In every host within the organization’s network, there should be a need for a router as the default gateway for every host to connect to the Internet. But what if the gateway router goes offline or the default gateway IP is changed during configuration?
Replacing the gateway router will cause a longer service interruption to the users within the organization, and that is not a reactive way to handle the issue. This is where FHRP will take place.
The below diagram is an example of a network topology without FHRP implementation:
What is First Hop Redundancy Protocol (FHRP)?
First Hop Redundancy Protocol (FHRP) is a hop redundancy protocol that is designed to provide redundancy to the gateway router within the organization’s network by the use of a virtual IP address and virtual MAC address.
To implement FHRP, there should be two or more routers that will be used as a gateway router. The virtual IP address and virtual MAC address will be used on both the router. The virtual IP address will be the default gateway IP address for all the devices inside the organization’s network. One router will be used as an active router (gateway router), and the other router will be standby. If the active router goes offline, the standby router will take its place to be the gateway router for all the hosts.
The below diagram is an example of network topology with FHRP implemented:
First Hop Redundancy Protocol (FHRP) Options
We have three ways to implement FHRP. These are by using the following First Hop Redundancy Protocols:
Hot Standby Router Protocol (HSRP)
HSRP, or Hot Standby Router Protocol, is a Cisco-proprietary router redundancy protocol that enables a cluster of routers to cooperate, and all routers are willing to be a default router. All the routers within the cluster will have the same virtual IP address and virtual mac address.
The Two Hot Standby Router Protocol (HSRP) Router States:
Active Router– the router that actively sends and receives a packet to the host within the organization. It is the default gateway router. Only one active router will be selected among the cluster of routers.
Standby Router– the router/s that in case the incumbent active router will go offline, among the standby router will be chosen as the active router.
If the active router goes offline, router failover will occur. These changes will not affect the hosts. The host keeps the same IP address and MAC address setting. The default gateway IP address will be the same still on all hosts. There will be no changes on the host’s ARP table as the gateway router’s virtual MAC address will be the same. Changes in failover only happen on router and switch, and hosts are not affected.
NOTE Preemption in HSRP is not enabled by default. Preemption must be configured manually on the router.
Virtual Router Redundancy Protocol (VRRP)
VRRP, Virtual Router Redundancy Protocol, is a vendor-neutral redundancy protocol that groups a cluster of physical routers (two or more routers) to produce a new single virtual router. It enables redundancy by assigning the same virtual gateway IP address and MAC address on all physical routers within the VRRP group. Currently, VRRP is at version 2. It almost has the same concept as HSRP. The only difference is that preemption is enabled by default on VRRP, while on HSRP, it needs to be configured manually.
Two states of Virtual Router Redundancy Protocol (VRRP):
Master Router– It is the current default gateway of all the hosts within the organization. It is actively sending and receiving packets to the hosts.
Backup Router – The backup router will take the role of the master router during the failover or when the master router goes offline.
NOTE VRRPv3 supports IPv6 and is more scalable than VRRPv2.
Gateway Load Balancing Protocol (GLBP)
As compared to HSRP and VRRP, Gateway Load Balancing Protocol is a bit different. With GLBP, routers within the group are allowed to do load balancing. To put it simply, all the traffic that is transmitted to the default gateway IP address will be load-balanced one at a time or in a round-robin manner among the routers within the group. GLBP has the same state as HSRP, which is called active and standby. The mechanism of GLBP’s active and standby state is the same as HSRP’s active and standby state.
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First Hop Redundancy Protocol (FHRP) is a hop redundancy protocol that is designed to provide redundancy to the gateway router within the organization's network by the use of a virtual IP address and virtual MAC address. To implement FHRP, there should be two or more routers that will be used as a gateway router.
A first hop redundancy protocol (FHRP) is a computer networking protocol which is designed to protect the default gateway used on a subnetwork by allowing two or more routers to provide backup for that address; in the event of failure of an active router, the backup router will take over the address, usually within a ...
The three types of FHRP protocols are Hot Standby Router Protocol (HSRP), Virtual Router Redundancy Protocol (VRRP), and Gateway Load Balancing Protocol (GLBP). All of these protocols mentioned above are designed to provide redundancy and load balancing for the default gateway used on a subnetwork.
HSRP is Cisco's standard method of providing high network availability by providing first-hop redundancy for IP hosts on an IEEE 802 LAN configured with a default gateway IP address. HSRP routes IP traffic without relying on the availability of any single router.
When HSRP is configured on a network segment, it provides a virtual MAC address and an IP address that is shared among a group of routers running HSRP. The address of this HSRP group is referred to as the virtual IP address. One of these devices is selected by the protocol to be the active router.
The hop count refers to the number of network devices through which data passes from source to destination (depending on routing protocol, this may include the source/destination, that is, the first hop is counted as hop 0 or hop 1). An illustration of hops in a wired network (assuming a 0-origin hop count).
FHRP ensures that if the first hop fails, another device can take over and continue to provide connectivity for devices on the network. FHRP is important because it provides redundancy for the first hop of a network. If the first hop fails, devices on the network will lose connectivity.
The default priority is 100. The range is 0-255. If the routers have the same priority, the router with the highest IP address becomes the active router.
The purpose of a First Hop Redundancy Protocol (FHRP) is to provide IP Routing Redundancy by allowing transparent fail-over at the First-Hop IP Router. Default gateway redundancy allows a network to recover from the failure of the device acting as the Default Gateway for end nodes on a physical segment.
FHRP virtual IP address is the default gateway for hosts on the common subnet. FHRP is not a routing protocol and virtual IP address is not installed in the routing table. It is a default gateway address where packets are forwarded for routing services.
What are some critical differences between HSRP and VRRP? HSRP must use a separate virtual IP as the shared IP address.VRRP on the other hand, can use one of the router's physical IPs as the shared IP. By default, HSRP uses a 3-second hello timer, while VRRP uses a 1-second advertisem*nt interval.
IP routing redundancy is designed to allow for transparent fail-over at the first-hop IP router. Both HSRP and VRRP enable two or more devices to work together in a group, sharing a single IP address, the virtual IP address.
Network redundancy provides a network strategy and multiple fallback plans in case a network failure occurs to keep services up and valuable data flowing through the network. Redundant networks are synonymous with a reliable network that will greatly benefit the customers.
VRRP is an IP routing redundancy protocol designed to allow for transparent failover at the first-hop IP router. VRRP enables a group of routers to form a single virtual router . The LAN clients can then be configured with the virtual router as their default gateway.
GLBP operates virtual gateway redundancy in the same way as HSRP. One gateway is elected as the AVG, another gateway is elected as the standby virtual gateway, and the remaining gateways are placed in a listen state. If an AVG fails, the standby virtual gateway will assume responsibility for the virtual IP address.
HOP counts refer to the number of devices, usually routers, that a piece of data travels through. Each time that a packet of data moves from one router (or device) to another — say from the router of your home network to the one just outside your county line — that is considered one HOP.
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