HSRP config

Unanswered Question
Nov 20th, 2007

Hi ,

how can i effectively implement HSRP using 1 router with 2 fastethernet ports(3845) and 2 core layer switches (3750)

and 5 access layer switches (2960).

wan connectivity is using DS3 card .

I have this problem too.
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Jon Marshall Tue, 11/20/2007 - 00:26

Hi

Without fully understanding your topology this may not be what you want but i'm assuming that your 2 core layer switches are responsible for the intervlan routing

So

1) Create your L3 SVI's on both core switches and configure HSRP between them eg

Csw1

interface vlan 10

ip address 192.168.5.2

standby 10 ip 192.168.5.1

standby 10 pri 110

standby 10 preempt

standby 10 authentication "cisco123"

Csw2

interface vlan 10

ip address 192.168.5.3

standby 10 ip 192.168.5.1

standby 10 pri 100

standby 10 preempt

standby 10 authentication "cisco123"

The connect your 3845 router to your 2 core switches and use routed P2P links from each of the fast-ethernet ports so that the core switches will see two equal cost paths to each remote destination.

HTH

Jon

Kevin Dorrell Tue, 11/20/2007 - 00:47

I would go with the configuration that Jon posted. However, there is a side to you question that makes me wonder whether you are trying to do something else.

You mention that the 3845 has two FastEthernet ports. You should be aware that you cannot do HSRP between two ports on the same router. The HSRP would be between the core switches, offering a service to one interface of the 3845.

If the 3845 and core switches are trunking, the HSRP should be set up independently on each VLAN.

Kevin Dorrell

Luxembourg

Jon Marshall Tue, 11/20/2007 - 00:52

Hi Kevin

Yes, i wasn't totally clear on where the OP wanted to use HSRP either but the most logical way to set this up is to inter-vlan route on the core switches.

Could you just explain what you mean by

"The HSRP would be between the core switches, offering a service to one interface of the 3845"

Thanks

Jon

Kevin Dorrell Tue, 11/20/2007 - 01:56

Jon,

[P.P.S. Before I get even more confused, perhaps we need a better idea how the original poster imagined the topology ;-)]

[P.S. I just looked at your posting again, and I think I was talking at cross-purposes. I was thinking about HSRP on the router side rather than on the inter-VLAN side. I had assumed that the external router and the two core switches were on a VLAN with HSRP between the core switches, with the external router having a static route to 192.168.5.1. I had the idea that was what the OP was imagining. But as you point out, the better architecture is to use P2P layer-3 interface between the core switches and the 3845, and do the redundancy at layer-3.]

I mean that it would work the way you had it in your config. That is, the two core switches would be members of an HSRP group, presenting an HSRP "ip standby" address on the VLAN. One interface of the 2845 would then route to that standby address.

So many times I have seen people try to make two Ethernet interfaces on the same router be part of an HSRP group, to get link-redundancy. But that does not work because it would depend on the the two interfaces being on the same subnet, which of course is not possible.

HSRP can provide redundancy between two router, but it cannot provide link redundancy between two interfaces of the same router.

Kevin Dorrell

Luxembourg

Jon Marshall Tue, 11/20/2007 - 02:10

Kevin

Okay that makes sense. I guess i was just confused as to why you said "one" interface on the router as you could have both interfaces connected back to the 2 core switches and the router wouldn't use the HSRP address anyway if you were running a routing protocol between it and the core switches.

Jon

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