NetModule NB3700, User Manual

Page: 128 / 194

NB3700 User Manual 3.8
5.7.12. Redundancy
This page can be used to set up a redundant pair of NetModule routers (or other systems)
by running the Virtual Router Redundancy Protocol (VRRP) between them. A typical
VRRP scenario defines a first host playing the master and another the backup device,
they both define a virtual gateway IP address which will be distributed by gratuitous
ARP messages for updating the ARP cache of all LAN hosts and thus redirecting the
packets accordingly. A takeover will happen within approximately 3 seconds as soon as
the partner is not reachable anymore (checked via multicast packets). This may happen
when one device is rebooting or the Ethernet link went down. Same applies when the
WAN link goes down.
Figure 5.48.: VRRP Configuration
In case DHCP has been activated, please keep in mind that you will need to reconfigure
the DHCP gateway address offered by the server and let them point to the virtual
gateway address. In order to avoid conflicts you may turn off DHCP on the backup
device or even better, split the DHCP lease range across both routers in order to prevent
any lease duplication.
128