D

daemon

Background process that performs operations on behalf of the system software and hardware. Daemons normally start when the system software is booted, and they 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. The protocol accomplishes this by not advertising unstable routes.

data circuit-terminating equipment (DCE)

An RS-232-C device, typically used for a modem or printer, or a network access and packet switching node.

data-link connection identifier (DLCI)

Identifier for a Frame Relay virtual connection (also called a logical interface).

data service unit (DSU)

A device used to connect a DTE to a digital phone line. Converts digital data from a router to voltages and encoding required by the phone line. See also channel service unit/data service unit (CSU/DSU).

Data Terminal Equipment (DTE)

The RS-232-C interface that a computer uses to exchange information with a serial device.

Database Description packet

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

dcd

The JUNOS software interface process, called the Device Control Daemon.

deactivate

A 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

The amount of time 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.

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.

denial of service (DoS)

System security breach in which network services become unavailable to users.

dense mode

A method of forwarding multicast traffic to interested listeners. Dense mode forwarding assumes that the majority of hosts on the network wish to receive the multicast data. Routers flood packets and prune back unwanted traffic every 3 minutes.

dense wavelength-division multiplexing (DWDM)

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

designated router

In OSPF, a router selected by other routers that is responsible for representing the local segment to the remainder of the network, which reduces the amount of network traffic and the size of the routers’ topological databases.

destination prefix length

The number of bits used for the network portion of a CIDR IP address.

Differentiated Services Codepoint (DSCP)

The use of the first 6 bits of the IPv4 Type of Service byte. The use of the DSCP for classifying traffic allows an administrator to have 64 unique service levels in the network.

Diffie-Hellman

A public key scheme, invented by Whitfield Diffie and Martin Hellman, used for sharing a secret key without communicating secret information, thus precluding the need for a secure channel. Once correspondents have computed the secret shared key, they can use it to encrypt communications.

Diffserv

Differentiated Service (based on RFC 2474). Diffserv uses the ToS byte to identify different packet flows on a packet-by-packet basis. Diffserv adds a Class Selector Codepoint (CSCP) and a Differentiated Services Codepoint (DSCP).

Dijkstra algorithm

See shortest path first (SPF).

direct routes

See interface routes.

disable

A method of modifying the router’s active configuration. Portions of the hierarchy marked as disabled (mainly router interfaces) cause the router to use the configuration but stop the pertinent operation of the configuration.

discard

JUNOS software syntax command used in a routing policy or a firewall filter. It 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 may also be a next-hop attribute assigned to a route in the routing table.

distance-vector

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

Distance Vector Multicast Routing Protocol (DVMRP)

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.

Distributed Buffer Manager ASICs

Juniper Networks ASIC responsible for managing the router’s packet storage memory.

Down

OSPF adjacency state that is the starting state for the protocol.

drop profile

Drop probabilities for different levels of buffer fullness that are used by RED to determine if a packet is dropped from a queue or transmitted out an interface.

dual inline memory module (DIMM)

A 168-pin memory module that supports 64-bit data transfer.

Dynamic Host Configuration Protocol (DHCP)

Allocates IP addresses dynamically so that they can be reused when they are no longer needed.

dynamic label-switched path

An MPLS network path established by signaling protocols such as RSVP or LDP.

dynamic random access memory (DRAM)

Storage source on the router that can be accessed quickly by a process.