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Glossary         


A

abort error
An error indicating an attempted and failed connection.
acceptance policy
A set of rules that determine the path and route information the PortMaster accepts from a BGP peer for further processing. See also policy.
address
A number used to identify a computer or other device on a network or internetwork. See also IP address; MAC address.
address resolution
A method for translating one type of address into another-for example, an IP address into a media access control (MAC) address.
Address Resolution Protocol
See ARP.
adjacency
A relationship between two routers on the same physical network or between the endpoints of a virtual link that controls the distribution of routing protocol packets by limiting their exchange to those routers or endpoints.
advertisement policy
A set of rules that determine the path and route information the PortMaster advertises to a BGP peer. See also policy.
agent
A software program installed in a managed network device. An agent stores management information and responds to the manager's request for this information.
aggregation
The process of combining multiple prefixes from one or several routes so that a single prefix and route can be advertised. Route aggregation reduces the amount of information that a device running BGP must store and exchange with its BGP peers. See also summarization.
Annex-D
The ANSI T1.617 Frame Relay Annex-D version of the Local Management Interface (LMI) protocol. The Annex-D protocol has a more robust feature set than the proprietary Cisco/Stratacom LMI, but was developed later. Recent versions of the PortMaster software support either type of LMI. Earlier versions supported only the Cisco/Stratacom version. See also LMI.
area
In OSPF, a contiguous collection of networks and hosts. Each area runs a separate copy of the shortest-path-first (SPF) algorithm and has its own topological database.
area border router
In OSPF, a router that attaches to the backbone and one other area. An area border router runs separate copies of the shortest-path-first (SPF) algorithm for each area it attaches to. Area border routers condense the topological information of their attached areas and distribute it over the backbone to the other areas.
ARP
Address Resolution Protocol. A protocol that discovers the unique physical hardware address of a node or a LAN from its IP address. When an ARP request is sent to the network, naming the IP address, the machine with that IP address returns its physical address so that it can receive the transmission.
ASCII
American Standard Code for Information Interchange. A standard 8-bit code commonly used by computers and communications equipment.
autonomous system
A collection of routers under the control of a single technical administration, using one or more Interior Gateway Protocols (IGPs)-such as OSPF-to route packets within itself, and an Exterior Gateway Protocol (EGP)-such as BGP-to route packets to other autonomous systems. An autonomous system typically uses a common BGP policy and always presents a consistent view of network reachability to other autonomous systems.
autonomous system border router
In OSPF, a router that exchanges information with routers from other autonomous systems. Autonomous system border routers are also used to import routing information about RIP, direct, or static routes from non-OSPF attached interfaces.
autonomous system path list
In BGP, the list of autonomous systems that a packet must traverse to reach a given set of IP address destinations located within a single autonomous system destination. The list can consist of sequences, which are series of autonomous systems that must be traversed in the order specified, and sets, which are collections of autonomous systems one of more of which must be traversed in any order to the destination.

For example, an autonomous system path list might consist of Sequence 1, 2, 3, Set 4, 5, Sequence 6, 7. This list indicates that a packet traverses autonomous systems 1, 2, and 3 in order, then one or both of autonomous systems 4 and 5 in any order, and finally autonomous systems 6 and 7 in order. Autonomous system 7 is the destination autonomous system.

B

backbone
A network topology consisting of a single length of cable with multiple network connection points.
backbone area
In OSPF, an area consisting of networks and routers not contained in any area and autonomous system border routers. The backbone area is responsible for distributing routing information between areas. This backbone area must be contiguous either physically or through a virtual link. The number reserved for the backbone area is 0.0.0.0.
backbone router
In OSPF, a router that has an interface into the backbone area by a direct attachment or a virtual link.
Basic Rate Interface
See BRI.
baud
The number of discrete signal events per second occurring on a communications channel. Although not technically accurate, baud is commonly used to mean bit rate.
B channel
Bearer channel. A 64Kbps synchronous channel that is part of an ISDN Basic Rate Interface (BRI).
BGP
Border Gateway Protocol. A routing protocol for exchanging network reachability information among autonomous systems. A routing device can use this information to construct a "map" of autonomous system connectivity. Version 4 of this protocol (BGP-4), which supports classless interdomain routing (CIDR) and route aggregation, is the predominant routing protocol used to propagate routes between autonomous systems on the Internet. BGP uses TCP as its transport protocol.
BGP-4
Version 4 of BGP. See also BGP.
BONDING
Bandwidth on Demand Interoperability Group. A method for combining two B channels into a single 128Kbps channel.
booting
The process in which a device obtains information and begins to process it to attain a state of normal operation.
Border Gateway Protocol
See BGP.
bps
Bits per second. A unit for measuring the data rate.
BRI
Basic Rate Interface. An ISDN interface that consists of two 64Kbps
B channels for voice or data and one 16Kbps D channel for signaling. Compare PRI.
broadcast address
A special address reserved for sending a message to all stations. Generally, a broadcast address is a media access control (MAC) destination address of all 1s (ones).
broadcast packets
Packets that are sent to all network nodes.

