Lantech LGS-2624C User manual - page 264
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 (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 the DHCP relay
agents MAC address.
DHCP Snooping
DHCP Snooping is used to block intruder 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 at 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