Multicast and Routing Guide K/KA/KB.15.15

• Neighbor reachability
• Autoconfiguration of unicast addresses
• Resolution of destination addresses
• Changes to link-layer addresses.
An instance of Neighbor Discovery is triggered on a device when a new or changed IPv6 address
is detected. VRRPv3 provides a faster failover to a backup router by not using standard ND
procedures. A failover to a backup router can occur in approximately three seconds without any
interaction with hosts and with a minimum of VRRPv3 traffic.
Duplicate address detection (DAD)
Duplicate Address Detection verifies that a configured unicast IPv6 address is unique before it is
assigned to a VLAN interface. When the owner router fails, the backup VRRP router assumes the
master role. When the owner router becomes operational, DAD will fail as there is a backup VRRP
router in the master role that responds to the DAD request. To avoid this, virtual routers that are in
owner mode (priority = 255) will not send DAD requests for the VLAN interface on which the owner
VR is configured.
General operating rules
• IP routing (IPv4) or IPv6 unicast-routing (IPv6) must be enabled on the router before enabling
VRRP.
• IP must be enabled on a VLAN before creating a VR instance on the VLAN.
• VIP:
The VIP configured in a VR instance must match one of the IP addresses
configured in the VLAN interface on which the VR is configured.
On an owner
On a backup The VIP configured in a VR instance cannot be a "real" IP address
configured in a VLAN interface on that router.
NOTE: The VIP configured for one VR cannot be configured on another VR.
• Before changing a router from owner to backup, or the reverse, the VIP must be removed from
the configuration.
• The priority configuration on an owner can be only 255. The priority configuration on a
backup must be 254 or lower, the default being 100.
• Advertisement intervals:
• If a VRRP router has a different advertisement interval than a VRRP packet it receives, the
router drops the packet. For this reason, the advertisement interval must be the same for
the owner and all backups in the same VR.
• A VR exists within a single VLAN interface. If the VLAN ismultinetted, a separate VR can be
configured within the VLAN for each subnet. A VLAN allows up to 32 VRs, and the switch
allows up to 2048 VRs.
• All routers in the same VR must belong to the same network or subnet.
• The router supports the following maximums:
32 VRs per VLAN in any combination of masters and backups•
• 512 IPv4 and IPv6 VRs in combination
• 2048 Virtual IP addresses
• 512 VR sessions on the switch
General operation 279