FHRP (First Hop Redundancy Protocols)
- Implement router redundancy, multiple routers are configured to work together to present the illusion of a single router.
- By sharing an IP address and a MAC address, two or more routers can act as a single virtual router.
- The ability of a network to dynamically recover from the failure of a device acting as a default gateway is known as first hop redundancy
Steps for Router Failover(The ability to switch automatically and seamlessly to a reliable backup system)
- The standby router stops seeing Hello message from the forwarding router.
- The standby router assumes the role of the forwarding router.
HSRP (Hot Standby Router Protocols) [Cisco proprietary]
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The router with the highest priority will become the active router.
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The default priority is 100, it can be changed using ”’standby priority”’ command
R1(config-if)# standby priority - The range of the HSRP priority is 0 – 255
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- The router with numerically highest IPv4 address is elected as the active router.
HSRP Preemption
- By default, after a router becomes the active router, it will remain the active router even if there is another router which has higher priority comes online.
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To enable the re-election of the active router, using ”’standby preempt”’ command can force the process of the re-election when there is a new router comes online with a higher priority.
R1(config-if)# standby preempt - Only one router can be the active router. A router has the same priority bu higher IPv4 address will not preempt the role of active router.
HSRP States and Timers
| HSRP State | Description |
|---|---|
| Initial | An interface first becomes available |
| Learn | The router waits to hear from the active router |
| Listen | The router knows the virtual IP address, listens fro hello message from active router or standby router |
| Speak | The router sends periodic hello message and actively participate the election of active or standby router |
| Standby | The router is a candidate to become the next active router and sends periodic hello message. |
| Active | The router won the election |
- The active and standby HSRP routers send hello message to the HSRP group multicast address every 3 seconds by default.
- The standby router will become the active router, if it doesn’t receive a hello message from the active router after 10 seconds.
GLBP(Gateway Loading balancing protocol)[Cisco proprietary]
- It provides support for IPv6
- It provides one virtual IP address and multiple MAC addresses
- It support load balancing where multiple active routers can share the traffic load at a single time
HSRP Configuration
R1(config-if)# standby version 2
R1(config-if)# standby [group number] ip [virtual default gateway address]
R1(config-if)# standby [group number] priority [priority number 0-255]
R1(config-if)# standby [group number] preempt