H3C Technologies H3C SecPath F1000-E - Manual (Page 7)

6
• Checksum: 16-bit checksum for validating the data in VRRP packets.
• IP Address/IPv6 Address: Virtual IPv4 or IPv6 address entry of the VRRP group. The Count IP Addrs
or Count IPv6 Addrs field defines the number of the virtual IP v4 or IPv6 addresses.
• Authentication Data: Authentication key. Currently, this field is used only for simple authentication
and is 0 for any other authentication modes.
Principles of VRRP
• Routers in a VRRP group determine their roles by priority and IP address. The router with the highest
priority is the master, and the others are the backups. If the routers have the same priority, the one
with the highest IP address becomes the master. The master periodically sends VRRP advertisements
to notify the backups that it is working properly, and each of the backups starts a timer to wait for
advertisements from the master.
• In preemptive mode, when a backup receives a VRRP advertisement, it compares the priority in the
packet with its own priority. If the priority of the backup is higher, the backup becomes the master;
otherwise, it remains a backup.
• In non-preemptive mode, a router in the VRRP group remains as a master or backup as long as the
master does not fail. A backup does not become the master even if it is configured with a higher
priority.
• If the timer of a backup expires but the backup still does not receive any VRRP advertisement, it
considers that the master fails. In this case, the backup considers itself as the master and sends VRRP
advertisements to start a new master election.
VRRP Tracking
Tracking a specified interface
The interface tracking function expands the backup functionality of VRRP. It provides backup not only
when the interface to which a VRRP group is assigned fails but also when other interfaces (such as uplink
interfaces) on the router become unavailable.
• If the uplink interface of a router in a VRRP group fails, usually the VRRP group cannot be aware of
the uplink failure. If the router is the master of the VRRP group, hosts on the LAN are not able to
access external networks because of the uplink failure. This problem can be solved by tracking a
specified uplink interface. If the tracked uplink interface is down or removed, the priority of the
master is automatically decreased by a specified value and a higher priority router in the VRRP
group becomes the master.
Tracking a track entry
By monitoring a track entry, you can:
• Monitor an uplink and change the priority of the router according to the state of the uplink. If the
uplink fails, hosts in the LAN cannot access external networks through the router. In this case, the
state of the monitored track entry is negative and the priority of the router decreases by a specified
value. Then, a higher priority router in the VRRP group becomes the master to maintain the proper
communication between the hosts in the LAN and external networks.
• Monitor the master on a backup. If the master fails, the backup immediately preempts as the master
to maintain normal communication.
NOTE:
For more information about track entry tracking, see Track Configuration in the System Volume.