View source for Server Message Block

{{Short description|Network communication protocol for providing shared access to resources}}
[[File:Map Network Drive.PNG|thumb|Map Network Drive dialog in Windows 10, connecting to a local SMB network drive]]
'''Server Message Block''' ('''SMB''') is a [[communication protocol]]<ref>{{cite web|url=https://msdn.microsoft.com/en-us/library/aa365233(VS.85).aspx|title=Microsoft SMB Protocol and CIFS Protocol Overview|publisher=[[Microsoft]]|date=October 22, 2009|access-date=April 10, 2019|archive-url=https://web.archive.org/web/20160802013033/https://msdn.microsoft.com/en-us/library/aa365233(vs.85).aspx|archive-date=August 2, 2016|url-status=live}}</ref> used to share files, [[Printer (computing)|printers]], [[serial port]]s, and miscellaneous communications between [[Node (networking)|nodes]] on a [[Computer network|network]]. On [[Windows]], the SMB implementation consists of two vaguely named [[Windows service]]s: "Server" (ID: <code>LanmanServer</code>) and "Workstation" (ID: <code>LanmanWorkstation</code>).<ref name=":0">{{Cite web |title=Lan Manager Networking Concepts |url=http://support.microsoft.com/kb/86899 |url-status=dead |archive-url=https://web.archive.org/web/20121230184225/http://support.microsoft.com/kb/86899 |archive-date=December 30, 2012 |access-date=September 18, 2014 |website=Support |publisher=Microsoft}}</ref> It uses [[NTLM]] or [[Kerberos (protocol)|Kerberos]] protocols for user authentication. It also provides an authenticated [[inter-process communication]] (IPC) mechanism.

SMB was originally developed in 1983 by Barry A. Feigenbaum at IBM<ref name="tridgemyths" /> to [[shared access|share access]] to [[Computer file|files]] and [[Printer (computing)|printers]] across a network of systems running [[IBM PC DOS]]. In 1987, [[Microsoft]] and [[3Com]] implemented SMB in [[LAN Manager]] for [[OS/2]], at which time SMB used the [[NetBIOS]] service atop the [[NetBIOS Frames]] protocol as its underlying transport. Later, Microsoft implemented SMB in [[Windows NT 3.1]] and has been updating it ever since, adapting it to work with newer underlying transports: [[TCP/IP]] and [[NetBIOS over TCP/IP|NetBT]]. SMB over [[QUIC]] was introduced in [[Windows Server 2022]]. 

In 1996, Microsoft published a version of SMB 1.0<ref name=":2" /> with minor modifications under the '''Common Internet File System''' ('''CIFS''' {{IPAc-en|s|ɪ|f|s}}) moniker. CIFS was compatible with even the earliest incarnation of SMB, including [[LAN Manager]]'s.<ref name=":2" /> It supports symbolic links, hard links, and larger file size, but none of the features of SMB 2.0 and later.<ref name=":2">{{cite web|date=18 July 2012|title=Common Internet File System|url=https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-2000-server/cc939973(v=technet.10)|website=Windows 2000 Web and Application Services Technical Overview|publisher=Microsoft|via=[[Microsoft Docs]]|access-date=30 January 2022|archive-date=30 January 2022|archive-url=https://web.archive.org/web/20220130134645/https://docs.microsoft.com/en-us/previous-versions/windows/it-pro/windows-2000-server/cc939973(v=technet.10)|url-status=live}}</ref><ref>{{cite web|last1=Coulter|first1=David|last2=Satran|first2=Michael|last3=Batchelor|first3=Drew|date=8 January 2021|title=Microsoft SMB Protocol and CIFS Protocol Overview|url=https://docs.microsoft.com/en-us/windows/win32/fileio/microsoft-smb-protocol-and-cifs-protocol-overview|website=Windows App Development|publisher=[[Microsoft]]|via=[[Microsoft Docs]]|access-date=30 January 2022|archive-date=28 January 2022|archive-url=https://web.archive.org/web/20220128051636/https://docs.microsoft.com/en-us/windows/win32/fileio/microsoft-smb-protocol-and-cifs-protocol-overview|url-status=live}}</ref> Microsoft's proposal, however, remained an [[Internet Draft]] and never achieved standard status.<ref name="IETF" /> Microsoft has since discontinued the CIFS moniker but continues developing SMB and publishing subsequent specifications. [[Samba (software)|Samba]] is a [[free software]] reimplementation of the SMB protocol and the Microsoft extensions to it.

