Dynamic Host Configuration Protocol (DHCP) is a protocol used by networked devices (clients) to obtain the information necessary for operation in an Internet Protocol network. This protocol reduces system administration workload, allowing devices to be added to the network with little or no manual intervention.
Applicability:
Dynamic Host Configuration Protocol is a way to manage network parameter assignment from a single DHCP server, or a group of DHCP servers arranged in a fault-tolerant manner. Even in small networks, Dynamic Host Configuration Protocol is useful because it can make it easy to add new machines to the local network.
DHCP is also recommended even in the case of servers whose addresses rarely change, so that if a server needs to be readdressed (RFC 2071), changes can be made in as few places as possible. For devices such as routers and firewalls that should not use DHCP, it can be useful to put Trivial File Transfer Protocol (TFTP) or SSH servers on the same machine that runs DHCP, which also serves to centralize administration.
DHCP can be used to assign addresses directly to servers and desktop machines, and, through a Point-to-Point Protocol (PPP) proxy, to dialup and broadband on-demand hosts, as well as for residential Network address translation (NAT) gateways.
History:
DHCP emerged as a standard-track protocol in October 1993 as defined in RFC 1531, succeeding the BOOTP. The next update, RFC 2131 released in 1997 is the current DHCP definition for IPv4 networks. The extensions of DHCP for IPv6 (DHCPv6) were published as RFC 3315.
Basic protocol operation:
The Dynamic Host Configuration Protocol (DHCP) automates the assignment of IP addresses, subnet masks, default gateway, and other IP parameters.
When a DHCP-configured client (be it a computer or any other network-aware device) connects to a network, the DHCP client sends a broadcast query requesting necessary information from a DHCP server. The DHCP server manages a pool of IP addresses and information about client configuration parameters such as the default gateway, the domain name, the DNS servers, other servers such as time servers, and so forth. Upon receipt of a valid request the server will assign the computer an IP address, a lease (the length of time for which the allocation is valid), and other IP configuration parameters, such as the subnet mask and the default gateway. The query is typically initiated immediately after booting and must be completed before the client can initiate IP-based communication with other hosts.
DHCP provides four modes for allocating IP addresses. The best-known mode is dynamic, in which the client is provided a "lease" on an IP address for a period of time. Depending on the stability of the network, this could range from hours (a wireless network at an airport) to months (for desktops in a wired lab). At any time before the lease expires, the DHCP client can request renewal of the lease on the current IP address. A properly-functioning client will use the renewal mechanism to maintain the same IP address throughout its connection to a single network, otherwise it may risk losing its lease while still connected, thus disrupting network connectivity while it renegotiates with the server for its original or a new IP address.
The other modes for allocation of IP addresses are automatic , in which the address is permanently assigned to a client, and manual, in which the address is selected by the client (manually by the user or any other means) and the DHCP protocol messages are used to inform the server that the address has been allocated.
The automatic and manual methods are generally used when finer-grained control over IP address is required (typical of tight firewall setups), although typically a firewall will allow access to the range of IP addresses that can be dynamically allocated by the DHCP server.
The process of address allocation is known as ROSA. Request, Offer, Send, Accept.
Reference Wikipedia.
Applicability:
Dynamic Host Configuration Protocol is a way to manage network parameter assignment from a single DHCP server, or a group of DHCP servers arranged in a fault-tolerant manner. Even in small networks, Dynamic Host Configuration Protocol is useful because it can make it easy to add new machines to the local network.
DHCP is also recommended even in the case of servers whose addresses rarely change, so that if a server needs to be readdressed (RFC 2071), changes can be made in as few places as possible. For devices such as routers and firewalls that should not use DHCP, it can be useful to put Trivial File Transfer Protocol (TFTP) or SSH servers on the same machine that runs DHCP, which also serves to centralize administration.
DHCP can be used to assign addresses directly to servers and desktop machines, and, through a Point-to-Point Protocol (PPP) proxy, to dialup and broadband on-demand hosts, as well as for residential Network address translation (NAT) gateways.
History:
DHCP emerged as a standard-track protocol in October 1993 as defined in RFC 1531, succeeding the BOOTP. The next update, RFC 2131 released in 1997 is the current DHCP definition for IPv4 networks. The extensions of DHCP for IPv6 (DHCPv6) were published as RFC 3315.
Basic protocol operation:
The Dynamic Host Configuration Protocol (DHCP) automates the assignment of IP addresses, subnet masks, default gateway, and other IP parameters.
When a DHCP-configured client (be it a computer or any other network-aware device) connects to a network, the DHCP client sends a broadcast query requesting necessary information from a DHCP server. The DHCP server manages a pool of IP addresses and information about client configuration parameters such as the default gateway, the domain name, the DNS servers, other servers such as time servers, and so forth. Upon receipt of a valid request the server will assign the computer an IP address, a lease (the length of time for which the allocation is valid), and other IP configuration parameters, such as the subnet mask and the default gateway. The query is typically initiated immediately after booting and must be completed before the client can initiate IP-based communication with other hosts.
DHCP provides four modes for allocating IP addresses. The best-known mode is dynamic, in which the client is provided a "lease" on an IP address for a period of time. Depending on the stability of the network, this could range from hours (a wireless network at an airport) to months (for desktops in a wired lab). At any time before the lease expires, the DHCP client can request renewal of the lease on the current IP address. A properly-functioning client will use the renewal mechanism to maintain the same IP address throughout its connection to a single network, otherwise it may risk losing its lease while still connected, thus disrupting network connectivity while it renegotiates with the server for its original or a new IP address.
The other modes for allocation of IP addresses are automatic , in which the address is permanently assigned to a client, and manual, in which the address is selected by the client (manually by the user or any other means) and the DHCP protocol messages are used to inform the server that the address has been allocated.
The automatic and manual methods are generally used when finer-grained control over IP address is required (typical of tight firewall setups), although typically a firewall will allow access to the range of IP addresses that can be dynamically allocated by the DHCP server.
The process of address allocation is known as ROSA. Request, Offer, Send, Accept.
Reference Wikipedia.
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