Hot Standby Router Protocol

aliases:

• HSRP

Proprietary protocol developed by Cisco. Allows multiple physical routers to serve as a single default gateway for a subnet.

Each router part of the mesh needs an interface connected with the subnet, a unique MAC address and a unique IP address. Then, the mesh needs to be configured to share a common virtual IP address and a common MAC address. A group of routers configured this way is called a standby group.

Standby groups communicate among each other using IP multicasts and choose an active router based on a priority list configured by the network administrator. The active routers responds to incoming connections sent to the virtual IP address. Should the active router go down, the next one in line (called a standby router) assumes control and sets the next standby router based on the priority list. The standby router is also responsible for monitoring active connections, ensuring that there is no downtime between the failure of the active router and the standby router stepping up.