FROM MSDN
DHCP Lease Process
A DHCP-enabled client obtains a lease for an IP address from a DHCP server. Before the lease expires, the DHCP server must renew the lease for the client or the client must obtain a new lease. Leases are retained in the DHCP server database approximately one day after expiration. This grace period protects a client's lease in case the client and server are in different time zones, their internal clocks are not synchronized, or the client is off the network when the lease expires.
The DHCP lease process is a process that occurs when a computer which is a DHCP client initially boots up on the network, to provide an IP address and any additional TCP/IP configuration parameters to these clients.
The terminology and concepts used when discussing DHCP leasing or the DHCP lease process is summarized below:
DHCP lease: This is the amount of time for which a DHCP client is allowed to make use of a specific IP addresses. The default setting for the DHCP lease is 8 days.
DHCP lease process: The process which occurs when the client initially boots up on the network. The DHCP lease process enables DHCP clients to automatically obtain IP addresses from a DHCP server.
DHCP Discovery Broadcast message: This is a message sent over the network by a client computer that wants to obtain an IP address from a DHCP server.
DHCP Offer message: This is message sent by DHCP servers that serves as a reply to a Discovery Broadcast message.
DHCP Request Broadcast message: This message indicates that the client accepted an IP address offer from the first DHCP server which responded to it. The client broadcasts this particular message so that all the other DHCP servers that offered addresses to the client can withdraw their IP addresses.
DHCP Acknowledge message: This message is sent by the DHCP server to the DHCP client, and is the process whereby which the IP address lease is assigned to the client.
Unlimited lease duration: If you do not want the IP address assigned for a particular client to expire, you assign an unlimited lease duration.
DHCP scopes: A scope can be defined as a set of IP addresses which the DHCP server can allocate or assign to DHCP clients. A scope contains specific configuration information for clients that have IP addresses which are within a particular scope. Scope information for each DHCP server is specific to that particular DHCP server only, and is not shared between DHCP servers. During the DHCP lease process, the DHCP scopes configured for a DHCP server is used to provide a DHCP client with an IP address.
You can configure different lease duration settings for each DHCP scope.
The lease duration rules which should be implemented when you determine the lease duration time for the scope of each of your subnets are:
Use a shorter lease duration time if you have numerous mobile users, and if you are working in an environment that constantly has configuration changes.
Use a longer lease duration time if the following statements are true:
There are no mobile computers
The environment does not continually experience configuration changes
Increase the default setting of 8 days if the number of IP addresses for each subnet is by far greater than the number of DHCP devices within your environment.
Use a shorter lease duration period if you have a limited number of IP addresses for each subnet, and you are near to meeting limit.
In a TCP/IP based network, to uniquely identify computers on the network, each computer must have a unique IP address. To communicate on the internet and private TCP/IP network, all hosts defined on the network must have IP addresses. The 32-bit IP address identifies a particular host on the network. With DHCP, the system assigns IP addresses to clients, which in turn leads to less incorrect configurations of IP addresses. This is mainly due to IP configuration information being entered at one location, and the server distributing this information to clients. Duplicated IP addresses are also prevented.
The DHCP lease process that occurs between the DHCP server and client is a simple process. The negotiation process for an IP address consists of four messages sent between the DHCP server and the DHCP client.
Two messages from the client
Two messages from the DHCP server
When the server assigns IP addresses to DHCP clients, it starts allocating addresses commencing from the bottom of its scope range, and starts moving to the top of its scope range.
All unused addresses have to be used before the DHCP server:
Allocates a previously used IP addresses to a new DHCP client. The DHCP server first assigns IP addresses that have not been used for the longest amount of time prior to assigning other previously used IP addresses.
Allocates an expired IP addresses to a new DHCP client
During the four-step DHCP lease process, the events that occur are defined by the types of DHCP messages which are exchanged between the DHCP server and DHCP client:
DHCPDISCOVER message: This message is used to request an IP address lease from a DHCP server. The message is sent when the client boots up on the network. The message is sent as a broadcast packet over the network, requesting for a DHCP server to respond to it
DHCPOFFER message: This message is a response to a DHCPDISCOVER message, and is sent by one or numerous DHCP servers.
DHCPREQUEST message: The client sends the initial DHCP server which responded to its request a DHCP Request message. The message basically indicates that the client is requesting the particular IP address for lease. The other DHCP servers who offered addresses withdraw those addresses at this point.
DHCPACK message: The DHCP Acknowledge message is sent by the DHCP server to the DHCP client and is the process whereby which the DHCP server assigns the IP address lease to the DHCP client.
The four steps involved in the DHCP lease process is often called DORA:
Discover
Offer
Request
Acknowledge
The client
The port 67 and port 68 are used by DHCP and the DHCP clients.
The use of a DHCP relay agent is an agent that relays DHCP between DHCP clients and DHCP servers on different IP networks. The DHCP relay agent is compliant with RFC 1542.
1. DHCP was designed to replace the older BOOTP 2. BOOTP can only provide an IP to a computer while it is booting while DHCP can provide an IP when the OS is already loaded 3. DHCP is primarily used to seamlessly provide IP addresses to computers while BOOTP is used to configure and boot diskless computers or thin clients 4. BOOTP has a 30 day lease on the IP address as a default while DHCP only sets 8 as a default 5. DHCP can automatically rebind or renew their leases while BOOTP requires a system restart
15
WIndows and non-Windows systems install DHCP in different ways, but the basic idea is the same group of steps:Add the DHCP service role to the systemActivate the serviceAdd the scope of IP addresses and exclusions to the DHCP serviceActivate the scopeOff you go - addresses!
The Dynamic Host Configuration Protocol (DHCP) lease process consists of four processes. The processes are 1. Discover 2. Offer 3. Request 4. Acknowledgment In the Discover process the DHCP client initiates the process by trying to discover any DHCP servers in the network. This discover packet is a broadcast packet.
D. You didn't list answers.
two
2
Those are the four phases of acquiring an IP address via DHCP. More information would be needed to indicate which of the 4 phases are being used at this point.
Router is usually configured as a DHCP client for WAN (Internet) network and as a DHCP server for local network.
DHCP stands for Dynamic Host Configuration Protocol
Terms you'll need to understand: * DHCP * Lease duration * Scopes * Superscopes * Multicast scopes * Scope options Techniques you'll need to master: * Installing DHCP * Understanding the DHCP lease process * Creating scopes, superscopes, and multicast scopes * Configuring the lease duration * Configuring optional IP parameters that can be assigned to DHCP clients * Understanding how DHCP interacts with DNS * Configuring DHCP for DNS integration * Authorizing a DHCP server in Active Directory * Managing a DHCP server * Monitoring a DHCP server The TCP/IP protocol is an Active Directory operational requirement. This means that all computers on a Windows 2000 network require a unique IP address to communicate with the Active Directory. Static IP addresses can add a lot of administrative overhead. Not only can management of static IP addresses become time consuming, but such management also increases the chances of misconfigured parameters. Imagine having to manually type 10,000 IP addresses and not make a single error. The Dynamic Host Configuration Protocol (DHCP) can be implemented to centralize the administration of IPaddresses. Through DHCP, many of the tasks associated with IP addressing can be automated. However, implementing DHCP also introduces some security issues because anyone with physical access to the network can plug in a laptop and obtain IP information about the internal network. In this chapter, you'll learn how to implement a DHCP server, including the installation process, authorization of the server, and the configuration of DHCP scopes. The chapter ends by looking at how to manage a DHCP server and monitor its performance.
hope this would help: http://www.tech-faq.com/dhcp-relay-agent.shtml
DHCPREQUEST
The client