VRRP

Virtual Router Redundancy Protocol:

• Consists of Master and backups, whereby the master does all the routing a a given point of time
• Uses 00-00-5E-00-01-XX as it's MAC address, with XX being its Virtual Router ID (VRID). The physical routers in a Virtual Router communicate within themselves using packets with Multicast IP of 224.0.0.18, port 112.
• The routers use a priority method to determine the master, highest priority wins, numbers are allocated between 1-255. This can and should be administratively set when planning a master swap in order to bypass hold time expiration timers (3xAdvertisment + skew time).
• If a backup router fails to receive a packet from the master router three times, the backup will assume connectivity to the master is down and and election process is started throughout the group of routers with multicast packets.
• Backup routers should only send multicast packets during elections, if all backup routers have the same priority, the router with the highest IP will become the master.
• Orderly Election time is made effective by the use of skew time (Skew time = 1-(priority/256)) This reduces the chance of a Thundering herd issue.
• If load sharing is used, backup router utilization is improved