Complex HSRP Design Issue

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Oct 7th, 2005
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I work for a company and we want to implement HSRP. We are a small ISP and most of our customers come into a fastethernet port on subinterfaces. We have fastethernet 0/1.100 through 0/1.125. So 25 customers, each with their own network addressing come into this one port.

The problem is, some of these network are /30 so there is only room for two usable IP doesnt seem like I can implement HSRP in this instance UNLESS I can make the Virtual HSRP (standby IP) address the current default gateway of the user and then put a completely different network address on the two physical ethernet interfaces.

Does that make sense? So if customer has the network, then he is and I am Can I make the Standby IP of the router to be and then change the physical address of the ethernet port on each router to be say on the network?

If so, how would the routing work.

I have always gotten good feedback here, I hope it happens again.

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dnewell24 Fri, 10/07/2005 - 09:51
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My understanding is your customers come in on one physical subinterface. The customer router and provider router establish IP connectivity over the link using /30 addresses. Or are these IP work stations? Regardless, why would you want to implement HSRP over this link? I believe HSRP would be appropriate on the customer router interface facing the LAN. And you still would require another router at the customer site to act as the Hot Standby Router.

If you are adding another provider router into the mix utilize a routing protocol or static routes for fault tolerance.

In the scenario you’re describing I don’t see a need for a Hot Standby Router. There might be something I’m missing. If you have any further information please provide.


jfraasch Fri, 10/07/2005 - 17:43
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Thanks for the response.

The issue is that if I need to upgrade the code on this router then I want all customer traffic to fail over to the standby router.

The connections we provide are 100% ethernet. So all customer traffic terminates on ethernet ports on our routers and on theirs. The configuration is much like a serial point to point connection.

Maybe HSRP isnt even the answer...I dont know if that is direction you are trying to push this topic but I am certainly open to alternatives.

The main idea is that I need customers to stay up when I need to reload, upgrade, or replace the primary router.

Thanks again.


mlund Mon, 10/10/2005 - 00:36
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I did just answer a similar question in the WAN forum, so I just copy that answer.

I'm not sure if this config is working, but it's worth to try.


int eth0

ip address ( faked address )

standby ip

standby ip secondary ( real adress )

ip route eth 0

ip route eth 0


ip address ( faked address )

standby ip

standby ip secondary ( real adress )

ip route eth 0

ip route eth 0



jfraasch Mon, 10/10/2005 - 12:18
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I currently have that config but there seems to be some sort of routing issue going from a customer side all the way through the router....I am going to look into it and maybe I can but static null routes to make it work.

I will post on Wednesday the results.


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