Avaya 8800 Planning And Engineering, Network Design page 118

Layer 3 network design
which they are actively sending traffic and only after the node receives no positive indication that the
neighbors are up for a period of time. Using the default ND parameters, it takes a host
approximately 38 seconds to learn that a router is unreachable before it switches to another default
router. This delay is very noticeable to users and causes some transport protocol implementations
to timeout.
While you can decrease the ND unreachability detection period by modifying the ND parameters,
the current lower limit that can be achieved is five seconds, with the added downside of significantly
increasing ND traffic. This is especially so when there are many hosts all trying to determine the
reachability of one of more routers.
To provide fast failover of a default router for IPv6 LAN hosts, the Avaya Ethernet Routing Switch
8800/8600 supports the Virtual Router Redundancy Protocol (VRRP v3) for IPv6 (defined in draft-
ietf-vrrp-ipv6-spec-08.txt).
VRRPv3 for IPv6 provides a faster switchover to an alternate default router than is possible using
the ND protocol. With VRRPv3, a backup router can take over for a failed default router in
approximately three seconds (using VRRPv3 default parameters). This is accomplished without any
interaction with the hosts and with a minimum amount of VRRPv3 traffic.
The operation of Avaya's IPv6 VRRP implementation is similar to the IPv4 VRRP operation,
including support for hold-down timer, critical IP, fast advertisements, and backup master. With
backup master enabled, the backup switch routes all traffic according to its routing table. It does not
Layer 2-switch the traffic to the VRRP master.
New to the IPv6 implementation of VRRP, you must specify a link-local address to associate with
the virtual router. Optionally, you can also assign global unicast IPv6 addresses to associate with
the virtual router. Network prefixes for the virtual router are derived from the global IPv6 addresses
assigned to the virtual router.
With the current implementation of VRRP, one active master switch exists for each IPv6 network
prefix. All other VRRP interfaces in a network are in backup mode.
The following figure shows a sample IPv6 VRRP configuration with SMLT. Because the backup
router is configured as the backup master, routing traffic is load-shared between the two devices.
June 2016 Planning and Engineering — Network Design
Comments on this document? infodev@avaya.com
118