VRRP Advertisement Packets

VRRP Advertisement packets are multicast packets that can be forwarded only within a single broadcast domain, such as a VLAN or VSI. They are used to notify all backup devices in a VRRP group of the master's priority and status.

Two VRRP versions currently exist: VRRPv2 and VRRPv3. VRRPv2 applies only to IPv4 networks, and VRRPv3 applies to both IPv4 and IPv6 networks. VRRP is classified as VRRP for IPv4 (VRRP4) or VRRP for IPv6 (VRRP6) by network type. VRRP for IPv4 supports VRRPv2 and VRRPv3, whereas VRRP for IPv6 supports only VRRPv3.

On an IPv4 network, VRRP packets are encapsulated into IPv4 packets and sent to an IPv4 multicast address assigned to a VRRP group. In the IPv4 packet header, the source address is the primary IPv4 address of the interface that sends the packets (not the virtual IPv4 address), the destination address is 224.0.0.18, the TTL is 255, and the protocol number is 112.
On an IPv6 network, VRRP packets are encapsulated into IPv6 packets and sent to an IPv6 multicast address assigned to a VRRP6 group. In the IPv6 packet header, the source address is the link-local address of the interface that sends the packets (not the virtual IPv6 address), the destination address is FF02::12, the TTL is 255, and the protocol number is 112.

You can manually switch VRRP versions on a NetEngine 8000 F. Unless otherwise specified, VRRP packets in this document refer to VRRPv2 packets.

VRRP Packet Structure

Figure 1 and Figure 2 show VRRPv2 and VRRPv3 packet structures, respectively.

Figure 1 VRRPv2 packet structure

Table 1 describes the fields in a VRRPv2 packet.

**Table 1** Fields in a VRRPv2 packet
Field	Description
Version	VRRP version number. The value is 2.
Type	Type of a VRRP packet. The value is 1, indicating an Advertisement packet.
Virtual Rtr ID	Virtual router ID.
Priority	Priority of the master device in a VRRP group.
Count IPv4 Addrs	Number of virtual IPv4 addresses in a VRRP group.
Auth Type	Authentication type of a VRRP packet. Three authentication types are defined: 0: Non Authentication, indicating that authentication is not performed. 1: Simple Text Password, indicating that simple authentication is performed. 2: IP Authentication Header, indicating that MD5 authentication is performed.
Adver Int	Interval (in seconds) at which VRRP packets are sent.
Checksum	16-bit checksum, used to check the data integrity of a VRRP packet.
IPv4 Address	Virtual IPv4 address configured for a VRRP group. The number of virtual IPv4 addresses configured is carried in the Count IPv4 Addrs field.
Authentication Data	Authentication key of a VRRP packet. This field applies only when simple or MD5 authentication is used. For other authentication types, this field is fixed at 0.

Figure 2 VRRPv3 Packet Structure

Table 2 describes the fields in a VRRPv3 packet.

**Table 2** Fields in a VRRPv3 packet
Field	Description
Version	VRRP protocol version. The value is 3.
Type	Type of a VRRP packet. The value is 1, indicating an Advertisement packet.
Virtual Rtr ID	Virtual router ID.
Priority	Priority of the master device in a VRRP group.
Count IPvX Addrs	Number of virtual IPvX addresses configured for a VRRP group.
rsvd	Field reserved in a VRRPv3 packet. The value is fixed at 0.
Adver Int	Interval (in centiseconds) at which VRRP packets are sent.
Checksum	16-bit checksum, used to check the data integrity of a VRRP packet.
IPvX Address	Virtual IPvX address configured for a VRRP group. The number of configured virtual IPvX addresses is carried in the Count IPvX Addrs field.

The main differences between VRRPv2 and VRRPv3 are as follows:

Authentication: VRRPv3 does not support authentication, whereas VRRPv2 does.
Time unit of the interval for sending VRRP Advertisement packets: VRRPv3 uses centiseconds, whereas VRRPv2 uses seconds.