MHSRP - Multi-group Hot Standby Router Protocol

Most router and switch administrators are familiar with the Hot Standby Router Protocol a.k.a. HSRP, which, like VRRP, the Virtual Router Redundancy Protocol, is used to allow two routers on the same access-subnet to provide fault-tolerance for users or servers on that network. If you're not familiar with it, HSRP is configured on each router to provide a virtual IP address, which is given to the users and server administrators as their "default gateway". Each of the routers are given a priority and one router assumes an active role, responding to ARPs for the virtual IP address with its own MAC address. The other router or routers act as "standby" routers and poll the active router. When the active router becomes unavailable (e.g. in a failure, or if it is offline for maintenance), then the other router takes over so the clients see no disruption.

The downside to this configuration is that all the traffic from users and servers will go to the active router and none of the traffic will go to the standby router. If these routers are gigabit connected to the rest of your campus, that's probably not a big deal. But if they're connected by a pair of T1s to your WAN, it most likely means you're only going to use half the bandwidth you're paying for.

Although there are more complex ways of dealing with the challenge of load-balancing across circuits terminated in separate routers for redundancy, a simple and fairly effective approach to this problem is Multi-group

    Requires Free Membership to View

Hot Standby Router Protocol. In HSRP, all the routers assigned to a given IP address are known as a "group". In MHSRP, you simply configure more groups.

For example, if your first group is router A and router B and their addresses are and /24, then you might assign the virtual IP address of and configure the priority of router A so that it is active. You can also create a second group with a virtual IP of using the same two routers, A and B.

The trick here is to make router B the preferred and active router for the second virtual IP address of Now, when you configure your DHCP for your users on this subnet, create two pools and give the first pool a default gateway of and the second pool a default gateway of By doing this, half your users will send their packets to router A and the other half will send their traffic to router B. Assuming all your people use the same applications, statistically, you will have a good chance of a fairly even distribution of traffic across your circuits.

Tom Lancaster, CCIE# 8829 CNX# 1105, is a consultant with 15 years experience in the networking industry, and co-author of several books on networking, most recently, CCSPTM: Secure PIX and Secure VPN Study Guide published by Sybex.

This was first published in March 2004

There are Comments. Add yours.

TIP: Want to include a code block in your comment? Use <pre> or <code> tags around the desired text. Ex: <code>insert code</code>

REGISTER or login:

Forgot Password?
By submitting you agree to receive email from TechTarget and its partners. If you reside outside of the United States, you consent to having your personal data transferred to and processed in the United States. Privacy
Sort by: OldestNewest

Forgot Password?

No problem! Submit your e-mail address below. We'll send you an email containing your password.

Your password has been sent to:

Disclaimer: Our Tips Exchange is a forum for you to share technical advice and expertise with your peers and to learn from other enterprise IT professionals. TechTarget provides the infrastructure to facilitate this sharing of information. However, we cannot guarantee the accuracy or validity of the material submitted. You agree that your use of the Ask The Expert services and your reliance on any questions, answers, information or other materials received through this Web site is at your own risk.