[WinMac] Mac DHCP client behaviour with NT4 DHCP Server Service
Daniel L. Schwartz(expresso[at]snip.net)
Wed, 14 Jul 1999 08:08:37 -0400
Good morning!
From <http://til.info.apple.com/techinfo.nsf/artnum/n58372>, I quote the
last paragraph:
TCP/IP Options (Mac OS 8.6)
---------------------------
For administrators who prefer the 8.1 DHCP client behavior, the TCP/IP
Options control panel will allow users to revert to the old behavior. By
checking the box for "don't retain DHCP lease on shutdown, " the Mac will
always start up with DHCPDISCOVER, and always send a DHCPRELEASE upon
unloading the IP stack.
DAN'S COMMENT:
--------------
This will fix the problem with MacOS 8.5 & 8.5.1's DHCP client and
NT4/Server DHCP Service. The problem was an improper Open Transport 2.0.1 &
2.0.2 startup in an INIT-REBOOT state
ENTIRE ARTICLE:
---------------
TITLE
Open Transport: DHCP Client Behavior Article ID:
Created:
Modified: 58372
5/12/99
5/12/99
---------------------------------------------------------------------------
TOPIC
This article describes the behavior of the DHCP client in different
versions of Open Transport.
---------------------------------------------------------------------------
DISCUSSION
In response to customer feedback, Apple has changed the DHCP client
implementation in MacOS 8.5, and again in MacOS 8.6. A given DHCP client
may behave in unexpected ways with certain DHCP servers. This document is
to aid in troubleshooting DHCP problems by providing a reference for the
expected behavior for each version of Open Transport and the MacOS.
For a complete description of the terms terms used below, and for a
description of the DHCP protocol, see RFC 2131.
Mac OS 8.1 and earlier (Open Transport 1.3.1 and earlier)
---------------------------------------------------------
IP Load
------
Every time the IP stack loads, the DHCP client sends out a DHCPDISCOVER
packet. If the Mac receives no response to this, IP will not load and any
application trying to use IP services will return an error.
Loading IP in this manner does not attempt to keep the same IP address
across reboots. Depending on the DHCP server configuration, the client may
receive a different IP address every time the IP stack loads.
IP Unload
---------
When the IP stack unloads, the DHCP client will send a DHCPRELEASE.
Mac OS 8.5.x (OpenTransport 2.0.1 & 2.0.2)
------------------------------------------
IP Load
-------
The DHCP client was modified in 8.5 so that the client would attempt to
regain the previously assigned IP address if the lease is still active when
the IP stack loads. This makes it much more likely that a machine will
retain the same IP address across reboots.
The IP stack can load in two different states in MacOS 8.5:
INIT
----
A client will start up in the INIT phase when (a) the previous lease has
expired when the client starts up, or (b) there is no previous lease
information (this is the first startup with DHCP, or the previous attempt
to load IP timed out). In the INIT state, the Mac will send out a
DHCPDISCOVER, requesting a lease from any DHCP server on the network.
If the Mac client receives no response to the DHCPDISCOVER after about a
16-20 second wait, DHCP will generate a randomly chosen in the range
169.254.0.0 to 169.254.254.255 inclusive and a subnet mask of 255.255.0.0.
There will be no DNS server or gateway address included with the temporary
configuration. The client will attempt to contact a DHCP server at 5 minute
intervals if this happens.
INIT-REBOOT
-----------
If the client's last assigned DHCP lease has not expired, then the client
starts up in the INIT-REBOOT state in an attempt to regain the most
recently used IP address. The Mac will broadcast a DHCPREQUEST asking to
use its last IP address.
The server should respond to a DHCPREQUEST in one of two ways:
1. Server sends the client DHCPACK, which tells the client that it may use
the requested IP address. In this case the client will proceed with a new
lease on the same IP address.
2. Server sends the client DHCPNACK, which tells the client that it may not
use the requested IP address. The client then moves to the INIT state and
sends out DHCPDISCOVER as noted above.
If the Mac begins in the INIT-REBOOT state and receives no response to its
DHCPREQUEST, this attempt to load the IP stack fails and the client will
not have IP services. The state of the client is changed so the next stack
load will start in the INIT state described above.
IP Unload
When the IP stack unloads, the DCHP client will send out a DHCPRELEASE.
This lets the the server know that the client no longer needs the IP
address and frees the server to allocate the address to another client.
Mac OS 8.6 (OpenTransport 2.0.3)
--------------------------------
IP Load
-------
The DHCP client behaves similarly to MacOS 8.5 in that IP initially loads
in the INIT state, and will load in the INIT-REBOOT state (sending out a
DHCPREQUEST) if its previously assigned lease has not expired. However,
unlike MacOS 8.5, if no DHCP server responds and INIT-REBOOT times out, the
machine will automatically revert to the INIT state, send out a
DHCPDISCOVER, and search for another DHCP server on the network.
If there is no response to the DHCPDISCOVER after a few tries, it will pick
a randomly generated IP address as in MacOS 8.5.
IP Unload
---------
When the IP stack unloads, the DHCP client will no longer send a DHCPRELEASE.
Furthermore, once a DHCP lease is obtained, the IP stack will not unload,
regardless of whether or not "Load Only When Needed" is checked (this is
not true for PPP links, since this wouldn't allow users to automatically
hang up after a specified period of idle time). The Mac will only unload
the IP stack if it is shutdown, restarted, or inactivated in the TCP/IP
control panel. In addition, the stack will unload on a PowerBook when it is
put to sleep. Otherwise, it will continue to renew the DHCP lease.
TCP/IP Options (Mac OS 8.6)
---------------------------
For administrators who prefer the 8.1 DHCP client behavior, the TCP/IP
Options control panel will allow users to revert to the old behavior. By
checking the box for "don't retain DHCP lease on shutdown, " the Mac will
always start up with DHCPDISCOVER, and always send a DHCPRELEASE upon
unloading the IP stack .
* Windows-MacOS Cooperation List *
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on Wed Jul 14 1999 - 05:57:05 PDT
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