Hostname differences between servers

[Neufeld, Keith]

In the previous example, e8802ea2eb7f (an Apple device) is requesting
10.45.13.196. One server, landlord02, is erroneously stating that the
client hostname is android-9375f90cad51e32f. It turns out that, a few
days ago, landlord02 offered this IP address to an Android device with
the hostname of android-9375f90cad51e32f. Looking at the source code,
it appears that dhcpd is not reporting the hostname found in the
packet, but rather, the information collected from its lease file.

Norman, since we see the REQUEST relayed by your router, it’s a broadcast REQUEST.  I’m assuming this is part of the initial broadcast DISCOVER - OFFER - REQUEST - ACK sequence, and not a later REQUEST being broadcast?  (That can happen but only under special circumstances.)

I speculate that this happened:

1.  The client did a broadcast DISCOVER that was relayed to both servers.  Possibly both of them logged the correct client-hostname in their DISCOVER messages.
2.  Both servers sent OFFERs back toward the client via the relay.  landlord01’s OFFER was for 10.45.13.196 ; landlord02’s OFFER was for some other IP.
3.  The client decided to accept landlord01’s offer and broadcast a REQUEST for that offer.
4.  landlord01 received the REQUEST and logged it correctly.
5.  landlord02 received the REQUEST and, recognizing that it was in response to an OFFER made by its peer, logged it without inspecting the packet for current supplemental data, leaving in place the cached client-hostname from the last client to hold this lease (IP) when offered by landlord02.

That is to say, client-hostname tends to stay cached a long time, misleadingly, in the lease database of the peer of the server that’s handling the client currently holding that lease / IP.

That’s … more difficult to phrase than I expected it to be.  Perhaps there’s an easier way to describe it.

--
Keith Neufeld
Director of Networking, Telecommunications, and IT Security
Wichita State University

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