Cisco CCNP / BCMSN Exam Tutorial: Configuring PortFast And BPDU Guard
With your CCNA research, you discovered about PortFast and The difficulty it might cause if configured on the incorrect port! Ideal just for swap ports related directly to a single host, PortFast allows a port operating STP to go directly from blocking to forwarding method.
A Cisco router offers you a warning any time you configure PortFast:
SW1(config)#int rapid 0/5
SW1(config-if)#spanning-tree portfast
%Warning: portfast need to only be enabled on ports linked to a
single host. Connecting hubs, concentrators, switches, bridges, and so on…
to this interface when portfast is enabled, can result in temporary
bridging loops. Use with Warning
%Portfast continues http://edition.cnn.com/search/?text=토토사이트 to be configured on FastEthernet0/five but will only
have influence if the interface is in 메이저사이트 the non-trunking method.
SW1(config-if)#
Not just will the switch warn you about the right utilization of PortFast, but you need to set the port into entry mode prior to PortFast will take influence.
Now, you’d imagine that can be adequate of a warning, appropriate? But there is a chance – just a chance – that somebody will probably take care of to attach a swap to some port managing Portfast. That might result in two important complications, the initial getting the development of the switching loop. Keep in mind, the reason We have now listening and Finding out modes is to aid reduce switching loops. The following difficulty is always that there could be a whole new root bridge elected – and it may be a change that isn’t even in your community!
BPDU Guard safeguards in opposition to this disastrous likelihood. If any BPDU comes in over a port that’s jogging BPDU Guard, the port will likely be shut down and placed into mistake disabled state, revealed within the change as err-disabled. A port placed in err-disabled state need to be reopened manually.
BPDU Guard is off on all ports by default, and it is enabled as shown in this article:
SW1(config-if)#spanning-tree bpduguard allow
It’s a good idea to empower BPDU Guard on any port you’re jogging PortFast on. There’s free of charge in overhead, and it does stop the potential of a switch sending BPDUs into a port configured with PortFast – in addition to the potential of a switch not less than your Manage turning out to be a root change to the community!