RA
registration authority. Optional PKI entity (separate from the CAs) that does not sign either digital certificates or CRLs but has responsibility for recording or verifying some or all of the information (particularly the identities of subjects) needed by a CA to issue certificates and CRLs and to perform other certificate management functions.
RADIUS
Remote Authentication Dial-In User Service. Database for authenticating modem and ISDN connections and for tracking connection time.
random early detection
Congestion avoidance algorithm in which a small percentage of packets are dropped when congestion is detected and before the queue in question overflows completely.
RARP
Reverse Address Resolution Protocol. Protocol in the TCP/IP stack that provides a method for finding IP addresses based on MAC addresses. Compare with ARP.
RAS
1. Registration, Admission, and Status Protocol. Protocol that is used between endpoints and the gatekeeper to perform management functions. RAS signalling function performs registration, admissions, bandwidth changes, status, and disengage procedures between the VoIP gateway and the gatekeeper.
2. remote access server.
reassembly
The putting back together of an IP datagram at the destination after it has been fragmented either at the source or at an intermediate node. See also fragmentation.
redirect
Part of the ICMP and ES-IS protocols that allows a router to tell a host that using another router would be more effective.
redistribution
Allowing routing information discovered through one routing protocol to be distributed in the update messages of another routing protocol. Sometimes called route redistribution.
redundancy
In internetworking, the duplication of devices, services, or connections so that, in the event of a failure, the redundant devices, services, or connections can perform the work of those that failed. See also redundant system.
redundant system
Computer, router, switch, or other system that contains two or more of each of the most important subsystems, such as two disk drives, two CPUs, or two power supplies.
rendezvous point
Router specified in PIM sparse mode implementations to track membership in multicast groups and to forward messages to known multicast group addresses. See also PIM sparse mode.
repeater
Device that regenerates and propagates electrical signals between two network segments. See also segment.
replay attack
Attack in which a valid data transmission is maliciously or fraudulently repeated, either by the originator or by an adversary who intercepts the data and retransmits it, possibly as part of a masquerade attack.
replication
Process of keeping a copy of data, either through shadowing or caching. See also caching and shadowing.
repudiation
Denial by a system entity that was involved in an association (especially an association that transfers information) of having participated in the relationship.
RFC
Request For Comments. Document series used as the primary means for communicating information about the Internet. Some RFCs are designated by the IAB as Internet standards. Most RFCs document protocol specifications, such as Telnet and
FTP, but some are humorous or historical. RFCs are available online from numerous sources.
RFP
request for proposal.
RIP
Routing Information Protocol. IGP supplied with UNIX BSD systems. The most common IGP in the Internet. RIP uses hop count as a routing metric. See also hop count, IGP, and OSPF.
RISC
reduced instruction set computing.
risk assessment
Process that systematically identifies valuable system resources and threats to those resources, quantifies loss exposures (that is, loss potential) based on estimated frequencies and costs of occurrence, and (optionally) recommends how to allocate
resources to countermeasures so as to minimize total exposure.
risk management
Process of identifying, controlling, and eliminating or minimizing uncertain events that might affect system resources.
RJ connector
registered jack connector. Standard connectors originally used to connect telephone lines. RJ connectors are now used for telephone connections and for 10BaseT and other types of network connections. RJ-11, RJ-12, and RJ-45 are popular types of RJ connectors.
rlogin
remote login. Terminal emulation program, similar to Telnet, offered in most UNIX implementations.
RMON
remote monitoring. MIB agent specification described in RFC 1271 that defines functions for the remote monitoring of networked devices. The RMON specification provides numerous monitoring, problem detection, and reporting capabilities.
root account
Privileged account on UNIX systems used exclusively by network or system administrators.
root bridge
Exchanges topology information with designated bridges in a spanning-tree implementation to notify all other bridges in the network when topology changes are required. This prevents loops and provides a measure of defense against link failure.
root CA
Ultimate CA, which signs the certificates of the subordinate CAs. The root CA has a self-signed certificate that contains its own public key.
root certificate
Certificate for which the subject is a root. Hierarchical PKI usage: The self-signed public-key certificate at the top of a certification hierarchy.
root key
Public key for which the matching private key is held by a root.
route
Path through an internetwork.
route distinguisher
An 8-byte value that is concatenated with an IPv4 prefix to create a unique VPN IPv4 prefix. This is used in MPLS networks.
