VRRP , An Overview and Implementation

VRRP: Virtual Router Redundancy protocol

To reach remote networks we use the following methods to discover the first hop to our remote network:

• Dynamic process
• Static configurations

The problem with dynamic exploration is extra network overhead, and usually static configuration is recommended as it gives the next hop detail in advance thus reducing the extra network overhead. But the problem with static next hop or in simple words default gateway configuration is redundancy as it creates a single point of failure. To overcome this, we use different redundancy configuration techniques, in which we configure a single virtual IP on a group of routers. In case one virtual gateway fails, the load is instantly shifted to the next available router according to priority. VRRP is one of those techniques as are GLBP and HSRP. In VRRP we define a Master Router and a bunch of back up routers; these backup routers are the point of redundancy in case of Master router failure. 

For example in above scenario, we have configured VRRP on all the three routers and made it a part of VRRP group 1. The mentioned virtual IP address is configured on each router. Suppose if Router A is currently active and some things abnormal happens to it, Router B or Router C will take the backup gateway place according to the priority defined for these routers in VRRP group configurations. In the same fashion we can also create different groups, with different priorities and VRRP advertisements timer values.

Quick Facts about VRRP:

• VRRP uses 224.0.0.18 and protocol number 112
• VRRP has virtual MAC Address 0000.5e00.01xx with xx being group number
• VRRP default Hello interval is 1 second
• VRRP default priority is 100
• VRRP preemption is enabled by default 

Configuration example:

In the basic configuration of VRRP, we will cover the following topics:

• Basic VRRP Configuration
• VRRP priority and preempt
• VRRP MD5 authentication
• VRRP Packet Analysis

We are using below mentioned GNS3 topology for VRRP. It’s the same topology that we used in GLBP, but this time we are creating redundancy via VRRP.

We have created a VRRP Group 1 on R3 and R4 and have configured virtual gateway IP 192.168.1.10. The configurations are done on both router Fast Ethernet 0/0 interfaces.

VRRP Configuration done on R3 Fast Ethernet 0/0 interface is :

VRRP Configuration done on R4 Fast Ethernet 0/0 interface is:

As you can see, we have enable VRRP group 1 on R3 and R4, with clear text authentication. To verify, VRRP is in action, we can check it via show vrrp command on both routers:

From above commands output, you can see that R3 is our Master router and R4 is our backup router. Preemption is enabled on both routers by default. R3 priority is higher (120) then R4 (100). The clear text authentican password is set to cisco.

The same scenario can be used with different VRRP groups, if we want to creat multiple virtual GWs on our network for efficient load balancing and traffic handling as all hosts load on a single router can increase the work/processing load on it. VRRP is preferred routing protocol as it’s not vendor specific like GLBP. With multi-vendor interoperability, VRRP is the ultimate choice in network redundancy design.