Chapter 6

First Hop Redundancy Protocol

(FHRP)
Computer Network II (NET461)
Topics Overview:
• First Hop Redundancy Protocol (FHRP)
• Host Standby Router Protocol (HSRP)
• Virtual Router Redundancy Protocol (VRRP)
• Gateway Load Balancing Protocol (GLBP)

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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.
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This diagram is an example of a network topology without FHRP implementation:

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The below diagram is an example of network topology with FHRP implemented:

• To allow redundancy for your clients, you

might want to connect two routers as
exits from the networks.
• The issue is that the PC’s (End-stations)
will be configured with a single default
gateway address.
• FHRP technology allows the two routers
to share a single IP Address. This shared IP
Address is commonly referred to as the
Virtual IP or the VIP.
• You have the ability to prefer a specific
router as the preferred Active router by
manipulating the FHRP priority of the
Router. 5
First Hop Redundancy Protocol Implementations
• There are two main FHRP implementations, they are HSRP & VRRP.
• 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.
• VRRP, or 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. 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.

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Hot Standby Router Protocol (HSRP)
• HSRP is a Cisco proprietary redundancy protocol for establishing a fault-
tolerant default gateway Redundancy.
• HSRP enables two or more devices to work together in a group, sharing a
single IP address, the virtual IP address. The virtual IP address is configured in
each end user's workstation as a default gateway address and is cached in the
host's Address Resolution Protocol (ARP) cache.
• One router is elected to handle all requests sent to the virtual IP address. This
router is known as the active router.
• A HSRP group has one active router, at least one standby router, and perhaps
many listening routers.

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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.
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Virtual Router Redundancy Protocol (VRRP)
• Virtual Router Redundancy Protocol (VRRP) is an open standard redundancy
protocol for establishing a fault-tolerant default gateway Redundancy.
• VRRP also enables two or more devices to work together in a group, sharing a
single IP address, the virtual IP address. The virtual IP address is configured in
each end user's workstation as a default gateway address and is cached in the
host's Address Resolution Protocol (ARP) cache.
• One router is elected to handle all requests sent to the virtual IP address. This
router is known as the Master router.
• A VRRP group has one master router and one or more backup routers.

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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.

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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.
• 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.

* A round robin is an arrangement of choosing all elements

in a group equally in some rational order, usually from the
top to the bottom of a list and then starting again at the top
of the list and so on.

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 Gateway Load Balancing Protocol (GLBP)
• With Round-Robin our “Active Virtual Gateway”
is going to be Responding to “ARP Queries”, by
giving out the Virtual Mac-Addresses of all of
the Active Virtual Forwarder’s and equal times
of amount.
• In this example, that Active Virtual Gateway is
going to respond “One ARP Request” by saying
“The Mac-Address for 10.1.1.1 is the all
1111.1111.1111’s Mac-Address”, and it will
respond to the next “ARP Request” by saying
“it’s all 2222.2222.2222’s Mac-Address”.
• Then it will go back to the all 1111.1111.1111’s
then the all 2222.2222.2222’s in order. 12