== Features ==
Server Message Block (SMB) enables [[file sharing]], [[Print server|printer sharing]], network browsing, and [[inter-process communication]] (through [[Named pipe|named pipes]]) over a [[computer network]]. SMB serves as the basis for Microsoft's [[Distributed File System (Microsoft)|Distributed File System]] implementation.

SMB relies on the [[Transmission Control Protocol|TCP]] and [[Internet Protocol|IP]] protocols for transport. This combination allows file sharing over [[Internetworking|complex, interconnected networks]], including the public Internet. The SMB [[Client–server model|server component]] uses [[Transmission Control Protocol|TCP]] [[Port (computer networking)|port]] 445. SMB originally operated on [[NetBIOS]] over [[IEEE 802.2]] - [[NetBIOS Frames]] or NBF - and over [[IPX/SPX]], and later on [[NetBIOS over TCP/IP]] (NetBT), but Microsoft has since [[deprecated]] these protocols. On NetBT, the server component uses three TCP or [[User Datagram Protocol|UDP]] ports: 137 (NETBIOS Name Service), 138 (NETBIOS Datagram Service), and 139 (NETBIOS Session Service).

In Microsoft Windows, two [[Windows service]]s implement SMB. The "Server" service (ID: <code>LanmanServer</code>) is in charge of serving [[shared resource]]s. The "Workstation" service (ID: <code>LanmanWorkstation</code>) maintains the computer name and helps access shared resources on other computers.<ref name=":0" /> SMB uses the [[Kerberos (protocol)|Kerberos]] protocol to authenticate users against [[Active Directory]] on [[Windows domain]] networks. On simpler, peer-to-peer networks, SMB uses the [[NTLM]] protocol.

[[Windows NT 4.0|Windows NT 4.0 SP3]] and later can [[Digital signature|digitally sign]] SMB messages to prevent some [[man-in-the-middle attack]]s.<ref>{{cite web|date=24 November 2021|title=Overview of Server Message Block signing|url=https://docs.microsoft.com/en-US/troubleshoot/windows-server/networking/overview-server-message-block-signing|website=Windows Server troubleshooting|publisher=[[Microsoft]]|via=[[Microsoft Docs]]|access-date=29 January 2022|archive-date=29 January 2022|archive-url=https://web.archive.org/web/20220129191652/https://docs.microsoft.com/en-US/troubleshoot/windows-server/networking/overview-server-message-block-signing|url-status=live}}</ref><ref name=":1">{{cite web|author=Johansson|first=Jesper M.|date=20 May 2005|title=How to Shoot Yourself in the Foot with Security, Part 1|url=https://docs.microsoft.com/en-us/previous-versions/tn-archive/cc512612(v=technet.10)|website=Security Guidance|publisher=[[Microsoft]]|via=[[Microsoft Docs]]|quote=This article addresses [...] Server Message Block (SMB) message signing.|access-date=19 October 2018|archive-date=19 October 2018|archive-url=https://web.archive.org/web/20181019041254/https://docs.microsoft.com/en-us/previous-versions/tn-archive/cc512612(v=technet.10)|url-status=live}}</ref><ref>{{cite web|author=Barreto|first=Jose|date=1 December 2010|title=The Basics of SMB Signing (covering both SMB1 and SMB2)|url=https://docs.microsoft.com/en-us/archive/blogs/josebda/the-basics-of-smb-signing-covering-both-smb1-and-smb2|url-status=live|archive-url=https://web.archive.org/web/20121202155239/http://blogs.technet.com/b/josebda/archive/2010/12/01/the-basics-of-smb-signing-covering-both-smb1-and-smb2.aspx|archive-date=2 December 2012|website=Jose Barreto's Blog Archive|publisher=[[Microsoft]]|via=[[Microsoft Docs]]|quote=This security mechanism in the SMB protocol helps avoid issues like tampering of packets and "man in the middle" attacks. [...] SMB signing is available in all currently supported versions of Windows, but it’s only enabled by default on Domain Controllers. This is recommended for Domain Controllers because SMB is the protocol used by clients to download Group Policy information. SMB signing provides a way to ensure that the client is receiving genuine Group Policy.}}</ref> SMB signing may be configured individually for incoming SMB connections (by the "LanmanServer" service) and outgoing SMB connections (by the "LanmanWorkstation" service). The default setting for Windows [[domain controller]]s running [[Windows Server 2003]] and later is to not allow unsigned incoming connections.<ref>{{cite web | url = http://support.microsoft.com/kb/887429 | title = MSKB887429: Overview of Server Message Block signing | publisher = [[Microsoft]] | date = November 30, 2007 | quote = By default, SMB signing is required for incoming SMB sessions on Windows Server 2003-based domain controllers. | access-date = October 24, 2012 | archive-url = https://web.archive.org/web/20101120173639/http://support.microsoft.com/kb/887429 | archive-date = November 20, 2010 | url-status = live }}</ref> As such, earlier versions of Windows that do not support SMB signing from the get-go (including [[Windows 9x]]) cannot connect to a Windows Server 2003 domain controller.<ref name=":1" />

