2.5.3. DHCP Administrative Web Page

DHCP (Dynamic Host Configuration Protocol) allows you to control the network configuration of all your computers or devices from your IPCop machine. When a computer (or a device like a printer, pda, etc.) joins your network it will be given a valid IP address and its DNS and WINS configuration will be set from the IPCop machine. To use this feature new machines must be set to obtain their network configuration automatically.

Figure 2.27. DHCP settings

DHCP Server Web Page

You can choose if you want to provide this service to your Green network and/or your Blue network (if installed). Just tick the relevant box.

2.5.3.1. DHCP Server Parameters

The following DHCP parameters can be set from the web interface:

Enabled Check this box to enable the DHCP server for this interface.

IP Address/Netmask The IP Address of the network interface and it's Netmask are displayed here for reference.

Start Address (optional).  You can specify the lowest and highest addresses that the server will hand out to other requestors. If you have machines on your network that do not use DHCP, and have their IP addresses set manually, you should set the start and end address so that the server will not hand out any of these manual IPs.

You should also make sure that any addresses listed in the fixed lease section (see below) are also outside this range.

End Address (optional).  Specify the highest address you will handout (see above).

Note

To enable DHCP to provide fixed leases without handing out dynamic leases, leave both Start and End Address fields blank. However, if you provide a Start Address, you also have to provide an End Address, and vice versa.

Default lease time This can be left at its default value unless you need to specify your own value. The default lease time is the time interval IP address leases are good for. Before the lease time for an address expires your computers will request a renewal of their lease, specifying their current IP address. If DHCP parameters have been changed, when a lease renewal request is made the changes will be propagated. Generally, leases are renewed by the server.

Domain name suffix (optional).  There should not be a leading period in this box. Sets the domain name that the DHCP server will pass to the clients. If any host name cannot be resolved, the client will try again after appending the specified name to the original host name. Many ISP's DHCP servers set the default domain name to their network and tell customers to get to the web by entering “www” as the default home page on their browser. “www” is not a fully qualified domain name. But the software in your computer will append the domain name suffix supplied by the ISP's DHCP server to it, creating a FQDN for the web server. If you do not want your users to have to unlearn addresses like www, set the Domain name suffix identically to the one your ISP's DHCP server specifies.

Allow bootp clients Check this box to enable bootp Clients to obtain leases on this network interface. By default, IPCop's DHCP server ignores Bootstrap Protocol (BOOTP) request packets.

Primary DNS Specifies what the DHCP server should tell its clients to use for their Primary DNS server. Because IPCop runs a DNS proxy, you will probably want to leave the default alone so the Primary DNS server is set to the IPCop box's IP address. If you have your own DNS server then specify it here.

Secondary DNS (optional).  You can also specify a second DNS server which will be used if the primary is unavailable. This could be another DNS server on your network or that of your ISP.

Primary NTP Server (optional).  If you are using IPCop as an NTP Server, or want to pass the address of another NTP Server to devices on your network, you can put its IP address in this box. The DHCP server will pass this address to all clients when they get their network parameters.

Secondary NTP Server (optional).  If you have a second NTP Server address, put it in this box. The DHCP server will pass this address to all clients when they get their network parameters.

Primary WINS server address (optional).  If you are running a Windows network and have a Windows Naming Service (WINS) server, you can put its IP address in this box. The DHCP server will pass this address to all hosts when they get their network parameters.

Secondary WINS server address (optional).  If you have a second WINS Server, you can put its IP address in this box. The DHCP server will pass this address to all hosts when they get their network parameters.

When you press Save, the change is acted upon.

2.5.3.2. Fixed Leases

If you have machines whose IP addresses you would like to manage centrally, but require that they always get the same IP address, you can tell the DHCP server to assign a “static”, or “fixed”, IP address based on the MAC address of the network card in the machine, or the hostname of the machine.

This is different to using manual addresses as these machines will still contact the DHCP server to ask for their IP address and will take whatever we have configured for them.

Figure 2.28. Add a new fixed lease

Add a new fixed lease screenshot

You can specify the following fixed lease parameters:

Enabled Click on this check box to tell the DHCP server to hand out this fixed lease. If the entry is not enabled, it will be stored in IPCop's files, but the DHCP server will not issue this lease.

MAC Address The six octet/byte colon separated MAC address of the machine that will be given the fixed lease.

Warning

The format of the MAC address is xx:xx:xx:xx:xx:xx, not xx-xx-xx-xx-xx-xx, as some machines show, i.e. 00:e5:b0:00:02:d2

IP Address The fixed lease IP address that the DHCP server will always hand out for the associated MAC address. Do not use an address in the server's dynamic address range.

Hostname or FQDN (optional).  You can specify a hostname here that will always be allocated to a device with a particular hardware address. A hostname specified like this overrides any supplied by the DHCP client on the machine.

Alternatively, if you don't specify a hardware address the IP address will apply to any machine claiming that name.

Router IP Address (optional).  To set a default route for a fixed lease, add the IP Address here.

DNS Server (optional).  To inform a fixed lease client to use a particular DNS Server, add it's IP Address here.

Remark (optional).  If you want, you can include a string of text to identify the device using the fixed lease.

next-server (optional).  Some machines on your network may be thin clients that need to load a boot file from a network server. You can specify the server's address here if needed.

filename (optional).  Specify the boot file for this machine.

root-path (optional).  If the boot file is not in the default directory then specify the full path to it here.

2.5.3.3. Current fixed leases

The current fixed leases are displayed at the foot of this section, and they can be enabled/disabled, edited or deleted.

You can sort the display of the fixed leases by clicking on the underlined headings MAC Address or IP Address. Another click on the heading will reverse the sort order.

Figure 2.29. List of fixed leases

Fixed lease screenshot

To enable or disable an entry - click on the checkbox in the Action column for the particular item you want to enable or disable. The icon changes to an empty box when a fixed lease is disabled. Click on the checkbox to enable it again.

To edit a lease click on its Yellow Pencil icon. The entry's data will be displayed in the form above. Make your changes and click the Update button.

To delete an entry click on its Trash Can icon.

2.5.3.4. Current dynamic leases

If DHCP is enabled, this section lists the dynamic leases contained in the /var/run/dnsmasq/dnsmasq.leases file. The IP Address, MAC Address, hostname (if available) and lease expiry time of each record are shown, sorted by IP Address.

You can re-sort the display of dynamic leases by clicking on any of the four underlined column headings. A further click will reverse the sort order.

To hand one of the devices in the dynamic list a fixed lease, click the Add a new fixed lease icon at the right hand side of the table (the Green Pencil Plus symbol). This will move it to the Add a new fixed lease section above, and populate the fields for you, ready to select an IP Address.

Figure 2.30. Current dynamic leases

Current dynamic leases screenshot

2.5.3.5. Additional DHCP options

If you have any special parameters you want to distribute to your network via the DHCP server, then add them to the file /var/ipcop/dhcp/dnsmasq.local provided for user's use. After you have modified the file, restart the DHCP server via the web interface or restartdhcp so your changes propagate to the network.

Refer to the section on customizing dnsmasq.local for examples.

2.5.3.6. Error messages

An error message will appear at the top of the page if a mistake is found in the input data, after you press the Save button.