[c-nsp] FHRP's and STP

[Ross Vandegrift]

On Tue, Nov 18, 2008 at 03:52:35PM +0000, Phil Mayers wrote:
> Variations on the STP/FHRP problem have been discussed a number of times 
> on this list.
> 
> It ought to be reasonably trivial to make FHRP follow STP - make the 
> standby group follow a numbered track object:
> 
> track 10 stub-object
> int VlanXX
>   standby prio [100 for slave | 101 for master]
>   standby track 10 10
>   standby preempt
> 
> ...the write a pretty simple EEM applet triggered on the relevant STP 
> syslog messages, to parse the root/not-root status from:
> 
> sh spanning-tree vlan XX summary | inc ^Root
> 
> ...and down/up the stub track object.
> 
> The problem is that STP is a deeply sub-optimal solution to many of the 
> cases where this matters.

This seems awfully complicated, but I suppose could be the only way to
do it if you don't use MSTP.

It's really trivial to do with MSTP and HSRP.  We have two gateway
routers that run HSRP.  Odd VLANs are mapped to MSTi 1, even to MSTi 2.
Switch 1 is root bridge for MSTi 1 and HSRP active for odd VLANs.
Switch 2 is root bridge for MSTi 2 and HSRP active for even VLANs.

Works great if your gear supports MSTP correctly (which, admittedly, is
not as much of a given as it should be these days...).


-- 
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