Dynamic Host Configuration Protocol (Dhcp); Dhcp Packet Format And Options - Dell Force10 Z9000 Configuration Manual

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Dynamic Host Configuration Protocol (DHCP)

DHCP is an application layer protocol that dynamically assigns IP addresses and other configuration parameters to network end-

stations (hosts) based on configuration policies determined by network administrators.

DHCP relieves network administrators of manually configuring hosts, which can be a tedious and error-prone process when hosts

often join, leave, and change locations on the network and it reclaims IP addresses that are no longer in use to prevent address

DHCP is based on a client-server model. A host discovers the DHCP server and requests an IP address, and the server either leases

or permanently assigns one. There are three types of devices that are involved in DHCP negotiation:

This is a network device offering configuration parameters to the client.

This is a network device requesting configuration parameters from the server.

This is an intermediary network device that passes DHCP messages between the client and server when the

server is not on the same subnet as the host.

DHCP uses the user datagram protocol (UDP) as its transport protocol.

The server listens on port 67 and transmits to port 68; the client listens on port 68 and transmits to port 67. The configuration

parameters are carried as options in the DHCP packet in Type, Length, Value (TLV) format; many options are specified in RFC 2132.

To limit the number of parameters that servers must provide, hosts specify the parameters that they require, and the server sends

only those parameters. Some common options are shown in the following illustration.

Figure 27. DHCP packet Format

The following table lists common DHCP options.

Number and Description

Specifies the client's subnet mask.

Specifies the router IP addresses that may serve as the client's default gateway.

Dynamic Host Configuration Protocol (DHCP)