Principles Of Vrrp; Vrrp Interface Tracking; Vrrp Application (Taking Ipv4-Based Vrrp For Example) - H3C S9500 Series Operation Manual

Operation Manual – VRRP
H3C S9500 Series Routing Switches

1.1.5 Principles of VRRP

1) With VRRP enabled, the routers determine their respective roles in the VRRP
group by priority. The router with the highest priority becomes the master, while
the others are the backups. The master sends VRRP advertisement packets
periodically to notify the backups that it is working properly, and each of the
backups starts a timer to wait for advertisement packets from the master.
2) In preemptive mode, when a backup receives a VRRP advertisement, it compares
the priority in the packet with that of its own. If its priority is lower, it remains a
backup; otherwise, it becomes the master.
3) In non-preemptive mode, the router in the VRRP group remains as a master or
backup as long as the master does not fail. The backup will no become the master
even if the former is configured with a higher priority.
4) If the timer of a backup expires but the backup still does not receive any VRRP
advertisement packet, it considers that the master fails. In this case, the backup
considers itself as the master and sends VRRP advertisements to start the
election process to elect a new master for forwarding packets.

1.1.6 VRRP Interface Tracking

The VRRP 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 on the router become unavailable. When a monitored
interface goes down, the priority of the router owning the interface is automatically
decreased by a specified value, allowing a higher priority router in the VRRP group to
become the master.

1.1.7 VRRP Application (Taking IPv4-Based VRRP for Example)

I. Master/backup
In master/backup mode, only one router, the master, provides services. When the
master fails, a new master is elected from the original backups. This mode requires
only one VRRP group, in which each router holds different priorities and the one with
the highest priority becomes the master, as shown in Figure
1-8
Chapter 1 VRRP Configuration
1-5.