HSRP Operation

HSRP Operation

Routers accept associates of an HSRP accumulation afterwards actuality configured with a standby IP

address on an Ethernet interface in accession to the approved IP address. All routers in a accumulation are

configured with the aforementioned standby IP address, and an centralized action in anniversary router creates a

standby MAC abode of 0000.0c07.ac**, area the two stars represent the HSRP accumulation number.

(It follows that up to 256 HSRP groups could be configured.)

HSRP routers accelerate accost packets, based on a three-second absence timer (configurable, of

course), out of this interface, announcement the actuality that they are now in a basic router group.

These accost packets accommodate the accumulation ID of the HSRP accumulation and the advertised antecedence of the

router sending the hello.

Based on a antecedence system, one router assumes the role of the alive router in the group.

Other routers will accept the standby condition. Alive routers, on cancellation of a packet that needs

to be forwarded, will advanced the packet. Standby routers will bead the packet, alike though

they additionally accept a route.

This accompaniment charcoal changeless as continued as the accost packets are always accustomed from the active

router. Should these abort to arrive, again afterwards the authority time has been exceeded, the abutting senior

standby router assumes the alive role and starts to advanced packets. The absence authority timer is

10 seconds, but is configurable.

Figure 20.11 shows the action of the accost packets as they acquaint their priorities

on a specific standby group. The diagram shows router Terry sending hellos with a default

priority of 100, and router Jack switched off. When router Jack is started, it sends out a

hello with the configured antecedence of 105. Router Terry realizes that it is no best the active

router and now advertises that it is standby. Note that the hellos appear from the “natural”

Ethernet IP address.