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D

daemon — Background process that performs operations for the system software and hardware. Daemons normally start when the system software is booted, and run as long as the software is running. In the JUNOS software, daemons are also referred to as processes.

damping — Method of reducing the number of update messages sent between BGP peers, thereby reducing the load on these peers without adversely affecting the route convergence time for stable routes.

database description packet — OSPF packet type used in the formation of an adjacency. The packet sends summary information about the local router’s database to the neighboring router.

data circuit-terminating equipment — See DCE.

data-driven multicast distribution tree tunnel — See data-MDT.

Data Encryption Standard — See DES.

data-link connection identifier — See DLCI.

data link switching — See DLSw.

data-MDT — Data-driven multicast distribution tree tunnel. A multicast tunnel created and deleted based on defined traffic loads and designed to ease loading on the default MDT tunnel.

data packet — Chunk of data transiting the router from the source to a destination.

data plane — Virtual network path used to distribute data between nodes. See also control plane.

data service unit — See CSU/DSU.

data terminal equipment — See DTE.

dcd — Device control process. A JUNOS software interface process (daemon).

DCE — Data circuit-terminating equipment. An RS-232-C device, typically used for a modem or printer, or a network access and packet switching node.

D-channel — Delta channel. A circuit-switched channel that carries signaling and control for B-channels. In Basic Rate Interface (BRI) applications, it can also support customer packet data traffic at speeds up to 9.6 kbps. See also B-channel, BRI.

DCU — Destination class usage. A means of tracking traffic originating from specific prefixes on the customer edge router and destined for specific prefixes on the provider core router, based on the IP source and destination addresses.

DE — Discard-eligible bit. In a Frame Relay network, a header bit notifying devices on the network that traffic can be dropped during congestion to ensure the delivery of higher priority traffic.

deactivate — Method of modifying the router’s active configuration. Portions of the hierarchy marked as inactive using this command are ignored during the router’s commit process as if they were not configured at all.

dead interval — Amount of time that an OSPF router maintains a neighbor relationship before declaring that neighbor as no longer operational. The JUNOS software uses a default value of 40 seconds for this timer.

dead peer detection — See DPD.

default address — Router address that is used as the source address on unnumbered interfaces.

default route — Route used to forward IP packets when a more specific route is not present in the routing table. Often represented as 0.0.0.0/0, the default route is sometimes referred to as the route of last resort.

delta channel — See D-channel.

demand circuit — Network segment whose cost varies with usage, according to a service level agreement with a service provider. Demand circuits limit traffic based on either bandwidth (bits or packets transmitted) or access time. See also multicast.

denial of service — See DoS.

dense mode — Method of forwarding multicast traffic to interested listeners. Dense mode forwarding assumes that most of the hosts on the network will receive the multicast data. Routers flood packets and prune unwanted traffic every 3 minutes.

dense wavelength-division multiplexing — See DWDM.

DES — Data Encryption Standard. A method for encrypting information using a 56-bit key. Considered to be a legacy method and insecure for many applications. See also 3DES.

designated router — In OSPF, a router selected by other routers that is responsible for sending link-state advertisements (LSAs) that describe the network, thereby reducing the amount of network traffic and the size of the routers’ topological databases.

destination class usage — See DCU.

destination prefix length — Number of bits of the network address used for the host portion of a CIDR IP address.

destination service access point — See DSAP.

device control process — See dcd.

DFC — Dynamic flow capture. Process of collecting packet flows that match a particular filter list to one or more content destinations using an on-demand control protocol that relays requests from one or more control sources.

