diff options
Diffstat (limited to 'docs-xml/Samba4-HOWTO/protocol.xml')
| -rw-r--r-- | docs-xml/Samba4-HOWTO/protocol.xml | 204 |
1 files changed, 204 insertions, 0 deletions
diff --git a/docs-xml/Samba4-HOWTO/protocol.xml b/docs-xml/Samba4-HOWTO/protocol.xml new file mode 100644 index 0000000000..f2961116e0 --- /dev/null +++ b/docs-xml/Samba4-HOWTO/protocol.xml @@ -0,0 +1,204 @@ +<chapter id="protocol"> + <title>The SMB/CIFS protocol</title> + + <!-- + Some parts shamelessly borrowed from myself. + Original on http://jelmer.vernstok.nl/publications/cifs-developments.pdf + --> + + <para> + "SMB" (also known as "CIFS") is a + file-sharing protocol that has been used since the mid-eighties. + Most people know SMB as the protocol behind the "Network Neighbourhood" + and remote printing in Windows. + </para> + + <para> + Several parts of the protocol are not discussed in this chapter, such + as mailslots, browsing and dfs, to prevent it from getting too complex. + CIFS internals are documented in detail in <citation>Hertel, 2003</citation>. + </para> + + + <sect1> + <title>History</title> + + <sect2> + <title>Invention by IBM</title> + + <para> + SMB is not very old, but it has a long history of modifications and extensions. + The original protocol was meant to run over ``NetBIOS'', which was the + name of the DOS interface to a very simple LAN system developed by IBM. + NetBIOS was developed because SNA, IBM's other main + protocol at the time, was much too advanced for use in DOS. + </para> + + <para> + The NetBIOS API in these days (early eighties) was nothing more then the + interface to a very simple link-layer protocol + over which several protocols, including SMB, were used. It could do reads and + writes to services on remote hosts, which were identified by case-insensitive + names, and discover all available hosts and services. + </para> + + <para> + Dr. Barry Feigenbau, an IBM employee, invented the core of the original SMB protocol, + which he initially named after himself: ``BAF''. He later changed the name to + be ``SMB'' (for ``Server Message Block''). Every packet in the protocol + starts with a byte $0xFF$ and these three letters. + </para> + + <para> + IBM, Microsoft, 3Com and Intel made up the rest of the initial protocol + together. The commands the protocol supported at this stage were basically + a mirror of the DOS File IO API calls, which meant the protocol wasn't very + efficient. The protocol also lacked authentication support. Everybody on the + network could do reads and writes, which meant this protocol + wasn't very suitable for large enterprises. + </para> + + <para> + NetBIOS is an API that has had various implementations; there is + NetBIOS over TCP/IP (NBT), NetBIOS over IPX, NetBIOS over SNA and + even NetBIOS over DECNEt. Mostly used these days is + NetBIOS over TCP (NBT). + </para> + + <para> + This is also were things are starting to get hairy. Since NetBIOS identifies + hosts by their name, NetBIOS clients had to start doing IP broadcasts to + figure out the IP of the host they had to connect to. Several schemes were + introduced to do name lookups crossing subnet boundaries, using name servers, + etc. We're basically emulating a NetBIOS LAN in order to be able to run SMB. + </para> + + <para> + Doing NetBIOS over IP is not very sane, however, the NBT implementation itself + in Windows isn't very nice either. It has horrible + limits, special exceptions, several broken schemes for looking up + names (including two kinds of name servers). NetBIOS and NetBIOS over TCP/IP + are described in RFC1001 and RFC1002. + </para> + </sect2> + + <sect2> + <title>The various incarnations of SMB</title> + + <para>Over the years, several usage models for SMB have been developed. While SMB originally started out as a file sharing protocol, it was later extended to include support for network management and other network services + as well.</para> + + <para> + One of the reasons for the various "upgrades" of the SMB + protocol is the fact that networks have become larger + and larger and with them the need for privilege separation + and scalability has increased. + </para> + + <sect3> + <title>DOS</title> + + <para> + The original model in which SMB was used was as a + simple file-sharing service in a NetBIOS-environment. + </para> + + <para> + File sharing worked basically by specifying a list of directories that had + to be shared and what name they had to be shared under ("shares"). Eventually, + one could password-protect a share. At most one password per share could be set. + </para> + </sect3> + + <sect3> + <title>Windows For Workgroups</title> + + <para> + After the ``CORE'' dialect, + IBM and Microsoft implemented a new dialect known as ``LANMAN''. + This dialect was used by Windows for + Workgroups, OS/2 and Windows 9x which all know it under a different name. A + 'virtual' file system was also added, which was used for doing remote function + calls (RAP, for ``Remote Administration Protocol''). + </para> + + <para> + Computers are grouped into "Workgroups" in this model. Everybody is equal to + the others and there is no central point of control. + </para> + </sect3> + + <sect3> + <title>Windows NT</title> + <para> + For Windows NT, yet another dialect was added, named 'NT'. The NT dialect + had it's own set of file I/O functions (similar to the NT File I/O API) + and it had support for yet another way of doing remote function calls: + DCE/RPC. RPC's are used for DCOM and several of the subsystems in NT + that can be accessed remotely (registry, printing, user management, logging + on, etc). + </para> + + <para> + Windows NT works with a new concept for grouping computers called ``domains''<footnote>In the protocol, domains are actually an upgraded version of a workgroup</footnote>. Each computer is member of exactly one domain. There are several roles a computer can have in the domain: PDC (primary domain controller, the "manager" of the domain, that coordinates all authentication and authorization), BDC (Backup domain controller, in case the PDC goes down) or just a regular domain member. The PDC decides who is to be a member of the domain. + </para> + </sect3> + + <sect3> + <title>Windows 2000</title> + <para> + In Windows NT 5 (marketing name: Windows 2000), NetBIOS-less SMB was + introduced. This means SMB is used directly over TCP port 445 instead of + via NetBIOS over TCP/IP. DNS + is used for looking up machine names. + </para> + + <para>Windows 2000 was also the first operating system from Microsoft + that had support for Active Directory. Active Directory is very + similar to the "domain" concept used by NT4, though it + is implemented differently (using modified open protocols), + and has some additional features (one of the most important ones being decentralized). + </para> + + <para> + Active directory no longer uses a central point of authority + and there are fewer limits to the size of a domain. Several + DC's can exist, so there is no longer a single point of + failure as well as better scalability. + </para> + </sect3> + </sect2> + + <sect2> + <title>Samba versions and their support for the SMB models</title> + + <sect3> + <title>Samba 2.2</title> + + <para>Full CORE and Workgroup support. Somewhat basic + NT4-style support.</para> + </sect3> + + <sect3> + <title>Samba 3.0</title> + + <para>Full CORE and Workgroup support. Almost complete + NT4-style support. + </para> + </sect3> + + <sect3> + <title>Samba 3.2</title> + + <para>FIXME</para> + </sect3> + + <sect3> + <title>Samba 4.0</title> + + <para>Full CORE, Workgroup, NT4 and ADS support.</para> + + </sect3> + </sect2> + </sect1> +</chapter> |