C

callback
A port configuration allowing the PortMaster to call back dial-in users before providing access. Callback provides an extra layer of security and can simplify telephone charges.
CCITT
Consultative Committee for International Telegraph and Telephone. International organization formerly responsible for the development of communications standards. Now called the ITU-T. See also ITU-T.
CD
Carrier Detect. A signal that indicates whether an interface is active. Also, a signal generated by a modem indicating that a call has been connected.
Challenge Handshake Authentication Protocol
See CHAP.
channelized T1
An access link operating at 1.544Mbps that is subdivided into 24 channels of 56Kbps each for dial-in use.
channel service unit
See CSU.
CHAP
Challenge Handshake Authentication Protocol. A Point-to-Point Protocol (PPP) authentication method for identifying a dial-in user. CHAP does not itself prevent unauthorized access, it merely identifies the remote end. See also PAP.
CIDR
Classless interdomain routing. A technique supported by BGP-4 that eliminates the necessity for network address classes by explicitly advertising the length (netmask) associated with each prefix.
CIR
Committed information rate . The minimum bandwidth guaranteed to be available if required on a virtual circuit. This value is also known as guaranteed bandwidth.
classless interdomain routing
See CIDR.
client/server environment
An environment where a computer system or process requests a service from another computer system. For example, a workstation can request services from a file server across a network.
cluster
A group of internal BGP peers that share a common set of route reflectors. See also cluster ID; route reflection; route reflector. Compare confederation.
cluster ID
An identifier, in dotted decimal format, that uniquely identifies a BGP route reflection cluster within an autonomous system. All route reflectors within the cluster must be configured with the same cluster ID. Internal peers that are not reflectors within the cluster must not be configured with a cluster ID. The cluster ID is typically set to the BGP router ID of one of the route reflectors within the cluster. See also cluster; route reflection; route reflector.
CMAS
Confederation member autonomous system. A subdivision of an autonomous system that is recognized only by other peers within the confederation and not by peers external to the confederation. Within the confederation, each BGP peer treats only the peers in its own CMAS as internal peers. Peers in different CMASs are treated as external peers.
committed information rate
See CIR.
community
A label that identifies a group of BGP destinations for the purpose of policy enforcement. Assembling destinations into identifiable "communities" lets BGP peers base policy decisions on the identity of the group rather than on individual destinations. The community identifier, which consists either of one 32-bit value or two 16-bit values, is advertised in update messages between BGP peers.
community string
A character string assigned to a Simple Network Management Protocol (SNMP) agent to restrict read and write access to the SNMP variables.
ComOS
The operating system for PortMaster communications servers, routers, and access servers.
confederation
In BGP, an autonomous system that has been subdivided into smaller autonomous systems called confederation member autonomous systems. (CMASs). A confederation appears like a single autonomous system to other autonomous systems and is recognized only by other confederation members. Subdivision of an autonomous system into a confederation changes the peer relationships of confederation members in different CMASs from internal to external. Use of confederations in an autonomous system requires that all routers in the autonomous system belong to a CMAS; however, the policies used by BGP peers can change across confederation boundaries.
Confederations are one method for avoiding the overhead of having all peers within an autonomous system fully communicate to-be fully meshed with-each other. Route reflection clusters provide an easier method, but require the use of identical policies on all peers within the autonomous system. See also route reflection.
confederation member
Any router running BGP and recognizing that its autonomous system is subdivided into smaller autonomous systems called confederation member autonomous systems. (CMASs). The CMASs are recognized only by confederation members and not by peers external to the confederation. Subdivision of an autonomous system into a confederation changes the peer relationships of confederation members in different CMASs from internal to external.
confederation member autonomous system
See CMAS.
console port
A serial port on a PortMaster attached to a terminal or PC through which you enter commands to communicate with ComOS.
CRC error
Cyclic redundancy check error. These errors can indicate problems with source station hardware, receivers, retiming modules and/or repeaters, bridges, cabling, or transceivers.
CSU
Channel service unit. An ancillary device needed to adapt the V.35 or X.21 interface to a port on a telephone carrier switch. The CSU is placed between the data terminal equipment (DTE) and the switch.
cyclic redundancy check
See CRC error.

