IBM SC30-3681-08 S

rlogin (remote login). Aservice, offered by Berkeley

UNIX-based systems, that allows authorized users of

one machine to connect to other UNIX systems across

an internet and interact as if their terminals were

connected directly.The rlogin software passes

information about the user’s environment (for example,

terminal type) to the remote machine.

RNR packet. Apacket used by a data terminal

equipment (DTE) or by a data circuit-terminating

equipment (DCE) to indicate a temporary inability to

accept additional packets for a virtual call or permanent

virtual circuit.

root bridge. The bridge that is the root of a spanning

tree formed between other active bridges in the bridging

network. The root bridge originates and transmits bridge

protocol data units (BPDUs) to other active bridges to

maintain the spanning tree topology.It is the bridge with

the highest priority in the network.

route. (1)An ordered sequence of nodes and

transmission groups (TGs) that represent a path from

an origin node to a destination node traversed by the

traffic exchanged between them. (2) The path that

network traffic uses to get from source to destination.

route bridge. Afunction of an IBM bridge program

that allows two bridge computers to use a

telecommunication link to connect two LANs. Each

bridge computer is connected directly to one of the

LANs, and the telecommunication link connects the two

bridge computers.

route extension (REX). In SNA, the path control

network components, including a peripheral link, that

make up the portion of a path between a subarea node

and a network addressable unit (NAU) in an adjacent

peripheral node. See also

explicit route (ER)

path

, and

virtual route (VR)

Route Selection control vector (RSCV). Acontrol

vector that describes a route within anAPPN network.

The RSCV consists of an ordered sequence of control

vectors that identify the TGs and nodes that make up

the path from an origin node to a destination node.

router. (1)A computer that determines the path of

network traffic ﬂow.The path selection is made from

several paths based on information obtained from

speciﬁc protocols, algorithms that attempt to identify the

shortest or best path, and other criteria such as metrics

or protocol-speciﬁc destination addresses. (2)An

attaching device that connects two LAN segments,

which use similar or different architectures, at the

reference model network layer.(3) In OSI terminology, a

function that determines a path by which an entity can

be reached. (4) In TCP/IP,synonymous with

gateway

(5) Contrast with

bridge

routing. (1) The assignment of the path by which a

message is to reach its destination. (2) In SNA, the

forwarding of a message unit along a particular path

through a network, as determined by parameters carried

in the message unit, such as the destination network

address in a transmission header.

routing domain. In Internet communications, a group

of intermediate systems that use a routing protocol so

that the representation of the overall network is the

same within each intermediate system. Routing domains

are connected to each other by exterior links.

Routing Information Protocol (RIP). In the Internet

suite of protocols, an interior gateway protocol used to

exchange intradomain routing information and to

determine optimum routes between internet hosts. RIP

determines optimum routes on the basis of route

metrics, not link transmission speed.

routing loop. Asituation that occurs when routers

circulate information among themselves until

convergence occurs or until the networks involved are

considered unreachable.

routing protocol. Atechnique used by a router to ﬁnd

other routers and to remain up to date about the best

way to get to reachable networks.

routing table. Acollection of routes used to direct

datagram forwarding or to establish a connection. The

information is passed among routers to identify network

topology and destination feasibility.

Routing TableMaintenance Protocol (RTMP). In

AppleTalknetworks, a protocol that provides routing

information generation and maintenance on the

transport layer by means of theAppleTalk routing table.

TheAppleTalk routing table directs packet transmission

through the internet from source socket to destination

socket.

RouTing update Protocol (RTP). The VIrtual

NEtworking System (VINES) protocol that maintains the

routing database and allows the exchange of routing

information between VINES nodes. See also

Internet

Control Protocol (ICP)

rsh. Avariant of the rlogin command that invokes a

command interpreter on a remote UNIX machine and

passes the command-line arguments to the command

interpreter,skipping the login step completely.

SAP. Seeservice access point.

seed router. InAppleTalk networks, a router that

maintains conﬁguration data (network range numbers

and zone lists, for example) for the network. Each

network must have at least one seed router.The seed

router must be initially set up using the conﬁgurator tool.

Contrast with

nonseed router

708 MRS V3.2 Software User’s Guide