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Hot Standby Router protocol (HSRP) – StalinBabu.com – My Personal Blog
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Technology

Hot Standby Router protocol (HSRP)

This is cisco proprietary protocol and communicates via UDP multicast to 224.0.0.2 at port 1985. It uses active and standby routers. The active router forwards the virtual mac address. The standby checks to make sure if the active router is active and will take over the virtual MAC if active goes down.

Facts:

  • The virtual MAC used is always 0000.0c07.acxx where xx is the HSRP group ID. 0c07 is used a virtual mac identifier.
  • The router with the highest priority will become the active HSRP router. If they have the same priority, the one with the highest IP address will become active.
  • Preemption is disabled by default
  • Default hello timer is 3 seconds. Hold timer is 10 seconds
  • HSRP comes in two version. V1 supports 255 group members and v2 supports 4095.

HSRP States:

Initial – State the router begin HSRP Process
Listen – Listening hello messages from the other HSRP routers
Speak – The router sends hello message and participate in the election of active or standby
Standby – Ready to become the active router and sends hello messages
Active – Active router and servicing clients. Sends hello messages

Sample Configuration

The following are configuration commands for cisco

R1

interface fa0/1
ip address 191.0.0.2 255.255.255.0
standby 1 ip 191.0.0.1
standby 1 priority 120

standby 1 preempt delay minimum 10 (prempt with delay option)
standby 1 authentication md5 key-string XYZ (authentication)
standby 1 timers msec XXX msec YYY (set hello and hold timers)
standby 1 track <interface> <value>
standby 1 track <object> decrement <value>

R2

interface fa0/1
ip address 191.0.0.3 255.255.255.0
standby 1 ip 191.0.0.1
standby 1 priority 100
standby 1 preempt

Verification Commands
Show standby
show standby brief
bebug standby events
show ip arp