D

data communications equipment
See DCE.
data link connection identifier
See DLCI.
data service unit
See DSU.
Data Set Ready
See DSR.
data terminal equipment
See DTE.
Data Terminal Ready
See DTR.
DCE
Data communications equipment. Devices and connections of a communications network that make up the network end of the interface between the network and the user. The DCE provides a physical connection to the network, forwards traffic, and provides a clocking signal to synchronize data transmission between DCE and DTE devices. Modems and interface cards are DCEs.
DDE
Dynamic data exchange. A form of interprocess communication that uses shared memory to exchange data between applications. Applications can use a one-time data transfer or ongoing exchanges.
degree of preference
In BGP, an arbitrary rating number that the PortMaster assigns to every route it receives from a BGP peer. A higher numbers indicates a greater preference for a route when more than one exists to a destination. A route from an internal peer is assigned the local preference number that the PortMaster learned with the route. For a route learned from an external peer, the PortMaster calculates a number based on the autonomous system path length; the shortest path is preferred. You can use a routing policy rule to override the calculated or learned value and assign your own degree of preference to a route. See also local preference.
destination
In BGP, the final autonomous system in the autonomous system path whose IP address prefixes and associated netmasks are reported in the network layer reachability information (NLRI) field of an update message. A destination and its path comprise a BGP route. See also path; route.
dialback
See callback.
dial group
A number that is used to associate dial-out locations with ports.
digital service unit
See DSU.
direct memory access
See DMA.
DHCP
The underlying protocol for a network administration software tool that enables network managers to set up servers to automatically supply IP addresses and configuration settings to clients. DHCP extends and enhances the BOOTP protocol by providing reusable IP addresses and allocating IP addresses based on subnet, client ID string, or media access control (MAC) address.
DLCI
Data link connection identifier. A unique number that represents a particular permanent virtual circuit (PVC) on a particular physical segment of the Frame Relay network. As the frame is passed through each switch, the DLCI is remapped automatically by the switch as necessary.
DMA
Direct memory access. Transfer of data from a peripheral device, such as a hard disk drive, into a computer memory without mediation by a microprocessor.
DNS
Domain Name System. The system used on the Internet for translating the names of network hosts into IP addresses.
DRAM
Dynamic random access memory. A type of semiconductor random access memory (RAM) that stores information in integrated circuits containing capacitors.
DSR
Data Set Ready. The circuit that is activated when data communications equipment (DCE) is powered up and ready for use. See also DCE.
DSU
Digital service unit or data service unit. An ancillary device needed to adapt the physical interface on a data terminal equipment (DTE) device-such as a V.35 interface on a port-to a transmission facility-such as leased line or a Frame Relay switch. If the DTE lacks complete digital line interface capability, the DSU can be located with the channel service unit (CSU) on the customer's site and known as a CSU/DSU. See also CSU.
DTE
Data terminal equipment. A device at the user end of the interface between the network and the user. The DTE connects to a data network through a data communications equipment (DCE)-such as a modem or an interface card. DTEs convert user information into data signals for transmission, and reconvert received data signals into user information. Compare DCE.
DTR
Data Terminal Ready. The circuit that is activated to inform the data communications equipment (DCE) when the data terminal equipment (DTE) is ready to send and receive data. See also DCE; DTE.
dynamic data exchange
See DDE.
Dynamic Host Configuration Protocol
See DHCP.
dynamic random access memory
See DRAM.

E

E1
Digital WAN carrier facility used predominantly in Europe that carries data at a rate of 2.048Mbps. E1 lines can be leased for private use from common carriers. Compare T1.
easy-multihome
A specialized, predefined BGP policy that simplifies the use of PortMaster routers in straightforward multihomed environments. When you define easy-multihome for a peer, you restrict what the PortMaster handles from the peer to information that is no more than two autonomous system hops away from the PortMaster. Only information that meets this criterion is accepted from the peer, put into the routing table used to forward packets to their destinations, and advertised to other peers. If you define easy-multihome for a peer, you must also define a default route on each router in your autonomous system to point them to destinations more distant than two hops. See also multihome routing; policy.
EBGP
Exterior BGP. The BGP used between peers in different autonomous systems, or, when confederations are in use, between peers in different confederation member autonomous systems (CMASs). Unlike internal BGP peers, EBGP peers need not have full connectivity with one another.
echo test
A diagnostic test used to check network reachability in which an Internet Control Message Protocol (ICMP) Echo Request packet or Simple Network Management Protocol (SNMP) test packet is sent to elicit a standard response.
endpoint discriminator
A 12-digit identifier used to associate multiple chassis in a Multichassis PPP domain.
Ethernet
A network communications system developed and standardized by Digital Equipment Corporation, Intel, and Xerox using baseband transmission, carrier sense multiple access/carrier detect (CSMA/CD) access, logical bus topology, and coaxial cable. The successor IEEE 802.3 standard provides for integration of Ethernet into the Open System Interconnection (OSI) model and extends the physical layer and media with repeaters and implementations that operate on fiber optic cable, broadband, and unshielded twisted pair.
Exterior BGP
See EBGP.
external peer
A peer that resides in a different autonomous system-or, when confederations are in use, in a different confederation member autonomous system (CMAS)-from the current PortMaster.

F

File Transfer Protocol
See FTP.
filter
Generally, a process or device that screens network traffic for certain characteristics, such as source address, destination address, or protocol, and determines whether to forward or discard that traffic based on the established criteria.
filter table
A database used to store filters.
Flash RAM
See nonvolatile RAM.
flow control
A technique for ensuring that a transmitting entity, such as a modem, does not overwhelm a receiving entity with data. When the buffers on the receiving device are full, a message is sent to the sending device to suspend the transmission until the data in the buffers has been processed. Flow control can be software-based, or hardware-based.
FRAD
Frame Relay access device. A network device that links any non-Frame Relay connection to a Frame Relay WAN.
frame
A packaging structure for network data and control information. A frame consists of a destination address, source address, length field, data, padding, and frame check sequence. The 802.3 standard for Ethernet specifies that the minimum size data frame is 64 bytes and the maximum size data frame is 1518 bytes.
Frame Relay
An industry-standard switched data link layer protocol that handles multiple virtual circuits using high-level data link layer control (HDLC) encapsulation between connected devices. It is used across the interface between user devices (for example, hosts and routers) and network equipment (for example, switching nodes). Frame Relay is more efficient than X.25, the protocol it replaced.
Frame Relay access device
See FRAD.
FTP
File Transfer Protocol. A TCP/IP protocol used to transfer files between network hosts.

G

gateway
A device that connects two or more networks that use different protocols. Gateways provide address translation services, but do not translate data. Gateways must be used in conjunction with special software packages that allow computers to use networking protocols not originally designed for them.
graphical user interface
See GUI.
GUI
Graphical user interface. A software interface based on pictorial representations and menus of operations and files.

