Dynamic Host Configuration Protocol (DHCP) - Automatic Configuration Protocol
• Dynamic Host Configuration Protocol (DHCP) is an automatic configuration protocol used on IP networks.
• DHCP allows a computer to join an IP-based network without having a pre-configured IP address.
• DHCP is a protocol that assigns unique IP addresses to devices, then releases and renews these addresses as devices leave and re-join the network.
• If a computer is connected to a network, DHCP can provide it with all the necessary information for full system integration into the network,
• eg. Addresses of a DNS server and the default router, the subnet mask, the domain name, and an IP address,
• providing an IP address makes DHCP very attractive for mobile IP as a source of Care of address.
• DHCP client sends a request to the server (DHCPDISCOVER) in the example) to which the server responds.
• A client request using MAC broadcasts to reach all devices in the LAN
• The client broadcasts a DHCPDISCOVER into the subnet.
• There might be a rely to forward this broadcast.
• In this case shown, two servers receive this broadcast and determine the configuration they can offer to client
• Servers reply to the client’s request with DHCPOFFER and offer a list of configuration parameters.
• The client can now choose one of the configurations offered.
• The client in turn replies to the servers, accepting one of the configurations and rejecting the others using DHCPREQUEST.
• If the server receives a DHCP request with a rejection, it can free the reserved configuration for other possible clients.
• The server with the configuration accepted by the client now confirms the configuration with DHCPPACK.
• This completes the initialization phase.
• If the client leaves a subnet, it should release the configuration received by the server using DHCPRELEASE.
• Now the server can free the context stored for the client and offer the configuration again.
• In configuration, a client gets from a server is only leased for a certain amount of time,
• It has to be reconfirmed from time to time.
• Otherwise the server will free the configuration.
• This timeout of configuration helps in the case of crashed nodes or nodes moved away without releasing the context.
• DHCP is a good candidate for supporting the acquisition of care-of-addresses for mobile nodes.
• The same holds for all other parameters needed, such as addresses of the default router, DNS servers, the timeserver etc.
• A DHCP server should be located in the subnet of the access point of the mobile node, or atleast a DHCP relay should provide forwarding of the messages.
• RFC 3118 specifies authentication for DHCP messages so as to provide protection from malicious DHCP servers.
• Without authentication, a DHCP server cannot trust the mobile node and vice versa.
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