DIGITAL TCP/IP Services for OpenVMS
Concepts and Planning

initial sequence number: The first sequence number used for sending or receiving on a connection.

inode: A UNIX file structure used to address a file block. There is a unique inode allocated for each active file with a name made up of a device/i-number pair.

interface: The boundary between two parts of a system across which communication is possible; may be defined through hardware or software.

The host address of an attached network interface. This is the address of a broadcast, nbma, or loopback interface, and the remote address of a point-to-point interface. As with any host address, it can be specified symbolically.

The connection between a router and one of its attached networks. A physical interface may be specified by a single IP address, domain name, or interface name. (Unless the network is an unnumbered point-to-point network.) Multiple levels of reference in the configuration language allow the identification of interfaces by using wildcard, interface type name, or delete word address. Be careful using interface names, as future versions might allow more than one address per interface. Dynamic interfaces can be added or deleted and indicated as up or down as well as changes to address, netmask, and metric parameters.

Interior Gateway Protocol (IGP): The protocol used to propagate network reachability and routing information within an autonomous system; RIP is among the most popular.

One of a class of routing protocols used to exchange routing information within an autonomous system.

interface list: A list of one or more interface names, including wildcard names (names without a number) and names that may specify more than one interface or address, or the token all-for-all interfaces.

intermediate system: An OSI system that performs Internet layer forwarding. A routing system receives data packets from a system on one subnet and passes them on to a system on another subnet; it receives data packets from a source end system, or from the previous intermediate system on the route, and passes them on to the destination end system, or to the next intermediate system on the route.

internet: A shortened form of internetwork; a network of networks; interconnected TCP/IP networks that function as one large virtual network. Differs from the Internet by their lack of connectivity with the global Internet.

Internet: The worldwide network of networks and gateways that use the TCP/IP protocol suite and function as one virtual network; provides universal connectivity and three levels of network services: unreliable, connectionless packet delivery; reliable, full-duplex stream delivery; and application level services such as electronic mail that build on the first two. The Internet connects many universities, government research labs, military installations, and private businesses.

Internet architecture: A four-layered communications model that consists of the following: Application layer, Transport layer, Internet layer, and Network Interface layer.

Internet Architecture Board (IAB): The technical body that oversees the development of the Internet suite of protocols (commonly referred to as "TCP/IP"). It has a research task force and an engineering task force, each responsible for investigating a particular area.

Internet Autonomous System: A system that consists of a set of gateways, each of which can reach any other gateway in the same system using paths by means of gateways only in that system. The gateways of a system cooperatively maintain a routing database using an interior gateway protocol.

Internet Control Message Protocol (ICMP): An extension to the Internet Protocol; used by gateways to communicate with the network software in hosts.

Internet header length: An IP header field that indicates the number of 32-bit words making up the Internet header.

Internet layer: The layer in the TCP/IP network model where data is transferred between hosts across networks. Also referred to as Network Interface layer.

Internet number: See IP address.

Internet Protocol (IP): A connectionless best-effort packet switching protocol that resides in the Internet layer and has two major functions: internet addressing and fragmentation of messages.

Internetwork: A collection of many different computing systems which communicate with each other. The computing systems can include different hardware architectures, operating systems and network technologies.

interoperability: The ability of software and hardware on multiple machines from multiple vendors to communicate meaningfully.

InterNIC Registration Services: The Internet Network Information Center; organization that provides the Internet community with registration, directory, database and information services.

I/O status block (IOSB): A data structure associated with the $QIO system service. The IOSB holds information about how the I/O request completes.

IP: See Internet Protocol.

IP address: An address that identifies the connection between the network controller of a node using TCP/IP and the network cable. The 32-bit address is composed of two parts: network number and host number.

IP datagram: The basic unit of information passed across the Internet; contains source and destination addresses, the data, and fields that define the length of the datagram, the header checksum, and flags to say whether the datagram can be (or has been) fragmented. An IP datagram is to the Internet what a hardware packet is to a physical network. See also datagram.

IP forwarding: A configurable kernel options that controls whether a host forwards IP datagrams. Generally, hosts do not forward IP datagrams.

IP trailer protocol: A protocol in which the protocol header follows the data.

KA9Q: A popular implementation of TCP/IP and associated protocols for amateur radio systems.

Kbps: See Kilobits per second.

kernel: The software that provides the standard API for application programs. Generally speaking, the kernel embodies the policy and structure of an operating system. In a narrower sense, the kernel provides a programmatic interface to any hardware resources available. In a UNIX system, the kernel is a program that contains the device drivers, the memory management routines, the scheduler, and system calls; always running while the system is operating.

Kilobits per second (Kbps or Kb/s): The measure of data transmission rate.

