[c-nsp] Question on HSRT and MST protocol

[Ed Ravin]

On Thu, Sep 07, 2006 at 11:57:38AM -0300, Juan Angel Menendez wrote:
>          Each HSRP group will use a different "Virtual MAC address'". 
> So if you're using different physical interfaces or VLANs in a 
> switched environment you can reuse the HSRP group numbers. This is 
> useful when you reach the max HSRP group limitation (which varies on 
> each platform).

But don't forget, by default, each HSRP group uses the SAME Virtual
MAC address - if you re-use an HSRP group number on a different
VLAN without changing the default virtual MAC address, you'll have
the same MAC address appearing twice on your network, though in
different VLANs.  Some switches (notably the ancient but otherwise
venerable HP4000m/HP2424m/HP8000m series) can't handle that.  And
you may have other systems in place (like arpwatch) that might complain
about it.

So if you reuse an HSRP group number, you should take a close look
at the MAC address implications, and consider using the "standby N mac-address"
command to change the virtual MAC address.