Appendix C:
Glossary
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D
DEI
DEI is an acronym for
D
rop
E
ligible
I
ndicator. It is a 1-bit field in the VLAN tag.
DES
DES is an acronym for
D
ata
E
ncryption
S
tandard. It provides a complete description of a
mathematical algorithm for encrypting (enciphering) and decrypting (deciphering) binary
coded information.
Encrypting data converts it to an unintelligible form called cipher. Decrypting cipher converts
the data back to its original form called plaintext. The algorithm described in this standard
specifies both enciphering and deciphering operations which are based on a binary number
called a key.
DHCP
DHCP is an acronym for
D
ynamic
H
ost
C
onfiguration
P
rotocol. It is a protocol used for
assigning dynamic IP addresses to devices on a network.
DHCP used by networked computers (clients) to obtain IP addresses and other parameters
such as the default gateway, subnet mask, and IP addresses of DNS servers from a DHCP
server.
The DHCP server ensures that all IP addresses are unique, for example, no IP address is
assigned to a second client while the first client's assignment is valid (its lease has not
expired). Therefore, IP address pool management is done by the server and not by a human
network administrator.
Dynamic addressing simplifies network administration because the software keeps track of IP
addresses rather than requiring an administrator to manage the task. This means that a new
computer can be added to a network without the hassle of manually assigning it a unique IP
address.
DHCP Relay
DHCP Relay is used to forward and to transfer DHCP messages between the clients and the
server when they are not on the same subnet domain.
The DHCP option 82 enables a DHCP relay agent to insert specific information into a DHCP
request packets when forwarding client DHCP packets to a DHCP server and remove the
specific information from a DHCP reply packets when forwarding server DHCP packets to a
DHCP client. The DHCP server can use this information to implement IP address or other
assignment policies. Specifically the option works by setting two sub-options: Circuit ID