DHCP — Dynamic Host Configuration Protocol. Allocates IP addresses dynamically so that they can be reused when no longer needed.

dial backup — Feature that reestablishes network connectivity through one or more backup ISDN dialer interfaces after a primary interface fails. When the primary interface is reestablished, the ISDN interface is disconnected.

dialer filter — Stateless firewall filter that enables dial-on-demand routing backup when applied to a physical ISDN interface and its dialer interface configured as a passive static route. The passive static route has a lower priority than dynamic routes. If all dynamic routes to an address are lost from the routing table and the router receives a packet for that address, the dialer interface initiates an ISDN backup connection and sends the packet over it. See also dial-on-demand routing (DDR) backup, floating static route.

dialer interface (dl) — Logical interface for configuring dialing properties and the control interface for a backup ISDN connection.

dialer profile — Set of characteristics configured for the ISDN dialer interface. Dialer profiles allow the configuration of physical interfaces to be separated from the logical configuration of dialer interfaces required for ISDN connectivity. This feature also allows physical and logical interfaces to be bound together dynamically on a per-connection basis.

dialer watch — Dial-on-demand routing (DDR) backup feature that provides reliable connectivity without relying on a dialer filter to activate the ISDN interface. The ISDN dialer interface monitors the existence of each route on a watch list. If all routes on the watch list are lost from the routing table, dialer watch initiates the ISDN interface for failover connectivity. See also dial-on-demand routing (DDR) backup.

dial-in — Feature that enables J-series Services Routers to receive calls from the remote end of a backup ISDN connection. The remote end of the ISDN call might be a service provider, a corporate central location, or a customer premises equipment (CPE) branch office. All incoming calls can be verified against caller IDs configured on the router’s dialer interface. See also callback.

dial-on-demand routing (DDR) backup — Feature that provides a J-series Services Router with full-time connectivity across an ISDN line. When routes on a primary serial T1, E1, T3, E3, Fast Ethernet, or PPPoE interface are lost, an ISDN dialer interface establishes a backup connection. To save connection time costs, the Services Router drops the ISDN connection after a configured period of inactivity. Services Routers with ISDN interfaces support two types of dial-on-demand routing backup: on-demand routing with a dialer filter and dialer watch. See also dialer filter, dialer watch.

Differentiated Services — See DiffServ.

Differentiated Services aware — See DiffServ-aware.

Differentiated-Services-aware traffic engineering — Type of constraint-based routing that can enforce different bandwidth constraints for different classes of traffic. It can also do call admission control (CAC) on each traffic engineering class when a label-switched path (LSP) is established.

Differentiated Services code point — See DSCP.

Differentiated Services domain — Routers in a network that have Differentiated Services enabled.

Diffie-Hellman — Method of key exchange across a nonsecure environment, such as the Internet. The Diffie-Hellman algorithm negotiates a session key without sending the key itself across the network by allowing each party to pick a partial key independently and send part of it to each other. Each side then calculates a common key value. This is a symmetrical method and keys are typically used only for a short time, then discarded and regenerated.

DiffServ — Differentiated Services (based on RFC 2474). DiffServ uses the type-of-service (ToS) byte to identify different packet flows on a packet-by-packet basis. DiffServ adds a Class Selector code point (CSCP) and a Differentiated Services code point (DSCP).

DiffServ-aware — Paradigm that gives different treatment to traffic based on the experimental (EXP) bits in the MPLS label header and allows you to provide multiple classes of service.

digital certificate — Electronic file based on private and public key technology that verifies the identity of the certificate’s holder to protect data exchanged online. Digital certificates are issued by a certificate authority (CA).

Dijkstra algorithm — See SPF.

DIMM — Dual inline memory module. A 168-pin memory module that supports 64-bit data transfer.

direct routes — See interface routes.

disable — Method of modifying the router’s active configuration. When portions of the hierarchy are marked as disabled (mainly router interfaces), the router uses the configuration but ignores the disabled portions.

discard — JUNOS software syntax command used in a routing policy or a firewall filter. The command halts the logical processing of the policy or filter when a set of match conditions is met. The specific route or IP packet is dropped from the network silently. It can also be a next-hop attribute assigned to a route in the routing table.

discard-eligible bit — See DE.

distance-vector — Method used in Bellman-Ford routing protocols to determine the best path to all routers in the network. Each router determines the distance (metric) to the destination and the vector (next hop) to follow.