SMB supports opportunistic locking (see below) on files in order to improve performance. Opportunistic locking support has changed with each Windows Server release.

=== Opportunistic locking ===
In the SMB protocol, opportunistic locking is a mechanism designed to improve performance by controlling [[cache (computing)|caching]] of network files by the client.<ref>{{cite web|date=May 31, 2018|title=Opportunistic Locks|url=https://docs.microsoft.com/en-us/windows/win32/fileio/opportunistic-locks|access-date=August 19, 2021|publisher=Microsoft|archive-date=August 19, 2021|archive-url=https://web.archive.org/web/20210819174457/https://docs.microsoft.com/en-us/windows/win32/fileio/opportunistic-locks|url-status=live}}</ref> Unlike traditional [[Lock (computer science)|locks]], opportunistic lock (OpLocks) are not strictly [[file locking]] or used to provide mutual exclusion.

There are four types of opportunistic locks.

; Batch Locks: Batch OpLocks were created originally to support a particular behavior of DOS batch file execution operation in which the file is opened and closed many times in a short period, which is a performance problem. To solve this, a client may ask for an OpLock of type "batch". In this case, the client delays sending the close request and if a subsequent open request is given, the two requests cancel each other.<ref name="Sphere2014">{{cite web|year=2014|title=All About Opportunistic Locking|url=https://sphereit.uk/all-about-opportunistic-locks/|access-date=August 19, 2021|website=Sphere IT|archive-date=August 19, 2021|archive-url=https://web.archive.org/web/20210819154425/https://sphereit.uk/all-about-opportunistic-locks/|url-status=live}}</ref>
; Level-1 OpLocks / Exclusive Locks: When an application opens in "shared mode" a file hosted on an SMB server which is not opened by any other process (or other clients) the client receives an '''exclusive OpLock''' from the server. This means that the client may now assume that it is the only process with access to this particular file, and the client may now cache all changes to the file before committing it to the server. This is a performance improvement, since fewer round-trips are required in order to read and write to the file. If another client/process tries to open the same file, the server sends a message to the client (called a ''break'' or ''revocation'') which invalidates the exclusive lock previously given to the client. The client then flushes all changes to the file.
; Level-2 OpLocks: If an exclusive OpLock is held by a client and a locked file is opened by a third party, the client has to relinquish its exclusive OpLock to allow the other client's write/read access. A client may then receive a "Level&nbsp;2 OpLock" from the server. A Level&nbsp;2 OpLock allows the caching of read requests but excludes write caching.
; Filter OpLocks: Added in Windows NT 4.0, Filter Oplocks are similar to Level&nbsp;2 OpLocks but prevent sharing-mode violations between file open and lock reception. Microsoft advises use of Filter OpLocks only where it is important to allow multiple readers and Level&nbsp;2 OpLocks in other circumstances. Clients holding an OpLock do not really hold a lock on the file, instead they are notified via a ''break'' when another client wants to access the file in a way inconsistent with their lock. The other client's request is held up while the break is being processed.
; Breaks: In contrast with the SMB protocol's "standard" behavior, a break request may be sent ''from'' server ''to'' client. It informs the client that an OpLock is no longer valid. This happens, for example, when another client wishes to open a file in a way that invalidates the OpLock. The first client is then sent an OpLock break and required to send all its local changes (in case of batch or exclusive OpLocks), if any, and acknowledge the OpLock break. Upon this acknowledgment the server can reply to the second client in a consistent manner.

