Shorter convergence time for reduncancy using HSRP

Unanswered Question
May 9th, 2007

Hi All,

I currently purchase 2 routers and would like to use it as a redundancy for my network.

I have subscribe 2 different lines from my local service provider, and I use the HSRP to create a fault-tolerance network. In my setting, R1 is the active router and R2 is a standby router. In between of my routers and the service provider, there are some other routers belong to the service provider. My Router R1 and R2 is runnig on OSPF protocol.

My question is, how can I have a shorter convergence time for the backup router to be active router when there is a failure on my router R1? Can any one please help me with this.

Attach is a copy of my network diagram.

Thanks & Regards,

WEI

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ankbhasi Wed, 05/09/2007 - 19:53

Hi Winni,

The standby router takes over the active once the holdtime expires. By default, this equals to three hello packets from the active router having been missed.

The actual convergence time depends on the HSRP timers configured for the group and possibly on routing protocol convergence. The HSRP hellotime timer defaults to 3 sec and the holdtime timer defaults to 10 sec.

Though it is recommended to leave the default timers as it is but if your network requiremnet is like that you can configure hello timer to 2 seconds and holdtimer to 6 seconds.

HTH

Ankur

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winniewei81 Wed, 05/09/2007 - 22:09

Hi Ankur,

Thanks for the solution. I'm doing an experiment on the HSRP base on my previous HSRP network diagram.

In my experiment, I make router R1 and R2 as my network router. The router R3 and R4 is consider as the router in a WAN network where I don't have any access to change the "hello" time. AS for router R5 and R6 I consider the router as the router in the service provider router.

In this testing, I configure R1 and R2 with HSRP where R1 is the active router and R2 is the standby router. A virtual ip router is create so that the test pc only have one default gateway.

I also configure my network and service provider network with ospf routing protocol.

Just wonder is this the correct way to set up a HSRP? Do I need to set the HSRP in the router R2 and R3 as well?

Hope you can help me with this.

Thanks & Regards,

Wei

ankbhasi Wed, 05/09/2007 - 22:22

Hi Wei,

HSRP is basically a gateway redundancy protocol so it should in general be configured between end host and the first hop route and is not required to configure on R3 and R4.

As you mentioned you already have OSPF running between your network and service provider network it will take care of redundancy and convergance between you wan and service provider.

For lan gateway redundancy you just need to configure HSRP on R1 and R2 lan interfaces and whatever virtual ip address you assign you can configure the same as your gateway address on test machine.

Also because you do not have any l3 link and routing protocol running between R1 and R2 directly you have to configure "tracking" command on your HSRP lan interfaces to track your WAN interfaces so that once WAN interface of R1 goes down tracking command can redunce the priority of R1 router and R2 router can take the role of active router.

To read more about tracking command have a look at this link

http://www.cisco.com/univercd/cc/td/doc/cisintwk/ics/cs009.htm#wp3475

HTH

Ankur

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bjornarsb Wed, 05/09/2007 - 22:59

Hi,

The total convergency is not actually relying on HSRP. HSRP only manages a switchover of you default gateway and that can be tuned to be real fast.

The convergence time is a actually depending on how yor service provider has set up routing. Sticking to default parameteres I hope they use OSPF (faster convergence than RIP, BGP and EIGRP).

So you need to talk to your provider, and test the failover properly!

HTH

Regards,

Bjornarsb

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