Spanning-Tree Portfast Config

Answered Question
Jan 28th, 2008

Scenario: 400 user LAN (30 VLANs - L2 througout - L3 routing at the core) with about 30% of the users having small 5-port gig switches because they must run 3-4 machines. Physically we can only deliver 2 ports/user and each user has a Cisco IP phone. Current policy allows end-users to use these small switches in their offices.

Question: Is the following config safe to use globally on our access switches (3750G L2 running 12.37.SE1)?

Config Snips:


spanning-tree mode rapid-pvst

spanning-tree loopguard default

spanning-tree portfast bpduguard default

spanning-tree extend system-id


interface GigabitEthernet1/0/2

switchport access vlan 2

switchport voice vlan 20

srr-queue bandwidth share 10 10 60 20

srr-queue bandwidth shape 10 0 0 0

queue-set 2

priority-queue out

mls qos trust device cisco-phone

mls qos trust cos

auto qos voip cisco-phone

spanning-tree portfast


Thanks in advance,


I have this problem too.
0 votes
Correct Answer by Edison Ortiz about 8 years 8 months ago

Looks good.



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Overall Rating: 5 (2 ratings)
bbentley05 Mon, 01/28/2008 - 16:01

Thanks for reviewing Edison. I wanted a second opinion. We ran BPDU guard and loop detection tests by using multilpe hubs and switches and looping them back into the network. Switches and RSPT handled the loop detection and port err_disablement perfectly. The network didn't skip a beat.

Thanks again,


dnewell24 Tue, 01/29/2008 - 05:12

With RSTP I though portfast was an inherent state or role of ports connected to none STP speaking devices??

Jon Marshall Tue, 01/29/2008 - 05:20


If i understand you correctly then yes portfast is the equivalent of an "edge" port in RSTP. However you still need to use portfast keyword ie. from Cisco doc


Edge Ports

The edge port concept is already well known to Cisco spanning tree users, as it basically corresponds to the PortFast feature. All ports directly connected to end stations cannot create bridging loops in the network. Therefore, the edge port directly transitions to the forwarding state, and skips the listening and learning stages. Neither edge ports or PortFast enabled ports generate topology changes when the link toggles. Unlike PortFast, an edge port that receives a BPDU immediately loses edge port status and becomes a normal spanning tree port. At this point, there is a user-configured value and an operational value for the edge port state. The Cisco implementation maintains that the PortFast keyword be used for edge port configuration. This makes the transition to RSTP simpler.




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