Cisco CCNP / BCMSN Test Tutorial: Configuring PortFast And BPDU Guard
Inside your CCNA scientific studies, you realized about PortFast and The difficulty it might cause if configured on the incorrect port! Ideal just for swap ports connected directly to only one host, PortFast allows a port operating STP to go directly from blocking to forwarding method.
A Cisco router gives you a warning whenever you configure PortFast:
SW1(config)#int speedy 0/5
SW1(config-if)#spanning-tree portfast
%Warning: portfast should only be enabled on ports connected to a
single host. Connecting hubs, concentrators, switches, bridges, etc…
to this interface when portfast is enabled, can cause non permanent
bridging loops. Use with CAUTION
%Portfast is configured on FastEthernet0/five but will only
have effect once the interface is in a very non-trunking method.
SW1(config-if)#
Not merely will the swap warn you about the correct usage of PortFast, but you need to put the port into entry mode right before PortFast will get result.
Now, you’d imagine that could well be ample of the warning, right? But there's a chance – just a chance – that somebody will almost certainly handle to connect a change into a port jogging Portfast. That can lead to two significant troubles, the first getting the formation of the switching loop. Keep in mind, The key reason why We've got listening and Finding out modes is that will help protect against switching loops. The subsequent trouble is that there may very well be a whole new root bridge elected – and it could be a switch that isn’t even with your community!
BPDU Guard shields in opposition to this disastrous possibility. If any BPDU comes in on the port that’s managing BPDU Guard, the port might be shut down and put into mistake disabled point out, demonstrated about the swap as err-disabled. A port put in err-disabled condition has to be reopened manually.
BPDU Guard is off on all ports by default, and is enabled as shown right here:
SW1(config-if)#spanning-tree bpduguard allow
It’s a smart idea to empower BPDU Guard http://www.bbc.co.uk/search?q=토토사이트 on any port you’re running PortFast on. There’s no cost in overhead, and it does protect against the possibility of a swap sending BPDUs into a port configured with PortFast – as well as the opportunity of a swap not underneath your control turning out to be a root swap to your more info community!