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Mobile Backhaul by Esa Metsala, Juha Salmelin

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7.4 IP Layer

7.4.1 VRRP

VRRP (Virtual Router Redundancy Protocol) allows two (or more) separate routers to present themselves as a single virtual router to the hosts. One router is always active (Master Virtual Router) while the others are passive in a VRRP group. IP packets from hosts are sent to the default gateway address which is the virtual IP address of the VRRP group. VRRP protocol [17] (RFC5798) supports both IPv4 and IPv6.

The VRRP group consists of a master virtual router and one or more backup virtual routers. VRRP messages are sent within the routers in the group. With IPv4, the master router sends VRRP advertisements using an IP multicast address 224.0.0.18 with a protocol number of 112. For IPv6, the assigned multicast address is FF02:0:0:0:0:0:0:12, with 112 as the IANA assigned number for the IPv6 Next header field.

During a failover of the master router, a backup router with the highest priority is elected as a new master. When the original master recovers, it then again assumes the master role.

VRRP master router responds to ARP requests (IPv4) and replies with a virtual MAC address. This allows the same IP and MAC address to be kept, irrespective of which of the routers assumes the master virtual router role.

With VRRP a single router is active while others are passive. For load balancing over all routers, multiple VRRP groups may be created, with each group having a different VRRP master.

7.4.2 Load Sharing

One of the benefits of IP is the capability of having ...

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