First Hop Redundancy Protocol (FHRP) is a protocol that enables two or more devices to work together in a group, sharing a single IP address, the virtual IP address. One router is elected to handle all requests sent to the virtual IP address. With HSRP, this is the active router. An HSRP group has one active router and at least one standby router.
Virtual Router Redundancy Protocol (VRRP) is one of the First Hop Redundancy Protocols that is supported by Cisco. Unlike HSRP and GLBP (which are Cisco proprietary protocols), VRRP is an industry standard protocol.
HSRP consists of 6 states:
|Initial||This is the beginning state. It indicates HSRP is not running. It happens when the configuration changes or the interface is first turned on|
|Learn||The router has not determined the virtual IP address and has not yet seen an authenticated hello message from the active router. In this state, the router still waits to hear from the active router.|
|Listen||The router knows both IP and MAC address of the virtual router but it is not the active or standby router. For example, if there are 3 routers in HSRP group, the router which is not in active or standby state will remain in listen state.|
|Speak||The router sends periodic HSRP hellos and participates in the election of the active or standby router.|
|Standby||In this state, the router monitors hellos from the active router and it will take the active state when the current active router fails (no packets heard from active router)|
|Active||The router forwards packets that are sent to the HSRP group. The router also sends periodic hello messages|
Please notice that not all routers in a HSRP group go through all states above. In a HSRP group, only one router reaches active state and one router reaches standby state. Other routers will stop at listen state.
There are three First Hop Redundancy Protocols which are HSRP, VRRP and GLBP. HSRP and GLBP are Cisco proprietary protocols while VRRP is a standards-based protocol.
HSRP election is based on a priority value (0 to 255) that is configured on each router in the group. By default, the priority is 100. The router with the highest priority value (255 is highest) becomes the active router for the group. If all router priorities are equal or set to the default value, the router with the highest IP address on the HSRP interface becomes the active router. Below is an example of assigning HSRP priority of 200 to R1:
R1(config-if)# standby 1 priority 200
The “preempt” command enables the HSRP router with the highest priority to immediately become the active router. For example if we have a new router joining an HSRP of 1 and we want this router becomes the active router immediately (provided it had the highest HSRP priority) then we will need this additional command:
New_Router(config-if)#standby 1 preempt
Both HSRP version 1 & version 2 support preempt command -> Answer A is not correct.
In HSRP version 1, group numbers are restricted to the range from 0 to 255. HSRP version 2 expands the group number range from 0 to 4095 -> B is correct.