The previous post dealt with Hot Standby Router Protocol (HSRP) that is a Cisco Proprietary protocol, when dealing with a mixed networking environment, the added features and IEEE compatibility of Virtual Router Redundancy Protocol (VRRP) could be used.
VRRP similar to HSRP allows for two or more routers to be grouped forming a virtual router. In VRRP like HSRP one router is elected to handle end-device requests to the virtual IP address. Review HSRP for the concepts. In VRRP there is Master Router and one or more Backup Router(s).
VRRP and HSRP differ in these ways:
- VRRP is an IEE standard (RFC 2338) for router redundancy whereas HSRP is Cisco Proprietary.
- The Virtual Router, representing a group of routers is known as a VRRP Group.
- The Active Router is referred to as the Master Virtual Router.
- The Master Virtual Router may have the same IP Address as the Virtual Router Group.
- Multiple routers can function as Backup Routers.
- VRRP is supported on Ethernet, Fast Ethernet, Gigabit Ethernet; and on Multiprotocol Label Switching (MPLS) virtual Private Networks (VPNs) and VLANs.
VRRP offers these redundancy features:
- VRRP provides redundancy for the real IP address of a router or for a Virtual IP address shared among the VRRP group members.
- If a real IP address is used, the router with that address becomes the master. If a Virtual IP Address is used, the master is the router with the highest priority.
- A VRRP group has one master router and one or more backup routers. The master router uses VRRP messages to inform the group members that it is the master.
Like always I work better with pictures. Take note (NB) there aren’t exactly district areas (distribution, access) for this network diagram but I like boxing things into areas for my own benefit. To get those distinctions one would have to get a Access switch (Layer-2). The figure shows VRRP is configured so that routers A and B share the load of default gateway for end-devices. Routers A and B act as backup for each other should either one fail.
In the diagram two routers groups are configured. Virtual Router 1 (router A) and Virtual Router 2 (router B). Router A owns 192.168.0.1 and is backup for 192.168.0.2 and Router B owns 192.168.0.2 and is backup for 192.168.0.1
As discussed in the introduction of the post, the IP address of the VRRP group is the physical interface of one of the group members, the router that owns that address will be the Master Router of that group. Its priority is set to 255. The Backup router priority will therefore be set between 1 and 254; default is 100. The priority value of 0 has special meaning in that when 0 the current Master Router has stopped and Backup Routers must transition quickly to Master without having to wait for the Master Router to time out.
In VRRP only the Master Router sends advertisements (HSRP hellos). The master sends advertisements on multicast 244.0.0.18 protocol number 112 on a default interval of 1 second.
Dynamic failover, when the Master Router becomes unavailable, VRRP uses three timers:
Advertisement Interval: the time interval between advertisements (seconds). default 1 sec
Master Down Internal: the time interval for backups to declare the master is down (seconds). default 3 x advertisement interval + the skew time
The Stew Time: ensures the Backup router with the highest priority becomes the new master. (256 – priority / 256) milliseconds
Making the interface a member of a virtual group identified with the Virtual IP Address.
switch(config)#interface vlan 10
switch(config-if)#ip address 192.168.10.1 255.255.255.0
switch(config-if)#vrrp group-number ip virtual-ip-gateway-address
switch(config-if)#vrrp group-number priority priority_value 1-255
Configure the master router with this parameter to advertise the value to the other group members
switch(config-if)#vrrp group-number timers advertise timres-value
Configure the non-master routers with this parameter to learn timer values from the master
switch(config-if)#vrrp group-number timers learn
switchA(config)#interface vlan 10
switchA(config-if)#ip address 192.168.10.1 255.255.255.0
switchA(config-if)#vrrp 1 ip 192.168.0.199
switchA(config-if)#vrrp 1 priority 150
switchA(config-if)#vrrp 1 timers advertise 4
switchB(config)#interface vlan 10
switchB(config-if)#ip address 192.168.10.1 255.255.255.0
switchB(config-if)#vrrp 1 ip 192.168.10.200
switchB(config-if)#vrrp 1 priority 100
switchB(config-if)#vrrp 1 timers advertise 4
Notes and Notices:
This is a part of my personal BCMSN notes and research to assist myself in learning and understanding the concepts and theory for the BCMSN exam. I learn by making notes reading and writing things down and wish to file them where I can’t lose them. These notes are not to be seen, judged or mistaken for replacements to Cisco recognized and authorized training which I personally support and attend and suggest you undertake if you are going for the BCMSN Certification.