HSRP Versions
HSRPv1 - Version 1 is the default version of HSRP. It has the following features:
- The HSRP group number range is from 0 to 255.
- HSRPv1 uses the multicast IP address 224.0.0.2.
- HSRPv1 and CGMP are mutually exclusive.
HSRPv2 - Version 2 has these features:
- extends the group number range to 0-4095 (group number can match all VLAN IDs)
- virtual MAC address from 0000.0C9F.F000 to 0000.0C9F.FFFF
- uses the multicast IP address 224.0.0.102
- HSRPv2 and CGMP are not mutually exclusive, both can be enabled at the same time
- HSRPv2 has different packet format than HSRPv1
Default HSRP Configuration
- HSRP version: Version 1
- HSRP groups: None configured
- Standby group number: 0
- Standby MAC address: System assigned as 0000.0C07.ACxx, where xx is the HSRP group number
- Standby priority: 100
- Standby delay: 0 (no delay)
- Standby track interface priority: 10
- Standby Hellotime: 3 seconds
- Standby Holdtime: 10 seconds
HSRP Configuration Guidelines
- HSRP for IPv4 and HSRP for IPv6 are mutually exclusive, both cannot be enabled simultaneously.
- HSRPv1 and HSRPv2 are mutually exclusive. HSRPv2 is not interoperable with HSRPv1 on an interface and the reverse.
- Support up to 32 instances of HSRP groups.
- The interface must be a Layer 3 interface, either a router port or an SVI.
- All Layer 3 interfaces must have IP addresses assigned.
- Configure only on instance of an FHRP.
- The HSRP version can be changed from HSRPv2 to HSRPv1 only if the group number is less than 256.
- For HSRPv2 and HSRP for IPv6, group numbers that are multiples of 256 must be used; valid ranges are 0 to 255, 512 to 767, 3840 to 4095, and so on.
- If the HSRP version is changed on an interface, each HSRP group resets because it now has a new virtual MAC address.
Enabling HSRP
standby version {1 | 2}
- (Optional) Configures the HSRP version on the interface.
- 1 for HSRPv1, 2 for HSRPv2.
- If not specified, the interface runs HSRPv1 by default.
standby [gp-num] ip [ip-add]
- (Optional) [gp-num] specifies the group number for which HSRP is enabled.
- (Optional on all but one interface) [ip-add] sets the virtual IP address for the HSRP group. Must be set on at least one interface, can be learned by other interfaces.
Example
standby version 1
standby 47 ip 10.0.47.1
Configuring HSRP Priority
- The standby priority, standby preempt, and standby track commands are used to set characteristics for finding the active and standby routers.
- Assigning a priority allows allows the active and standby routers to be manually defined.
- If preemption is enabled, the router with the highest priority becomes the active router.
- If priorities are equal, the current active router does not change.
- The highest numerical value (1 to 255) represents the highest priority (most likely to become the active router).
- The priority can change dynamically if an interface is tracked, and the status goes down.
- By default, the priority is decreased by 10.
- If an interface is not tracked, its state change does not affect the priority.
- When multiple tracked interfaces are down, the configured priority decerements are cumulative.
- If tracked interface were not configured with a decrement priority, the default decrement is 10, and it is non-cumulative.
- When routing is first enabled for the interface, it does not have a complete routing table. If it is configured to preempt, it becomes the active router, even though it is unable to provide adequate routing services. To solve this problem, configure a delay time to allow the router to update its routing table.
standby [gp-num] priority [value] preempt
- Sets a priority value used in choosing the active router.
- (Optional) [value] The range is 1 to 255 (100 by default), the highest number represents the highest priority.
- (Optional) preempt, so that when the local router has a higher priority than the active router, it assumes control as the active router.
standby [gp-num] track [int-num] [int-prio]
- Configures an interface to track another interface so that if it goes down, the priority is lowered.
- [int-num] is the interface identifier of the tracked interface.
- (Optional) [int-prio] specifies the amount by which the priority is decremented, when the interface goes down (10 by default).
Example
standby 47 priority 150 preempt
standby 47 track GigabitEthernet0/0 60
Configuring HSRP Authentication and Timers
- The authentication string is sent unencrypted in all HSRP messages.
- The same authentication string must be configured on all routers.
- Authentication mismatch prevents a device from learning the virtual IP address, and timer values from other routers.
- Routers on which timer values are not configured can learn timer values from the active or standby router.
- The timers configured on an active router always override any other timer settings.
- All routers in an HSRP group should use the same timer values.
- Normally, the Holdtime is greater than or equal to 3 times the Hellotime.
standby [gp-num] authentication [string]
- (Optional) [string] sets the authentication string to be carried in all HSRP messages, up to eight characters in length (the default is cisco).
standby [gp-num] timers [Hello] [Hold]
- Configures the time between Hello packets and the time before other routers declare the active router to be down.
- [Hello] sets the Hello interval in seconds, the range is from 1 to 255 (3 by default).
- [Hold] sets the time in seconds before th active or standby router is declared to be down, the range is from 1 to 255 (10 by default).
Example
standby 47 authentication hsrpstring
standby 47 timers 5 15
Verification
Applied the following configuration.
SW01#
interface Vlan47
ip address 10.0.47.101 255.255.255.0
standby version 2
standby 47 ip 10.0.47.1
standby 47 priority 150
standby 47 preempt
SW02#
interface Vlan47
ip address 10.0.47.102 255.255.255.0
standby version 2
standby 47 ip 10.0.47.1
Verying the configuration.
SW01#show standby brief
P indicates configured to preempt.
Interface Grp Pri P State Active Standby Virtual IP
Vl4 47 150 P Active local 10.0.47.102 10.0.47.1
SW02#show standby brief
P indicates configured to preempt.
Interface Grp Pri P State Active Standby Virtual IP
Vl4 47 100 Standby 10.0.47.101 local 10.0.47.1
SW01#show standby
Vlan47 - Group 47 (version 2)
State is Active
5 state changes, last state change 00:04:48
Virtual IP address is 10.0.47.1
Active virtual MAC address is 0000.0C9F.F02F
Local virtual MAC address is 0000.0C9F.F02F (v2 default)
Hello time 3 sec, hold time 10 sec
Next hello sent in 0.086 secs
Preemption enabled
Active router is local
Standby router is 10.0.47.102
Priority 150 (configured 150)
Group name is hsrp-Vl4-47 (default)
SW02#show standby
Vlan47 - Group 47 (version 2)
State is Standby
3 state changes, last state change 00:07:06
Virtual IP address is 10.0.47.1
Active virtual MAC address is unknown
Local virtual MAC address is 0000.0C9F.F02F (v2 default)
Hello time 3 sec, hold time 10 sec
Next hello sent in 0.739 secs
Preemption disabled
Active router is 10.0.47.101
Standby router is local
Priority 100 (default 100)
Group name is hsrp-Vl4-47 (default)
As a bonus, proof that the HSRPv2 devices are communicating using the multicast IP address 224.0.0.102.
SW01#debug ip packet
IP: s=10.0.47.102 (Vlan47), d=224.0.0.102 len 29, rcvd 2
SW01#
IP: s=10.0.47.101 (local), d=224.0.0.102 (Vlan47), len 29, sending broad/multicast
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