H

hardwired
A continuous connection between two sites. A port on a PortMaster that is configured for hardwired use cannot be simultaneously used for any other type of connection.
hello
Protocol used by OSPF routers to acquire neighbors and to synchronize their topological databases.
high-water mark
The number of bytes of queued network traffic required to open an additional dial-out line to a remote location.
hop
The transmission of a data packet between two network nodes-for example, between two routers.
hop count
Measurement of the distance between a source and destination that is used as a metric to compare routes. If a packet traverses six routers between source and destination nodes, the hop count for the packet will be 6 when it arrives at its destination node.
host
A single, addressable device on a network. Computers, networked printers, and routers are hosts.
hunt group
A group of multiple telephone circuits that allows telephone calls to find an idle circuit to establish a link.

I

IBGP
Interior BGP. The BGP used between peers in the same autonomous system, or, when confederations are in use, between peers in the same confederation member autonomous system (CMAS). All IBGP peers must maintain direct BGP connections to-be fully meshed with-every other internal peer, but need not be physically attached to one another.
ICMP
Internet Control Message Protocol. The part of the Internet Protocol (IP) that allows for generation of error messages, test packets, and informational messages related to IP. This protocol is used by the ping function to send an ICMP Echo Request to a network host, which replies with an ICMP Echo Reply.
in-band signaling
Signaling over the data path.
injection policy
A set of rules that determine the path and route information the PortMaster takes from BGP and places into its routing table used to forward packets to their destinations. The PortMaster uses the information to determine how packets it receives are forwarded to their ultimate destinations. See also policy.
Integrated Services Digital Network
See ISDN.
interface
Connection and interaction between hardware, software, and the user. The interface between components in a network is called a protocol. On the PortMaster, the virtual connection between a PortMaster port and the network to which it is connected is called an interface. The connection can be permanent as with the Ethernet interface or network hardwired ports, or it can be temporary, as with ports used for dial-in or dial-out connections.
Interior BGP
See IBGP.
internal peer
A peer that resides in the same autonomous system-or, when confederations are in use, in the same confederation member autonomous system (CMAS)-as the current PortMaster.
internal router
In OSPF, a router with all of its directly connected interfaces or physical networks belonging to the same area and containing no virtual connections to the backbone area.
International Organization for Standards
See ISO.
Internet
The world-wide internetwork consisting of several large national backbone networks and several regional and campus networks.
Internet Control Message Protocol
See ICMP.
Internet Network Information Center
See InterNIC.
Internet Protocol
See IP.
internetwork
A network of networks.
InterNIC
Internet Network Information Center. An organization that provides information and services related to networking technologies.
IP
Internet Protocol. The protocol defined in RFC 791.
IP address
A 32-bit number assigned by the system administrator, usually written in the form of four decimal fields separated by periods-for example, 192.9.200.1. Any computing device that uses IP must be assigned an Internet or IP address. Part of the Internet address is the IP network number (IP network address), and part is the host address (IP host address). All machines on a given IP network use the same IP network number, and each machine has a unique IP host address. The system administrator sets the subnet mask to specify how much of the address is network number and how much is host address.
IP address prefix
An IP address number that, when paired with a netmask length, represents a range of addresses rather than a single IP network. For example, the prefix and netmask length 128.0.0.0/8 describe all networks whose IP addresses begin with 128. See also netmask length.
IP Control Protocol
See IPCP.
IPCP
IP Control Protocol. A protocol used by the Point-to-Point Protocol (PPP) for establishing and configuring an IP link over PPP.
IPX
Internet Packet Exchange. Internet protocol defined by Novell, Inc.
IPXWAN
IPX Wide Area Network protocol. The protocol used to establish and configure an IPX link over the Point-to-Point Protocol (PPP), as described in RFC 1634.
IPX Wide Area Network
See IPXWAN.
ISDN
Integrated Services Digital Network. A digital communications standard designed to allow the transmission of voice, data, images, and video over existing copper phone lines.
ISO
International Organization for Standards. The international organization that sets standards for network communication protocols.
ITU-T
International Telecommunication Union Telecommunication Standardization Sector. International organization that develops worldwide standards for telecommunications technologies. The ITU-T carries out the functions of the former CCITT. See also CCITT.

K

KB
Kilobyte(s). 1024 bytes.
Kb
Kilobit(s). 1024 bits.
Kbps
Kilobits per second.
keepalive message
A periodic message sent between BGP peers to keep their BGP sessions open. If a preset amount of time elapses between keepalive messages from a peer, the PortMaster identifies the peer as no longer operational and drops the session-and any information learned from that peer.

