DHCP stands for Dynamic Host Configuration Protocol. At the most basic level, it dynamically assigns IP addresses to devices connected to your network. DHCP is essentially a protocol, i.e., it is a set of rules and instructions on how devices on a network will communicate.
- Setup a quick and easy DHCP server on Windows using dhcpd32. Decide what range of IP addresses you would like to use. You should use a 'Private IP Range', otherwise you may well have problems related to traffic to and from your network.
- DHCP or Dynamic Host Configuration Protocol works like this: for each session that a computer comes up on a network, it doesn't know its TCP/IP address, so it broadcasts to the entire segment its on once to say 'I need an ip address' which the DHCP server on its segment supplies. DHCP reduces the number of duplicate ip addresses on a network.
- The Dynamic Host Configuration Protocol (DHCP) is a network management protocol used on Internet Protocol (IP) networks for automatically assigning IP addresses and other communication parameters to devices connected to the network using a client–server architecture.
- The second type of computer is a server, which helps to process and send data for other computers. DHCP servers are those with several IP addresses stored and ready to assign to hosts when they join the network. Another key part of the DHCP name you need to understand is the word “Dynamic.”.
Dynamic Host Configuration Protocol (DHCP) is a standard protocol defined by RFC 1541 (which is superseded by RFC 2131) that allows a server to dynamically distribute IP addressing and configuration information to clients. Normally the DHCP server provides the client with at least this basic information:
Default GatewayOther information can be provided as well, such as Domain Name Service (DNS) server addresses and Windows Internet Name Service (WINS) server addresses. The system administrator configures the DHCP server with the options that are parsed out to the client.
The following Microsoft products provide DHCP client functionality:
Windows NT Server versions 3.5, 3.51, and 4.0
Windows NT Workstation versions 3.5, 3.51, and 4.0
Microsoft Network Client version 3.0 for MS-DOS
Microsoft LAN Manager Client version 2.2c for MS-DOS
Microsoft TCP/IP-32 for Windows for Workgroups versions 3.11, 3.11a, and 3.11b
Different DHCP clients support different options that they can receive from the DHCP server.
The following Microsoft server operating systems provide DHCP server functionality:
Windows NT Server version 3.5
Windows NT Server version 3.51
Windows NT Server version 4.0
When a client is initialized for the first time after it is configured to receive DHCP information, it initiates a conversation with the server.
Below is a summary table of the conversation between client and server, which is followed by a packet-level description of the process:
The detailed conversation between DHCP client and DHCP server is as follows:
The client sends a DHCPDISCOVER packet. The following is an excerpt from a network monitor capture showing the IP and DHCP portions of a DHCPDISCOVER packet. In the IP section, you can see the Destination address is 255.255.255.255 and the Source address is 0.0.0.0. The DHCP section identifies the packet as a Discover packet and identifies the client in two places using the physical address of the network card. Note the values in the CHADDR field and the DHCP: Client Identifier field are identical.
The DHCP server responds by sending a DHCPOFFER packet. In the IP section of the capture excerpt below, the Source address is now the DHCP server IP address, and the Destination address is the broadcast address 255.255.255.255. The DHCP section identifies the packet as an Offer. The YIADDR field is populated with the IP address the server is offering the client. Note the CHADDR field still contains the physical address of the requesting client. Also, we see in the DHCP Option Field section the various options being sent by the server along with the IP address. In this case the server is sending the Subnet Mask, Default Gateway (Router), Lease Time, WINS server address (NetBIOS Name Service), and the NetBIOS Node Type.
What Is My Dhcp Server
The client responds to the DHCPOFFER by sending a DHCPREQUEST. In the IP section of the capture below, the Source address of the client is still 0.0.0.0 and the Destination for the packet is still 255.255.255.255. The client retains 0.0.0.0 because the client hasn't received verification from the server that it's okay to start using the address offered. The Destination is still broadcast, because more than one DHCP server may have responded and may be holding a reservation for an Offer made to the client. This lets those other DHCP servers know they can release their offered addresses and return them to their available pools. The DHCP section identifies the packet as a Request and verifies the offered address using the DHCP: Requested Address field. The DHCP: Server Identifier field shows the IP address of the DHCP server offering the lease.
The DHCP server responds to the DHCPREQUEST with a DHCPACK, thus completing the initialization cycle. The Source address is the DHCP server IP address, and the Destination address is still 255.255.255.255. The YIADDR field contains the client's address, and the CHADDR and DHCP: Client Identifier fields are the physical address of the network card in the requesting client. The DHCP Option section identifies the packet as an ACK.
If the client has previously had a DHCP assigned IP address and it is restarted, the client will specifically request the previously leased IP address in a special DHCPREQUEST packet. The Source address is 0.0.0.0 and the Destination is the broadcast address 255.255.255.255. Microsoft clients will populate the DHCP Option Field DHCP: Requested Address with the previously assigned address. Strictly RFC compliant clients will populate the CIADDR Field with the address requested. The Microsoft DHCP server will accept either.
At this point, the server may or may not respond. The behavior of the Windows NT DHCP server depends on the version of the operating system being used as well as other factors such as superscoping. If the server determines that the client can still use the address, it will either remain silent or ACK the DHCPREQUEST. If the server determines that the client cannot have the address, it will send a NACK.
What Is My Dhcp Address
The client will then begin the discover process, but the DHCPDISCOVER packet will still attempt to lease the same address. In many instances, tth client will get the same address but may not.
DHCP information obtained by the client from a DHCP server will have a lease time associated with it. The lease time defines how long the client can use the DHCP-assigned information. When the lease reaches certain milestones, the client will attempt to renew its DHCP information.
To view IP information on a Windows or Windows for Workgroups client, use the IPCONFIG utility. If the client is Windows 95, use WINIPCFG.
What Is My Dhcp Server Hostname
Dhcp Server Ip Address
For more information about DHCP, see RFC1541 and RFC2131. RFCs may be obtained via the Internet at numerous sites, for example: http://www.rfc-editor.org/and http://www.tech-nic.qc.ca/