spanning tree porfast trunk?

rakem

Whats the deal with the spanning tree porfast trunk command?

I can't find a lot of information on it?

Seems to be a bit confusing to me, since you couldnt't normally enable portfast on a trunk port.

Cheers.

tmlerdal

I found this link, but can't really come up with a reason you'd want to put a trunk port into portfast mode:
http://www.cisco.com/en/US/docs/switches/lan/catalyst4500/12.1/13ew/command/reference/S1.html#wp1070681

nel

Its too enable portfast on trunk ports. we use it when connecting voip phones and clients to access switches when using a trunk

cisco_trooper

Yep, another real world example of this would be when trunking VLANs over to a VM environment....

rakem

nel wrote:

Its too enable portfast on trunk ports. we use it when connecting voip phones and clients to access switches when using a trunk

I thought an access port is normally used for voice VLANs... (i'm a bit rusty so i could be wrong)

networker050184

rakem wrote:

I thought an access port is normally used for voice VLANs... (i'm a bit rusty so i could be wrong)

An access port is in a single VLAN. If you use a voice and data VLAN on a port then it is a trunk ie it carries traffic for more than one VLAN.

rakem

networker050184 wrote:

rakem wrote:

I thought an access port is normally used for voice VLANs... (i'm a bit rusty so i could be wrong)

An access port is in a single VLAN. If you use a voice and data VLAN on a port then it is a trunk ie it carries traffic for more than one VLAN.

yea but you don't actually configure it to be a trunk with the switchport mode trunk command do you?

from cisco:
"You should configure voice VLAN on switch access ports; voice VLAN is not supported on trunk ports. You can only configure a voice VLAN on Layer 2 ports"


Plus portfast is automatically enabled when you configure a port for a voice vlan.

http://www.ciscosystems.com/en/US/docs/switches/metro/catalyst3750m/software/release/12.2_25_ey/configuration/guide/swvoip.html#wp1033944

dtlokee

Yes the correct way to configure a voice VLAN is to set the port as access and use the "switchport voice vlan" command along with spanning tree portfast.

The "old way" was to configure the switchport as trunk, modify the allowed VLAN list to only allow the data VLAN and the voice VLAN, configure the "switchport voice vlan" command. The issue with this configuration is that portfast won't work on an interface configured this way. Spanning-tree portfase trunk was introduced later (I don't remember when). I have seen engineers turn off spanning tree on the access layer switches and use routed uplinks to the distribution layer to avoid loops. It's far more complex than it need be and is not the best method.

The only good case I have seen for portfast trunk is putting the IPSec SPA in a 6500, there is a case where you need to build a trunk to the SPA but also want it to utilize portfast.

rakem

Yea, the reason i asked is because i have just started a new job and while looking through some switches almost all of them have the spanning-tree portfast trunk command on them