Arie & Christian,
Thanks for the replies. So re-using HSRP group #s doesn't create any
conflicts? That's good to know. It also won't reduce the load? That's
unfortunately. For some reason I had it in my mind that you could
create some sort of collective HSRP instance over a common L2
infrastructure that would share hellos and switch as one common unit.
It would be list MST for HSRP essentially.
One design scenario I didn't ask about was if I could do the same thing
with HSRP instances on sub-ints of a router. On the other end of these
MPLS/VPNs is a pair of ISRs facing a 3560 with 1Q trunks. On each ISR
is an int facing the 3560 and that int is broken up into several
sub-ints. I have HSRP instances on those as well. I have a matching
instance on each ISR for each customer VLAN. However I just tried to
create a new sub-int with the same HSRP group # and it yelled at me.
Apparently it isn't supported on the same physical interface.
% Must use unique HSRP group number for each logical interface
that is a member of the same physical interface.
This isn't a problem for me. Our contiguous L2 infrastructure isn't so
big that 4096 HSRP group numbers won't handle it. I doubt if we'll have
more than 1000 before I'm breaking it up into smaller pieces for
bandwidth reasons.
Thanks for the info
Justin
Arie Vayner (avayner) wrote:
Justin,
The group number sets the virtual MAC address assigned to that group.
If you have some transparent L2 infrastructure (such as a VPLS domain
you try to transit) this could cause issues, and using different groups
per different VLANs is critical. In most other cases there is no need to
change group numbers between VLANs.
Take a look here:
http://www.cisco.com/en/US/docs/ios/ipapp/command/reference/iap_s2.html#
wp1073440
Another point is that you can use HSRPv2, which extends the group number
to 4096:
http://www.cisco.com/en/US/docs/ios/ipapp/command/reference/iap_s3.html#
wp1063204
Arie
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Justin Shore
Sent: Monday, December 22, 2008 21:19
To: 'Cisco-nsp'
Subject: [c-nsp] Sharing HSRP group numbers across multiple HSRP
instances
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
Justin
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