L

LAN
Local area network. A local collection, usually within a single building or several buildings, of personal computers and other devices connected by cabling to a common transmission medium, allowing users to share resources and exchange files. Compare WAN.
latency
1) The delay between the time a device requests access to a network and the time it is granted permission to transmit. 2) The delay between the time when a device receives a frame and the time that frame is forwarded out the destination port.
LCP
Link Control Protocol. The protocol used by the Point-to-Point Protocol (PPP) for establishing, configuring, and testing the data link connection.
LED
Light-emitting diode.
line speed
The speed of the physical wire attached to the interface or interface hardware. The line speed is 10Mbps for Ethernet and 1.544Mbps for T1. Fractional T1 is often implemented with a wire speed of T1 (1.544Mbps) and a lower port speed. Upgrading line speed is generally a hardware change. See also port speed.
Link Control Protocol
See LCP.
link state advertisement
See LSA.
LMI
Local Management Interface. A protocol used to communicate link status and permanent virtual circuit (PVC) status in Frame Relay. Two types of LMI are available on Frame Relay: the original proprietary Cisco/Stratacom LMI, and the ANSI T1.617 Annex-D LMI. Although the PortMaster supports both, LMI on the PortMaster refers to the Cisco/Stratacom implementation. See also Annex-D.
local area network
See LAN.
Local Management Interface
See LMI.
local preference
In BGP, the degree-of-preference number that the PortMaster assigns to every external route it advertises to an internal or confederation-member BGP peer. A higher number indicates a greater preference for a route when more than one exists to a destination. Internal and confederation-member peers receiving this route use this local preference rather than calculating their own degree of preference for a route. You can use a routing policy rule to override this value and assign your own local preference to a route you advertise. See also degree of preference.
location
A dial-out destination.
location table
A database on the PortMaster where location settings are stored. See location.
lockstep
A feature of BGP on the PortMaster that ensures consistency of routing information between the BGP and non-BGP routers within its autonomous system. Lockstep forces the PortMaster to advertise a route learned from an internal BGP peer only when it has learned the same route via an Interior Gateway Protocol (IGP)-OSPF or RIP-or a static route. See also transit service.
LSA
Link state advertisement. The state of the router links (interfaces), networks, summaries, or autonomous system external links of an OSPF router that it periodically advertises. Link states are also advertised when a link state changes.

M

MAC address
Media access control address. A unique 48-bit binary number-usually represented as a 12-digit hexadecimal number-encoded in the circuitry of a device to identify it on a LAN.
Management Information Base
See MIB.
management station
A workstation or PC capable of retrieving and analyzing statistical information from networked Simple Network Management Protocol (SNMP) agents.
master
In Multichassis PPP, the PortMaster through which an initial connection for a given user is made. Every master also has a corresponding slave. Masters are for a given connection only, and a PortMaster that functions as a master for one user's connection can be a slave for a different user's connection. See also slave.
maximum transmission unit
See MTU.
MB
Megabyte(s). 1,048,576 bytes.
Mbps
Megabits per second. A unit for measuring data rates.
MD5
Message digest algorithm 5. The algorithm used for message authentication in Simple Network Management Protocol (SNMP) v.2. MD5 verifies the integrity of the communication, authenticates the origin, and checks for timeliness. ComOS uses the RSA Data Security, Inc. MD5 Message-Digest Algorithm.
media access control address
See MAC address.
message digest algorithm 5
See MD5.
MIB
Management Information Base. A set of variables that a Simple Network Management Protocol (SNMP)-based management station can query from the SNMP agent of a network device.
modem
Modulator-demodulator. A device that converts the digital signals used by computers to analog signals that can be transmitted over telephone lines.
modem table
A database resident on the PortMaster containing configuration information for commonly used modems.
MTU
Maximum transmission unit. The largest frame or packet that can be sent through a port on a PortMaster without fragmentation.
Multichassis PPP
Multilink PPP over two or more chassis.
multiexit discriminator
In BGP, an arbitrary rating number that the PortMaster can use to enforce the use of preferred exit and entry points when multiple connections exist between its autonomous system and another. The PortMaster assigns the multiexit discriminator to any route that it advertises to its external peers, and forwards any multiexit discriminator it learns from its external peers on to its internal peers. A lower number indicates a greater preference for a route when more than one exists to a destination through multiple peers within the same neighboring autonomous system. You can use a routing policy rule to override this value and assign your own multiexit discriminator to a route that you learn or advertise.
multihome routing
In BGP, the process of choosing among multiple exit points to route packets out of a single autonomous system, typically to the Internet. Routers in a multihomed autonomous system usually store large amounts of network reachability information to help them select the best exit point. See also easy-multihome.
multiline load balancing
The ability of a PortMaster to add additional lines when network traffic is heavy. If more than one line to a remote location is established, the PortMaster balances the traffic among the lines. Multiline load balancing is distinct from Multilink PPP.
Multilink PPP
A protocol defined in RFC 1990 that allows a PortMaster to automatically bring up additional ISDN B channels as bandwidth needs increase. See also Multichassis PPP.

