Should this device fail, then all of the users who are on a specific segment using it as their default gateway will be unable to reach any other subnet including the Internet. There are a number of different solutions to this problem, and most of these are all grouped together and referred to as First Hop Redundancy Protocols FHRP. This article specifically looks at HSRP and how it operates along with the main concepts that should be known before attempting to configure it. The general idea behind HSRP is rather simple: Configure multiple devices that all exist on the same subnet and are able to act as gateways to the hosts on the subnet. Basic redundancy can be configured by configuring some of the hosts to use one gateway and the other hosts to use another.
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From the group of routers configured in an HSRP group, there is one router elected as the active router and another as a standby router. The active router assumes the role of forwarding packets sent to the virtual IP address.
If the active router fails, the standby router takes over as the new active router. This address is also referred to as the standby IP address. Each router in this group must define with the same virtual IP address using the standby [group-number] ip [Virtual ip-address] command.
This can be accomplished with the standby [group-number] priority [priority] commands. The default priority value is The router in the HSRP group with the highest priority value becomes the active router. The standby preempt command is needed in situations when you want an occurring state change of a tracked interface to cause a standby router to take over from the active router.
For example, an active router tracks another interface and decrements its priority when that interface goes down. The standby router priority is now higher and it sees the state change in the hello packet priority field. If preempt is not configured, it cannot take over and failover does not occur.
The standby router reads this value from the hello packet priority field, and becomes primary if this value is lower than its own priority and the standby preempt command is configured.
You can configure by how much the router must decrement the priority. This ensures that only authorized routers can become part of the HSRP group. The string must match all routers in the HSRP group.
If the msec option is specified, hello interval is in milliseconds. Basic configuration Example: In this scenario, on site A multiple clients reside on the fast Ethernet segment of To accomplish this, R1 is selected as the primary router, and R2 is the secondary router. You need to use To provide redundancy, you also need to track the serial interfaces. When tracking is used, two potential situations can cause R2 to become the primary router.
Most of the company in the world has a connection to the Internet. This can be done manually or automatically via DHCP. After some time, your boss wants to implement some redundant methods so that even the Router fails, all PCs can still access the Internet without any manual configuration at that time. So we need one more router to connect to the Internet as the topology below: But now we have a problem: There is only one default gateway on each host, so if Router1 is down and we want to access the Internet via Router2, we have to change the default gateway to Also, when Router1 comes back we have to manually change back to the IP address on Router1. And no one can access to the Internet in the time of changing the default gateway. HSRP can solve all these problems!
CCNA 5.5: Configure, verify, and troubleshoot basic HSRP
This command was introduced. Usage Guidelines To use this command, you must be in a user group associated with a task group that includes the proper task IDs. If you suspect user group assignment is preventing you from using a command, contact your AAA administrator for assistance. The hsrp ipv4 command activates HSRP on the configured interface. If an IP address is specified, that address is used as the designated address for the Hot Standby group. If no IP address is specified, the virtual address is learned from the active router.