D-Link DGS-6600-48TS Configuration Guide - Page 341
Behavior of a master router
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Volume 4-Layer 3 Configurations / Chapter 32-Virtual Router Redundancy Protocol (VRRP) Chapter Overview The following diagram shows a simple network with two VRRP routers implementing one virtual router and none of the routers is IP address Owner. Figure 32-2 a simple network with two VRRP routers implementing one virtual router In this case, Router-1 is configured with a priority value (PRI) of 200 and Router-2 100. The higher value gets higher priority. So the Router-1 becomes the master and Router-2 becomes the backup of the virtual router. Behavior of a master router When a router becomes the master, it would broadcast a ARP request containing the virtual router's MAC address, 00-00-5E-00-01-XX The last byte of the address (XX) is the Virtual Router Identifier. Master router sends periodic VRRP Advertisement message with multicast IP address 224.0.0.18 and IP protocol number 112 for decare the master router's state and its priority. And it forwards the packets from host that send to this virtual router Behavior of the backup router The backup router will not send VRRP advertisement message, Instead it monitors the advertisement message that is sent from the master. If the Advertisement message isn't received within a certain period of time (3 * Advertisement Interval) - ((256 - priority)/256)), it will assume that the master router is dead. The virtual router then transitions into an unsteady state and an election process is initiated to select the next master router from the backup routers. If a backup router receives an advertisement message sent from a lower priority master, it will attempt to preempt the master if it has higher priority. There is a "preempt-mode" designed in the backup master controls which is used when a higher priority backup router preempts a lower priority master. By default, the router preempt mode is enabled on the router, the backup takes over as master router for the virtual router if it has a higher priority than the current master router. When preempt mode set to disabled, the backup will not attempt to preempt the master router even if it has a higher priority than the master router. One exception is when the router that is the virtual IP address owner always preempts. DGS-6600 Configuration Guide 341