LAN: See local area network.

layer: (1) The grouping of related communication functions that provide a well defined service to a client independently of the protocols and other means used to provide it. (2) A software protocol levels that make up network architectures; each layer performs certain functions for the layers above and below it.

limited use protocol: A classification in Internet standards for protocols that are for use in limited circumstances; possibly due to their experimental state, specialized nature, limited functionality, or historic state.

line printer daemon (LPR/LPD): The DIGITAL TCP/IP Services for OpenVMS remote printing services for UNIX and OpenVMS client hosts.

line speed: The maximum rate at which data can be reliably transmitted over a line; varies with the capability of the modem or hardware device that performs the transmitting.

link: A directory entry referring to a file; one file may have several links to it.

little endian: The format for storage or transmission of binary data in which the least significant byte comes first. The reverse convention is called big endian.

load broker: A TCP/IP Services component that provides configurable, calculated methods for distributing BIND services among systems in a cluster.

local address: The address of a host within a subnet.

The host address of an attached interface. This is the address of a broadcast, nbma, or loopback interface, and the local address of a point-to-point interface. As with any host address, it may be specified symbolically.

local area network (LAN): A self-contained group of computers and communications devices (such as modems, routers, servers, and repeaters) that offers a high-speed, reliable communications channel. LANs span a limited distance such as a building or group of buildings, but can be connected to wide area networks (WANs) with gateways. Contrast with wide area network (WAN).

local data: Any data stored locally by a system.

local network: A network directly attached to a host or gateway.

local node: A node at which the user is located.

local subnet: A subnet directly attached to a host or gateway.

lock manager: An NFS component that allows an NFS client to lock portions of files that reside on an NFS server.

logical connectivity: The ability of nodes to communicate.

logical link: A temporary connection between processes on source and destination nodes (or between two processes on the same node).

Logical Link Control: The upper portion of the Data Link layer that presents a uniform interface to the user of the data link service, usually the Internet layer.

loop node: A local node that is associated with a particular address and is treated as if it were a remote node. All traffic to the loop node is sent over the associated address; used for loopback testing.

loopback: A program that sends packets to a remote host on the Internet and looks for replies; works by means of the echoing facility provided by the ICMP protocol and is a way to determine if an Internet host is reachable from your host. See also packet internet groper.

LPR/LPD: See remote line printing or line printer daemon.

mail bridge: A mail gateway that forwards electronic mail between two or more networks while ensuring that the messages it forwards meet certain administrative criteria; specialized form of mail gateway that enforces an administrative policy with regard to what mail it forwards.

mail exchange record (MX record): The Domain Name Service resource record type indicating which host can handle mail for a particular domain or host.

mail exchanger (MX): The DIGITAL TCP/IP Services for OpenVMS implementation of a mail exchanger that allows hosts in a local network to forward mail to systems that might not be directly connected to the local network.

mail exploder: The part of an electronic mail delivery system that allows a message to be delivered to a list of addressees. Users send messages to one address (e.g., hacks@somehost.edu) and the mail exploder handles delivery to the individual mailboxes.

mail gateway: A host that connects two or more electronic mail systems (especially dissimilar mail systems on two different networks) and transfers messages between them.

mail path: A series of hosts used to direct electronic mail from one user to another.

Management Information Base (MIB): A database used by the Simple Network Management Protocol (SNMP) to check network statistics and configurations. An SNMP management station can query a MIB or set it in an SNMP agent (for example, router). Standard, minimal MIBs have been defined (MIB I, MIB II), and vendors often have custom entries. In theory, any SNMP manager can talk to any SNMP agent with a properly defined MIB.

Management Information Base II (MIB II): Data that can be accessed by a network management protocol; for DIGITAL TCP/IP Services for OpenVMS, the database maintained by a gateway running SNMP.

management station: The workstation of a network manager running SNMP.

mask: A means of subdividing networks using address modification. A mask is a dotted quad specifying the bits of the destination that are significant. Except when used in a route filter, GATED only supports contiguous masks.

mask length: The number of significant bits in the mask.

master file directory (MFD): The root of an OpenVMS file system on a particular physical device.

master server: The name server that is the authority for a specific domain space. See also BIND server.

maximum transmission unit (MTU): The largest possible unit of data that can be sent on a given physical medium. See also fragmentation.

MBUFs: See memory buffers.

memory buffers (MBUFs): The portions of memory that act as queues for data arriving at a port before the process is ready to claim that data.

message: A message block, or a series of message blocks, that constitute a logical grouping of information; each is delimited by communications control characters.

metric: One of the units used to help a system determine the best route. Metrics may be based on hop count, routing delay, or an arbitrary value set by the administrator depending on the type of routing protocol. Routing metrics may influence the value of assigned internal preferences. (See preference.)

