XGS-5240-Series User Manual

Configuration Guide of XGS-5240-Series
60-29
Chapter 60 VRRP Configuration
60.1 Introduction to VRRP
VRRP (Virtual Router Redundancy Protocol) is a fault tolerant protocol designed to
enhance connection reliability between routers (or L3 Ethernet switches) and external d
evices. It is developed by the IETF for local area networks (LAN) with multicast/broadc
ast capability (Ethernet is a Configuration 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 se
rving 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 r
outes. There is an active router (the "Master") and one or more backup routers (the "B
ackup") 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 add
ress of some router in the Standby cluster), and routers in the Standby cluster also ha
ve their own IP address. Since VRRP runs on routes or Ethernet Switches only, the St
andby cluster is transparent to the hosts with the segment. To them, there exists only t
he IP address of the Virtual Router instead of the actual IP addresses of the Master a
nd Backup(s). And the default gateway setting of all the hosts uses the IP address of t
he 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 achieve
d.
To sum it up, in a VRRP Standby cluster, there is always a router/Ethernet servin
g 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 ti
me. Should the Master fail, a new Master will be elected by all the Backups to take ov