N

name server
A server connected to a network that resolves hostnames into network addresses.
name service
The software system that provides a database of authorized users for a computer, subnet, or network. The system can reside on one device, or be distributed across several devices in a network.
neighbor
(1) In OSPF, two routers that have interfaces to a common network are neighbors. On multiaccess networks, neighbors are dynamically discovered by the OSPF Hello protocol.
(2) In Multichassis PPP, PortMaster products in the same Multichassis PPP domain.
netmask
A 32-bit number that distinguishes the portion of an IP address referring to the network or subnet from the portion referring to the host. Compare subnet mask.
netmask length
A number between 0 and 32 preceded by a slash (/) and following an IP address prefix. The netmask length indicates the number of high-order bits in the prefix that an IP address must match to fall within the range indicated by the prefix. For example, the prefix and netmask length 128.0.0.0/8 describe all networks whose IP addresses begin with 128. See also IP address prefix.
network
A collection of computers, terminals, and other devices and the hardware and software that enable them to exchange data and share resources over short or long distances.
network handle
A number assigned to an active socket that can be used to close the socket manually, rather than by a request from the client.
Network Information Service
See NIS.
network interface card
See NIC.
network layer reachability information
See NLRI.
network management
In the Open System Interconnection (OSI) model, the five functional application areas of accounting management, configuration management, fault management, performance management, and security management.
NIC
Network interface card. A card that provides network communication capabilities to and from a computer system. A NIC is also known as an adapter.
NIS
Network Information Service. A protocol developed by Sun Microsystems for the administration of network-wide databases.
NLRI
Network layer reachability information. The part of a BGP route containing the IP address prefixes and associated netmask lengths that are reachable via the path described in the route. The networks indicated by these prefixes and netmasks reside in the destination autonomous system-the final one listed in the path.
node
A device, such as a PC, server, switching point, bridge, or gateway, connected to a network at a single location. A node can also be called a station. See host.
nonvolatile RAM
See NVRAM.
notification message
A message sent between BGP peers to inform the receiving peer that the sending peer must terminate the BGP session because an error occurred. The message contains information that explains the error. See also keepalive message; open message; update message.
not-so-stubby-area
See NSSA.
NSSA
Not-so-stubby-area. In OSPF, an area similar to a stub area except that Type 1 and Type 2 external routes can be learned from it. Any external routes learned from an NSSA are translated into Type 1 and Type 2 external routes for the backbone area or other areas that accept external routes. Like stub areas, NSSAs can have default costs set for them but cannot have external routes advertised into them.
NT1
Network termination 1 device. The device that provides an interface between the ISDN Basic Rate Interface (BRI) line used by the telephone company and a customer's terminal equipment. The NT1 also provides power for the terminal equipment, if necessary. In North America, where ISDN BRI is a U loop, the customer must supply the NT1 device; in Japan and the European countries where BRI is an S/T bus, the telephone company supplies the NT1. The PortMaster integrates the NT1 device into its ISDN BRI ports that are U interfaces.
NVRAM
Nonvolatile random access memory. Nonvolatile storage that can be erased and reprogrammed electronically, allowing software images to be stored, booted, and rewritten as necessary.

O

ODI
Open Datalink Interface. A Novell specification that isolates the protocol stack from the network adapter drivers to provide hardware independence for network connectivity.
Open Datalink Interface
See ODI.
open message
A message sent between BGP peers to establish communication. See also keepalive message; notification message; update message.
Open Shortest Path First
See OSPF.
OSPF
Open Shortest Path First. A link-state interior gateway routing protocol designed for a hierarchical routing structure. OSPF chooses routes on a best-path, least-cost basis and supports variable-length subnet masks (VLSMs) for "classless" networking, allows up to 255 hops between routers, and provides packet authentication. See also RIP.
out-of-band connection
A remote connection, or a connection outside connected networks, established over a modem. This type of connection is useful when network communications are not available.

P

packet
A unit of data sent across a network.
PAP
Password Authentication Protocol. An authentication protocol that allows PPP peers to authenticate one another. The remote router attempting to connect to the local router is required to send an authentication request. Unlike the Challenge Handshake Authentication Protocol (CHAP), PAP passes unencrypted passwords. PAP does not itself prevent unauthorized access, but merely identifies the remote end. The router or access server then determines if that user is allowed access. See also CHAP.
parity check
A process for checking the integrity of a character. A parity check appends a bit to a character or word to make the total number of binary 1 digits in the character or word (excluding the parity bit) either odd (for odd parity) or even (for even parity).
partition
Electronic isolation of an Ethernet device from network communications.
Password Authentication Protocol
See PAP.
path
In BGP, a autonomous system path list and a collection of attributes that provide descriptions of and explain how to reach a given collection of IP address destinations in a single autonomous system. A path and its destination comprise a BGP route. See also destination; autonomous system path list; route.
peer
(1) In BGP, a router with which a BGP speaker exchanges open messages, notification messages, update messages, and keepalive messages. A PortMaster can have both internal and external peers. See also internal peer; external peer.
(2) In Multichassis PPP, the relationship between a master and slave. A peer is distinct from a neighbor.
permanent virtual circuit
See PVC.
physical circuit
A physical connection between two devices.
ping
Packet Internet Groper. A program that is useful for testing and debugging networks. Ping sends an ICMP echo packet to the specified host and waits for a reply. Ping reports success or failure and sometimes statistics about its operation.
Point-to-Point Protocol
See PPP.
policy
In BGP, the rule or set of rules the PortMaster follows for accepting, injecting, and/or advertising BGP routes to its BGP internal and external peers. You assign policies to a peer when you add it to the PortMaster during configuration. You can use the default policy easy-multihome, or create and assign your own policies. One policy can handle all three functions, or you can create separate policies for acceptance, injection, and advertisement. See also acceptance policy; advertisement policy; injection policy.
port
The physical channel or connection through which data flows.
port speed
The rate at which data is accepted by the port at the end of the wire. For example, when a T1 line exists between a site and a telecommunications provider, the telecommunications provider accepts only the number of bits per second ordered by the customer into the port on its equipment. Upgrading port speed is generally a software change.
PPP
Point-to-Point Protocol. A protocol that provides connections between routers and between hosts and networks over synchronous and asynchronous circuits. See also SLIP.
PRI
Primary Rate Interface. The ISDN interface to primary rate access. Primary rate access consists of a single 64Kbps D channel plus 23 (T1) or 30 (E1) 64Kbps B channels for voice or data. Compare BRI.
Primary Rate Interface
See PRI.
propagation
The process of translating and forwarding routes from one routing protocol into another. Route propagation is also known as route redistribution. Lucent Remote Access recommends using route filters in propagation rules to ensure that you redistribute information without creating routing loops. Compare summarization.
provisioning
The process of supplying telecommunications service and equipment to a user. In ISDN provisioning, for example, a telephone service provider configures its own switch that connects via an ISDN line to the user's ISDN hardware. Because switch configuration varies according to hardware, telephone company, switch, and available ISDN line, user and provider must work together to establish the correct settings.erc
proxy Address Resolution Protocol
See proxy ARP.
proxy ARP
Proxy Address Resolution Protocol. A variation of the ARP protocol in which a router or other device sends an ARP response to the requesting host on behalf of another node. Proxy ARP can reduce the use of bandwidth on slow-speed WAN links. See also ARP.
PVC
Permanent virtual circuit. A circuit that defines a permanent connection in a switched digital service such as Frame Relay. Frame Relay is the only switched digital service that uses PVCs supported by PortMaster products.