The following sample shows the range of possible values for each routing protocol metric and the value used by each protocol to reach a destination:

SAMPLE ROUTING PROTOCOL METRICS Protocol Metric Represents Range Unreachable -------- ----------------- ----- ----------- RIP distance (hop-count) 0-15 16 HELLO delay (milliseconds) 0-29999 30000 OSPF cost of path 0-????? Delete EGP distance (unused) 0-65535 255 BGP unspecified 0-65534 65535

MFD: See master file directory.

MIB: See Management Information Base.

MIB II: See Management Information Base II.

MIME: Multipurpose Mail Extensions; a specification for the transfer of nontext files with regular Internet e-mail.

mode: A protection placed on a file.

modem (modulator/demodulator): A device that translates digital signals (electrical impulses) generated by a computer into analog signals (tones) that can be transmitted over telephone lines, and vice versa.

mount: An NFS process that makes a remote directory available to local users.

mount point: A directory on an NFS client that is associated with a remote file system. The directory must exist before NFS can use it as a mount point.

MTU: See maximum transmission unit.

multiaccess networks: Physical networks that support the attachment of multiple (more than two) routers. Each pair of routers on such a network is assumed to be able to communicate directly.

multicast: A transmission of network traffic intended for multiple hosts (but not all connected hosts) within a network or internet.

multicast address: An address that designates a subset of nodes that are all listening for packets destined to this address.

multicast addressing: An addressing mode in which a data packet is targeted to a group of nodes that are of the same type, for example, all level 1 routers or all level 2 routers.

multihomed host: A host that has two or more hardware connections to a network; requires multiple IP addresses.

multiplexing: Using a single connection to carry several data streams and the mechanism for assigning these streams to that connection.

multipoint circuit: A circuit that connects multiple systems.

multiprocessing system: A network consisting of multiple processors.

MX record: See mail exchange record.

NAK: See negative acknowledgment.

name resolution: The process of mapping a host name to its corresponding address. See Domain Name Service.

named: The BIND Name Server daemon.

namespace: A commonly distributed set of names in which all names are unique.

negative acknowledgment (NAK): The response to receipt of a corrupted packet of information. See also acknowledgment.

neighbor: Another router with which implicit or explicit communication is established by a routing protocol. Neighbors are usually on a shared network, but not always. This term is mostly used in OSPF and EGP. Usually synonymous with peer.

neighboring routers: Two routers that have interfaces to a common network. On multiaccess networks, routers are dynamically discovered by OSPF's HELLO protocol.

network: A group of computer systems that can communicate with each other; can be composed of computers in a single building (local area networks or LANs), or computers thousands of miles apart (wide area networks or WANs). The Internet is a worldwide collection of computer networks that can intercommunicate.

Any packet-switched network. A network may be specified by its IP address or network name. The host bits in a network specification must be zero. Default may be used to specify the default network (0.0.0.0).

The IP address of a network. Usually specified as a dotted quad, with one to four values in the range from 0 to 255 inclusive, separated by dots (.). For example, 132.236.199, 132.236, or 10. It may also be specified as a hexadecimal string preceded by 0x with an even number of digits between two and eight. For example, 0x??????, 0x???? or 0x0a. Also allowed is the symbolic value default that has the value 0.0.0.0, the default network. If options noresolv statement is not specified, this can also be a symbolic network name. For example, nr-tech-prod, cornellu-net, and arpanet. The numeric forms are preferred over the symbolic form.

network address: A unique identifier of a specific system on a network, usually represented as a number or series of numbers. See also IP address.

network architecture: The specification of a network's functions and its parts, together with the ways in which the network is organized; specifies the layers of different functions in the network, ranging from data transmission at the lowest levels to user applications at the highest levels.

network byte order: The order in which bytes of information are sent or received by network applications as oppossed to how the bytes are stored in memory by different operating systems and hardware architectures. The standard network byte order is Big Endian.

network class: A definition of the type of network addressing scheme being used; high-order bits in the network number designate the network class of the IP address.

network database: The DIGITAL TCP/IP Services for OpenVMS database that allows users to refer to networks by name rather than network number; contains network names, IP addresses for the networks, and any alias names for the networks.

network delay: The time it takes to get a unit of data from the source of a transmission to the destination; usually refers to delay from the network and not by system-dependent application processing delays at source and destination nodes.

A HELLO metric. Valid values are from 0 to 30000, inclusive. The value of 30000 is the maximum metric and means unreachable. See metric and HELLO.

network diameter: The distance (number of hops) between the two nodes in the network with the greatest reachability distance. The reachability distance is the path with fewest number of hops between two nodes.

Network File System (NFS): A protocol developed by Sun Microsystems that allows a computer system to access files over a network as if they were on its local disks.

