Windows Server Note (v): DHCP (1)

Configuring TCP/IP clients manually in addition to being a time-consuming chore, setting errors can also cause network communication failures. DHCP avoids these errors and provides many other advantages, including automatic assignment of the new address of the computer from one subnet to another, and automatic recycling when not in use.

The process of DHCP configuration:

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1. The DHCP client sends DHCP Discover packets to the DHCP server in the network by means of broadcast.

2. The DHCP server receives after the DHCP Discover packet, respond to a DHCP offer packet and give the IP address. TTL lease period and other related parameters;

3, the DHCP client will pick the first received IP address (multi-DHCP server), and broadcast the way to confirm the IP address;

4. The DHCP server responds to a DHCP client with a DHCP ACK packet, giving confirmation and completing the entire lease process.

DHCP Renewal:

● Each restart of a DHCP client sends a DHCP Request packet to the DHCP server, making a renewal request, if

DHCP corresponds, the client can continue to use the same IP address and has a new lease term.

when the lease is halfway (the lease time is typically 8 days), the DHCP client will provide the DHCP server that originally provided the IP address send out

DHCP Request Packet Extraction

A renewal request, if the DHCP server responds, the client obtains a new lease term. If the DHCP server does not

Response, the client cannot successfully renew the contract, but it still has half the time to continue using the original IP address.

When 87.5% is reached, the DHCP client updates the lease to all DHCP servers in the network.

If the client must stop using the current IP immediately after it expires, then the DHCP client begins a new DHCP lease process, attempting to

Lease a new IP address.

To manually update a lease:

If you need to update DHCP configuration information, you can use:

Ipconfig/release

Ipconfig/renew

DHCP defines three different IP allocation methods:

1. Dynamic allocation: The most common distribution method we usually use. The administrator delimits an address pool, andtheDHCP Server chooses an address from the address pool to assign to the client .

2, auto-assign (Automatic allocation) : dhcp The server will be permanently assigned to the same ip address.

3, Manual Assignment (Manual allocation):theDHCP server will be based on the pre-configured client MAC Address-based the IP Allocation table is assigned an address.

1and the2the difference is that if the clientAacquired in the first access networkIPaddress is10.0.0.1, then when the clientAaccessing this network again will also get10.0.0.1thisIPaddress.

In addition to IP addresses, DHCP can provide additional TCP/IP configuration for clients, including subnet masks, default gateways, and DNS.

Automatic Private IP Addressing (APIPA)

When Windows clients are unable to lease IP addresses to DHCP servers, they automatically create a dedicated IP address with a network number of 169.254.0.0/16 and use this IP address to communicate with other computers.

DHCP Server Licensing

If you install the DHCP server arbitrarily, and the leased address is set arbitrarily, when a client obtains an IP address to DHCP, it is likely to obtain an IP address from the DHCP server, then the client address may not be able to access the network properly, but also increase the administrative burden of the system administrator.

So when the DHCP server is installed, it is not immediately possible to assign IP to the client, it also requires authorization.

DHCP Server Licensing considerations:

1. AD DS Environment

2. Must be a member of Enterprise Admins group

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