R

RADIUS
Remote Authentication Dial-In User Service. A client/server security protocol created by Lucent.
RARP
Reverse Address Resolution Protocol. A protocol used in network routers that provides a method for finding IP addresses based on media access control (MAC) addresses. Compare ARP.
Remote Authentication Dial-In User Service
See RADIUS.
Request for Comments
See RFC.
Reverse Address Resolution Protocol
See RARP.
RFC
Request for Comments. One of a series of documents that communicate information about the Internet. Most RFCs document protocol specifications, such as those for IP and BGP. Some RFCs are designated as standards.
RIP
Routing Information Protocol. A protocol used for the transmission of IP or IPX routing information.
rlogin
Remote login. A terminal emulation program, similar to Telnet, offered in most UNIX implementations.
route
A way for a packet to reach its target via the Internet. A BGP route provides a path of autonomous systems-plus any path attributes-to a single destination autonomous system that contains particular IP address prefixes and associated netmasks. Packets whose targets fall within the networks identified by these prefixes and netmasks can use this BGP route. BGP peers advertise routes to each other in update messages.
router
A device that connects two or more networks and can direct traffic based on addresses.
route reflection
In BGP, a method for maintaining path and attribute information across an autonomous system, while avoiding the overhead of having all peers within an autonomous system fully communicate to-be fully meshed with-each other. To reduce the number of links, all internal peers are divided into clusters, each of which has one or more route reflectors. A route received by a route reflector from an internal peer is transmitted to its clients, which are the other peers in the cluster that are not route reflectors. Route reflection requires that all internal peers use identical policies.
Confederations are another way to avoid configuring a fully meshed set of peers in a single autonomous system. In contrast to route reflection clusters, confederations require all routers in the autonomous system to operate as confederation members. However, confederations provide a finer control of routing within the autonomous system by allowing for policy changes across confederation boundaries. See also cluster; cluster ID; confederation; route reflector.
route reflector
A router configured to transmit routes received from internal BGP peers to one or more other internal peers within its same cluster. These peers are called the route reflector's clients. See also cluster; cluster ID; route reflection.
router ID
One of the interface addresses configured on a BGP speaker. The router ID is chosen as the address that uniquely identifies the BGP speaker on the Internet.
Routing Information Protocol
See RIP.
routing table
A database of routes to particular network destinations, stored on a router or other device. The routing table stored on the PortMaster contains the following information for each route: IP address and netmask length of the destination, IP address of the gateway, source of the route (if any), type of route, hop-count metric, and PortMaster interface used to forward packets along the route.
RS-232 interface
A standard for data communication using serial data and control signals.
runt packet
A packet with a frame size between 8 and 63 bytes with frame check sequence (FCS) or alignment errors. The runt packet is presumed to be a fragment resulting from a collision.

S

SAP
Service Advertisement Protocol. An IPX protocol that provides a means of informing network clients, via routers and servers, of available network resources and services. See also IPX.
Serial Line Internet Protocol
See SLIP.
serial port
A bidirectional channel through which data flows one bit as a time. Asynchronous serial ports most often use 10 bits for a character of data including 1 start bit, 8 data bits, and 1 stop bit.
server
A computer or a specialized device that provides and manages access to shared network resources, such as hard disks and printers.
Service Advertisement Protocol
See SAP.
service profile identifier
See SPID.
Simple Network Management Protocol
See SNMP.
slave
In Multichassis PPP, a PortMaster through which a subsequent connection for a particular user is made. (The port through which the connection is made is called the slave port.) Every slave has a corresponding master. Slaves are for a given connection only, and a PortMaster that functions as a slave for one user's connection can be a master for a different user's connection. See also master.
SLIP
Serial Line Internet Protocol. The protocol, obsoleted by the Point-to-Point Protocol (PPP), for point-to-point serial connections using TCP/IP. See also PPP.
SNMP
Simple Network Management Protocol. A protocol defined in RFC 1157, used for communication between management consoles and network devices.
speaker
A single BGP router that is able to communicate with other routers that run BGP. When two BGP speakers communicate with each other, they are called BGP peers.
SPID
Service profile identifier. A number used by some service providers to define the services to which an ISDN device subscribes. The ISDN device uses the SPID when accessing the switch that initializes the connection to a service provider.
station
See host.
stub area
In OSPF, an area into which no external routes are imported. A stub area cannot contain autonomous system border routers and cannot be a transit area for virtual links. Summary advertisements external to the area are by default imported into the stub area but might be squelched to further reduce area database size. In this case, the default route advertisement by the autonomous system border routers handle all routes external to the area.
subnet mask
A 32-bit netmask used to indicate the bits of an IP address that are being used for the subnet address. Compare netmask.
summarization
The process of combining routing information from one routing protocol into another for advertisement. For example, the PortMaster summarizes non-BGP route information it receives internally via the Interior Gateway Protocol (IGP) OSPF or RIP, or via a static route, into BGP for advertisement to BGP internal and external peers. Summarized routing information must comply with BGP advertisement policy rules before advertisement. Compare propagation.
SVC
Switched virtual circuit. A connection established between two physical circuits, such as an ordinary telephone call. The call creates a virtual circuit between the originator and the party called.
switched virtual circuit
See SVC.

