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Cisco Industrial Ethernet 4000 Series Switch Software Configuration Guide
Chapter Configuring HSRP and VRRP
Understanding HSRP
HSRP Versions
The switch supports these Hot Standby Redundancy Protocol (HSRP) versions:
• HSRPv1—Version 1 of the HSRP, the default version of HSRP. It has these features:
–
The HSRP group number can be from 0 to 255.
–
HSRPv1 uses the multicast address 224.0.0.2 to send hello packets, which can conflict with
Cisco Group Management Protocol (CGMP) leave processing. You cannot enable HSRPv1 and
CGMP at the same time; they are mutually exclusive.
• HSRPv2—Version 2 of the HSRP has these features:
–
To match the HSRP group number to the VLAN ID of a subinterface, HSRPv2 can use a group
number from 0 to 4095 and a MAC address from 0000.0C9F.F000 to 0000.0C9F.FFFF.
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HSRPv2 uses the multicast address 224.0.0.102 to send hello packets. HSRPv2 and CGMP
leave processing are no longer mutually exclusive, and both can be enabled at the same time.
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HSRPv2 has a different packet format than HRSPv1.
A switch running HSRPv1 cannot identify the physical router that sent a hello packet because
the source MAC address of the router is the virtual MAC address.
HSRPv2 has a different packet format than HSRPv1. A HSRPv2 packet uses the
type-length-value (TLV) format and has a 6-byte identifier field with the MAC address of the
physical router that sent the packet.
If an interface running HSRPv1 gets an HSRPv2 packet, the type field is ignored.
Multiple HSRP
The switch supports Multiple HSRP (MHSRP), an extension of HSRP that allows load sharing between
two or more HSRP groups. You can configure MHSRP to achieve load balancing and to use two or more
standby groups (and paths) from a host network to a server network. In Figure 47-95, half the clients are
configured for Router A, and half the clients are configured for Router B. Together, the configuration for
Routers A and B establishes two HSRP groups. For group 1, Router A is the default active router because
it has the assigned highest priority, and Router B is the standby router. For group 2, Router B is the
default active router because it has the assigned highest priority, and Router A is the standby router.
During normal operation, the two routers share the IP traffic load. When either router becomes
unavailable, the other router becomes active and assumes the packet-transfer functions of the router that
is unavailable.
Note For MHSRP, you need to enter the standby preempt interface configuration command on the HSRP
interfaces so that if a router fails and then comes back up, preemption restores load sharing.
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