1 Subject: DHCP Server Configuration for SMB Clients
4 Contributor: John H Terpstra <jht@samba.org>
5 Support: This is an unsupported document. Refer to documentation that is
6 supplied with the ISC DHCP Server. Do NOT email the contributor
8 ===============================================================================
13 We wish to help those folks who wish to use the ISC DHCP Server and provide
14 sample configuration settings. Most operating systems today come ship with
15 the ISC DHCP Server. ISC DHCP is available from:
16 ftp://ftp.isc.org/isc/dhcp
18 Incorrect configuration of MS Windows clients (Windows9X, Windows ME, Windows
19 NT/2000) will lead to problems with browsing and with general network
20 operation. Windows 9X/ME users often report problems where the TCP/IP and related
21 network settings will inadvertantly become reset at machine start-up resulting
22 in loss of configuration settings. This results in increased maintenance
23 overheads as well as serious user frustration.
25 In recent times users on one mailing list incorrectly attributed the cause of
26 network operating problems to incorrect configuration of Samba.
28 One user insisted that the only way to provent Windows95 from periodically
29 performing a full system reset and hardware detection process on start-up was
30 to install the NetBEUI protocol in addition to TCP/IP. This assertion is not
33 In the first place, there is NO need for NetBEUI. All Microsoft Windows clients
34 natively run NetBIOS over TCP/IP, and that is the only protocol that is
35 recognised by Samba. Installation of NetBEUI and/or NetBIOS over IPX will
36 cause problems with browse list operation on most networks. Even Windows NT
37 networks experience these problems when incorrectly configured Windows95
38 systems share the same name space. It is important that only those protocols
39 that are strictly needed for site specific reasons should EVER be installed.
41 Secondly, and totally against common opinion, DHCP is NOT an evil design but is
42 an extension of the BOOTP protocol that has been in use in Unix environments
43 for many years without any of the melt-down problems that some sensationalists
44 would have us believe can be experienced with DHCP. In fact, DHCP in covered by
45 rfc1541 and is a very safe method of keeping an MS Windows desktop environment
46 under control and for ensuring stable network operation.
48 Please note that MS Windows systems as of MS Windows NT 3.1 and MS Windows 95
49 store all network configuration settings a registry. There are a few reports
50 from MS Windows network administrators that warrant mention here. It would appear
51 that when one sets certain MS TCP/IP protocol settings (either directly or via
52 DHCP) that these do get written to the registry. Even though a subsequent
53 change of setting may occur the old value may persist in the registry. This
54 has been known to create serious networking problems.
56 An example of this occurs when a manual TCP/IP environment is configured to
57 include a NetBIOS Scope. In this event, when the administrator then changes the
58 configuration of the MS TCP/IP protocol stack, without first deleting the
59 current settings, by simply checking the box to configure the MS TCP/IP stack
60 via DHCP then the NetBIOS Scope that is still persistent in the registry WILL be
61 applied to the resulting DHCP offered settings UNLESS the DHCP server also sets
62 a NetBIOS Scope. It may therefore be prudent to forcibly apply a NULL NetBIOS
63 Scope from your DHCP server. The can be done in the dhcpd.conf file with the
65 option netbios-scope "";
67 While it is true that the Microsoft DHCP server that comes with Windows NT
68 Server provides only a sub-set of rfc1533 functionality this is hardly an issue
69 in those sites that already have a large investment and commitment to Unix
70 systems and technologies. The current state of the art of the DHCP Server
71 specification in covered in rfc2132.
73 This document aims to provide enough background information so that the
74 majority of site can without too much hardship get the Internet Software
75 Consortium's (ISC) DHCP Server into operation. The key benefits of using DHCP
78 1) Automated IP Address space management and maximised re-use of available IP
81 2) Automated control of MS Windows client TCP/IP network configuration,
83 3) Automatic recovery from start-up and run-time problems with Windows95.
87 Client Configuration for SMB Networking:
88 ========================================
89 SMB network clients need to be configured so that all standard TCP/IP name to
90 address resolution works correctly. Once this has been achieved the SMB
91 environment provides additional tools and services that act as helper agents in
92 the translation of SMB (NetBIOS) names to their appropriate IP Addresses. One
93 such helper agent is the NetBIOS Name Server (NBNS) or as Microsoft called it
94 in their Windows NT Server implementation WINS (Windows Internet Name Server).
