[c-nsp] VSS Best Practices

[Ross Vandegrift]

On Tue, Aug 11, 2009 at 08:15:36AM +1200, Ivan wrote:
> I don't believe the section of the best practice guide below relates  
> directly to dual-active detection as LACP is presented as a recommended  
> option.  Any other ideas for why explicit trunks are not recommend are  
> welcome.

LACP does a good job of detecting when links have mis-matched speed or
duplex parameters.  My guess for Cisco's rationale would be that it
prevents accidental misconfiguration from splitting your stack.

I've seen accidently broken LACP port-channel members, and IOS splits
off the incompatible members into another sub-group (that gets named
like "Po4A").  This can happen while leaving the currently-active
member of the bundle undisturbed.

On the other hand, I've also seen statically configured port-channels
have members with speed and duplex broken.  This way lies madness -
some platforms handle this gracefully (2960 forcibly disables the
just-changed member), others don't (6500 stops switching on the port
channel and any members, causing loss of connectivity).

Ross

-- 
Ross Vandegrift
ross at kallisti.us

"If the fight gets hot, the songs get hotter.  If the going gets tough,
the songs get tougher."
	--Woody Guthrie