[c-nsp] Sharing HSRP group numbers across multiple HSRP instances

Justin Shore justin at justinshore.com
Mon Dec 22 14:18:59 EST 2008

I have a situation in which I'm wondering if I can use the same HSRP 
group number for multiple SVIs on a pair of 7600s.  The VLANs all 
perform similar functions in groups of 3; outside of FWSM contexts, 
inside of FWSM context, SVI for terminating client IPSec VPNs.  Ie, each 
customer has 3 VLANs that perform these functions.  I have multiple 
customers and each has 3 VLANs in VRFs (where applicable) on my 7600s 
carved out for these specific functions.

Can I use the same HSRP group for each of the individual 3 VLANs across 
multiple customers?  ie:

Customer	VLAN	Purpose
1		1501	Outside
1		1601	Inside
1		1701	CVPN
2		1502	Outside
2		1602	Inside
2		1702	CVPN
3		1503	Outside
3		1603	Inside
3		1703	CVPN

Purpose		HSRP Group
FWSM outside	100
FWSM inside	101
CVPN		102

VLANs 1501-1503 get group 100, 1601-1603 get group 101, 1701-1703 get 
group 102.  Each customer VLAN performing that specific role shares that 
HSRP group #.  That's worded better.  All VLANs share the same L2 
infrastructure (actually they never leave the 7600s).

Is this doable or should I just use HSRPv2 and one of the 4096 group #s 
available to me?  Would sharing group #s result in few HSRP hellos send 
and processed, thus lower RP overhead?

Just curious.  Thanks

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