fhrp isolation

How to configure HSRP?- Exclusive Explanation

How to configure HSRP?- Exclusive Explanation

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HSRP is a Cisco-proprietary First Hop Redundancy Protocol (FHRP) planned to allow for transparent failover of a first-hop IPv4 device. It allows configuring two or more routers as standby routers and only a single router as an active router at a time which ensure high network availability by providing first-hop routing redundancy for IPv4 hosts on networks configured with an IPv4 default gateway address.

All the routers in a single HSRP group share a single MAC address and IP address, which acts a default gateway to the local network. It selects an active router as well as a standby router in the group.

The active router responsible for forwarding traffic to the network and sends the hello packet to the standby router. If it fails and the Standby router doesn’t receive a hello packet for three specific times, it takes up all the responsibilities of the active router and forwards the traffic.

The HSRP configuration can be complicated at times, so this article will cover the basic points step by step. Now, look at the topology in the figure below.

HSRP

Basic HSRP Configuration

The above topology contains two HSRP routers (Router2 and Router3) both can act as the default gateway for the network 192.168.10.0/24 network. At a particular time, only one of these routers will be active with a virtual IP address of 192.168.10.1.

So, virtual IP 192.168.10.1 will be configured as the default gateway for all devices on the network 192.168.10.0/24. So let’s configure the Router1 and Router2 as HRSP router. The following configuration is enough for achieving basic HSRP configuration, the configuration on Router2 is as follow:

  • Router2>enable
  • Router2#config terminal
  • Router2(config)# interface gigabitEthernet 0/1
  • Router2(config-if)#no shutdown
  • Router2(config-if)#ip address 192.168.10.2 255.255.255.0
  • Router2(config-if)#standby 1 ip 192.168.10.1
  • Router2(config-if)#exit
  • Router2(config)#do wr

The configuration on Router3 is as follow:

  • Router3>enable
  • Router3#config terminal
  • Router3(config)# interface gigabitEthernet 0/1
  • Router3(config-if)#no shutdown
  • Router3(config-if)#ip address 192.168.10.3 255.255.255.0
  • Router3(config-if)#standby 1 ip 192.168.10.1
  • Router3(config-if)#exit
  • Router3(config)#do wr

Standby 1, 1 is the HSRP group number. This group number can be any number between 0 and 255 in HSRP version 1 and the only requirement is that you must use the same number across devices in the same HSRP group. So now we can verify the HSRP configuration using the “show standby” command.

The two figures below illustrate the output of the show standby command on Router2 and Router3. You can see the virtual IP address 192.168.10.1 on both router HSRP configuration, which is the default gateway for all the hosts in the network 192.168.10.0/24. You can also see the virtual MAC address for the virtual router.

You can see that Router3 is in the Active state while Router2 is in the standby state. Currently, we have not configured the priority, and both routers are configured with default priority 100.

So, with the same priority, the router with the highest IP address will be elected as the active router. However, we can control the configuration of the active router by configuring the priority that will be also discussed in this article.

Now the entire host will be configured with the default gateway address 192.168.10.1 and the Router3 which is currently active will receive traffic destined for the address 192.168.10.1. We have not advertised the network 192.168.10.0/24 in any routing protocol because Routes are not replicated between HSRP routers.

This means that Router1 and Router2 must individually know how to reach the 172.31.10.1 network used in our example. We have configured the default route on both routers to reach the 172.16.10.0/24 network, suppose it is the internet server, or it is your ISP. So, now if router3 is failed for any reason Router2 will start act as the active router.

HSRP Priority Configuration

HSRP the priority value can control the Active Router election. We can change the default priority value which is 100. For example, what if we wanted Router2 to be the Active router instead of Router3? To force a particular router to be the active router in an HSRP group you will need to use the priority command.

The higher priority determines the active router. If both routers are set to the same priority, the first router to come up will be the active router otherwise router with the highest IP address will be active. Let’s configure the Router priority higher then Router3, so Router2 will ever active when it is power up.

  • Router2>enable
  • Router2#config terminal
  • Router2(config)# interface gigabitEthernet 0/1
  • Router2(config-if)#standby 1 priority 110
  • Router2(config-if)#exit
  • Router2(config)#do wr

We have changed and increased the priority value of the Router2 but, it will remain in the standby mode because preemption is disabled.

HSRP Preempt

If Rouer3 fails, Router2 will become active as we have seen. But, if Router3 restores and returns to service, Router2 will continue to stay active. There are times when you may always want Router3 to be in an active state in the HSRP group.

In our case, we want Router2 as an active router ever for which we increase the priority of the HRSP on the Router2. But it not changes into active mode.

Cisco provides a method for users to control this by using the preempt command. Preempt to ensure a router to be active after recovering from a failure.

