FHRP - HSRP Resign Message
The Hot Standby Router Protocol (HSRP) is a Cisco proprietary protocol designed to ensure high availability and redundancy for IP traffic by providing failover capability within a group of routers. The "resign" message is a critical part of the HSRP protocol. Here's an explanation of this message in HSRP:
HSRP Overview
HSRP allows multiple routers to work together to present the appearance of a single virtual router or default gateway to the hosts on a LAN. In an HSRP group, routers are assigned roles such as Active or Standby based on their priorities and states. The Active router is responsible for forwarding packets sent to the virtual IP address, while the Standby router takes over if the Active router fails.
Resign Message
Purpose:
- Role Transition: The resign message is sent by the Active router to indicate that it is stepping down from its role as the Active router. This can happen due to various reasons, such as a manual shutdown, configuration change, or the router detecting that it is no longer capable of serving as the Active router.
- Trigger Failover: Upon receiving a resign message, the Standby router (or other routers in the group) will initiate an election process to determine which router should become the new Active router.
When It's Sent:
- Manual Intervention: An administrator manually changes the configuration or priority of the Active router or shuts down the interface acting as one of the redundant default gateways..
- Failure or Preemption: A higher-priority router becomes available, or the current Active router encounters an issue that prevents it from continuing its role.
Links:
https://forum.networklessons.com/t/hsrp-hot-standby-routing-protocol/1150/206?u=lagapidis
https://networklessons.com/cisco/ccie-routing-switching/hsrp-hot-standby-routing-protocol/