3550 HSRP question 1

[brad182]

I have two 3550 L3 switches which i will be using to do the bulk of the routing for a medium to small sized network, my question is regarding hsrp and its implementation.
Say there are several local sub-networks that get routed through these devices, should hsrp have a seperate "hsrp group" defined for each one of the networks e.g. three addresses from each subnet reserved for SwitchA, SwitchB, Virtual Switch.

e.g. Switch A ---- Virtual IP ---- Switch B
192.10.1.0 | 192.10.1.1 192.10.1.3 192.10.1.2
192.10.2.0 | 192.10.2.1 192.10.2.3 192.10.2.2
192.10.3.0 | 192.10.3.1 192.10.3.3 192.10.3.2
...
...

Is this the correct implementation, or do you simply use a single HSRP group and route to that from each network.

Thanks
Brad

 

[ADB100]

The configurations you suggest are correct - you will need to reserve 3 addresses per network; 2 for the physical interfaces of the routers (in this case the 3550's) and a Virtual address that will be the default gateway for devices in each network. Because these are separate networks you can use the same HSRP group for each one, they don't have to be different as they are all logically segmented anyway. If you are running fallback bridging as well as routing IP (bridge-groups) then you will have to use unique HSRP groups per VLAN or Physical Interface.

interface Vlan100
ip address 192.168.1.1 255.255.255.0
standby 1 ip 192.168.1.3
!
interface Vlan101
ip address 192.168.2.1 255.255.255.0
standby 1 ip 192.168.2.3
!
etc


remember that HSRP is used purely for default gateway redundancy for IP hosts that don't support (or you don't want to run) routing protocols. If you don't have any hosts on any of these networks/subnets then you would use a routing protocol and rely on the dynamic routing/re-routing inherant in a dynamic routing protocol.

Andy