So we want Router2 to take over the active function when it recovers from a failure, we can change our configuration on Router2 to include the standby 1 preempt command.

  • Router2>enable
  • Router2#config terminal
  • Router2(config)# interface gigabitEthernet 0/1
  • Router2(config-if)#standby 1 preempt
  • Router2(config-if)#

%HSRP-6-STATECHANGE: GigabitEthernet0/1 Grp 1 state Standby -> Active

  • Router2(config-if)#exit
  • Router2(config)#do wr

Advanced HSRP Configuration – Load Balancing

Load Balancing is an important aspect of any network. In the above topology, one router will ever standby. This is not a good practice.

To solve this problem, we can configure HSRP load balancing between routers. The load balancing is not possible in the single HSRP group, but for multiple HSRP groups, we can extend the load and have each HSRP group be active on different routers.

For our example, let’s add Laptop0 and Laptop1 to another group (Group-2). Router2 will be active for Group1 while Router3 will be active for Group2. This means that R2 will be standby for Group2 while Router3 will be standby for Group1. The HRSP load balancing configuration is following for both routers.

The full configuration on Router2 is as follows:

  • Router2>enable
  • Router2#config terminal
  • Router2(config)# interface gigabitEthernet 0/1
  • Router2(config-if)# ip address 192.168.10.2 255.255.255.0
  • Router2(config-if)# standby 1 ip 192.168.10.1
  • Router2(config-if)#standby 1 priority 110
  • Router2(config-if)#standby 1 preempt
  • Router2(config-if)#standby 1 name Group1
  • Router2(config-if)#standby 2 ip 192.168.1.250
  • Router2(config-if)#standby 2 name Group2
  • Router2(config-if)#exit
  • Router2(config-)#exit
  • Router2#wr

The full configuration on Router3 is as follows:

  • Router3>enable
  • Router3#config terminal
  • Router3(config)# interface gigabitEthernet 0/1
  • Router3(config-if)# ip address 192.168.10.3 255.255.255.0
  • Router3(config-if)# standby 1 ip 192.168.10.1
  • Router3(config-if)#standby 1 name Group1
  • Router3(config-if)#standby 2 ip 192.168.1.250
  • Router3(config-if)#standby 2 priority 110
  • Router3(config-if)#standby 2 preempt
  • Router3(config-if)#standby 2 name Group2
  • Router3(config-if)#exit
  • Router3(config-)#exit
  • Router3#wr

This configuration allows and puts both routers in working mode. We have also configured the HSRP group name to help better describe each HSRP group. This is helpful in the case of many HSRP groups.

To test this configuration, we can use the traceroute command to 172.16.10.1 from both Groups. Remember that Laptop0 and Laptop1 are in Group2 and the default gateway for these hosts is 192.168.10.250 and the other two hosts on Group1 use the previous Default Gateway 192.168.10.1.

What is FHRP? – Exclusive Explanation

What is FHRP? – Exclusive Explanation

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When the active router fails, the First Hop Redundancy Protocol (FHRP) changes the standby router to an active router. If the active router fails, the standby router stops seeing Hello messages from the forwarding router.

Then, the standby router assumes the role of the forwarding router because it assumes both the IP and MAC addresses of the virtual router, and the host devices see no disturbance in service. This process is possible due to the First Hop Redundancy Protocols (FHRPs). The difference FHRPs are the following:-

Host Standby Router Protocol (HSRP)

It is a Cisco-proprietary First-Hop Redundancy Protocol (FHRP) planned to allow transparent failover of a first-hop IPv4 device. It allows configuring two or more routers as standby routers and only a single router as an active router at a time. This ensures high availability by providing first-hop routing redundancy for IPv4 hosts on networks configured with an IPv4 default gateway address.

All the routers in a single HSRP group share a single MAC address and IP address, which acts as a default gateway to the local network. It selects an active router and a standby router in the group.

The active roster forwards traffic to the network and sends the hello packet to the standby router. If it fails and the Standby router doesn’t receive a hello packet for three specific times, it takes up all the responsibilities of the active router and forwards the traffic.

FHRP

HSRP for IPv6

This is also Cisco-proprietary FHRP, which is the same as HSRP. The difference is that HSRP works in an IPv4 environment, and HSRP for IPv6 works in IPv6 environments. An HSRP IPv6 group uses a virtual MAC address resulting from the HSRP group number and a virtual IPv6 link-local address.

Periodic router advertisements (RA) messages would be sent to the HSRP virtual IPv6 link-local address when the HSRP group is active. When the group becomes inactive for any reason, the Router Advertisement (RAs) messages stop after a final RA is sent when the group would be leaving the active state.

Virtual Router Redundancy Protocol Version 2 (VRRPv2)

Virtual Router Redundancy Protocol (VRRP) is an election protocol that provides redundancy to routers within a Local Area Network.

