There are an increasing number of network attached devices, and trying to keep them organized gets to be challenging. Since different devices might require different IP configuration settings and statically configuring them isn’t realistic.
There are several approaches to deal with this.
One of the most popular is to create a VLAN just for those devices, the most common example is the typical voice VLAN where your VoIP sets are in its own VLAN, with its own DHCP scope and possible a specific quality of service configuration.
How to Capture DHCP and Determine Option 60
Presently there are all sorts of devices that you might want to define its own DHCP range, examples would be printers, webcams, various tablets or access points. I’ve also worked on a few issues where the vendor changed the DHCP Vendor Class Identifier (VCI) with a firmware upgrade, so this is a good technique to learn.
While working with a client, this topic came up and we needed to determine the device’s DHCP Vendor Class Identifier (VCI) or option 60. For those of you familiar with option 60, this paper will not cover the specific mechanics of this protocol, other related options (like 43) but to simply help you identify what value 60 your device is using.
The key here is to capture the device’s DHCP Discover packet. In most cases this will be a broadcast packet, so as long as you are in the same broadcast domain, or VLAN or subnet, you should be able to capture the packet.
In this video, I demonstrate how to capture DHCP and determine what the option 60 is.
Want to read more articles like this? Then subscribe to Garland’s blog and get my feed.
