ZyXEL Communications MGS3600-24F User Manual page 362

F M A A
RONT ATTER PPENDIX
D
DEI
DEI (Drop Eligible Indicator) is a 1-bit field in the VLAN tag.
DES
DES (Data Encryption Standard) provides a complete description of a mathematical algorithm for encrypting (enciphering) and decrypting (deci-
phering) binary coded data. Encrypting data converts it to an unintelligible form called cipher. Decrypting cipher converts the data back to its origi-
nal 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 (Dynamic Host Configuration Protocol) is 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 clients and the server when they are not on the same subnet.
The DHCP option 82 enables a DHCP relay agent to insert specific information into DHCP request packets when forwarding client DHCP packets
to a DHCP server and remove the specific information from 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 Circuit ID is 4 bytes in length and its format is {vlan_id}{module_id}{port_no}. The vlan_id is the first two bytes. The module_id is the third byte
(in standalone switches it always equal 0, in stackable switches it means switch ID). The port_no is the fourth byte.
MGS3600-24F/XGS3600-26F/XGS3600-28F A-4 U ' G
SER S UIDE