Introduction to Gateway Redundancy

In this lesson we’ll take a look at different protocols for gateway redundancy. So what is gateway redundancy and why do we need it? Let’s start with an example!

In this lesson we’ll take a look at different protocols for gateway redundancy. So what is gateway redundancy and why do we need it? Let’s start with an example! https://vimeo.com/121896181 The network in the picture above is fairly simple. I have one computer connected to a switch. In the middle yo

gateway redundancy scenario

The network in the picture above is fairly simple. I have one computer connected to a switch. In the middle you’ll find two multilayer switches (SW1 and SW2) that both have an IP address that could be used as the default gateway for the computer. Behind SW1 and SW2 there’s a router that is connected to the Internet.

Which gateway should we configure on the computer? SW1 or SW2? You can only configure a one gateway after all…

gateway redundancy crashed switch

If we pick SW1 and it crashes, the computer won’t be able to get out of its own subnet because it only knows about one default gateway. To solve this problem we will create a virtual gateway:

virtual gateway

Between SW1 and SW2 we’ll create a virtual gateway with its own IP address, in my example this is 192.168.1.3.

The computer will use 192.168.1.3 as its default gateway. One of the switches will be the active gateway and in case it fails the other one will take over.

There are three different protocols than can create a virtual gateway:

In the next lessons I will explain each of these protocols and show you how to configure them. For now, I hope this lesson has helped to understand why we need a virtual gateway in the network.

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Forum Replies

  1. Can you run virtual gateway redundancy (HSRP, VRRP, GLBP) over access – to – distribution lines that are running etherchannel as well?

  2. Jason,
    This depends on how the access layer connects to the distribution layer. A single Etherchannel is not supported between one physical switch and two different physical switches (unless those two switches using Stackwise, VSS, or vPC). By this, I meaning the following is NOT allowed:

    
                            ---------Distribution SW1 
    Access ---- Etherchannel                         --------VRRP
                            ---------Distribution SW2
    

    You can, however, have Etherchanel across two links that connect two switches together. So, in the case below

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  3. If you could choose, which gateway redundancy protocol & version would you choose and why? Personally, It sounds like GLBP is the best because it combines the redundancy that HSRP & VRRP provide, while providing actual load-balancing. Oddly, I’ve read/seen HSRP used much more frequently than GLBP; do you think this is simply because more people are familiar with HSRP/ Cisco pushes it harder or is there a legitimate design reason?

    -Bartley

  4. Hello Bartley

    Both HSRP and GLBP are Cisco proprietary protocols while VRRP is an IEEE standard. From my experience, VRRP should only be used when configuring gateway redundancy with other vendors’ equipment. Compared to HSRP and GLBP, it has no load balancing capabilities.

    When using Cisco IOS devices, HSRP does not support load balancing while GLBP does, as you correctly state. However, for Nexus devices, HSRP does automatically perform load balancing across multiple gateways. So from a functional standpoint, GLBP should be used with IOS devices, and eith

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  5. Hello Walter

    In the case where you have many subnets, you would have multiple SVIs within each of the L3 switches, acting as the default gateways. For each one of these SVIs you would configure gateway redundancy such that you create a virtual gateway for each subnet/VLAN. Take a look at the following diagram:

    https://cdn-forum.networklessons.com/uploads/default/original/2X/f/f14bbf97d794bb94938256f0f81432121c40ad2c.png

    Here you have 10 VLANs/subnets all of which have SVIs in both devices. You configure 10 virtual gateways, one for each VLAN/subnet. In such

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