Dynamic Host Configuration Protocol (DHCP)

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DHCP

Dynamic Host Configuration Protocol

DHCP (Dynamic Host Configuration Protocol) is a network management protocol used to assign an Internet Protocol (IP) address dynamically to any device or node on a network so that they can communicate using IP. DHCP automates and centrally manages these configurations rather than requiring network administrators to manually assign IP addresses to all network devices.

How DHCP works

DHCP runs at the application layer of the Transmission Control Protocol/IP (TCP/IP) protocol. It can dynamically assign IP addresses to DHCP clients and to allocate TCP/IP configuration information to DHCP clients. This includes default gateway IP addresses, subnet mask information and domain name system (DNS) addresses.

DHCP is a client-server protocol in which servers can manage a pool of unique IP addresses, as well as information about client configuration parameters, and assign addresses out of those address pools. DHCP-enabled clients send a request to the DHCP server whenever they connect to a network.

The clients configured with DHCP can broadcast a request for the DHCP server and request network configuration information for the local network to which they’re attached. The DHCP server can respond to the client request by providing IP configuration information previously specified by a network administrator. If an assignment is refreshed, DHCP client requests the same parameters, but the DHCP server may assign a new IP address based on policies set by administrators.

A DHCP server manages a record of all the IP addresses that are allocated to network nodes. If a node is relocated in the network, the server identifies it using its Media Access Control (MAC) address, which prevents accidentally configuring multiple devices with the same IP address.

DHCP is not a routable protocol and also not a secured one. It is limited to a specific local area network (LAN), which means a single DHCP server per LAN is adequate, or two servers for use in case of a failover. Larger networks may have a wide area network (WAN) for multiple individual locations. Multiple DHCP servers can be set up to handle the distribution of addresses which depends upon the connections between these points and the number of clients in each location. If a DHCP server is used by network administrators to provide addressing to multiple subnets on a given network, they must configure DHCP relay services located on interconnecting routers that DHCP requests have to cross. These agents relay messages between DHCP clients and servers located on different subnets.

DHCP lacks any built-in mechanism that would allow clients and servers to authenticate each other. Both are vulnerable to deception (one computer pretending to be another) and to attack, where rogue clients can exhaust a DHCP server’s IP address pool.

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