Re: Spanning-Tree portfast

jain.nitin · ‎02-12-2009

HI Guys, could you please let me know should I put spanning-tree portast on the ports where routers are connected or no need to put this command..can any body explain..

Edison Ortiz · ‎02-12-2009

Routers aren't running any STP instance so it's safe to enable STP PortFast on those ports.

Now, if you enable bridging on those routers, it's highly recommend to disable STP Portfast on those ports.

HTH,

__

Edison.

b.julin · ‎02-12-2009

spanning tree portfast is relatively safe if you also add spanning tree bpdufilter enable

Edison Ortiz · ‎02-12-2009

Brian,

I'm glad you bring up the spanning-tree bpdufilter enable command.

There are 2 variations of such command.

1) When used globally, the command is spanning-tree portfast bpdufilter default

2) When used in the interface, the command is the one you mentioned.

Differences?

Well, the first one removes the portfast status on a port that receives a bpdu while the second command disables the ability to send bdpdus on that port (not good, as this can create loops in a network).

http://www.cisco.com/en/US/docs/switches/lan/catalyst3750/software/release/12.2_46_se/command/reference/cli3.html#wp1945458

HTH,

__

Edison.

b.julin · ‎02-12-2009

I have seen numerous references to the "removing a port from portfast mode when a BPDU is received" but the manual says simply that it applies bpdufilter enable to any and all ports that are in portfast mode. It also explicitly says the second command overrides the first.

The manual also specifies that spanning-tree bpdufilter enable drops both incoming and outgoing bpdus.

Edison Ortiz · ‎02-12-2009

One command relates to portfast functionality while the other one doesn't.

The link I posted does not make reference to the 'removal of portfast status' but I've tested this feature many times.

__

Edison.

b.julin · ‎02-12-2009

Well that's good to know.

I just checked a recent manual and the behavior is documented there, though poorly -- the verbiage that draws equivalence between the commands is still there, just the actual behavior is described later down in the usage guidelines.