It is a non-proprietary protocol that allows several routers on a multi-access link to use the same virtual IPv4 address. VRRP was designed to remove a single point of failure in a static default-route environment by dynamically assigning virtual IP routers to participating hosts.

In a VRRPv2 configuration, one router is elected as the virtual router master, and other routers act as backups if the master fails.

A virtual router is a collection of physical routers whose interfaces must belong to the same IP subnet. Each virtual router is assigned a virtual router ID, but there is no restriction against reusing a VRID with a different address mapping on different LANs.

VRRPv3

VRRPv3 supports IPv6 addresses, including IPv4 addresses, for dual-stack networks configured with VRRP or VRRP-E. It is compliant with RFC 5798. It provides a faster switchover to backup devices than can be achieved using standard IPv6 neighbor discovery mechanisms.

With VRRPv3, a backup router can become a master router only in seconds with less overhead traffic and no relations with the hosts. It works in multi-vendor environments and is more scalable than VRRPv2.

Gateway Load Balancing Protocol (GLBP)

GLBP is the Cisco-proprietary FHRP. It is the abbreviation of the Gateway Load Balancing Protocol, which protects data traffic from a failed router or circuit, like HSRP and VRRP. GLBP also allows load sharing between a group of redundant routers.

GBLP is specially designed to overcome the limitations of HSRP and VRRP. Gateway Load Balancing Protocol’s additional feature is loading share between the gateways. In HSRP and VRRP, the standby routers are configured for redundancy and act as standby only, becoming active only when the active router fails.

GLBP for IPv6

It is also a Cisco-proprietary FHRP that provides the same function as GLBP but in an IPv6 environment. It provides automatic router backup for IPv6 hosts configured with a single default gateway on a LAN. Multiple first-hop routers on the local area network join to offer a single virtual first-hop IPv6 router while sharing the IPv6 packet forwarding load.

ICMP Router Discovery Protocol (IRDP)

RFC 1256 specifies it as a legacy FHRP. The ICMP Router Discovery Protocol (IRDP) allows IPv4 hosts to locate routers that provide IPv4 connectivity to nonlocal IP networks.

It uses Internet Control Message Protocol (ICMP) router advertisements and router solicitation messages to allow a host to discover the addresses of operational routers on the subnet.

FAQs

Q1: What is a First Hop Redundancy Protocol (FHRP)? 

A1: FHRP is a computer networking protocol designed to ensure the availability of a default gateway in a network. It allows multiple routers to provide backup for a single IP address, ensuring continuous network availability even if one router fails.

Q2: Why is FHRP important in networking? 

A2: FHRP is crucial because it provides redundancy and high availability for the default gateway, essential for maintaining network connectivity and minimizing downtime in case of router failures.

Q3: What are the common types of FHRP? 

A3: The most common types of FHRP include:

  • Hot Standby Router Protocol (HSRP)
  • Virtual Router Redundancy Protocol (VRRP)
  • Gateway Load Balancing Protocol (GLBP)

Q4: How does HSRP work? 

A4: HSRP works by creating a virtual router with a virtual IP address and MAC address. Multiple routers participate in the HSRP group, one acting as the active router and another as the standby router. If the active router fails, the standby router takes over the virtual IP address, ensuring continuous network service.

Q5: What is the difference between HSRP and VRRP? 

A5: While both HSRP and VRRP provide redundancy for the default gateway, their implementation and standards differ. HSRP is a Cisco proprietary protocol, whereas VRRP is an open standard protocol defined by the IETF. Additionally, VRRP allows multiple routers to share the load, whereas HSRP typically has one active and one standby router.

Q6: Can FHRP protocols be used together? 

A6: FHRP protocols can be used together in a network to enhance redundancy and load balancing. For example, HSRP can be used with GLBP to provide redundancy and load balancing.

Q7: What are the benefits of using GLBP? 

A7: GLBP provides load balancing in addition to redundancy. It allows multiple routers to share the network traffic load, improving overall network performance and resource utilization.

Q8: How do I configure FHRP on my network? 

A8: Configuring FHRP involves setting up the protocol on your routers, assigning virtual IP addresses, and defining priority levels for the routers. The specific configuration steps vary depending on the protocol (HSRP, VRRP, or GLBP) and the network equipment used.

Q9: What are some common issues with FHRP, and how can they be resolved? 

A9: Common issues with FHRP include misconfigurations, network topology changes, and hardware failures. These can be resolved by verifying configuration settings, ensuring proper network design, and regularly monitoring and maintaining network equipment.

Q10: Where can I find more information about FHRP? 

A10: More information about FHRP can be found in networking textbooks, online resources, and vendor documentation from companies like Cisco. Additionally, the original article on NetworkUstad provides a detailed overview of FHRP.