Data Networking/Spring 2015/GROUP4/DHCP

DHCP

Understanding the Protocol

Behavior of the protocol

Dynamic Host Configuration Protocol (DHCP) is a client/server protocol that automatically provides an Internet Protocol (IP) host with its IP address and other related configuration information such as the subnet mask and default gateway.With dynamic IP adressing,each time when a host a connected to the network will be addressed dynamically. This TCP/IP standard reduces the complexity and administrative overhead of managing network client IPv4 / IPv6 addresses and other configuration parameters.

Signaling

DHCP servers and DHCP clients communicate through a series of DHCP messages. To obtain a lease, the DHCP client initiates a conversation with a DHCP server using a series of these DHCP messages.

The common messages that can be sent between DHCP clients and servers are as follows:

DHCPDiscover Broadcast by a DHCP client when it first attempts to connect to the network. This message requests IP address information from a DHCP server.

DHCPOffer Broadcast by each DHCP server that receives the client DHCP Discover message and has an IP address configuration to offer to the client. The DHCPOffer message contains an unleased IP address and additional TCP/IP configuration information, such as the subnet mask and default gateway.

DHCPRequest Broadcast by a DHCP client after it selects a DHCPOffer. The DHCPRequest message contains the IP address from the DHCPOffer that it selected. If the client is renewing or rebinding to a previous lease, this packet might be unicast directly to the server.

DHCPAck Broadcast by a DHCP server to a DHCP client acknowledging the DHCPRequest message. Upon receipt of the DHCPAck, the client can use the leased IP address to participate in the TCP/IP network and complete its system startup. This message is typically broadcast, because the DHCP client does not officially have an IP address that it can use at this point.

DHCPNack, DHCPDecline, DHCPRelease and DHCPInform are the other common messages used by the server and client.