TCP/IP Lean: Web Servers for Embedded Systems, Second Edition
Learn the "nuts and bolts" of programming for Web appliances with this in-depth guide.
TABLE OF CONTENTS TCP/IP Lean: Web Servers for Embedded Systems, Second Edition
Chapter 15: Dynamic Host Configuration Protocol: DHCP
Overview
So far, the microcontroller TCP/IP software has relied on its IP address being stored in the on-chip nonvolatile memory. This means that each system must be individually configured with the correct IP address, which can be highly inconvenient in large installations. What is needed is an autoconfiguration capability, which would obtain an IP address (and also the gateway address and subnet mask) automatically from a central server.
The standard way of achieving this is through the Dynamic Host Configuration Protocol (DHCP). It is still necessary to equip each network node with a unique six-byte Ethernet (MAC) address; otherwise, the nodes would be indistinguishable from each other. However, armed with this MAC address, a node can interrogate a DHCP server to obtain its IP address and other optional parameters.
DHCP Methodology
Although DHCP uses UDP as the basis for all its communications, it does make extensive use of broadcasts, in a fashion similar to ARP. Each network is assumed to have at least one DHCP server, which has a database containing the configuration information for the whole network.
When the client requests an IP address, it is not assigned permanently to that node but is issued in the form of a lease, which will expire after a specific time and have to be renewed. This allows a large number of nodes to share a smaller number of addresses, so long as the total number of nodes online doesn't exceed the limit at any one time The servers are intelligent...
Copyright Jeremy Bentham 2002 under license agreement with Books24x7
