Managing DHCP servers

You can use the DHCP service to create DHCP subnets. Each subnet can have several dynamic and static IP ranges defined.

Dynamic ranges are used to provide the DHCP server with a pool of IP addresses in the DHCP subnet that it can dynamically allocate to requesting hosts.

Static assignments are used to allocate fixed IP addresses to nominated hosts. This is done by referencing the unique MAC address of the requesting host’s network interface card. This is used to make sure that certain hosts are always leased the same IP address, as if they were configured with a static IP address.

In addition to the manually adding static DHCP assignments, you can add static assignments automatically from MAC addresses detected in the ARP table.

Note: You need to perform further configuration so that the DHCP server can assign these settings to requesting hosts. You must add dynamic ranges and static assignments to the DHCP subnet so that the server knows the addresses it should allocate to the various network hosts.

Procedure

  1. On the SERVICES menu, under the DHCP submenu, click DHCP server.
    • Create a DHCP subnet:
      1. Under the DHCP subnet section, from the list, select "Empty", click Select and enter a meaningful Subnet name.
      2. Under the Settings section, enter the Network IP address that specifies the network ID of the subnet when combined with the network mask value entered in the Netmask box. For example: 192.168.10.0.
      3. To define the subnet range, enter a Netmask, for example, 255.255.255.0.
      4. Enter the value that a requesting network host will receive for the Primary DNS server it should use.
      5. Optionally, enter the value that a requesting network host will receive for the Secondary DNS server it should use.
      6. Enter the value that a requesting network host will receive for the Default gateway it should use.
      7. Optionally, click Advanced» to configure more network settings:
          1. Enter the value that a requesting network host will receive for the Primary WINS and Secondary WINS server it should use. Very small Microsoft Windows networks often don't need this.
          2. Enter the IP address of the Primary Network Time Protocol (NTP) and Secondary Network Time Protocol (NTP) server that the clients will use if they support this feature. Tip: Enter the Smoothwall’s IP address. Clients can use its time services if turned on.

        Tip: If turned on, clients can use the time services by entering the IP address of the Smoothwall Filter and Firewall.

        1. Enter the Default lease time in minutes assigned to network hosts that do not request a specific lease time. The default value is usually enough.
        2. Enter the Max lease time limit in minutes to prevent network hosts requesting, and being granted, impractically long DHCP leases. The default value is usually enough.
        3. Enter the Trivial File Transfer Protocol (TFTP) server that devices are to use from the network when starting up.
        4. Specify to the network client the Network boot filename to download off the selected TFTP server when starting up.
        5. Enter the Domain name suffix that is appended to the requesting host's hostname.
        6. Specify the Automatic proxy config URL that clients will use for determining proxy settings. It should reference a proxy auto-config (PAC) file and only some systems and web browsers support this feature.
        7. Any custom options that you have specified on the Custom options page appear here so that you can enter the value for the custom option.
    • Add a Dynamic DHCP Range:
      1. Choose an existing DHCP subnet from the DHCP subnet list and click Select.
      2. Under the Add a new dynamic range section, enter the Start address of an IP range over which the DHCP server should supply dynamic addresses from. This address range should not contain the IPs of other devices on your LAN with static IP assignments.
      3. Enter the End address of an IP range over which the DHCP server should supply dynamic addresses to. For example, enter 192.168.10.15. This address range should not contain the IPs of other devices on your LAN with static IP assignments.
      4. Enter a descriptive Comment of this dynamic range and click Add dynamic range.
    • Add a static DHCP assignment:
      1. Choose an existing DHCP subnet from the DHCP subnet list and click Select.
      2. Under the Add a new static assignment section, enter the MAC address of the network host’s NIC as reported by an appropriate network utility on the host system. This is entered as six pairs of hexadecimal numbers, with a space, colon or other separator character between each pair, for example, 12 34 56 78 9A BC or 12:34:56:78:9A:BC.
      3. Enter the IP address that the host should be assigned and a descriptive Comment for this static assignment.
    • Add a static DHCP assignment from the ARP table:
      1. Choose an existing DHCP subnet profile from the DHCP subnet list and click Select.
      2. Under the Add a new static assignment from ARP table section, select one or more MAC addresses from those listed and click Add static from ARP table.
      3. Click Save.
  2. Click Save.

Follow-up tasks

  • To delete or edit a server, from the DHCP Subnet list, select the subnet and click Select, either click Delete or edit the settings displayed in the Settings section and click Save.
  • To delete or edit a Dynamic DHCP range, from the DHCP Subnet list, select the subnet and click Select, under the Current dynamic ranges section, Mark the relevant range, and either click Remove dynamic range or edit the settings displayed in the Add a new dynamic range section and click Save.
  • To delete or edit a static assignment, from the DHCP Subnet list, select the subnet and click Select, from the Current static assignments section, Mark the relevant assignment, either click Remove static or click Edit static, edit the settings displayed in the Add a new static assignment section and click Save.