Network Information Service (NIS): A set of services in the Network File System that propagate information out from masters to recipients; used for the maintenance of system files on complex networks.

Network Interface: A device driver that communicates with the IP layer of the TCP/IP protocol suite and the network interface card.

Network Interface layer: The layer in the TCP/IP architecture model that provides the mechanism for connecting the hosts to the networks.

network management: See MIB II and Simple Network Management Protocol (SNMP).

network mask: A mask used to determine the subnet in the IP address; each bit that is turned on (binary one) in the mask is interpreted as part of the network and subnet address. Synonymous with subnet mask.

A means of subdividing networks using address modification. A mask is a dotted quad specifying the bits of the destination that are significant. Except when used in a route filter, gated only supports contiguous masks.

network meltdown: The state of complete network overload; the network equivalent of thrashing. See also broadcast storm.

network number: The part of an IP address that designates the network to which the destination host belongs.

network performance: The description of how a network performs, as measured against the expectations or requirements of users, customers, designers, or implementors, or as claimed by sales and marketing personnel. The criteria for network performance include parameters such as throughput, response time, and resource utilization.

network status notification: Information about the state of logical and physical links over which two tasks communicate. A nontransparent task can use this information to take appropriate action under conditions such as third-party disconnections and a partner's exiting before I/O completion.

network task: A nontransparent task that can process multiple inbound connection requests; that is, it has a declared network name or object number.

Network Time Protocol (NTP): The protocol that ensures accurate local timekeeping with reference to radio and atomic clocks located on the Internet; capable of synchronizing distributed clocks within milliseconds over long time periods.

NFS: See Network File System.

NFS client: The software that requests remote file services from an NFS server. Client system users access files that physically reside on an NFS server system.

NFS server: The software that provides remote file services to NFS clients.

NFS server (OpenVMS server): A computer system that offers services to NFS clients within an Internet environment; can be a single host, a whole OpenVMS cluster system, or members of an OpenVMS cluster system.

NIS: See Network Information Service.

nobody: A UNIX convention used when file ownership is not known; maps to an account with a UID and GID of --2.

node: (1) A system on a network; also referred to as a host. (2) One member in an OpenVMS cluster system.

node address: The required unique numeric identification of a specific node in the network.

node name: The alphanumeric identification associated with the node address for one-to-one mapping.

nonadjacent nodes: Nodes without direct lines between them; can communicate only if intermediate systems forward the data along the path between the source and the destination.

nonauthoritative answer: A name server's answer is said to be nonauthoritative when the server answer comes from its own cache.

nontransparent task: A form of device-dependent I/O that uses system services for network-specific functions; can initiate and complete a logical link connection, exchange messages between two tasks, and terminate the communication process. Application that has direct access to network-specific information and operations, such as optional user data on connects and disconnects and interrupt messages, to monitor the communications process; can receive and process multiple inbound connection requests.

normalization: The estimation of the change in a counter value over a specified time period.

nslookup: The DIGITAL TCP/IP Services for OpenVMS utility that allows you to interactively query domain name servers (BIND servers) and helps you set up and manage the BIND server software.

NTP: See Network Time Protocol.

NTP packet: A message sent over the network that conforms to the Network Time Protocol format. This format includes space for recording the current time. See also ``poll''.

null modem: A simple form of modem connection where only the data interchange circuits, not the modem control circuits, are used.

occluded mounting: A TCP/IP Services/NFS method of mouting an NFS file system onto a client mount point that is higher or lower in the directory structure than an active mount.

octet: A single, 8-bit unit of data; term used in networking rather than the term byte because some systems have bytes that are not 8-bits long.

ODS-2 disk structure: ODS-2 is an OpenVMS On-Disk Structure. This is the default disk structure of the OpenVMS operating system and you use it to share data between VAX and Alpha with full compatibility.

ODS-5 disk structure (Alpha Only) : ODS-5, an OpenVMS On-Disk Structure, is an extension to the existing ODS-2 disk structure. It adds the ability to use extended file names that can be more easily mapped between Windows and OpenVMS. ODS-5 expands the available character set and filename length to be consistent with Windows 95 and Windows NT, and sets the stage for future UNICODE file name support through PATHWORKS. ODS-5 also supports deeper directories.

On-Disk Structure (ODS): On-Disk Structure (ODS) refers to a logical structure given to information stored on a disk or CD-ROM. It is a hierarchical organization of files, their data, and the directories needed to gain access to them. The OpenVMS file system implements the On-Disk Structure and provides access control to the files located on the disk.

OPCOM: See Operator Communication Manager

OPCOM messages: Messages broadcast by the Operator Communication Manager (OPCOM). These messages are displayed on operator terminals and written to the operator log file. The messages might be general messages that you send, user requests, operator replies, or system events.