32.7. Adding and Editing Fixed Hosts
If you want to fix the IP address that is assigned to a specific host, you will need to add a host entry to the DHCP server configuration. This also allows you to set client options that apply only to that host, such as the DNS server addresses or default router.
The server identifies hosts by their MAC (Medium Access Control) address, which on an Ethernet LAN is the Ethernet address of the client's network card. Typically this address is fixed, but a few network cards allow it to be changed. On Linux systems, you can find the MAC address by running the ifconfig eth0 command as root and looking for a string of 6 bytes in hex separated by colons, like 00:D0:B7:1D:FB:A1. On Windows, the winipcfg program can provide the information, although it is displayed with dashes instead of colons. Other operating systems have their own ways of finding the Ethernet address.
Once you know the MAC address of the host, it can be added to the DHCP server configuration as follows:
1. | On the module's main page, click on the Add a new host link in the Hosts and Host Groups section. This will bring up the host creation form shown in Figure 32.5. Figure 32.5. Creating a new host.
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5. | If you want this host to inherit client options from a subnet, select Subnet from the menu in the Host assigned to field. The list next to it will be filled in with the names of all existing subnets, allowing you to select the one under which the host should be located. The fixed IP address must be within the subnet's network, however, and the client must be connected to its LAN. Hosts can also be created inside shared networks or host groups by choosing Shared Network or Group from the menu and selecting the appropriate entry from the list to the right. |
6. | If this host needs to network boot from a server, enter the name of that server into the Boot file server field. You must also fill in the Boot filename field with the path to an appropriate boot file (downloadable via TFTP) on the server. Generally, network booting is used by simple clients like X terminals and diskless workstations. For it to work, you must set up a TFTP server that contains the correct boot files for the client, which is not covered in this chapter. |
7. | Click the Create button at the bottom of the form, and you will be returned to the module's main page, which will now include an icon for the new host. |
8. | To edit the client options that are assigned to this host, click on its icon to go to its editing page, then on Edit Client Options. This is not always necessary if the host is a member of a subnet that already has these options set, or if they have been defined globally as explained in Section 32.6 “Editing Global Client Options”. |
9. | Fill in the form as you would for a subnet, as explained in Section 32.4 “Adding and Editing Subnets”. |
10. | Click the Save button to return to the host form. |
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Once a host has been created, you can change its fixed IP address, MAC address, and other options by clicking on its icon on the module's main page, which will take you to the host editing form. After making modifications, hit Save to update the server configuration and then Apply Changes to make them active. A host can also be deleted with the Delete button on the editing page. From then on, the client system will receive a dynamically allocated address from one of the ranges for its subnet rather than a fixed address.
A host can also be created by clicking on the Add a new host link on the subnet, shared network, or group editing page. If done this way, the Host assigned to field is no longer displayed on the creation form. Instead, the parent to which it will be added is shown at the top of the page. All the other steps in the process of adding the host are the same.
If you have a large number of hosts and want all of them to use the same client options, then they should be placed in a group or shared network. See the Section 32.9 “Adding and Editing Groups” for more information on group management. The DHCP server configuration allows you to define several levels of groups, which allows for quite complex configurations. If you have more than one fixed address host on your network, they definitely should be under a subnet or group to avoid duplicating settings.