RuggedCom RuggedRouter RX1100 - Manual (Page 189)

19. Configuring VRRP
Revision 1.14.3 189 RX1000/RX1100™
19. Configuring VRRP
19.1. Introduction
This chapter familiarizes the user with:
• Configuring VRRP
• Enabling And Starting VRRP
• Obtaining VRRP Status
19.1.1. VRRP Fundamentals
The Virtual Router Redundancy Protocol (VRRP) eliminates a single point of failure associated with
statically routed networks by providing automatic failover using alternate routers. The RuggedRouter
VRRP daemon (keepalived) is an RFC 2338 version 2 compliant implementation of VRRP.
19.1.1.1. The Problem With Static Routing
Many network designs employ a statically configured default route in the network hosts. A static default
route is simple to configure, requires little if any overhead to run and is supported by virtually every IP
implementation. When dynamic host configuration protocol (DHCP) is employed, hosts may accept
configuration for only a single default gateway.
Unfortunately, this approach creates a single point of failure. Loss of the router supplying the default
route or the router's WAN connection results in isolating the hosts relying upon the default route.
There are a number of ways that may be used to provide redundant connections to the host.
Some hosts can configure alternate gateways while others are intelligent enough to participate in
dynamic routing protocols such as Routing Information Protocol (RIP) or Open Shortest Path First
routing protocol (OSPF). Even when available, these approaches are not always practical due to
administrative and operation overhead.
19.1.1.2. The VRRP Solution
VRRP solves the problem by allowing the establishment of a “virtual router group”, composed of a
number of routers that provide a specific default route. VRRP uses an election protocol to dynamically
assign responsibility for the “virtual” router to one of the routers in the group. This router is called
the VRRP Master. If the Master (or optionally its WAN connection) fails, the alternate (i.e. backup)
routers in the group elect a new Master. The new master provides the virtual IP address and issues
a gratuitous ARP to inform the network of where the gateway can be reached.
Because the host's default route does not change and MAC address is updated, packet loss at the
hosts is limited to the amount of time required to elect a new router.
19.1.1.3. VRRP Terminology
Each physical router running VRRP is known as a VRRP Router. Two or more VRRP Routers can
be configured to form a “Virtual Router”. Each VRRP Router may participate in one or more Virtual
Routers.