FHRP - which ports should you configure
When configuring First Hop Redundancy Protocols like Hot Standby Router Protocol (HSRP) and Virtual Router Redundancy Protocol (VRRP), it is important to understand which ports must be configured with the appropriate configurations within a topology.
First of all, the configured ports must be Layer 3 ports. That means that they can be either a physical routed port on a switch, an SVI on a switch, or a physical port on a router.
Secondly, all the Layer 3 ports of all of the Layer 3 devices that will play the role of the redundant gateways must reside on the same subnet or broadcast domain. That means that all associated ports must be assigned IP addresses of the same subnet.
- If those ports are SVIs, it is enough for the involved multilayer switches to have trunks between them that include the VLAN of the SVIs in question.
- If those ports are ports on routers, or routed ports on switches, then an additional switch is required to ensure that those ports are connected to the same broadcast domain.
Links:
https://forum.networklessons.com/t/hsrp-hot-standby-routing-protocol/1150/202?u=lagapidis
https://forum.networklessons.com/t/hsrp-hot-standby-routing-protocol/1150/200?u=lagapidis
https://networklessons.com/cisco/ccie-routing-switching/introduction-gateway-redundancy