=== Performance ===
The use of the SMB protocol has often correlated with a significant increase in [[broadcast traffic]] on a network. However the SMB itself does not use broadcasts—the broadcast problems commonly associated with SMB actually originate with the [[NetBIOS]] service location protocol.{{clarify|reason=Does this refer to service location via name resolution or via the browser protocol?|date=March 2013}} By default, a [[Microsoft Windows NT 4.0]] server used NetBIOS to advertise and locate services. NetBIOS functions by broadcasting services available on a particular host at regular intervals. While this usually makes for an acceptable default in a network with a smaller number of hosts, increased broadcast traffic can cause problems as the number of hosts on the network increases. The implementation of name resolution infrastructure in the form of [[Windows Internet Naming Service]] (WINS) or [[Domain Name System]] (DNS) resolves this problem. WINS was a proprietary implementation used with Windows NT 4.0 networks, but brought about its own issues and complexities in the design and maintenance of a Microsoft network.

Since the release of Windows 2000, the use of WINS for name resolution has been deprecated by Microsoft, with hierarchical [[Dynamic DNS]] now configured as the default name resolution protocol for all Windows operating systems. Resolution of (short) NetBIOS names by DNS requires that a DNS client expand short names, usually by appending a connection-specific DNS suffix to its DNS lookup queries. WINS can still be configured on clients as a secondary name resolution protocol for interoperability with legacy Windows environments and applications. Further, Microsoft DNS servers can forward name resolution requests to legacy WINS servers in order to support name resolution integration with legacy (pre-Windows 2000) environments that do not support DNS.

[[Network planning and design|Network designers]] have found that [[Network latency|latency]] has a significant impact on the performance of the SMB 1.0 protocol, that it performs more poorly than other protocols like [[File Transfer Protocol|FTP]]. Monitoring reveals a high degree of "chattiness" and a disregard of network latency between hosts.<ref name="barreto">{{cite web|author=Jose Barreto|date=December 9, 2008|title=SMB2, a Complete Redesign of the Main Remote File Protocol for Windows|url=http://blogs.technet.com/josebda/archive/2008/12/05/smb2-a-complete-redesign-of-the-main-remote-file-protocol-for-windows.aspx|access-date=November 1, 2009|publisher=[[Microsoft]] Server & Management Blogs|url-status=dead|archive-url=https://web.archive.org/web/20130112180513/http://blogs.technet.com/b/josebda/archive/2008/12/05/smb2-a-complete-redesign-of-the-main-remote-file-protocol-for-windows.aspx|archive-date=January 12, 2013}}</ref> For example, a [[Virtual private network|VPN]] connection over the [[Internet]] will often introduce network latency. Microsoft has explained that performance issues come about primarily because SMB 1.0 is a block-level rather than a [[Streaming algorithm|streaming]] protocol, that was originally designed for small [[local area network|LANs]]; it has a block size that is limited to 64K, SMB signing creates an additional overhead and the [[TCP tuning|TCP window size]] is not optimized for WAN links.<ref>{{cite web|author=Neil Carpenter|date=October 26, 2004|title=SMB/CIFS Performance Over WAN Links|url=https://docs.microsoft.com/en-us/archive/blogs/neilcar/smbcifs-performance-over-wan-links|url-status=live|archive-url=https://web.archive.org/web/20200213113816/https://docs.microsoft.com/en-us/archive/blogs/neilcar/smbcifs-performance-over-wan-links|archive-date=February 13, 2020|access-date=February 13, 2020|publisher=[[Microsoft]]}}</ref> Solutions to this problem include the updated SMB 2.0 protocol,<ref>{{cite web|title=What's New in SMB in Windows Server|url=https://technet.microsoft.com/en-us/library/hh831474(v=ws.11).aspx|url-status=live|archive-url=https://web.archive.org/web/20170211075409/https://technet.microsoft.com/en-us/library/hh831474(v=ws.11).aspx|archive-date=February 11, 2017|access-date=6 February 2017|website=Microsoft| date=31 August 2016 }}</ref> [[Offline Files]], [[TCP window scale option|TCP window scaling]] and [[WAN optimization]] devices from various network vendors that cache and optimize SMB 1.0<ref>{{cite web|author=Mark Rabinovich, Igor Gokhman|title=CIFS Acceleration Techniques|url=https://www.snia.org/sites/default/orig/sdc_archives/2009_presentations/monday/MarkRabinovich-IgorGokhman-CIFS_Acceleration_Techniques.pdf|access-date=July 6, 2020|publisher=Storage Developer Conference, SNIA, Santa Clara 2009|archive-date=September 30, 2020|archive-url=https://web.archive.org/web/20200930145453/https://www.snia.org/sites/default/orig/sdc_archives/2009_presentations/monday/MarkRabinovich-IgorGokhman-CIFS_Acceleration_Techniques.pdf|url-status=live}}</ref> and 2.0.<ref>{{cite web|author=Mark Rabinovich|title=Accelerating SMB2|url=https://www.snia.org/sites/default/orig/SDC2011/presentations/wednesday/MarkRabinovichAccelerating_SMB2.pdf|access-date=July 6, 2020|publisher=Storage Developer Conference, SNIA, Santa Clara 2011|archive-date=May 31, 2024|archive-url=https://web.archive.org/web/20240531142910/https://www.snia.org/sites/default/orig/SDC2011/presentations/wednesday/MarkRabinovichAccelerating_SMB2.pdf|url-status=live}}</ref>

