ARP--Address Resolution Protocol (ARP). ARP performs a required function in IP routing. ARP finds the hardware address, also known as Media Access Control (MAC) address, of a host from its known IP address. ARP maintains a cache (table) in which MAC addresses are mapped to IP addresses. ARP is part of all Cisco IOS systems running IP.
active router--The primary router in an HSRP group that is currently forwarding packets for the virtual router.
active RP--The active RP that controls the system, provides network services, runs the routing protocols, and presents the system management interface.
BFD--Bidirectional Forwarding Detection. A detection protocol designed to provide fast forwarding path failure detection encapsulations, topologies, and routing protocols. In addition to fast forwarding, BFD provides a consistent failure detection method for network administrators.
client group--An HSRP group that is created on a subinterface and linked to the master group via the group name.
HSRP--Hot Standby Router Protocol. Protocol that provides high network availability and transparent network-topology changes. HSRP creates a router group with a lead router that services all packets sent to the HSRP address. The lead router is monitored by other routers in the group, and if it fails, one of these standby HSRP routers inherits the lead position and the HSRP group address.
ISSU--In Service Software Upgrade. A process that allows Cisco IOS software to be updated or otherwise modified while packet forwarding continues. In most networks, planned software upgrades are a significant cause of downtime. ISSU allows Cisco IOS software to be modified while packet forwarding continues, which increases network availability and reduces downtime caused by planned software upgrades.
master group--An HSRP group that is required on a physical interface for the purposes of electing active and standby routers.
NSF--nonstop forwarding. The ability of a router to continue to forward traffic to a router that may be recovering from a failure. Also, the ability of a router recovering from a failure to continue to correctly forward traffic sent to it by a peer.
RF--Redundancy Facility. A structured, functional interface used to notify its clients of active and standby state progressions and events.
RP--Route Processor. A generic term for the centralized control unit in a chassis. Platforms usually use a platform-specific term, such as the RSP on the Cisco 7500, the PRE on the Cisco 10000, or the SUP+MSFC on the Cisco 7600.
RPR--Route Processor Redundancy. RPR provides an alternative to the High System Availability (HSA) feature. HSA enables a system to reset and use a standby Route Processor (RP) if the active RP fails. Using RPR, you can reduce unplanned downtime because RPR enables a quicker switchover between an active and standby RP if the active RP experiences a fatal error.
RPR+--An enhancement to RPR in which the standby RP is fully initialized.
SSO--stateful switchover. SSO refers to the implementation of Cisco IOS software that allows applications and features to maintain a defined state between an active and standby RP. When a switchover occurs, forwarding and sessions are maintained. Along with NSF, SSO makes an RP failure undetectable to the network.
standby group--The set of routers participating in HSRP that jointly emulate a virtual router.
standby router--The backup router in an HSRP group.
standby RP--The backup RP.
switchover--An event in which system control and routing protocol execution are transferred from the active RP to the standby RP. Switchover may be a manual operation or may be induced by a hardware or software fault. Switchover may include transfer of the packet forwarding function in systems that combine system control and packet forwarding in an indivisible unit.
virtual IP address--The default gateway IP address configured for an HSRP group.
virtual MAC address--For Ethernet and FDDI, the automatically generated MAC address when HSRP is configured. The standard virtual MAC address used is: 0000.0C07.ACxy, where xy is the group number in hexadecimal. The functional address is used for Token Ring. The virtual MAC address is different for HSRP version 2.