VRRP (Virtual Router Redundancy Protocol)

VRRP (Virtual Router Redundancy Protocol) is very similar to HSRP (Hot Standby Routing Protocol) and can be used to create a virtual gateway. If you don’t know why we use virtual gateways then I suggest to read my Introduction to virtual gateways first. Also make sure you check the HSRP lesson first since many of the things I describe there also apply to VRRP.

VRRP is very similar to HSRP; if you understood HSRP you’ll have no trouble with VRRP which is a standard protocol defined by the IETF in RFC 3768. Configuration-wise it’s pretty much the same but there are a couple of differences.

Let’s start with an overview:

  HSRP VRRP
Protocol Cisco proprietary IETF – RFC 3768
Number of groups 16 groups maximum 255 groups maximum
Active/Standby 1 active, 1 standby and multiple candidates. 1 active and several backups.
Virtual IP Address Different from real IP addresses on interfaces Can be the same as the real IP address on an interface.
Multicast address 224.0.0.2 224.0.0.18
Tracking Interfaces or Objects Objects
Timers Hello timer 3 seconds, hold time 10 seconds. Hello timer 1 second, hold time 3 seconds.
Authentication Supported Not supported in RFC 3768

As you can see there are a number of differences between HSRP and VRRP. Nothing too fancy however. HSRP is a cisco proprietary protocol so you can only use it between Cisco devices.

Let’s see if we can configure it…

Configuration

This is the topology that I will use:

virtual gateway example topology

SW1 and SW2 are multilayer switches and their interfaces are configured as routed ports. We will create a virtual gateway using VRRP on the interfaces facing SW3:

SW1(config)#interface fa0/17
SW1(config-if)#vrrp 1 ip 192.168.1.3
SW1(config-if)#vrrp 1 priority 150
SW1(config-if)#vrrp 1 authentication md5 key-string mykey
SW2(config-if)#interface fa0/19
SW2(config-if)#vrrp 1 ip 192.168.1.3
SW2(config-if)#vrrp 1 authentication md5 key-string mykey

Here’s an example how to configure VRRP. You can see the commands are pretty much the same but I didn’t type “standby” but vrrp. I have changed the priority on SW1 to 150 and I’ve enabled MD5 authentication on both switches.

SW1#
%VRRP-6-STATECHANGE: Fa0/17 Grp 1 state Init -> Backup
%VRRP-6-STATECHANGE: Fa0/17 Grp 1 state Backup -> Master
SW2#
%VRRP-6-STATECHANGE: Fa0/19 Grp 1 state Init -> Backup 
%VRRP-6-STATECHANGE: Fa0/19 Grp 1 state Backup -> Master 
%VRRP-6-STATECHANGE: Fa0/19 Grp 1 state Master -> Backup

You will see these messages pop-up in your console. VRRP uses different terminology than HSRP. SW1 has the best priority and will become the master router. SW2 will become a standby router. Let’s see what else we have:

SW1#show vrrp 
FastEthernet0/17 - Group 1  
  State is Master  
  Virtual IP address is 192.168.1.3
    Secondary Virtual IP address is 192.168.1.4
  Virtual MAC address is 0000.5e00.0101
  Advertisement interval is 1.000 sec
  Preemption enabled
  Priority is 150 
  Authentication MD5, key-string "mykey"
  Master Router is 192.168.1.1 (local), priority is 150 
  Master Advertisement interval is 1.000 sec
  Master Down interval is 3.414 sec
SW2#show vrrp 
FastEthernet0/19 - Group 1  
  State is Backup  
  Virtual IP address is 192.168.1.3
  Virtual MAC address is 0000.5e00.0101
  Advertisement interval is 1.000 sec
  Preemption enabled
  Priority is 100 
  Authentication MD5, key-string "mykey"
  Master Router is 192.168.1.1, priority is 150 
  Master Advertisement interval is 1.000 sec
  Master Down interval is 3.609 sec (expires in 3.065 sec)

Use show vrrp to verify your configuration. The output looks similar to HSRP; one of the differences is that VRRP uses another virtual MAC address:

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Forum Replies

  1. Hi Yevgeniy,

    Good question and there’s a long answer…

    Originally on the 3550 and some of the 6500 supervisors only 16 HSRP groups were allowed but this limitation applied only to a single interface. You could use the same group number on different interfaces without any issues. On newer platforms this 16 limit doesn’t apply anymore…the 3750 supports 32 groups I think and my 2800 router supports 255.

    About authentication…originally the RFC 2338 standard described authentication but it was removed in RFC 3678 since it wasn’t secure. Not sure which RFC the Cisco i

    ... Continue reading in our forum

  2. Hi Taslim,

    For sure, it could be something as simple as this:

    R1(config)#track 1 interface FastEthernet 0/0 line-protocol
    R1(config)#interface FastEthernet 0/0
    R1(config-if)#vrrp 1 track 1 decrement 50
    

    or you can configure IP SLA and combine it with tracking like I did here:

    ... Continue reading in our forum

  3. Hi Ivaylo,
    The short answer to your question is that you will need a separate VRRP instance for each vlan that you want to have a highly available gateway.

    I have attached a new topology to discuss this. In it, you will see that Computers A and B are in different VLANs (A and B). Switch A and Switch B are both connected to the access-layer Switch C. Note: These connections must be configured as trunks, let’s say the modern 802.1Q standard with both VLAN A and VLAN B allowed. Additionally, it would be a good idea to have Switch A and Switch B directly connec

    ... Continue reading in our forum

  4. Hi,

    thank you for confirming. It’s clear now.

    Rgds,
    Oliver

  5. Hi Andrew,

    Just tested this, when the backup VRRP becomes the master, it uses its own timer values. Not the ones from the failed master.

    Rene

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