Distributed Buffer Manager ASIC — Juniper Networks ASIC responsible for managing the router’s packet storage memory.

DLCI — Data-link connection identifier. Identifier for a Frame Relay virtual connection (also called a logical interface).

DLSw — Data link switching. Method of tunneling IBM System Network Architecture (SNA) and NetBIOS traffic over an Internet Protocol (IP) network. (The JUNOS software does not support NetBIOS.) See also tunneling protocol.

DLSw circuit — Path formed by establishing data link control (DLC) connections between an end system and a local router configured for DLSw. Each DLSw circuit is identified by the circuit ID that includes the end system method authenticity check (MAC) address, local service access point (LSAP), and DLC port ID. Multiple DLSw circuits can operate over the same DLSw connection.

DLSw connection — Set of TCP connections between two DLSw peers that is established after the initial handshake and successful capabilities exchange.

DNS — Domain Name System. A system that stores information about hostnames and domain names. DNS provides an IP address for each hostname, and lists the e-mail exchange servers accepting e-mail addresses for each domain.

document type definition — See DTD.

Domain Name System — See DNS.

DoS — Denial of service. A system security breach in which network services become unavailable to users.

DPD — Dead peer detection. Protocol that recognizes the loss of the primary IPSec IKE peer and establishes a secondary IPSec tunnel to a backup peer.

DRAM — Dynamic random-access memory. Storage source on the router that can be accessed quickly by a process.

drop probability — Percentage value expresses the likelihood that an individual packet will be dropped from the network. See also drop profile.

drop profile — Mechanism of random early detection (RED) that defines parameters that allow packets to be dropped from the network. When you configure drop profiles, there are two important values: the queue fullness and the drop probability. See also drop probability, queue fullness, RED.

DSAP — Destination service access point. Service access point (SAP) that identifies the destination for which a logical link control protocol data unit (LPDU) is intended.

DS0 — Digital signal level 0. In T-carrier systems, a basic digital signaling rate of 64 Kbps. The DS0 rate forms the basis for the North American digital multiplex transmission hierarchy.

DS1 — Digital signal level 1. In T-carrier systems, a digital signaling rate of 1.544 Mbps. A standard used in telecommunications to transmit voice and data between devices. Also known as T1. See also T1.

DS3 — Digital signal level 3. In T-carrier systems, a digital signaling rate of 44.736 Mbps. This level of carrier can transport 28 DS1 level signals and 672 DS0 level channels within its payload. Also known as T3. See also T3.

DSCP — Differentiated Services code point or DiffServ code point. Values for a 6-bit field defined for IPv4 and IPv6 packet headers that can be used to enforce class-of-service (CoS) distinctions in routers.

DSU — Data service unit. A device used to connect a DTE to a digital phone line. DSU converts digital data from a router to voltages and encoding required by the phone line. See also CSU/DSU.

DTCP — Dynamic Tasking Control Protocol. A means of communicating filter requests and acknowledgments between one or more clients and a monitoring platform, used in dynamic flow capture (DFC) and flow-tap configurations. The protocol is defined in Internet draft draft-cavuto-dtcp-00.txt.

DTD — Document type definition. Defines the elements and structure of an Extensible Markup Language (XML) document or data set.

DTE — Data terminal equipment. An RS-232-C interface that a computer uses to exchange information with a serial device.

dual-core processor — Two process execution systems located on the same physical processor. The dual-core processor architecture enables faster computing speed and greater data throughput.

DVMRP — Distance Vector Multicast Routing Protocol. Distributed multicast routing protocol that dynamically generates IP multicast delivery trees using a technique called reverse-path multicasting (RPM) to forward multicast traffic to downstream interfaces.

DWDM — Dense wavelength-division multiplexing. Technology that enables data from different sources to be carried together on an optical fiber, with each signal carried on its own separate wavelength.

Dynamic Host Configuration Protocol — See DHCP.

dynamic label-switched path — MPLS network path established by signaling protocols such as RSVP and LDP.

Dynamic Tasking Control Protocol — See DTCP.

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