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designated router
An OSPF router that creates LSAs for a multi-access
network and is required to perform other special tasks in OSPF operations.
Multi-access OSPF networks that maintain a minimum of two attached
routers identify one router that is chosen by the OSPF Hello protocol, which
makes possible a decrease in the number of adjacencies necessary on a multi-
access network. This in turn reduces the quantity of routing protocol traffic
and the physical size of the database.
destination address
The address for the network devices that will receive
a packet.
dial backup
Dial backup connections are typically used to provide redun-
dancy to Frame Relay connections. The backup link is activated over an
analog modem.
A digital waveform is one where distinct ones and zeros provide the
data representation. See also: analog.
directed broadcast
A data frame or packet that is transmitted to a specific
group of nodes on a remote network segment. Directed broadcasts are
known by their broadcast address, which is a destination subnet address
with all the bits turned on.
discovery mode
Also known as dynamic configuration, this technique is
used by an AppleTalk interface to gain information from a working node
about an attached network. The information is subsequently used by the
interface for self-configuration.
distance-vector protocol
Type of routing protocol that sends complete
routing table on periodic intervals to neighbor routers.
distance-vector routing algorithm
In order to find the shortest path, this
group of routing algorithms repeats on the number of hops in a given route,
requiring each router to send its complete routing table with each update,
but only to its neighbors. Routing algorithms of this type tend to generate
loops, but they are fundamentally simpler than their link-state counterparts.
See also: link-state routing algorithm and SPF.
Distribution layer
Middle layer of the Cisco three-layer hierarchical
model, which helps you design, install, and maintain Cisco hierarchical net-
works. The Distribution layer is the point where Access layer devices con-
nect. Routing is performed at this layer.
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