In a business environment, there is something that is very valuable and a non-negotiable. That would be uptime. How do you achieve a great uptime? With redundancy. That is what this article will focus on. There are three protocols that will be discussed. They are:
- HSRP – Hot Standby Routing Protocol
- GLBP – Gateway Load Balancing Protocol
- VRRP – Virtual Router Redundancy Protocol
Each of these three have similarities, but also differences. The big thing that sticks out though about HSRP, GLBP, and VRRP is that it allows for multiple devices to act as the gateway for different networks.
Hot Standby Routing Protocol. Multiple devices in a network can be a part of HSRP for a specific subnet. There are active and standby routers that are configured to act as a certain gateway. In an IOS environment, there is a single active router and should that router have issues, the standby devices are ready to step in and act as the active router. A point to mention is that router is used as a general term and another device such as a L3 switch can be used.
For configuration, give this video a watch for the overview of commands and details:
Gateway Load Balancing Protocol. This protocol is very similar to HSRP except in this type of setup, there are not active and standby routing devices. Multiple routing devices can be active and respond to ARP requests for the gateway IP address. That is how the load balancing works. With GLBP, the way load balancing occurs can be done in a few different ways: weighted, host dependent, and round robin. Weighted is used when the routing devices are not equal in processing power for instance and you want a specific device to respond to more requests than the others. Host dependent ensures that a specific host on the network will always use the same routing device as its gateway (providing it is still online and responding to requests). Lastly, round robin lets the routing devices take turns (in order) to respond to ARP requests for the gateway. This allows traffic to be evenly distributed across all members in the GLBP group.
To see GLBP in action, take a look at this video:
Virtual Router Redundancy Protocol. This is the last of our three routing redundancy protocols. While HSRP is Cisco’s proprietary protocol for hot swap routers, there is another option for this type of redundancy and that is VRRP. On paper, HSRP and VRRP are very similar in how they work and what the network using them achieves. There is still an active router acting as the gateway and standby devices ready to take over should the active go down for any reason. That being said, configuration is a bit different and there are some things that need to be noted.
Here’s one last video for this post to outline some key VRRP topics: