2 Replies Latest reply on Jul 17, 2012 1:24 PM by daniel.blackmon

    How to Setup a DHCP Pool to Avoid Conflicts with Windows XP Machines

    daniel.blackmon Employee

      As Bluesocket APs become more widely used with AOS devices, it may be necessary to adjust any DHCP pools assuming the AOS device is acting as the DHCP server for a network. Bluesocket APs look for DHCP Option 43 to provide a list of Bluesocket controllers. However, using Option 43 with the built-in DNS server field of the AOS DHCP configuration may result in Windows XP clients not receiving the DNS servers. While Microsoft has documented a hotfix ( Some DHCP Options are not recognized on a Windows XP SP3-based client computer when the DHCP server offer includes option 43), there are times when applying the hotfix to individual clients is not reasonable. For example, a wireless environment where the client devices are not controlled.

       

      If the Microsoft hotfix is not feasbile, the following the steps can be used avoid conflicts with Windows XP devices (assuming the DHCP pool is already configured).

       

      1. Remove the DNS servers from the DHCP pool.

      2. Remove Option 43 from the DHCP pool.

      3. Configure numbered options, in order, as needed.

       

      If this is a new setup, then start at Step 3.

       

      To illustrate this procedure, let's say your DNS servers are 10.10.0.30 and 10.10.0.5 such that the DHCP configuration presently resembles the following.

       

      !

      ip dhcp-server pool "192.168.168.0/24"

        network 192.168.168.0 255.255.255.0

        dns-server 10.10.0.30 10.10.0.5

        netbios-node-type h-node

        default-router 192.168.168.10

        option 43 ascii 10.10.0.69

      !

       

       

      In order to convert the DNS servers' IP addresses to a hex string, you will want to first convert to binary. This is optional, but definitely helps keep things in order. The IP addresses are 10.10.0.30 and 10.10.0.5 which in binary are 0000.1010.0000.1010.0000.0000.0001.1110 and 0000.1010.0000.1010.0000.0000.0000.0101 respectively. Notice the periods used to segment the IP addresses into groups of 4 binary digits (binary 1111 is equivalent to 15 or hex E). Simply convert these groups into hex. For example, the IP address 10.10.0.30 when converted to hex is 0A0A001E. Now convert 10.10.0.5 to hex and apprend this to the first DNS server; the entire string would look like 0A0A001E0A0A0005. The DHCP pool is shown below.

       

      !

      ip dhcp-server pool "192.168.168.0/24"

        network 192.168.168.0 255.255.255.0

        netbios-node-type h-node

        default-router 192.168.168.10

        option 6 hex 0A0A001E0A0A0005

        option 43 ascii 10.10.0.69

      !