Manual

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Detection, which checks whether a neighbor node is failed by sending unicast neighbor
request messages to it. In order to reduce the overheads of sending neighbor request
messages, these messages are only sent to those neighbor nodes which are sending flows,
and are only sent if there is no instruction of UP state of the router in a period of time. In
Neighbor Unreachability Detection, if adopting default parameters, it will take about 38
seconds to detect an unreachable router, which is a delay not ignorable for users and might
cause a time-out in some transport protocols. Compared with NDP, VRRP provides a fast
default gateway switch. In VRRP, backup routers can take up the unavailable master router in
about 3 seconds (default parameter), and this process needs no interaction with hosts, which
means being transparent to hosts.
32.1.1 The Format of VRRPv3 Message
VRRPv3 has its own message format, VRRP messages are used to communicate the priority
of routers and the state of Master in the backup group, they are encapsulated in IPv6
messages to send, and are sent to the specified IPv6 multicast address. The format of
VRRPv3 message is shown in Graph 1. The source address of the IPv6 message
encapsulating the VRRPv3 message is the local address of the outbound interface of the
message, and the destination address of it is the IPv6 multicast address(the multicast
allocated to VRRPv3 is FF02:0:0:0:0:0:0:12). The number of hops should be limited to 255,
and the next message head is 112(representing a VRRP message).
The meaning of each field in a VRRPv3 message is shown as follows:
Version: The version of VRRPv3, whose value is 3;
Type: The type of VRRP messages. There is only one type: ADVERTISEMENT, and its value
is 1;
Virtual Rtr ID: The ID of the virtual router;
Priority: Priority, ranging from 0 to 255;
Count IPv6 Addr: The number of IPv6 addresses in a VRRPv3 message, the minimum of
which is 1;
Rsvd: Reserved field, whose value is 0;
Adver Int: The advertisement interval of VRRPv3 messages, in seconds;
Checksum: The checksum, taking account of the whole VRRPv3 message and an IPv6
pseudo head (please refer to RFC2460 for details);
IPv6 Address(es): one or more IPv6 addresses related to the virtual router, the number of
which is the same with ”Count IPv6 Addr”, and the first one of which should be the virtual IPv6
address of the virtual router.