route map
Method of controlling the redistribution of routes between routing domains.
route summarization
Consolidation of advertised addresses in OSPF and IS-IS. In OSPF, this causes a single summary route to be advertised to other areas by an area border router.
routed protocol
Protocol that can be routed by a router. A router must be able to interpret the logical internetwork as specified by that routed protocol. Examples of routed protocols include AppleTalk, DECnet, and IP.
router
Network layer device that uses one or more metrics to determine the optimal path along which network traffic should be forwarded. Routers forward packets from one network to another based on network layer information. Occasionally called a gateway (although this definition of gateway is becoming increasingly outdated). Compare with gateway. See also relay.
routing
Process of finding a path to a destination host. Routing is very complex in large networks because of the many potential intermediate destinations a packet might traverse before reaching its destination host.
routing domain
Group of end systems and intermediate systems operating under the same set of administrative rules. Within each routing domain is one or more areas, each uniquely identified by an area address.
routing metric
Method by which a routing algorithm determines that one route is better than another. This information is stored in routing tables. Metrics include bandwidth, communication cost, delay, hop count, load, MTU, path cost, and reliability. Sometimes referred to simply as a metric. See also cost.
routing protocol
Protocol that accomplishes routing through the implementation of a specific routing algorithm. Examples of routing protocols include IGRP, OSPF, and RIP.
routing table
Table stored in a router or some other internetworking device that keeps track of routes to particular network destinations and, in some cases, metrics associated with those routes.
routing update
Message sent from a router to indicate network reachability and associated cost information. Routing updates typically are sent at regular intervals and after a change in network topology.
RPC
remote-procedure call. Technological foundation of client/server computing. RPCs are procedure calls that are built or specified by clients and are executed on servers, with the results returned over the network to the clients. See also client/server computing.
RPF
Reverse Path Forwarding. Multicasting technique in which a multicast datagram is forwarded out of all but the receiving interface if the receiving interface is the one used to forward unicast datagrams to the source of the multicast datagram.
RS-232
Popular physical layer interface. Now known as EIA/TIA-232. See also EIA/TIA-232.
RS-422
Balanced electrical implementation of EIA/TIA-449 for high-speed data transmission. Now referred to collectively with RS-423 as EIA-530. See also EIA-530 and RS-423.
RS-423
Unbalanced electrical implementation of EIA/TIA-449 for EIA/TIA-232 compatibility. Now referred to collectively with RS-422 as EIA-530. See also EIA-530 and RS-422.
RS-449
Popular physical layer interface. Now known as EIA/TIA-449. See also EIA/TIA-449.
RSA
Acronym stands for Rivest, Shamir, and Adelman, the inventors of the technique. Public-key cryptographic system that can be used for encryption and authentication.
rsh
remote shell protocol. Protocol that allows a user to execute commands on a remote system without having to log in to the system. For example, rsh can be used to remotely examine the status of a number of access servers without connecting to each
communication server, executing the command, and then disconnecting from the communication server.
RSVP
Resource Reservation Protocol. Protocol that supports the reservation of resources across an IP network. Applications running on IP end systems can use RSVP to indicate to other nodes the nature (bandwidth, jitter, maximum burst, and so on) of
the packet streams they want to receive. RSVP depends on IPv6. Also known as Resource Reservation Setup Protocol. See also IPv6.
RTCP
RTP Control Protocol. Protocol that monitors the QOS of an IPv6 RTP connection and conveys information about the on-going session. See also RTP (Real-TimeTransport Protocol).
RTP
Real-Time Transport Protocol. Commonly used with IP networks. RTP is designed to provide end-to-end network transport functions for applications transmitting real-time data, such as audio, video, or simulation data, over multicast or unicast network services. RTP provides such services as payload type identification, sequence numbering, timestamping, and delivery monitoring to real-time applications.
RTSP
Real Time Streaming Protocol. Enables the controlled delivery of real-time data, such as audio and video. Sources of data can include both live data feeds, such as live audio and video, and stored content, such as pre-recorded events. RTSP is designed to work with established protocols, such as RTP and HTTP.
RTT
round-trip time. Time required for a network communication to travel from the source to the destination and back. RTT includes the time required for the destination to process the message from the source and to generate a reply. RTT is used by some routing algorithms to aid in calculating optimal routes.
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