Interlogix NS3550-8T-2S User Manual - Manual (Page 486)

User’s Manual of NS3550-8T-2S
486
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 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.
E
EEE
EEE is an abbreviation for Energy Efficient Ethernet defined in IEEE 802.3az.
EPS
EPS is an abbreviation for Ethernet Protection Switching defined in ITU/T G.8031.
Ethernet Type
Ethernet Type, or EtherType, is a field in the Ethernet MAC header, defined by the Ethernet networking standard. It is
used to indicate which protocol is being transported in an Ethernet frame.
F
FTP
FTP is an acronym for File Transfer Protocol. It is a transfer protocol that uses the Transmission Control Protocol (TCP)
and provides file writing and reading. It also provides directory service and security features.
Fast Leave
IGMP snooping Fast Leave processing allows the switch to remove an interface from the forwarding-table entry without
first sending out group specific queries to the interface. The VLAN interface is pruned from the multicast tree for the
multicast group specified in the original leave message. Fast-leave processing ensures optimal bandwidth
management for all hosts on a switched network, even when multiple multicast groups are in use simultaneously.
H