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NOTE: We recommend that you have some background understanding of the Address
Resolution Protocol (ARP) before you configure VRRP. See Address Resolution Protocol
in the JUNOSe IP, IPv6, and IGP Configuration Guide.
How VRRP Works
The advantage of using VRRP is that you gain a higher availability for the default
path without requiring configuration of dynamic routing or router discovery protocols
on every end host.
VRRP routers viewed as a redundancy group share the responsibility for forwarding
packets as if they owned the IP address corresponding to the default gateway
configured on the hosts. At any time, one of the VRRP routers acts as the master,
and other VRRP routers act as backup routers. If the master router fails, a backup
router becomes the new master. In this way, router redundancy is always provided,
allowing traffic on the LAN to be routed without relying on a single router.
A master always exists for the shared IP address. If the master goes down, the
remaining VRRP routers elect a new master VRRP router. The new master forwards
packets on behalf of the owner by taking over the virtual MAC address used by the
owner.
When implemented in your network, VRRP interprets any active link to a subnet to
indicate the router has access to the entire subnet. VRRP leverages the broadcast
capabilities of Ethernet. Provided that one of the routers in a VRRP configuration is
running, ARP requests for the IP addresses assigned to the default gateway always
receive replies. Additionally, end hosts can send packets outside their subnet without
interruption.
Configuration Examples
This section describes and illustrates three VRRP configuration examples.
Basic VRRP Configuration
As Figure 4 on page 108 shows, the basic VRRP configuration uses a single VRID (VRID
1). Because R1 is the address owner, it serves as the master router. Router R2 is the
backup router. The four end hosts on subnet 1 are configured to use 10.0.0.1/8 as
the default router. IP address 10.0.0.1 is associated with VRID 1.
In this example, if R1 becomes unavailable, R2 takes over VRID 1 and its associated
IP addresses. Packets sent to IP destinations outside the 10.x.x.x subnet using 10.0.0.1
RFC 3768 Virtual Router Redundancy Protocol (VRRP) (April 2004)
"Basic VRRP Configuration" on page 107
"Commonly Used VRRP Configuration" on page 108
"VRRP Configuration Without the Real Address Owner" on page 109
Chapter 5: Configuring VRRP
107
How VRRP Works
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