Glossary O

N

NAK

negative acknowledgment: A response sent from a receiver, telling the sender that the information was not received or contained errors. Contrast with: acknowledgment.

NAT

Network Address Translation: An algorithm instrumental in minimizing the requirement for globally unique IP addresses, permitting an organization whose addresses are not all globally unique to connect to the Internet, regardless, by translating those addresses into globally routable address space.

NCP

Network Control Protocol: A protocol at the Logical Link Control sublayer of the Data Link layer used in the PPP stack. It is used to enable multiple Network layer protocols to run over a nonproprietary HDLC serial encapsulation.

neighboring routers

Two routers in OSPF that have interfaces to a common network. On networks with multi-access, these neighboring routers are dynamically discovered by using the Hello protocol of OSPF.

NetBEUI

NetBIOS Extended User Interface: An improved version of the NetBIOS protocol used in a number of network operating systems including LAN Manager, Windows NT, LAN Server, and Windows for Workgroups, implementing the OSI LLC2 protocol. NetBEUI formalizes the transport frame not standardized in NetBIOS and adds more functions. See also: OSI.

NetBIOS

Network Basic Input/Output System: The API employed by applications residing on an IBM LAN to ask for services, such as session termination or information transfer, from lower-level network processes.

NetWare

A widely used NOS created by Novell, providing a number of distributed network services and remote file access.

network address

Used with the logical network addresses to identify the network segment in an internetwork. Logical addresses are hierarchical in nature and have at least two parts: network and host. An example of a hierarchical address is 172.16.10.5, where 172.16 is the network and 10.5 is the host address.

Network layer

In the OSI reference model, it is layer 3-the layer in which routing is implemented, enabling connections and path selection between two end systems. See also: Application layer, Data Link layer, Physical layer, Presentation layer, Session layer, and Transport layer.

NFFC

NetFlow Feature Card: A module installed on Cisco Catalyst 5000 series switches. It is capable of examining each frame's IP header as well as the Ethernet header. This in turn enables the NFFC to create flows.

NFS

Network File System: One of the protocols in Sun Microsystems' widely used file system protocol suite, allowing remote file access across a network. The name is loosely used to refer to the entire Sun protocol suite, which also includes RPC, XDR (External Data Representation), and other protocols.

NHRP

Next Hop Resolution Protocol: In a nonbroadcast multi-access (NBMA) network, the protocol employed by routers in order to dynamically locate MAC addresses of various hosts and routers. It enables systems to communicate directly without requiring an intermediate hop, thus facilitating increased performance in ATM, Frame Relay, X.25, and SMDS systems.

NHS

Next Hop Server: Defined by the NHRP protocol, this server maintains the next-hop resolution cache tables, listing IP-to-ATM address maps of related nodes and nodes that can be reached through routers served by the NHS.

NIC

network interface card: An electronic circuit board placed in a computer. The NIC provides network communication to a LAN.

NLSP

NetWare Link Services Protocol: Novell's link-state routing protocol, based on the IS-IS model.

NMP

Network Management Processor: A Catalyst 5000 switch processor module used to control and monitor the switch.

node address

Used to identify a specific device in an internetwork. Can be a hardware address, which is burned into the network interface card, or a logical network address, which an administrator or server assigns to the node.

non-blocking switch

A non-blocking switch introduces no delay to packets in the fabric.

nondesignated ports

The Spanning Tree Protocol tells a port on a layer 2 switch to stop transmitting, stopping a network loop. Only designated ports can send frames.

non-stub area

In OSPF, a resource-consuming area carrying a default route, intra-area routes, interarea routes, static routes, and external routes. Non-stub areas are the only areas that can have virtual links configured across them and exclusively contain an autonomous system boundary router (ASBR). Compare to: stub area. See also: ASBR and OSPF.

NRZ

Nonreturn to Zero: One of several encoding schemes for transmitting digital data. NRZ signals sustain constant levels of voltage with no signal shifting (no return to zero-voltage level) during a bit interval. If there is a series of bits with the same value (1 or 0), there will be no state change. The signal is not self-clocking. See also: NRZI.

NRZI

Nonreturn to Zero Inverted: One of several encoding schemes for transmitting digital data. A transition in voltage level (either from high to low or vice-versa) at the beginning of a bit interval is interpreted as a value of 1; the absence of a transition is interpreted as a 0. Thus, the voltage assigned to each value is continually inverted. NRZI signals are not self-clocking. See also: NRZ.

NT1

network termination 1: An ISDN designation to devices that understand ISDN standards.

NT2

network termination 2: An ISDN designation to devices that do not understand ISDN standards. To use an NT2, you must use a terminal adapter (TA).

NVRAM

non-volatile RAM: Random-access memory that keeps its contents intact while power is turned off.