Router Failover

Answered Question
Nov 4th, 2008

We have a 3845 router that has a DS3 connection, and a 3825 that has another DS3 connection. I want to stand up a 3845 router with 2 DS3 cards in it. I want to be able to have it as a hot standby router so if one of the other routers go down, the hot standby would take over. Sort of like the failover between two firewalls (a primary and backup). Is this at all possible?

I have this problem too.
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Correct Answer by tcordier about 8 years 1 month ago

This is exactly what HSRP between two routers does. They exchange hello packets and take over if the other router or the other link is down. With ASA firewalls you probably use VRRP, and HSRP works in a similar way (you could also use VRRP between the two routers).

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Collin Clark Tue, 11/04/2008 - 06:53

First off the 3845 can only handle one full-rate DS-3. You can have a second router backup two other routers (search Cisco for HSRP). Do you have second lines to the location the DS3's are servicing in case of failure? If not maybe configuring the router as a cold spare (able to backup either router) would make more sense?

krhashbarger Tue, 11/04/2008 - 07:03

It would be handling just one of the DS3s. We have two seperate routers for each DS3. The way I want to work it is if either goes down, then the 3rd would take over. I do have it as a cold spare right now, but if I am not at the work area, it will not take over automatically, which I want it to be able to do. The less time we have down the better. If worse comes to worse I will have to get another router to backup the other.

tcordier Tue, 11/04/2008 - 08:16

Why do you not configure HSRP between the 3845 and the 3825 with the existing DS-3 links? With HSRP (or GLBP if you need load-balancing) these two routers would be each others hot standby, and automatically fail-over if one of the DS-3 links fail. In this scenario, a third router could not be a "hot" standby since you have only two active links. You can configure the third as a cold standby. Or do I misinterpret the question?

HTH, Thomas

krhashbarger Tue, 11/04/2008 - 09:15

I am attaching a diagram. I want to use HSRP but not sure if I can use it for a hot standby for two routers. If one goes down then the hot standby would take over for it. If both routers go down, then we are up a creek anyways.

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Collin Clark Tue, 11/04/2008 - 09:19

I understand what you want to do and you can do it with HSRP (and you're right if both fail), but is there really a point of configuring it when you still have to do a manual swap of the cable?

krhashbarger Tue, 11/04/2008 - 09:37

I would configure it, and then get a device so I am able to use a split cable design, between the good router and the HSRP router. The ethernet ports will be connected to the same switch though.

tcordier Tue, 11/04/2008 - 09:40

I think HSRP between 1 and 2 on one site, and between 3 and 4 on the other site is a perfectly valid solution. If 1 goes down, 2 will take over and send traffic to 4. You can also configure HSRP to monitor the DS-3 and go into standby state when the DS-3 is down (tracking). Router 2 would in either case (router 1 down or DS-3 down) send traffic to router 4 (using EIGRP) from where traffic can go to the other LAN or into the cloud (via 3). The re-routing should be not a problem since 1-4 are all in AS 228 (not sure where the statics are). In this configuration, no cables need to be swapped (unless both 1 and 2 go down and you need to insert the cold standby in the configuration).

HTH, Thomas

krhashbarger Tue, 11/04/2008 - 12:26

The thing is I want to do the Hot Standby router like you can do with 2 ASA firewalls. Where they are in constant commnication with each other to update configurations, when the primary ASA goes down, the secondary takes over with-in a few seconds.

Correct Answer
tcordier Tue, 11/04/2008 - 14:10

This is exactly what HSRP between two routers does. They exchange hello packets and take over if the other router or the other link is down. With ASA firewalls you probably use VRRP, and HSRP works in a similar way (you could also use VRRP between the two routers).

Davy Ad Thu, 11/06/2008 - 03:31

Hello KURT ,

I will advice you to configure MHRSP instead , for loadbalancing.

DAK

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