DHCP Failover Pairs and Option 61 Client Identifier
David A. Evans
Evans_David_A at cat.com
Tue Jan 31 22:08:33 UTC 2012
I have been fighting an issue with HP printers, DDNS and our ISC
based fail over pair. I'm throwing this out on the list to document the
symptoms as I was unable to find a similar problem documented on this list
or via google.
It turns out there is one (1) model of HP printer that ALL give
back the exact same, non-null, non-unique, option 61 Client Identifier.
This caused some confusion on the fail over pair as much of the fail over
communication is based on option 61 being unique. What we first saw was
a constant change in theses printers IP's when more than one is on the
same subnet, as some of the printers kept getting the short lease time
from the 'backup' DHCP server. We also saw some of the printers just drop
off the network all together. I'm pretty sure this was due to IP
conflicts.
Someone that better understands the fail over communication can
explain this but what caused us to have to figure this out is the DHCP
fail over pair started deleting the wrong DNS entries. I'm sure it has to
do with the fact that one lease was expiring with the non-unique client
identifier and when that was communicated to the other DHCP server in the
pair, it matched it to the wrong lease in its database and then sent off
the wrong DDNS removal message.
HP is now aware of the issue, however I have yet to hear back on a
fix for the printer's firmware.
So I'm seeing this with this config:
1. Non-unique Option 61 (root cause and what is broken)
2. ISC based fail over pair
3. Fail over pair set to do DDNS on behalf of the client
David A. Evans
Enterprise IP/DNS Management
Network Infrastructure Tools and Services
Evans_David_A at cat.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <https://lists.isc.org/pipermail/dhcp-users/attachments/20120131/5a10316f/attachment.html>
More information about the dhcp-users
mailing list