Quick reminder about HSRP

In this article we will discuss about brief about HSRP 
Quick reminder about HSRP
  • Hot Standby Router Protocol (HSRP) is a Cisco proprietary protocol.
  • With HSRP, two or more devices support a virtual router with a fictitious MAC address and unique IP address
  • Hosts use this IP address as their default gateway and the MAC address for the Layer 2 header
  • The virtual router’s MAC address is 0000.0c07.ACxx , in which xx is the HSRP group. Multiple groups (virtual routers) are allowed.
  • The Active router forwards traffic. The Standby router is backup and monitors periodic hellos (multicast to 224.0.0.2,
  • UDP port 1985) to detect a failure of the active router.
  • The active router is chosen because it has the highest HSRP priority (default priority is 100). In case of a tie, the router
  • with the highest configured IP address wins the election
  • A new router with a higher priority does not cause an election unless it is configured to preempt.

HSRP States
  • Initial: HSRP is not running.
  • Learn: The router does not know the virtual IP address and is waiting to hear from the active router.
  • Listen: The router knows the IP and MAC of the virtual router, but it is not the active or standby router.
  • Speak: Router sends periodic HSRP hellos and participates in the election of the active router.
  • Standby: Router monitors hellos from active router and assumes responsibility if active router fails.
  • Active: Router forwards packets on behalf of the virtual router.

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