HSRP version 2 is
designed to address the following restrictions in HSRP version 1:
-
In HSRP version
1, millisecond timer values are not advertised or learned. HSRP version 2
advertises and learns millisecond timer values. This change ensures stability
of the HSRP groups in all cases.
-
In HSRP version
1, group numbers are restricted to the range that is from 0 to 255. HSRP
version 2 expands the group number range from 0 to 4095.
-
HSRP version 2
provides improved management and troubleshooting. With HSRP version 1, you
cannot use HSRP active hello messages to identify the physical device that
sends the message because the source MAC address is the HSRP virtual MAC
address. The HSRP version 2 packet format includes a 6-byte identifier field
that is used to uniquely identify the sender of the message. Typically, this
field is populated with the interface MAC address.
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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.
Version 1 is the
default version of HSRP.
HSRP version 2 uses
the new IP multicast address 224.0.0.102 to send hello packets instead of the
multicast address of 224.0.0.2, used by HSRP version 1. This new multicast
address allows CGMP leave processing to be enabled at the same time as HSRP.
HSRP version 2
permits an expanded group number range, 0 to 4095, and consequently uses a new
MAC address range 0000.0C9F.F000 to 0000.0C9F.FFFF. The increased group number
range does not imply that an interface can, or should, support that number of
HSRP groups. The expanded group number range was changed to allow the group
number to match the VLAN number on subinterfaces.
When the HSRP version
is changed, each group will reinitialize because it now has a new virtual MAC
address.
HSRP version 2 has a
different packet format than HSRP version 1. The packet format uses a
type-length-value (TLV) format. HSRP version 2 packets received by an HSRP
version 1 device will have the type field mapped to the version field by HSRP
version 1 and subsequently ignored.
HSRP version 2 is
effective from Cisco IOS Release 15.5(03)s.