Mobile Units Not Obtaining IP Addresses When Using DHCP

Article ID: 06528044

Symptom

Mobile Units Not Obtaining IP Addresses When Using DHCP Some Mobile Units do not get an IP address from a DHCP server, while other units on the same site do obtain an IP address.

Resolution

This situation typically arises in difficult RF environments where a Microsoft DHCP server is being used.  A Microsoft Windows DHCP server, by default, always sends DHCP responses as broadcast packets.  In addition to being needlessly delayed in the broadcast queue, a broadcast response is only ever transmitted once over the RF – it is never retried.  In difficult RF environments there exists a much higher probability of the MU missing the packet with undesirable consequences.

The Microsoft Windows DHCP server should be configured for unicast responses.  Details are provided in Microsoft Knowledge Base article number 161429 (formerly Q161429) entitled “Configuring a Microsoft Windows NT 4.0 DHCP Server for Unicast”.  

Note that this applies not only to NT 4.0 DHCP server but to later products as well and implementation will bring the DHCP server in line with the recommendations of RFC2131.