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Hot Standby Routing Protocol (HSRP)

HSRP is the redundant gateway to the other network. It is Cisco proprietary.

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Suppose that you are working with the network architecture shown as above and you are sending traffic using a routing protocol, we do not know what path will the router choose to send the traffic because we do not know the underlying routing protocol.

Now suppose that the Router B somehow fails to work then what will other routers do? The answer is the routing protocol will take care of it and will transmit traffic using Router D.

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By now everything is good despite failure in network but what if Router A fails to work.

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The other condition could be what if the Router A fails shown in following diagram. The problem is not with the routers the real problem is with end devices, the end devices have set their default gateway to 192.168.0.1, how will you change that if you are running hundreds of devices.
Let’s say you have DHCP configured and you say the new gateway will be generated by DHCP but it will take more time before the lease ends.
Another solution could be that you set the 192.168.0.1 address on Router B, but what when Router A comes live again then there will be conflict because there will be two routers with the same IP.

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HSRP works in the way as shown in the following diagram. It is the virtual gateway that floats between physical gateways and when any one of the gateway goes down the floating gateway takes its place. Notice that routers have to have their own unique IP address. In this way the end devices do not know that there was any change in the network and they always response to a virtual gateway which is always up and available.

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It is highly recommended that you use this protocol in core switches to move the traffic.

HSRP Configuration

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This is the only command that is needed to be executed to turn on HSRP.

There are 5 states of HSRP.

HSRP States

Initializing

This is the starting state of HSRP.

Listen

This is the state where device listens to the other devices that are running HSRP.

Speak

This state starts when device knows that Router-X is running HSRP and the device sends Hello message to become HSRP.

Standby

This state says that I am ready to active but cannot go active due to certain reasons. This states also tells that someone else is in active state.

Active

This state turns the mode into active where the HSRP is made.

HSRP MAC Address

HSRP is a virtual router and the router has to have a MAC address as well because it has an IP address. The MAC address for HSRP version-1 is 0000.0c07.acXX, here the first ten numbers are dedicated for HSRP version-1 so you should be able to recognize whether the device running HSRP or not, the last two numbers are dedicated to the group ID of HSRP. For example if we have assign group ID number 5 to HSRP the MAC address will be 0000.0c07.ac05. You can make up to 255 groups in HSRP version-1.

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HSRP Version 2

There are two versions of HSRP, 1 and 2. By default devices run version 1, however you can use version 2 by just executing following command in Interface configuration mode.

standby version 2

The version 2 was created to support more numbers of HSRP groups. This version can support up to 4095 groups where version 1 could only support 255 groups.

The MAC address of version 2 also differs from version 1.

0000.0C9F.F000 in this MAC address the first 9 digits are static and last 3 reserved for group IDs.

Prerequisites for 200-301

200-301 is a single exam, consisting of about 120 questions. It covers a wide range of topics, such as routing and switching, security, wireless networking, and even some programming concepts. As with other Cisco certifications, you can take it at any of the Pearson VUE certification centers.

The recommended training program that can be taken at a Cisco academy is called Implementing and Administering Cisco Solutions (CCNA). The successful completion of a training course will get you a training badge.

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