Due to the deficiencies of the original RIP specification, RIP version 2 (RIPv2) was
developed in 1993 and last standardized in 1998. It included the ability to carry subnet
information, thus supporting Classless Inter-Domain Routing (CIDR). To maintain
backward compatibility, the hop count limit of 15 remained. RIPv2 has facilities to fully
interoperate with the earlier specification if all Must Be Zero protocol fields in the RIPv1
messages are properly specified. In addition, a compatibility switch feature allows fine-
grained interoperability adjustments.
4.13 VRRP (Virtual Router Redundancy Protocol)
VRRP is a non-proprietary redundancy protocol described in RFC 3768 designed to
increase the availability of the default gateway servicing hosts on the same subnet. This
increased reliability is achieved by advertising a "virtual router" (an abstract
representation of master and backup routers acting as a group) as a default gateway
to the host(s) instead of one physical router. Two or more physical routers are then
configured to stand for the virtual router, with only one doing the actual routing at any
given time. If the current physical router that is routing the data on behalf of the virtual
router fails, an arrangement is made for another physical router to automatically
replace it. The physical router that is currently forwarding data on behalf of the virtual
router is called the master router. Physical routers standing by to take over from the
master router in case something goes wrong are called backup routers.
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