T

T1
Digital WAN carrier facility used to transmit data formatted for digital signal level 1 (DS-1) at 1.544 Mbps through the telephone-switching network, using alternate mask inversion (AMI) or binary 8-zero substitution (B8ZS) coding. Compare E1.
TCP/IP
An open network standard that defines how devices from different manufacturers communicate with each other over interconnected networks. TCP/IP protocols are the foundation of the Internet.
Telnet
The Internet standard protocol, described in RFC 854, for remote terminal connection service.
terminal adapter
A device that provides ISDN compatibility to non-ISDN devices. An asynchronous terminal adapter turns an asynchronous bit stream into ISDN and is treated by the PortMaster as if it were a modem. A synchronous terminal adapter takes a synchronous bit stream and turns it into ISDN, typically supports V.25bis dialing, and connects to a PortMaster synchronous port. Some terminal adapters can be configured for either synchronous or asynchronous operation.
terminal emulator
A program that makes a PC screen and keyboard act like the video display terminal of another computer.
TFTP
Trivial File Transfer Protocol. A simplified version of the File Transfer Protocol (FTP) that transfers files but does not provide password protection or user directory capability. TFTP can be used by diskless devices that keep software in ROM and use it to boot themselves. The PortMaster can be booted from the network by means of Reverse Address Resolution Protocol (RARP) and TFTP.
transit service
In BGP, the function provided by an autonomous system that is in the path of a route but not the origination or destination. To provide reliable transit service, an autonomous system must ensure that its BGP and non-BGP routers agree on the interior routes and exit and entry points for each transit route through the autonomous system. The PortMaster synchronizes routing information between the BGP and non-BGP routers within its autonomous system by means of the lockstep feature. See also lockstep.
Trivial File Transfer Protocol
See TFTP.
two-way
Relating to a port configuration that allows both incoming and outgoing calls.

U

UDP
User Datagram Protocol. A connectionless protocol defined in RFC 768. UDP exchanges datagrams but does not provide guaranteed delivery.
U interface
The ISDN interface defined as the connection between the network termination 1 device (NT1) and the telephone company local loop. The U interface standard is set by each country. The U interface described in PortMaster documentation refers to the U.S. definition.
UNIX
A multiuser, multitasking operating system originally developed by AT&T that runs on a wide variety of computer systems.
UNIX-to-UNIX Copy Program
See UUCP.
update message
A message sent between BGP peers to convey network reachability information in two parts. The first part lists the IP address prefixes and associated netmasks for one or more routes that the PortMaster is withdrawing from service because it can no longer reach them. The second part of an update message consists of a single BGP route. See also route.
User Datagram Protocol
See UDP.
UUCP
UNIX-to-UNIX Copy Program. Interactive communication system for connecting two UNIX computers to send and receive data.

V

V.120
An ITU-T standard for performing asynchronous rate adaptation into ISDN.
V.25bis
An ITU-T standard defining how to dial on synchronous devices such as ISDN or switched 56Kbps.
V.32bis
An ITU-T standard that extends the V.32 connection range from 4800bps to 14.4Kbps. V.32bis modems fall back to the next lower speed when line quality is impaired, and fall back further as necessary. They fall forward to the next higher speed when line quality improves.
V.34
An ITU-T standard that allows data rates as high as 28.8Kbps.
V.35
The ITU-T standard for data transmission at 48Kbps over 60kHz-to-108kHz group band circuits. It includes the 35-pin V.35 connector specifications normally implemented on a modular RJ-45 connector.
variable-length subnet mask
See VLSM.
virtual circuit
A logical connection between two endpoints on a switched digital network. Virtual circuits can be switched or permanent. A switched virtual circuit (SVC) is used when you make an ordinary telephone call, an ISDN connection, or a V.25 switched 56Kbps connection. A permanent virtual circuit (PVC) is used in Frame Relay. See also PVC; SVC.
virtual connection
In Multichassis PPP, a connection made when a slave forwards all the packets it receives for a particular connection to its corresponding master for processing.
virtual port
In Multichassis PPP, a port corresponding to the physical port of the slave.
 
virtual private network
See VPN.
VLSM
Variable-length subnet mask. A means of specifying a different subnet mask for the same network number on different subnets. VLSM often allows addresses to be assigned more efficiently. OSPF and BGP support "classless" or VLSM routes.
VPN
Virtual private network. A restricted network that uses public wires to connect nodes. A VPN provides a way to encapsulate, or "tunnel," private data cheaply, reliably, and securely through a public network, usually the Internet. IP packets are encapsulated in a VPN protocol. VPNs use encryption and other security mechanisms to prevent unauthorized users from accessing the network and intercepting the data.

W

WAN
Wide area network. Data communications network that serves users across a broad geographic area and often uses transmission devices provided by common carriers. Frame Relay is an example of a WAN. Compare LAN.
 
 


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