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DES:
DES is an acronym for Data Encryption Standard. 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 Dynamic Host Configuration Protocol. 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, the 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
to a DHCP request packet when forwarding client DHCP packets to a DHCP
server, and removing 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. The option
works by setting two sub
-
options: Circuit ID (option 1) and Remote ID
(option2). The Circuit ID sub
-
option is supposed to include information specific
to which circuit the request came in on. The Remote ID sub
-
option was
designed to carry information relating to the remote host end of the circuit.
The definition of Circuit ID in the switch is 4 bytes in length. The format is
"vlan_id" "module_id" "port_no". The parameter of "vlan_id" is the first two
bytes that represent the VLAN ID. The parameter of "module_id" is the third
byte for the module ID (In standalone switch, it always equal 0. In stackable
switch, it means switch ID). The parameter of "port_no" is the fourth byte that
represents the port number.
The Remote ID is 6 bytes in length, and the value is equal the DHCP relay
agents MAC address.
