TCP/IP II

 

DHCP

(Dynamic Host Configuration Protocol). It assigns IP addresses to computers automatically so that clients do not have to configure TCP/IP settings. Each time a DHCP client starts, it requests IP addressing information from a DHCP server, including the IP address, the subnet mask, and optional values. The optional values may include a default gateway address, Domain Name Server (DNS) address, and NetBIOS name server address.

When a DHCP server receives a request, it selects IP addressing information from a pool of addresses defined in its database and offers it to the DHCP client. If the client accepts the offer, the IP addressing information is leased to the client for a specified period of time. If there is no available IP addressing information in the pool to lease to a client, the client cannot initialize TCP/IP.

 

DHCP Phase

  1. IP lease request - The client requests for the location of a DHCP server and IP addressing information
  2. IP lease offer - All DHCP servers that have valid IP addressing information sends an offer to clients
  3. IP lease selection - The client selects the IP address
  4. IP lease acknowledgment - The DHCP server that made the offer respends to the message, and all other DHCP servers withdraw their offers. The IP addressing information is assigned to the client and an acknowledgment is sent. The client finishes initializing and binding the TCP/IP protocol. Once the automatic configuration process is complete, the client can use all TCP/IP services and utilities for normal network communications and connectivity to other IP hosts.

 

IP lease Renewal

All DHCP clients attempt to renew their lease when 50 percent of the lease time has expired. To renew its lease, a DHCP client sends a DHCPREQUEST message directly to the DHCP server from which it obtained the lease.

If the DHCP server is available, it renews the lease and sends the client a successful acknowledgment (DHCPACK) with the new lease time and any updated configuration parameters.

 

IPCONFIG

Ipconfig /all - displays host name, IP address, MAC address, node type (hybrid, peer-to-peer, mixed), NetBIOS scope ID, IP routing status, WINS proxy status, NetBIOS resolution status.

Ipconfig /renew - sends DCHPREQUEST message to DHCP server to get updated lease.

Ipconfig /release - sends DCHPRELEASE message to the DHCP server and give up its lease.

 

DHCP Server Requirements

Windows NT Server with static IP address, DHCP scope created on the DHCP server, DHCP service.

 

DHCP Client Requirements

MS Windows NT Server, Workstation 4.0, 95, 98, Windows for Workgroup 3.11, Network Client 3.0 for MS-DOS, Lan Manager 2.2

 

DHCP Relay Agent

If routers separate your DHCP clients and servers, you can configure Windows NT Server to be a DHCP relay agent. A relay agent will intercept DHCP broadcasts and forward the packets to the DHCP server, crossing IP routers. You add Microsoft DHCP Relay Agent through the Control Panel Network program.

The DHCP relay agent is configured with the IP address of the computer running Windows NT Server DHCP so that the agent will know where to forward requests from clients for available IP addresses.

 

DHCP Database

The DHCP database is automatically backed up every 60 minutes. If the Windows NT Server detects a corrupted database, it automatically restores a backup copy. Backup copies are stored in the \systemroot\system32\dhcp\backup\jet directory.

Jetpack utility can be used for manual backing up of DHCP database although it's automatic.

 

NetBIOS over TCP/IP