DHCP Option 43 Messes with Hewlett Packard JetDirect Configuration

[Anonymous user]

I'm creating this post for the benefit of anyone else who might experience this same (yet extremely obscure) case, and stumble across it with a web search.

I had to configure an AP9617 recently, and so in order to avoid breaking out the old laptop that I keep around only because it has a serial port, I added the APC Vendor-Specific Cookie (Option 43) to my network's DHCP server. Figuring leaving the option in place wouldn't cause issues with other DHCP leases, I left Option 43 configured on the DHCP server, thinking that if I ever had to install subsequent 1st Gen NMCs, they'd "just work" without any additional tinkering.

However, I noticed today that one of the HP LaserJets on the network was reporting as Offline. A printout of the printer's configuration page revealed that the printer was receiving its reserved IP address as normal (192.168.1.216) and proper default gateway was set (192.168.1.1), but that the Subnet Mask was being set as 49.65.80.67 (see attached scan of config page) instead of the standard 255.255.255.0.

Rebooting the printer (which renews its DHCP lease) resulted in no change.

Removing the APC Vendor-Specific Cookie option from the DHCP server, and then rebooting the printer resolved the issue.

So after you've set Option 43 to gain access to an old-school APC NMC (and probably removed the vendor specific cookie requirement in its network settings), don't forget to remove the option from your DHCP server!

[BillP · Accepted solution]

Good find! Thanks for sharing with us.

[blair.bissett]

If you have a single subnet containg hardware from multiple vendors, and want/need to provide specific DHCP options depending on the device type that is asking, Microsoft DHCP Policy Based Assignment can be useful here.

Assuming you're using Microsoft DHCP servers, you can define a Vendor Class Identifier for APC devices on your DHCP server, then create a DHCP policy on your scope that references the APC VCI you created, with your end result being that only APC devices that are requesting an IP address from your DHCP server would actually be offered an Option 43 setting at all.

I also leverage this to "partition my scope," where I group certain device types together; printers at 192.168.1.11 - 30, workstations at 192.168.1.31 - 100, etc., etc.).

This could lead you down a DHCP rabbit hole, such as wanting to harvest VCIs from across your network (logs at C:\Windows\System32\DHCP are your friend, at least for devices that include Option 60 when they reach out to DHCP) and use NetMon to watch DHCP activity on your DHCP server to see what device PRLs look like for the different device on your network.