2 !== BROWSING-Config.txt for Samba release TNG-alpha 01 May 2000
5 Contributor: John H Terpstra <jht@samba.org>
7 Subject: Cross Subnet Browsing / Cross Workgroup Browsing
8 ===============================================================================
13 This document should be read in conjunction with BROWSING.txt and may
14 be taken as the fast track guide to implementing browsing across subnets
15 and / or across workgroups (or domains). WINS is the best tool for resolution
16 of NetBIOS names to IP addesses. WINS is NOT involved in browse list handling
17 except by way of name to address mapping.
23 Firstly, all MS Windows networking is based on SMB (Server Message
24 Block) based messaging. SMB messaging is implemented using NetBIOS. Samba
25 implements NetBIOS by encapsulating it over TCP/IP. MS Windows products can
26 do likewise. NetBIOS based networking uses broadcast messaging to affect
27 browse list management. When running NetBIOS over TCP/IP this uses UDP
28 based messaging. UDP messages can be broadcast or unicast.
30 Normally, only unicast UDP messaging can be forwarded by routers. The
31 "remote announce" parameter to smb.conf helps to project browse announcements
32 to remote network segments via unicast UDP. Similarly, the "remote browse sync"
33 parameter of smb.conf implements browse list collation using unicast UDP.
35 Secondly, in those networks where Samba is the only SMB server technology
36 wherever possible nmbd should be configured on one (1) machine as the WINS
37 server. This makes it easy to manage the browsing environment. If each network
38 segment is configured with it's own Samba WINS server, then the only way to
39 get cross segment browsing to work is by using the "remote announce" and
40 the "remote browse sync" parameters to your smb.conf file.
42 If only one WINS server is used then the use of the "remote announce" and the
43 "remote browse sync" parameters should NOT be necessary.
45 Samba WINS does not support MS-WINS replication. This means that when setting up
46 Samba as a WINS server there must only be one nmbd configured as a WINS server
47 on the network. Some sites have used multiple Samba WINS servers for redundancy
48 (one server per subnet) and then used "remote browse sync" and "remote announce"
49 to affect browse list collation across all segments. Note that this means
50 clients will only resolve local names, and must be configured to use DNS to
51 resolve names on other subnets in order to resolve the IP addresses of the
52 servers they can see on other subnets. This setup is not recommended, but is
53 mentioned as a practical consideration (ie: an 'if all else fails' scenario).
55 Lastly, take note that browse lists are a collection of unreliable broadcast
56 messages that are repeated at intervals of not more than 15 minutes. This means
57 that it will take time to establish a browse list and it can take up to 45
58 minutes to stabilise, particularly across network segments.
61 A) Use of the "Remote Announce" parameter
62 ------------------------------------------
63 The "remote announce" parameter of smb.conf can be used to forcibly ensure
64 that all the NetBIOS names on a network get announced to a remote network.
65 The syntax of the "remote announce" parameter is:
67 remote announce = a.b.c.d [e.f.g.h] ...
69 remote announce = a.b.c.d/WORKGROUP [e.f.g.h/WORKGROUP] ...
72 a.b.c.d: is either the LMB (Local Master Browser) IP address
73 e.f.g.h: or the broadcst address of the remote network.
74 ie: the LMB is at 192.168.1.10, or the address
75 could be given as 192.168.1.255 where the netmask
76 is assumed to be 24 bits (255.255.255.0).
77 When the remote announcement is made to the broadcast
78 address of the remote network every host will receive
79 our announcements. This is noisy and therefore
80 undesirable but may be necessary if we do NOT know
81 the IP address of the remote LMB.
83 WORKGROUP: is optional and can be either our own workgroup
84 or that of the remote network. If you use the
85 workgroup name of the remote network then our
86 NetBIOS machine names will end up looking like
87 they belong to that workgroup, this may cause
88 name resolution problems and should be avoided.
91 B) Use of the "Remote Browse Sync" parameter
92 --------------------------------------------
94 The "remote browse sync" parameter of smb.conf is used to announce to
95 another LMB that it must synchronise it's NetBIOS name list with our
96 Samba LMB. It works ONLY if the Samba server that has this option is
97 simultaneously the LMB on it's network segment.
99 The syntax of the "remote browse sync" parameter is:
101 remote browse sync = a.b.c.d
104 a.b.c.d: is either the IP address of the remote LMB or else
105 is the network broadcast address of the remote segment.
