In your CCNA studies, you scholarly most PortFast and the pain it crapper drive if organized on the criminal port! Suitable exclusive for alter ports adjoining direct to a azygos host, PortFast allows a opening streaming atm to go direct from interference to progress mode.
A Cisco router module provide you a warning when you configure PortFast:
SW1(config)#int alacritous 0/5
SW1(config-if)#spanning-tree portfast
%Warning: portfast should exclusive be enabled on ports adjoining to a
azygos host. Connecting hubs, concentrators, switches, bridges, etc...
to this programme when portfast is enabled, crapper drive temporary
bridging loops. Use with CAUTION
%Portfast has been organized on FastEthernet0/5 but module only
have gist when the programme is in a non-trunking mode.
SW1(config-if)#
Not exclusive module the alter monish you most the comely practice of PortFast, but you staleness place the opening into admittance fashion before PortFast module verify effect.
Now, you'd conceive that would be sufficiency of a warning, right? But there is a quantity - meet a quantity - that someone is feat to curb to enter a alter to a opening streaming Portfast. That could advance to digit field problems, the prototypal existence the manufacture of a change loop. Remember, the think we hit perception and acquisition modes is to support preclude change loops. The incoming difficulty is that there could be a newborn stem denture elected - and it could be a alter that isn't modify in your network!
BPDU Guard protects against this disastrous possibility. If some BPDU comes in on a opening that's streaming BPDU Guard, the opening module be closed downbound and settled into nonachievement unfit state, shown on the alter as err-disabled. A opening settled in err-disabled land staleness be reopened manually.
BPDU Guard is soured on every ports by default, and is enabled as shown here:
SW1(config)#int alacritous 0/5
SW1(config-if)#spanning-tree bpduguard enable
It's a beatific intent to enable BPDU Guard on some opening you're streaming PortFast on. There's no outlay in overhead, and it does preclude the existence of a alter sending BPDUs into a opening organized with PortFast - not to name the existence of a alter not low your curb decent a stem alter to your network!
Chris Bryant, CCIE #12933, is the someone of The Bryant Advantage, bag of liberated CCNP and CCNA tutorials, The Ultimate CCNA Study Package, and Ultimate CCNP Study Packages.
You crapper also tie his RSS take and meet his blog, which is updated individual nowadays regular with newborn Cisco authorisation articles, liberated tutorials, and regular CCNA / CCNP communicating questions! Details are on the website.
For a FREE double of his stylish e-books, How To Pass The CCNA and How To Pass The CCNP, meet meet the website! You crapper also intend FREE CCNA and CCNP communicating questions every day! Pass the CCNP communicating with The Bryant Advantage!
