found this article on cisco's website that talks about PortFast, STP and all other things related. Would be a good read for you. Just remember to put up a sign that says you will be terminated and/or killed if you plug a switch into these ports without permission

*edit*
That article is older than I thought. It was using CatOS syntax. This article is will show you how to enable it for different switch models.

 

[spidey07]

That's why you use bpduguard and loopguard on all ports that are not connected to a switch. Or better yet, make any link to a switch a L3 link and not have to worry about spanning-tree.

If you don't use portfast on host ports what normally happens is the host will see link up and start sending frames and time out on certain requests before the port moves to forwarding state. You can also use the switchport host command which is recommended for host ports - turns off PaGP and DTP.

 

[cmetz]

>make any link to a switch a L3 link and not have to worry about spanning-tree.

Big seconded.

Broadcast storms are so 80s.

 

[Brovane]

Usually with or Access Layer Switches we place these two commands in the config

spanning-tree portfast default
spanning-tree portfast bpduguard default

This will turn on portfast and BPDUguard by default for any port that is in access mode.

 

[Cooky]

Thanks guys for the replies....I was mainly asking for the TRUNK option under portfast, and not portfast in general.

I believe only jlazzaro & spidey had really answered my question...