Chapter21 Vrrp Configuration; Introduction To Vrrp; Configuration Task Sequence - Accton Technology ES4710BD User Manual

Chapter21 VRRP Configuration

21.1 Introduction to VRRP

VRRP (Virtual Router Redundancy Protocol) is a fault tolerant protocol designed to enhance
connection reliability between routes (or L3 Ethernet switches) and external devices. It is developed
by the IETF for local area networks (LAN) with multicast/broadcast capability (Ethernet is a typical
example) and has wide applications.
All hosts in one LAN generally have a default route configured to specified default gateway,
any packet destined to an address outside the native segment will be sent to the default gateway via
this default route. These hosts in the LAN can communicate with the external networks. However, if
the communication link connecting the router serving as default game and external networks fails,
all hosts using that gateway as the default next hop route will be unable to communicate with the
external networks.
VRRP emerged to resolve such problem. VRRP runs on multiple routers in a LAN, simulating
a "virtual" router (also referred to as a "Standby cluster") with the multiple routes. There is an active
router (the "Master") and one or more backup routers (the "Backup") in the Standby cluster. The
workload of the virtual router is actually undertaken by the active router, while the Backup routers
serve as backups for the active router.
The virtual router has its own "virtual" IP address (can be identical with the IP address of some
router in the Standby cluster), and routers in the Standby cluster also have their own IP address.
Since VRRP runs on routes or Ethernet Switches only, the Standby cluster is transparent to the hosts
with the segment. To them, there exists only the IP address of the Virtual Router instead of the actual
IP addresses of the Master and Backup(s). And the default gateway setting of all the hosts uses the
IP address of the Virtual Router. Therefore, hosts within the LAN communicate with the other
networks via this Virtual Router. But basically, they are communicating with the other networks via
the Master. In the case when the Master of the Standby cluster fails, a backup will take over its task
and become the Master to serve all the hosts in the LAN, so that uninterrupted communication
between LAN hosts and external networks can be achieved.
To sum it up, in a VRRP Standby cluster, there is always a router/Ethernet serving as the active
router (Master), while the rest of the Standby cluster servers act as the backup router(s) (Backup,
can be multiple) and monitor the activity of Master all the time. Should the Master fail, a new
Master will be elected by all the Backups to take over the work and continue serving the hosts
within the segment. Since the election and take-over duration is brief and smooth, hosts within the
segment can use the Virtual Router as normal and uninterrupted communication can be achieved.

21.1.1 Configuration Task Sequence

1. Create/Remove the Virtual Router (required)
2. Configure VRRP dummy IP and interface (required)
3. Activate/Deactivate Virtual Router (required)
4. Configure VRRP authentication (optional)
5. Configure VRRP sub-parameters (optional)
1) Configure the preemptive mode for VRRP
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