[BBLISA] STP and Fast Link

[Benjamin Cline]

On 10/6/2010 8:55 AM, Edward Ned Harvey wrote:
> Fast Link is the opposite.  It's meant for use when you already know what's
> going to be at the other end of the wire attached to this port, and there's
> no possible way for it to cause a loop.  It's probably a device that you
> leave always on.... such as a printer, a server, or another switch that's
> very far away, in an area where there are no other switches connected to
> this switch.
>

That's not my understanding of how Fast Link works. Like Cisco's 
PortFast, Fast Link leaves spanning tree enabled but puts a port into 
forwarding mode immediately, eliminating the delay usually encountered 
when spanning tree transitions from blocking to forwarding after a new 
(physical) connection is made. Although there is the potential for 
bridge loops, they should still be stopped relatively quickly when a 
spanning tree data frame (BPDU) is received.

My recommendation for the original poster is, if bridge loops are a 
concern, would be to enable STP, hard set the root bridge to be a 
central (core) switch in the network, and enable Fast Link on host 
facing ports (Fast Link should NOT be enabled on ports used for switch 
to switch interconnects). I'd also suggest looking into the availability 
of 802.1w Rapid Spanning Tree (or the comparable 802.1D-2004 extensions 
to spanning tree) for the switches in question.

	Benji




	Benji


	Benji