Interlogix NS3702-24P-4S User Manual - Manual (Page 389)

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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 (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