111 Use of WINS (either Samba WINS _or_ MS Windows NT Server WINS) is highly
112 recommended. Every NetBIOS machine registers it's name together with a
113 name_type value for each of of several types of service it has available.
114 eg: It registers it's name directly as a unique (the type 0x03) name.
115 It also registers it's name if it is running the lanmanager compatible
116 server service (used to make shares and printers available to other users)
117 by registering the server (the type 0x20) name.
119 All NetBIOS names are up to 15 characters in length. The name_type variable
120 is added to the end of the name - thus creating a 16 character name. Any
121 name that is shorter than 15 characters is padded with spaces to the 15th
122 character. ie: All NetBIOS names are 16 characters long (including the
123 name_type information).
125 WINS can store these 16 character names as they get registered. A client
126 that wants to log onto the network can ask the WINS server for a list
127 of all names that have registered the NetLogon service name_type. This saves
128 broadcast traffic and greatly expedites logon processing. Since broadcast
129 name resolution can not be used across network segments this type of
130 information can only be provided via WINS _or_ via statically configured
131 "lmhosts" files that must reside on all clients in the absence of WINS.
133 WINS also serves the purpose of forcing browse list synchronisation by all
134 LMB's. LMB's must synchronise their browse list with the DMB (domain master
135 browser) and WINS helps the LMB to identify it's DMB. By definition this
136 will work only within a single workgroup. Note that the domain master browser
137 has NOTHING to do with what is referred to as an MS Windows NT Domain. The
138 later is a reference to a security environment while the DMB refers to the
139 master controller for browse list information only.
141 Use of WINS will work correctly only if EVERY client TCP/IP protocol stack
142 has been configured to use the WINS server/s. Any client that has not been
143 configured to use the WINS server will continue to use only broadcast based
144 name registration so that WINS may NEVER get to know about it. In any case,
145 machines that have not registered with a WINS server will fail name to address
146 lookup attempts by other clients and will therefore cause workstation access
149 To configure Samba as a WINS server just add "wins support = yes" to the
150 smb.conf file [globals] section.
152 To configure Samba to register with a WINS server just add
153 "wins server = a.b.c.d" to your smb.conf file [globals] section.
155 DO NOT EVER use both "wins support = yes" together with "wins server = a.b.c.d"
156 particularly not using it's own IP address.
159 D) Do NOT use more than one (1) protocol on MS Windows machines
160 ---------------------------------------------------------------
162 A very common cause of browsing problems results from installing more than
163 one protocol on an MS Windows machine.
165 Every NetBIOS machine take part in a process of electing the LMB (and DMB)
166 every 15 minutes. A set of election criteria is used to determine the order
167 of precidence for winning this election process. A machine running Samba or
168 Windows NT will be biased so that the most suitable machine will predictably
169 win and thus retain it's role.
171 The election process is "fought out" so to speak over every NetBIOS network
172 interface. In the case of a Windows 9x machine that has both TCP/IP and IPX
173 installed and has NetBIOS enabled over both protocols the election will be
174 decided over both protocols. As often happens, if the Windows 9x machine is
175 the only one with both protocols then the LMB may be won on the NetBIOS
176 interface over the IPX protocol. Samba will then lose the LMB role as Windows
177 9x will insist it knows who the LMB is. Samba will then cease to function
178 as an LMB and thus browse list operation on all TCP/IP only machines will
181 The safest rule of all to follow it this - USE ONLY ONE PROTOCOL!
184 E) Name Resolution Order
185 ========================
187 Resolution of NetBIOS names to IP addresses can take place using a number
188 of methods. The only ones that can provide NetBIOS name_type information
191 LMHOSTS: is static and hard to maintain.
192 Broadcast: uses UDP and can not resolve names across
195 Alternative means of name resolution includes:
196 /etc/hosts: is static, hard to maintain, and lacks name_type info.
197 DNS: is a good choice but lacks essential name_type info.
199 Many sites want to restrict DNS lookups and want to avoid broadcast name
200 resolution traffic. The "name resolve order" parameter is of great help here.
201 The syntax of the "name resolve order" parameter is:
203 name resolve order = wins lmhosts bcast host
205 name resolve order = wins lmhosts (eliminates bcast and host)
208 name resolve order = host lmhost wins bcast
211 "host" refers the the native methods used by the Unix system
212 to implement the gethostbyname() function call. This is normally
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