Hot Standby Routing Protocol (HSRP) Version 1, 2 & IPv6

HSRP is a Cisco Proprietary protocol and defaults to version 1.



HSRP version 2 will not interoperate with HSRP version 1. An interface cannot operate both version 1 and version 2 because both versions are mutually exclusive. However, the different versions can be run on different physical interfaces of the same router. 

When the HSRP version is changed (v1->v2 or v2->v1), each group will reinitialize because it now has a new virtual MAC address. You cannot change v2->v1 if you have configured groups above the group number range allowed for version 1 (0 to 255). 

Set the version using standby version {1 | 2} at the interface level.

Version 1

• Group numbers are restricted to the range from 0 to 255.
• Uses mac address 0000.0c07.acxx, where xx is the group number in hexadecimal.
• Sends traffic on port UDP/1985
• The multicast address 224.0.0.2 is used to send HSRP hello messages. This address can conflict with Cisco Group Management Protocol (CGMP) leave processing.
• Priority (not a metric so highest number wins) is 0-255 with the default of value of 100. 
  

Version 2

• Expands the group number range from 0 to 4095.
• Uses a new mac address range 0000.0C9F.Fxxx, where xx is the group number in hexadecimal.
• Sends traffic on port UDP/2029
• Uses the new IP multicast address 224.0.0.102 to send hello packets.
• Uses a different packet format than version 1. The packet format uses a type-length-value (TLV) format. Version 2 packets received by an version 1 router will have the type field mapped to the version field by version 1 and subsequently ignored. 
• Priority (not a metric so highest number wins) is 0-255 with the default of value of 100.
• Allow MD5 Authentication

HSRP IPv6 (with so many changes it should really be a new version!)

• Uses HSRP v2 packets and this must be enabled before adding ipv6 specific parameters.
• Uses same group range as HSRP v2
• Uses a new mac address range 0005.73A0.0xxx where xx is the group number in hexadecimal. A direct result of this is: virtual IPv6 link-local address is, by default, derived from the HSRP virtual MAC address.
• Uses same HSRP v2 UDP port
• Uses the new IP multicast address FF02::66 to send hello packets.
• Uses same HSRP v2 priority.

 In the case of an equal priority, the router with the highest IP address for the respective group is elected as active. Furthermore, if there are more than two routers in the group, the second highest IP address determines the standby router and the other router/routers are in the listen state. State of local router can be one of the following:

• Active—Indicates the current Hot Standby router.
• Standby—Indicates the router next in line to be the Hot Standby router.
• Speak—Router is sending packets to claim the active or standby role.
• Listen—Router is neither in the active nor standby state, but if no messages are received from the active or standby router, it will start to speak.
• Learn—Router is neither in the active nor standby state, nor does it have enough information to attempt to claim the active or standby roles.
• Init or Disabled—Router is not yet ready or able to participate in HSRP, possibly because the associated interface is not up. HSRP groups configured on other routers on the network that are learned via snooping are displayed as being in the Init state. Locally configured groups with an interface that is down or groups without a specified interface IP address appear in the Init state. For these cases, the Active addr and Standby addr fields will show "unknown." The state is listed as disabled in the fields when the standby ip command has not been specified.
HSRP IPv6