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LGB5128A User Manual
236
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 packet when forwarding client DHCP packets to a DHCP server and
remove the specific information from a DHCP reply packet 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 the 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 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 and it means the port number.
The Remote ID is 6 bytes in length, and the value is equal to the DHCP relay agents
MAC address.
DHCP Snooping
DHCP Snooping is used to block intruders on the untrusted ports of the switch device
when it tries to intervene by injecting a bogus DHCP reply packet to a legitimate
conversation between the DHCP client and server.
DNS
DNS is an acronym for Domain Name System. It stores and associates many types of
information with domain names. Most importantly, DNS translates human-friendly domain
names and computer hostnames into computer-friendly IP addresses. For example, the
domain name www.example.com might translate to 192.168.0.1.
DoS
DoS is an acronym for Denial of Service. In a denial-of-service (DoS) attack, an attacker
attempts to prevent legitimate users from accessing information or services. By targeting
network sites or network connection, an attacker may be able to prevent network users
from accessing email, web sites, online accounts (banking, etc.), or other services that
rely on the affected computer.
Dotted Decimal Notation
Dotted Decimal Notation refers to a method of writing IP addresses using decimal
numbers and dots as separators between octets.
An IPv4 dotted decimal address has the form x.y.z.w, where x, y, z, and w are decimal
numbers between 0 and 255.
DSCP
DSCP is an acronym for Differentiated Services Code Point. It is a field in the header of
IP packets for packet classification purposes.
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