96 A client needs to be configured so that it has a unique Machine (Computer)
99 This can be done, but needs a few NT registry hacks and you need to be able to
100 speak UNICODE, which is of course no problem for a True Wizzard(tm) :)
101 Instructions on how to do this (including a small util for less capable
102 Wizzards) can be found at
104 http://www.unixtools.org/~nneul/sw/nt/dhcp-netbios-hostname.html
107 All remaining TCP/IP networking parameters can be assigned via DHCP. These include:
111 c) Gateway (Router) Address,
113 e) DNS Server addresses,
114 f) WINS (NBNS) Server addresses,
120 Other assignments can be made from a DHCP server too, but the above cover the
123 Note: IF ever an entry has has been made to the NetBIOS Scope field of the
124 TCP/IP configuration panel on an MS Windows machine, and it has then been
125 committed, then that setting may become persistent. In such a c ase it is better
126 to configure the DHCP server with a NetBIOS Scope consisting of an empty string
130 DHCP Server Installation:
131 =========================
132 It is assumed that you will have obtained a copy of the GPL'd ISC DHCP server
133 source files from ftp://ftp.isc.org/isc/dhcp, it is also assumed that you have
134 compiled the sources and have installed the binary files.
136 The following simply serves to provide sample configuration files to enable
137 dhcpd to operate. The sample files assume that your site is configured to use
138 private IP network address space using the Class B range of 172.16.1.0 -
139 172.16.1.255 and is using a netmask of 255.255.255.0 (ie:24 bits). It is
140 assumed that your router to the outside world is at 172.16.1.254 and that your
141 Internet Domain Name is bestnet.com.au. The IP Address range 172.16.1.100 to
142 172.16.1.240 has been set aside as your dynamically allocated range. In
143 addition, bestnet.com.au have two print servers that need to obtain settings
144 via BOOTP. The machine linux.bestnet.com.au has IP address 172.16.1.1 and is
145 you primary Samba server with WINS support enabled by adding the parameter to
146 the /etc/smb.conf file: [globals] wins support = yes. The dhcp lease time will
151 Before dhcpd will run you need to install a file that speifies the
152 configuration settings, and another that holds the database of issued IP
153 addresses. On many systems these are stored in the /etc directory on the Unix
156 Example /etc/dhcpd.conf:
157 ========================
158 server-identifier linux.bestnet.com.au;
160 subnet 172.16.1.0 netmask 255.255.255.0 {
161 range 172.16.1.100 172.16.1.240;
162 default-lease-time 72000;
163 max-lease-time 144000;
164 option subnet-mask 255.255.255.0;
165 option broadcast-address 172.16.1.255;
166 option routers 172.16.1.254;
167 option domain-name-servers 172.16.1.1, 172.16.1.2;
168 option domain-name "bestnet.com.au";
169 option time-offset 39600;
170 option ip-forwarding off;
171 option netbios-name-servers 172.16.0.1, 172.16.0.1;
172 option netbios-dd-server 172.16.0.1;
173 option netbios-node-type 8;
174 option netbios-scope "";
177 ; Note: The above netbios-scope is purposely an empty (NULL) string.
180 next-server 172.16.1.10;
181 option subnet-mask 255.255.255.0;
182 option domain-name "bestnet.com.au";
183 option domain-name-servers 172.16.1.1, 172.16.0.2;
184 option netbios-name-servers 172.16.0.1, 172.16.0.1;
185 option netbios-dd-server 172.16.0.1;
186 option netbios-node-type 8;
187 option netbios-scope "SomeCrazyScope";
188 option routers 172.16.1.240;
189 option time-offset 39600;
191 hardware ethernet 06:07:08:09:0a:0b;
192 fixed-address 172.16.1.245;
195 hardware ethernet 01:02:03:04:05:06;
196 fixed-address 172.16.1.242;
201 Creating the /etc/dhcpd.leases file:
202 ====================================
203 At a Unix shell create an empty dhcpd.leases file in the /etc directory.
204 You can do this by typing: cp /dev/null /etc/dhcpd.leases
207 Setting up a route table for all-ones addresses:
208 ================================================
209 Quoting from the README file that comes with the ISC DHCPD Server:
213 In order for dhcpd to work correctly with picky DHCP clients (e.g.,
214 Windows 95), it must be able to send packets with an IP destination
215 address of 255.255.255.255. Unfortunately, Linux insists on changing
216 255.255.255.255 into the local subnet broadcast address (here, that's
217 192.5.5.223). This results in a DHCP protocol violation, and while
218 many DHCP clients don't notice the problem, some (e.g., all Microsoft
219 DHCP clients) do. Clients that have this problem will appear not to
220 see DHCPOFFER messages from the server.
222 It is possible to work around this problem on some versions of Linux
223 by creating a host route from your network interface address to
224 255.255.255.255. The command you need to use to do this on Linux
225 varies from version to version. The easiest version is:
227 route add -host 255.255.255.255 dev eth0
229 On some older Linux systems, you will get an error if you try to do
230 this. On those systems, try adding the following entry to your
233 255.255.255.255 all-ones
237 route add -host all-ones dev eth0
240 For more information please refer to the ISC DHCPD Server documentation.