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User Manual - Configuration Guide (Volume 3)
Versatile Routing Platform
Chapter 2
Configuration of HSRP
2-1
Chapter 2 Configuration of HSRP
2.1 HSRP Overview
HSRP (Hot Standby Router Protocol), is a reliability protocol based on hot standby
mechanism. It aims, when using a router as the gateway, to enhance the connection
reliability between the network and the outside through hot standby mechanism. It will
be suffice to configure HSRP on a router, which does not affect the local host and there
is no need to make configuration on the local host.
Put two or more routers into a hot standby group to implement HSRP: from the local
host’s point of view, this hot standby group is a virtual router itself, with its own IP
address (a virtual IP address), and the local hosts use this virtual router as a gateway.
In the hot standby group, there is one active Router. It does the work of a virtual router
such as forwarding the local host’s data and messages to the virtual router. And there is
a router in the standby state that is ready to switch over to the active state at any time
when it is necessary. The other routers (if any) in the group are in a listen state. The
state of non-active routers (standby or listen) are determined by their own priority, i.e.,
the router with the highest priority will be in standby state, which leaves the other
routers to be in a listen state. If they have the same priority, then the one with a bigger
Ethernet interface IP address will be in a standby state, leaving the rest ones to be in a
listen state.
When fault occurs, a standby router will take over the work of the active router, and one
of the rest routers (if any) with the highest priority will be selected as the standby router.
Thus, the local host can keep using this virtual router gateway without any
modifications.
Ethernet
Router A (Active)
Virtual router
Router B (Standby)
IP address: 202.38.160.1
IP address: 202.38.160.2
Virtual IP address: 202.38.160.10
Virtual MAC address: 00-E0-FC-00-5F-01
Workstation
Gateway IP address:
202.38.160.10
Figure LC-2-1 Schematic diagram of HSRP application
In this figure, Router A and Router B form a hot standby group, which has the following
workflow:
A certain local host takes the IP address 202.38.160.10 of the hot standby group—
virtual router as its own gateway address. Before transmitting messages through
gateway, it sends out an ARP request in the hope of obtaining a virtual MAC address