Is there a use-case for spanning-tree Portfast on trunk links?

[keesepema]

I understand that spanning-tree portfast configuration is designated for end devices, so all in access mode.

From an article I learned that spanning tree portfast is also avalable for trunk links.

However I can not think of a situation that would make spanning-tree portfast trunk logical.

Can anyone point me out a use-case where spanning-tree portfast trunk would be recommended?

[MHM Cisco World]

SW - trunk-router or server

Here you can config portfast in trunk. 

[keesepema]

Thanks! However I don't understand why I should configure a switchport which links to a router as spanning-tree portfast trunk. Maybe if there is a dhcp pool configured on the router that has timing issues when a switchport is in non portfast mode?

[MHM Cisco World]

Yes but also for any other service need port to be as fast as be in forward status.

This feature work for router and server. 

[keesepema]

Can I summarize that spanning-tree portfast trunk is not recommended, but sometimes inevitable?

[MHM Cisco World]

 this order of operation for windows, image that these operation is delayed by stp blk.

So I recommend config portfast in trunk for server or router if the command is available. 

[keesepema]

Great explanation. But I'm also confused now. I learned that a loop-free network using spanning-tree is very important in redundant network design. Will portfast on trunks lead to more network-loops?

[MHM Cisco World · Accepted solution]

Portfast must use in any port connect to 

Host 

Router 

Server 

And cisco recommends to prevent any type of loop using bpdu guard with portfast.

[ryklebaron]

What do you define by host, a client? Because, of that is the case, a user can create a broadcast loop within the broadcast domain. This is a reason for me to not use portfast on ports for clients (read users). 

[Joseph W. Doherty · Accepted solution]

"Can anyone point me out a use-case where spanning-tree portfast trunk would be recommended?"

Where, for some reason, you need a trunk to come on-line quicker than when STP is blocking the link until it confirms there's no loop.

Of course, just like with Portfast on an edge port, you increase the risk of an unintentional loop not being blocked by STP.

Personally, I've never worked on a network that "needed" (or used) Portfast on an infrastructure link.

But, as you've noted, I have often seen host DHCP fail if Portfast NOT enabled on host edge ports.