Knowledgebase: DHCP
How can I ensure that DHCP always issues the same IP Address to one computer?
Posted by Gabriel Yu on 14 March 2008 05:47 AM

The most common reason for wanting to do this is where users have laptops which they use both at home and in the office. Both networks use different LAN IP Address ranges, and DHCP is used at both locations so the users don't have to keep manually changing their network connections. For most users this is sufficient and works well - but sometimes we want to give the user a fixed IP Address (e.g. for security or VoIP) and keep the convenience of DHCP.

Newer models/firmware have a LAN > Bind IP to MAC page which can achieve this.

The "ARP Table" list box on the left shows the IP Address and MAC address of currently connected computers; and the "IP Bind List" box on the right is the current list of IP-MAC bindings.

  • The easiest way to add a binding is to select PC in the ARP Table and click the [Add] button.
  • Alternatively you can enter IP Address and MAC address in the ADD and Edit fields then click [Add] button.
  • If you select one of the IP Bind List entries, its detail are displayed in the "Add and Edit" section. You can then click [Remove] button to delete the IP binding; or edit the details and click [Edit].


Older Vigor routers/firmware allow you to reserve LAN IP Addresses and allocate them via the DHCP server, but this must be done via the telnet command "srv dhcp fixip <IP Address> <MAC address> <host name>". For example "srv dhcp fixip add 192.168.1.111 00-11-22-33-44-55 test" reserves 192.168.1.111 for use by the computer with network card's MAC address of 00-11-22-33-44-55 and gives that machine a name of "test".

If using the Telnet interface, the list of DHCP-assigned IP Addresses (including the reserved addresses) is obtained by "srv dhcp status" command:

> srv dhcp status
DHCP server: Running
Default gateway: 192.168.124.7
Index IP Address MAC Address Leased Time HOST ID
1 192.168.124.7 00-50-7F-23-64-52 ROUTER IP
2 192.168.124.111 00-11-22-33-44-55 FIXED IP test

>


The same information is also available from the web interface, under "Diagnostic Tools > View DHCP Assigned IP Addresses", as shown here:

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