Purpose of "spanning-tree portfast trunk"

[firefox111_2000]

We are going to try out two wireless accesspoints.  I won't name the manufacturer.  Their tech support asked for two ports in our Catalyst 3750g to be configured as trunk, dot1q, etc., and with "spanning-tree portfast trunk".  What is the purpose of this?

Thanks in advance.

[InayathUlla Sharieff]

Hi,

The spanning-tree portfast has no effect on trunk ports. If you want to make a trunk port become Forwarding imediately after coming up, you need the spanning-tree porfast trunk command. Note that the RSTP has its own mechanism of putting a trunk port into the Forwarding state rapidly, and thus, the spanning-tree porfast trunk command is suitable only on trunk ports leading to Layer3 devices, e.g. routers or servers.

Best regards,

Inayath

[InayathUlla Sharieff]

More info you can refer to the below link:

https://supportforums.cisco.com/discussion/11125461/spanning-tree-portfast-vs-spanning-tree-portfast-trunk

If in case still you have querie please let me know.

HTH

Regards

Inayath

***Please rate if this info is usefull.

[firefox111_2000]

Thank you all for your response. 

[Aninda Chatterjee]

As Inayath as already described, traditional portfast does not apply to trunked ports. In order for a trunked port to take the portfast status, you need to specify the 'trunk' keyword.

The key thing to understand is why would you use this - trunked ports usually go between switches and you shouldn't be configuring portfast for such connections. However, keep in mind that you usually configure trunked interfaces for connections going to VMs, etc as well. These are typically treated as end hosts but since they may carry multiple VLANs over them, you can configure the port as a trunk.

In such situations, you can go ahead and configure such trunked ports for portfast status as well.

Regards,

Aninda