Network Glossary R

radio management aggregation Reduces the bandwidth necessary for radio management information, such as access point status messages, that is sent across the network by eliminating redundant management information.

RADIUS A protocol, defined in RFC 2865, that defines how to perform authentication between an authenticator (for example, a router) and an authentication server that holds a list of usernames and passwords.

Rapid Per-VLAN Spanning Tree Plus The combination of PVST+ and Rapid Spanning Tree. It provides subsecond convergence time and is compatible with PVST+ and MSTP. Rapid Spanning Tree Protocol Defined in IEEE 802.1w, a specification to enhance the 802.1d standard to improve the speed of STP convergence.

RARP See Reverse ARP.

RD See Reported distance or Route Distinguisher.

Ready To Send On a serial cable, the pin lead set by the DTE to tell the DCE that the DTE wants to send data.

receiver’s advertised window In TCP, a TCP host sets the TCP header’s Window field to the number of bytes it allows the other host to send before requiring an acknowledgement. In effect, the receiving host, by stating a particular window size, grants the sending host the right to send that number of bytes in a single window.

Red Alarm A T1 alarm state that occurs when a device has detected a local LOF/LOS/AIS condition. The device in Red alarm state then sends a Yellow alarm signal.regular expression A list of interspersed alphanumeric literals and metacharacters that are used to apply complex matching logic to alphanumeric strings. Often used for matching AS_PATHs in Cisco routers.

Reliable Transport Protocol A protocol used for reliable multicast and unicast transmissions. Used by EIGRP.

remaining bandwidth A CBWFQ and LLQ term referring to the bandwidth on an interface that is neither reserved nor allocated via a priority command.

remote label In MPLS, a term used to define a label that an LSR learned from a neighboring LSR.

rendezvous point In the PIM-SM design, the central distribution point to which the multicast traffic is first delivered from the source designated router.

Reply (EIGRP) An EIGRP message that is used by neighbors to reply to a query. Reply messages require an Ack.

reported distance With EIGRP, the metric (distance) of a route as reported by a neighboring router.

request-to-send/clear-to-send A mechanism that counters collisions caused by hidden nodes. If enabled, the station or access point must first send an RTS frame and receive a CTS frame before sending each data frame.

Report Suppression mechanism When a Query is received from a router, each host randomly picks a time between 0 and the Maximum Response Time period to send a Report. When the host with the smallest time period first sends the Report, the rest of the hosts suppress their reports.

Response In the context of SNMP, the Response command is sent by an SNMP agent, back to a manager, in response to any of the three types of Get requests, or in response to a Set request. It is also used by a manager in response to a received Inform command from another SNMP manager. The Response holds the value(s) of the requested variables.

Retransmission Timeout With EIGRP, a timer started when a reliable (to be acknowledged) message is transmitted. For any neighbor(s) failing to respond in its RTO, the RTP protocol causes retransmission. RTO is calculated based on SRTT.

Reverse ARP A standard (RFC 903) protocol by which a LAN-attached host can dynamically broadcast a request for a server to assign it an IP address. See also ARP.

RF channel The specific frequency subband on which the radio card or access point is operating. The RF channel is set in the access point or ad hoc stations.

RGMP See Router-Port Group Management Protocol.

RID See router ID.

ROMMON An alternative software loaded into a Cisco router, used for low-level debugging and for password recovery.

Root Guard Cisco-proprietary STP feature in which a switch port monitors for incoming superior Hellos, and reacts to a superior Hello to prevent any switch connected to that port from becoming root.

root port The single port on each nonroot switch upon which the best Hello BPDU is received.

Route Distinguisher A 64-bit extension to the BGP NLRI field, used by MPLS for the purpose of making MPLS VPN customer routes unique in spite of the possibility of overlapping IPv4 address spaces in different customer networks.

route map A configuration tool in Cisco IOS that allows basic programming logic to be applied to a set of items. Often used for decisions about what routes to redistribute, and for setting particular characteristics of those routes—for instance, metric values.

route poisoning The process of sending an infinite-metric route in routing updates when that route fails.

route redistribution The process of taking routes known through one routing protocol and advertising those routes with another routing protocol.

route reflector A BGP feature by which a router learns iBGP routes, and then forwards them to other iBGP peers, reducing the required number of iBGP peers while also avoiding routing loops.

route reflector client A BGP router that, unknown to it, is aided by a route reflector server to cause all iBGP routers in an AS to learn all eBGP-learned prefixes.

route reflector non-client A BGP router in an AS that uses route reflectors, but that is not aided by any RR server.

route reflector server A BGP router that forwards iBGP-learned routes to other iBGP routers.

Route Tag field A field within a route entry in a routing update, used to associate a generic number with the route. It is used when passing routes between routing protocols, allowing an inter-mediate routing protocol to pass information about a route that is not natively defined to that intermediate routing protocol. Frequently used for identifying certain routes for filtering by a downstream routing process.

Route Target In MPLS VPNs, a 64-bit Extended Community path attribute attached to a BGP route for the purpose of controlling into which VRFs the route is added.

routed interface An interface on a Cisco IOS–based switch that is treated as if it were an interface on a router.

Router Advertisement In IPv6, a Router Advertisement message used by an IPv6 router to send information about itself to nodes and other routers connected to that router.

router ID The 32-bit number used to represent an OSPF router.

Router-Port Group Management Protocol A Cisco-proprietary Layer 2 protocol that enables a router to communicate to a switch which multicast group traffic the router does and does not want to receive from the switch.

routing black hole A problem that occurs when an AS does not run BGP on all routers, with synchronization disabled. The routers running BGP may believe they have working routes to reach a prefix, and forward packets to internal routers that do not run BGP and do not have a route to reach the prefix.

RP See rendezvous point.

RPF check Designed to solve the problems of multicast duplication and multicast routing loops. For every multicast packet received, a multicast router examines its source IP address, consults its unicast routing table, determines which interface it would use to go in the reverse direction toward the source IP address, compares it with the interface on which the packet was received, and, if they match, accepts the packet and forwards it; otherwise, the router drops the packet.

RPVST+ See Rapid Per-VLAN Spanning Tree Plus.

RSTP See Rapid Spanning Tree Protocol.

RT See Route Target.

RTO See Retransmission Timeout.

RTP See Reliable Transport Protocol.

RTP header compression The process of taking the IP, UDP, and RTP headers of a voice or video packet, compressing them, and then uncompressing them on the receiving router.

RTS See Ready To Send.

RTS/CTS See request-to-send/clear-to-send.

RXBOOT An alternative software loaded into a Cisco router, used for basic IP connectivity—most useful when Flash memory is broken and you need IP connectivity to copy a new IOS image into Flash memory.