| Virtual
Router Redundancy Protocol |
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VRRP daemon (VRRPd) is an RFC 2338 compliant implementation
of the Virtual Router Redundancy Protocol (VRRP).
The Virtual Router Redundancy Protocol is designed
to eliminate the single point of failure associated
with statically routed networks by automatically providing
failover using multiple LAN paths through alternate
routers.
As specified in RFC 2338, VRRP uses
an election protocol that dynamically assigns responsibility
for a virtual router to one of the VRRP routers on
a LAN. When a VRRP router controls the IP address(es)
associated with a virtual router, it is called the
Master. The Master continues to forward packets sent
to these IP addresses until it has a problem that
causes the VRRP routers to hold an election. The election
process provides dynamic failover by electing a new
Master should the existing Master become unavailable.
The virtual router associated with each
alternate path under VRRP uses the same IP address
and MAC address as the routers for other paths. As
a result, the host's gateway information does not
change, no matter what path is used. Because of this
design, VRRP-based redundancy significantly reduces
administrative overhead when compared to redundancy
schemes that require hosts to be configured with multiple
default gateways.
The primary function of the Virtual
Router Redundancy Protocol is to provide routing redundancy
for specific IP addresses. In addition to this primary
function, RFC 2338 also states that the protocol should:
- Minimize the duration of black
holes.
- Minimize the steady state bandwidth
overhead and processing complexity.
- Function over a variety of
multiaccess LAN technologies that support IP traffic.
- Provide for election of multiple
virtual routers on a network for load balancing.
- Support multiple logical IP
subnets on a single LAN segment.
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