Discussion on the establishment process of DHCP server

When establishing a DHCP server, we must first understand the content of the DHCP protocol and BOOTP protocol. Next we will introduce the relevant content in detail. We hope that you will be able to understand the relevant content.

DHCP and BOOTP

DHCP is an extension of the Bootstrap Protocol (BOOTP) in the self-guided procedure. BOOTP (defined in RFC1532) is designed for two purposes: the client can request an IP address and other TCP/IP settings, the second is to make the diskless workstation request the location of the boot file information after obtaining the image through the TFTP protocol, so that the client can start from there. However, BOOTP does not support the concept of lease period. The hardware address of each client must be associated with an actual IP address.

Because windows supports DHCP but does not support BOOTP, there is no reason to use BOOTP in a windows-only environment. However, because windows NT supports DHCP, while DHCP is based on BOOTP, windows NT4.0ServicePack2 also supports BOOTP clients. This means that the DHCP server can respond to DHCP requests and BOOTP requests from UNIX clients or diskless workstations. This feature is useful in a hybrid environment where DHCP/BOOTP servers conflict with each other. With DHCP, windows can provide the BOOTP service for the remote subnet configured with the relay proxy. However, windows 2000 does not provide a configurable TFTP service for transferring startup image files.

This kind of support may seem a bit strange, but if you consider the use of the network service startup environment, this restriction does not seem so important, it certainly has no impact on the windows client. DHCP option or BOOTP option) is used to notify the BOOTP client to start the image file name and client. Windows 2000 DHCP ignores BOOTP requests unless at least one startup image file is configured in the BOOTP table. In addition, windows 2000 does not provide any information for BOOTP clients that do not have special request options.

Dynamic BOOTP extensions in windows 2000 reduce management by sharing IP addresses in the BOOTP scope. In the BOOTP scope, it is unnecessary to use a reserved client to link the hardware address and IP address together. Unless the BOOTP client does not support dynamic BOOTP or requires specific options. The BOOTP scope is created like a normal scope, but must be marked as a BOOTP request. The marked Method 15-13 is shown in the attributes in the scope.

Select "Both" or "BOOTPonly" on the "Advanced" tab of the dialog box. It is worth noting that all options on the DNS tab about using dynamic DNS update can be used by the BOOTP client.

To configure the Startup File, first change the default value in the "General" tab of the DHCP server attribute to make the "showtheBOOTPTableFolder check box selected, as shown in Figure 15-14.

1) Open the DHCP server management interface.

2) Click the server node, right-click the menu to select the server Properties dialog box.

3) on the General tab, select the "showtheBOOTPTableFolder" check box.

4) Click OK to close the Properties dialog box.

Because the server ignores the BOOTP request when the BOOTP table is empty, This is a necessary step. Then, you may select "NewBootImage" in the context menu of the BOOTP table node on the server console to provide boot image information. In response to the BOOTP request, the DHCP server returns the information in the table to the client.

1) Open the DHCP server management interface.

2) Expand the server node.

3) Click the BOOTP table node. If you cannot see the node, enable the BOOTP table in the server Properties dialog box.

4) The defined BOOTP image files are listed in the detail box on the right. In the context menu of the BOOTP table node, select "NewBootImage" to add an image file.

5) enter the TFTP server, the image file name, and the image path on the TFTP server, and then click "Add ".

BOOTP and DHCP packets are in almost the same format. By default, ports UDP67 and 68 are used on the server and client respectively. The response size of the BOOTP server is fixed, which may be smaller than the DHCP response, which means you must be cautious when configuring the return options for the scope that supports BOOTP. The BOOTP client does not have the lease concept. In traditional BOOTP, all BOOTP clients are reserved, so no leasing is not a problem. The windows 2000 DHCP server allows you to define a scope that provides the BOOTP service and dynamically allocate IP addresses. If dynamic BOOTP extensions are used, the DHCP server uses a method to test whether the IP address is not used after timeout to reclaim the IP address rented to the BOOTP client. BOOTP uses two-step exchange between the server and the client instead of four-step exchange, and there is no periodic update, but this has no impact.

To provide option information for each BOOTP client separately, you must retain the BOOTP client using the MAC address. This is also true for DHCP clients. Table 15-2 lists supported BOOTP client options. The BOOTP client must request the sending option, otherwise it will not receive any options.

Summary

Many people cannot or do not dare to use DHCP, because DHCP is generally not integrated with DNS in the early history of DHCP. Although Microsoft's earlier WINS solution allows DHCP, the instability of earlier WINS versions and the uniqueness of WINS make many people think that this solution is not a common solution.

This chapter explains that if Microsoft DHCP and DNS are used in combination and dynamic updates are allowed, computers on the network can dynamically obtain IP Address Allocation and still work under DNS without much management work. To use DHCP, consider the number and location of DHCP servers and the impact on DNS, such as the impact on cleanup. Then create and authorize the DHCP server, define and enable the scope and options, and configure the client as the DHCP client. When a certain DHCP Client exists, resetting the network configuration of the client is centrally managed by the transmitted DHCP options.