First Hop Redundancy Protocol | Hot Standby Router Protocol | HSRP, VRRP & GLBP | CCNA-200-301

FHRPs enable you to install multiple routers in a subnet to collectively act as a single default router. These routers share a virtual IP address.
One router is active router, which is forwarding the traffics, coming from hosts in the organizations.
And the other router is standby router. Standby router is a backup router when active router is failed. And the standby router take over the responsibility to forwarding traffics coming from hosts.
However, both routers are also configured with the virtual IP address. This virtual IP address is the default gateway address, configured on end devices.
A redundancy protocol provides, the mechanism for determining which router should take the active role in forwarding traffic.
It also determines, when, a standby router must take over the forwarding role. The transition from one forwarding router to another, is transparent to the end devices.
This capability of a network, to dynamically recover from the failure of a device, and acting as a default gateway, is known as first-hop redundancy.
when the active router fails:
1-The standby router stops seeing hello messages from the forwarding router.
2- The standby router assumes the role of the forwarding router.
3- Because the new forwarding router, assumes both the IP and MAC addresses of the virtual router, the end stations do not recognize a disruption in service.
Three Main options available for FHRPs:
■ Hot Standby Router Protocol (HSRP): A Cisco-proprietary protocol, designed to allow for transparent failover of a first-hop IPv4 device. Also support for IPv6 networks.
■ Virtual Router Redundancy Protocol (VRRP): An IETF standard that dynamically assigns responsibility for one or more virtual routers. Its operation is similar to that of HSRP. VRRPv3 supports IPv4 and IPv6.
■ Gateway Load Balancing Protocol (GLBP): A Cisco-proprietary FHRP that protects data traffic from a failed router, as in HSRP and VRRP. while also allowing load balancing or load sharing) between a group of redundant routers. GLBP for IPv6 provides support for IPv6 networks.
HSRP Operation
The next part of video I will discuss about Hot-Standby Router Protocol.
HSRP uses an active/standby model, in which, one router actively assumes the role of default gateway for devices on the subnet.
One or more routers on the same subnet are then in standby mode.
Before forming the HSRP, Each HSRP router will go through a number of states before it ends up, as an active or standby router, this is what will happen:
Initial state: This is the first state when HSRP starts. You’ll see this just after you configured HSRP or when the interface just got enabled.
Listen State: The router knows the virtual IP address and will listen for hello messages from other HSRP routers.
Speak State: The router will send hello messages and will join the election to see which router will become active or standby.
Standby State: The router didn’t become the active router but will keep sending hello messages. If the active router fails it will take over.
Active State: The router will actively forward packets from clients and sends hello messages.
The HSRP active router implements a virtual IP address and matching virtual MAC address. This virtual IP address is part of the HSRP configuration and belongs to the same subnet as the physical interface IP address, but it is a different IP address.
The router then automatically creates the virtual MAC address. All the cooperating HSRP routers know these virtual addresses, but only the HSRP active router uses these addresses at any one point in time.