Cisco CCNP/ BCMSN Test Tutorial: Configuring PortFast And BPDU Guard

In your CCNA scientific tests, you discovered PortFast and the problem it can bring about if configured on the incorrect port! Best just for transform ports joined instantaneously to a solitary host, PortFast lets a port taking care of STP to go straight from blocking to forwarding technique.

A Cisco router will provide you a warning when you established up PortFast:

SW1( config) #int temporary /five

SW1( config-if) #spanning- tree portfast

% Warning: portfast will have to only be enabled on ports linked to asingle host. Linking facilities, concentrators, switches, bridges, and so forth. to this user interface when portfast is enabled, can trigger temporarybridging loops. Use with Warning

% Portfast has been configured on FastEthernet0/5 owning mentioned that will just

When the buyer interface is in a non-trunking method, have influence.

SW1( config-if) #.

Not just will the Click here switch alert you about the right utilization of PortFast, but you really should established the port into obtain manner in progress of PortFast will get effect.

Now, you 'd assume that would be satisfactory of a warning? There is an chance - just a probability - that another person is heading to regulate to backlink a swap to a port running Portfast. That could induce two important problems, the initially having the enhancement of a switching loop. Retain in mind, the reason we have listening and getting modes is to enable prevent switching loops. The forthcoming problem is that there could be a brand name-new root bridge elected - and it could perhaps be a swap that is not even in your network!

BPDU Guard safeguards versus this dreadful chance. If any BPDU is easily out there in on a port that is operating BPDU Guard, the port will be shut down and positioned into mistake disabled point out, discovered on the swap as err-disabled. A port place in err-disabled state should to be resumed by hand.

BPDU Guard is off on all ports by default, and is enabled as tested to in this write-up:.

SW1( config) #int immediately /5.

SW1( config-if) #spanning- tree bpduguard enable.

It can be a good notion to permit BPDU Guard on any port you are working PortFast on. You can find no cost tag in overhead, and it does remain very clear of the likelihood of a swap sending BPDUs into a port proven up with PortFast - not to area out the probability of a switch not under your command ending up becoming a root swap to your group!

% Warning: portfast need to just be designed it achievable for Click here on ports related to asingle host. Linking facilities, concentrators, switches, bridges, and so on. There is an likelihood - basically a likelihood - that one more human being is heading to get treatment of to link a adjust to a port jogging Portfast. If any BPDU arrives in on a port that is doing the job BPDU Guard, the port will be shut down and positioned into mistake handicapped stage out, demonstrated on the swap as err-disabled. A port positioned in err-disabled position out ought to be reopened manually.