VRRP – Virtual Router Redundancy Protocol

VRRP is essentially the standardized version of HSRP.  As per usual, Cisco generally comes out with it’s own protocols before standardized ones are approved.  Since it’s pretty much the same, I’m just going to show a basic configuration for VRRP.  Let’s look at the same diagram we used in the HSRP post…

image

So the configuration is very similar to that of HSRP…

Router 1 Interface configuration
interface FastEthernet0/0
ip address 192.168.0.3 255.255.255.0
duplex auto
speed auto
vrrp 5 ip 192.168.0.1
vrrp 5 priority 90
end

Router 2 Interface configuration
interface FastEthernet0/0
ip address 192.168.0.4 255.255.255.0
duplex auto
speed auto
vrrp 5 ip 192.168.0.1
vrrp 5 priority 80
end

One major difference is that VRRP defaults to automatically preempting the other router.  In HSRP, you had to configure preemption to occur.  Also, the MAC address that’s used by the VRRP virtual IP is different but it follows the same sort of allocation where the last 2 bits show the group number…

Protocol  Address          Age (min)  Hardware Addr   Type   Interface
Internet  192.168.0.1             0   0000.5e00.0105  ARPA   FastEthernet0/0

And just like HSRP, you can configure the same kind of tracking.  The protocols are almost identical in most respects but her are some notable differences…

-VRRP uses the multicast address 224.0.0.18 to send it’s hello packets

-VRRP can be configured to use one of the physical interface IP’s as the virtual IP address.  HSRP can NOT use the physical IP address as the HSRP address.  If you do this, the router with the physical IP address matching the VRRP address will always be the ‘master’ router.  VRRP ensures this by increasing that router’s priority to 255 and the configurable range is 1-254…

Router#show vrrp
FastEthernet0/0 – Group 5
  State is Master
  Virtual IP address is 192.168.0.3
  Virtual MAC address is 0000.5e00.0105
  Advertisement interval is 1.000 sec
  Preemption enabled
  Priority is 255 (cfgd 90)
  Master Router is 192.168.0.3 (local), priority is 255
  Master Advertisement interval is 1.000 sec
  Master Down interval is 3.003 sec

-VRRP uses a different timer configuration for hellos and the down timer.  The advertisements are sent every second and the hold (master down) timer is a function of 3 times the advertisement (defaults to 1 second) + the skew time.  The skew time is calculated by taking 256 – the router priority / 256.  For instance, look at this routers configuration…

Router#show vrrp
FastEthernet0/0 – Group 5
  State is Backup
  Virtual IP address is 192.168.0.3
  Virtual MAC address is 0000.5e00.0105
  Advertisement interval is 1.000 sec
  Preemption enabled
  Priority is 50
  Master Router is 192.168.0.3, priority is 255
  Master Advertisement interval is 1.000 sec
  Master Down interval is 3.804 sec (expires in 3.616 sec)

The advertisement is 1 second but the master down interval is 3.804 seconds.  This is calculated as follows…

3 x 1 + 256 – 50 / 256

Which is equal to…

Master down interval x advertisement + 256 – priority / 256

Next up is GLBP which is truly different compared to HSRP and VRRP.

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