Dhcp Filtering - TP-Link TL-SG2424 User Manual

5.5 DHCP Filtering

Nowadays, the network is getting larger and more complicated. The amount of the PCs always
exceeds that of the assigned IP addresses. The wireless network and the laptops are widely used
and the locations of the PCs are always changed. Therefore, the corresponding IP address of the
PC should be updated with a few configurations. DHCP (Dynamic Host Configuration Protocol)
functions to solve the above mentioned problems.
However, during the working process of DHCP, generally there is no authentication mechanism
between Server and Client. If there are several DHCP servers in the network, network confusion
and security problem will happen. To protect the switch from being attacked by illegal DHCP
servers, you can configure the desired ports as trusted ports and only the clients connected to the
trusted ports can receive DHCP packets from DHCP severs. Here the DHCP Filtering function
performs to monitor the process of hosts obtaining IP addresses from DHCP servers.
DHCP Working Principle

DHCP works via the "Client/Server" communication mode. The Client applies to the Server for
configuration. The Server assigns the configuration information, such as the IP address, to the
Client, so as to reach a dynamic employ of the network source. A Server can assign IP address for
several Clients, which is illustrated in the following figure.
For different DHCP clients, DHCP server provides three IP address assigning methods:
(1) Manually assign the IP address: Allows the administrator to bind the static IP address to a
specific client (e.g.: WWW Server) via the DHCP server.
(2) Automatically assign the IP address: DHCP server assigns the IP address without an
expiry time limitation to the clients.
(3) Dynamically assign the IP address: DHCP server assigns the IP address with an expiry
time. When the time for the IP address expired, the client should apply for a new one.
Figure 5-17 Network diagram of DHCP
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