Planet IGS-5225 Series User Manual page 449

CDP
CDP is an acronym for Cisco Discovery Protocol.
D
DEI
DEI is an acronym for Drop Eligible Indicator. It is a 1-bit field in the VLAN tag.
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, 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 (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 and the format is "vlan_id" "module_id" "port_no".
The parameter of "vlan_id" is the first two bytes represent the VLAN ID. The parameter of "module_id" is the
third byte for the module ID. The parameter of "port_no" is the fourth byte and it means the port number.
The Remote ID is 6 bytes in length, and the value is equal the DHCP relay agents MAC address.
User's Manual of IGS-5225 series
449