DHCP server and Mac OSX clients

[lavigj]

On our university network, we recently deployed a Fedora Core 4 based DHCP server for the student segment. We have run into a problem though with Mac clients running OSX - they don't receive an address via DHCP. Linux and Windows clients can receive a DHCP address just fine from this server, the issue is only with Macs.

Here's our DHCP version info:

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DHCP Version information: 

 

Installed Packages

Name   : dhcp

Arch   : i386

Version: 3.0.2

Release: 14.FC4

Size   : 1.3 M

Repo   : installed

Summary: A DHCP (Dynamic Host Configuration Protocol) server and relay agent.

 

Description:

 DHCP (Dynamic Host Configuration Protocol) is a protocol which allows

individual devices on an IP network to get their own network

configuration information (IP address, subnetmask, broadcast address,

etc.) from a DHCP server. The overall purpose of DHCP is to make it

easier to administer a large network. The dhcp package includes the

DHCP server and a DHCP relay agent.

 

You should install dhcp if you want to set up a DHCP server on your

network. You must also install the dhclient package, which provides the

DHCP client, on machines that will obtain their IP address via DHCP.

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What is puzzling is the behavior of the client.

When on the linux based network, it looks something like this:
[mac client] DHCP DISCOVER
[linux server] DHCP OFFER
[mc] nothing

When on the windows based network, it looks something like:
[mc] DHCP REQUEST
[ls] DHCP ACK
[mc] receives an IP via dhcp

It is possible I just missed the Discover/Offer sequence on the windows network, but I tried the packet capture a coupe times and just didn't see it. It is possible that it happens during the boot sequence, but I am not sure.

Has anyone experienced similar problems with Macs/DHCP before? Any input would be greatly appreciated.

[fsck]

I know nothing about the Mac, but I do know BSD which is nearly the same thing. First thing, the dhcp sequence is like this (simplified):

Client: Do I have an outstanding DHCP lease to renew? If yes, send DHCP-REQUEST together with old lease.
Server: DHCP server will ACK or NACK depending on availability of requested least (i.e. wrong IP range will get NACK)
Client: If NACK, or If no lease to renew, send DHCP-DISCOVER
Server: If allowed, send DHCP-OFFER, else NACK/IGNORE depending on config
Client: Compare OFFER with required settings and apply to interface if correct

So the windows machine already has a lease, asks to renew using REQUEST and gets ACK.
The Mac has no existing workable lease, so broadcasts with DISCOVER, gets an OFFER and nothing happens.
My guess would be that the Mac "require"s some DHCP options the server is not providing. Depending on the DHCP client, you need to find "dhclient.conf" and check the "require" line. Mine looks like this:

request subnet-mask, broadcast-address, time-offset, routers,
        domain-name, domain-name-servers, host-name;
require subnet-mask, domain-name-servers, routers;
(snip)

There are some other options in there, but I don't think they concern us here..
If you use dhcpcd instead, I think it's all on the command line, man dhcpcd will tell you what the options mean.

Then you need to either change the DHCP server to provide the required options (probably best) or change the clients so they no longer require things the server does not provide.

Any of that make sense? I hope so!

C.

[lavigj]

That makes sense. Thanks for the clarification on the DHCP sequence too. I was close, but no cigar.

I could not find the file dhclient on a mac running OSX 10.4.2.

This problem does appear to be limited to OSX 10.4.3 because a G5 running 10.4.2 was able to connect to the same* DHCP server just fine. I am going to try to get a 10.4.3 to connect in the same way.

*Note: I say the same version of the DHCP server, because it is the same version of the dhcp server, and the same dhcpd.conf, just put on my laptop for portable testing. In this case, it is more practical to take the server and a hub to the afflicted computers, than vice versa.