On-demand self assignment of an IP address in a non-DHCP environment
Original Publication Date: 2009-Jan-19
Included in the Prior Art Database: 2009-Jan-19
IP address self-assignment in a non-DHCP environment that avoids statically assigned IP addresses whether or not they are active.
On-demand self assignment of an IP address in a non -DHCP environment
Described here is a method that allows a device to assign itself an IP address. It does this by promiscuous-mode analysis of network traffic. In this manner, the device checks to see if the address it wants to self-assign is already in use. This part of the method is already described by a Cisco Systems* patent, (US 5854901) . However, the Cisco implementation treats a statically-assigned IP address as "available" if the device that owns that IP address is currently off the network, powered down for example. When the device with the statically assigned IP address powers up, it will cause a network conflict since 2 devices will be on the network with the same IP address.
What is needed is a method for a device to self-assign an IP address that does not conflict with other devices on the subnet even where there might be a statically assigned IP address that is not currently up and running. This method, in addition to using ARP (Address Resolution Protocol) as Cisco currently describes, would use DNS (Domain Name System) lookup (nslookup or BIND's PTR query) , which would not rely on the device owning the IP address to be up and running. Thus, this method is able to detect that the IP address is, although not active, assigned to another device and not one that should be used.