Digi ConnectPort X4 User's Guide download pdf (Page 92)

Configuration through the web interface

Virtual Router Redundancy Protocol (VRRP) settings

Virtual Router Redundancy Protocol (VRRP) is a redundancy protocol for routers. VRRP allows

several routers on a subnet to use the same virtual IP address, with the physical routers

representing a “virtual router.” Two or more physical routers are configured to stand for the virtual

router, with only one doing the actual routing at any given time. The virtual router has a unique IP

address and MAC address that can be shared by all routers in a VRRP group. The advantage in

using a virtual router redundancy protocol is that systems can be configured with a single default

gateway, rather than running an active routing protocol.

There are two roles in VRRP: master, and backup. The master represents the virtual router and

forwards IP traffic. The physical router that is currently routing the data is known as the Master. If

the Master router fails, another Backup router automatically replaces it. Backup routers monitor

the health of the master router, and in the event that the master stops sending advertisements,

backup routers stage an election to determine which one will be the next master, and take over the

virtual router IP address. The time required to make the determination that the master is down and

hold elections depends on configuration, but typically occurs in about 3 seconds.

A number of VRRP groups (up to 255) can be configured on a LAN. A router may participate in

multiple groups. All routers must be within one hop of each other (does not route).

VRRP settings include:

 Virtual Router Identifier (VRID): The virtual router ID. All routers in the same VRID

communicate with each other. The VRID can be any value between 1 and 255. All

routers that are to communicate must have the same VRID.

 Priority: Determines which router is the master. The router with the highest priority is

the master. The default priority is 100.

 Advertisement Interval: The amount of time in milliseconds between VRRP master

advertisements. All routers in the virtual routing group should be set to the same value.

3000 msec (3 seconds) is typically used.

 Enable Preempt: This settings controls whether a higher priority Backup router

preempts a lower priority Master. Check to enable preemption; uncheck to prohibit

preemption. The default setting is enabled (checked).

 IP Address: The IP Address of the virtual router. All routers in the same VRID should

use the same virtual IP address. Clients should be configured to use this value as their

default gateway.

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Digi ConnectPort X4 User's Guide Page 92