== History ==

=== SMB 1.0 ===
Barry Feigenbaum originally designed SMB at [[IBM]] in early 1983 with the aim of turning [[DOS]] [[INT 21h]] local file access into a networked file system.<ref name='tridgemyths'>{{cite web|url=https://www.samba.org/samba/docs/myths_about_samba.html|title=Myths About Samba|author=Tridgell, Andrew|author-link=Andrew Tridgell|access-date=January 3, 2016|archive-url=https://web.archive.org/web/20171020045502/https://www.samba.org/samba/docs/myths_about_samba.html|archive-date=October 20, 2017|url-status=live}}</ref> [[Microsoft]] made considerable modifications to the most commonly used version and included SMB support in the [[LAN Manager]] operating system it had started developing for [[OS/2]] with [[3Com]] around 1990.<ref name="theregister/2018/06/08/smb1">{{cite news |last1=Speed |first1=Richard |title=Have to use SMB 1.0? Windows 10 April 2018 Update says NO |url=https://www.theregister.com/2018/06/08/windows_10_smb1/ |access-date=18 February 2023 |work=[[theregister.com]] |language=en |archive-date=18 February 2023 |archive-url=https://web.archive.org/web/20230218011417/https://www.theregister.com/2018/06/08/windows_10_smb1/ |url-status=live }}</ref><ref name="borncity/2017/06/15/retire-smbv1">{{cite news |author1=guenni |title=Microsoft plans to deactivate SMBv1 in Windows 10 V1709 |url=https://borncity.com/win/2017/06/15/microsoft-plans-to-retire-smbv1-in-fall-in-windows-10/ |access-date=18 February 2023 |work=Born's Tech and Windows World |date=15 June 2017 |archive-date=18 February 2023 |archive-url=https://web.archive.org/web/20230218011414/https://borncity.com/win/2017/06/15/microsoft-plans-to-retire-smbv1-in-fall-in-windows-10/ |url-status=live }}</ref><ref name="thurrott/265909">{{cite news |last1=Giret |first1=Laurent |title=Microsoft Gets Ready to Disable SMB1 Protocol on Windows 11 |url=https://www.thurrott.com/windows/265909/microsoft-gets-ready-to-disable-smb1-protocol-on-windows-11 |access-date=18 February 2023 |work=Thurrott.com |date=20 April 2022 |archive-date=31 May 2024 |archive-url=https://web.archive.org/web/20240531142913/https://www.thurrott.com/windows/265909/microsoft-gets-ready-to-disable-smb1-protocol-on-windows-11 |url-status=live }}</ref> Microsoft continued to add features to the protocol in [[Windows for Workgroups]] ({{circa|1992}}) and in later versions of Windows. LAN Manager authentication was implemented based on the original legacy SMB specification's requirement to use IBM "LAN Manager" passwords, but implemented [[Data Encryption Standard|DES]] in a [[LM hash#Security weaknesses|flawed manner]] that allowed passwords to be cracked.<ref>{{cite web|author=Christopher Hertel|year=1999|title=SMB: The Server Message Block Protocol|url=http://ubiqx.org/cifs/SMB.html|url-status=live|archive-url=https://web.archive.org/web/20100310140946/http://ubiqx.org/cifs/SMB.html|archive-date=March 10, 2010|access-date=November 1, 2009}}</ref> Later, [[Kerberos (protocol)|Kerberos]] authentication was also added. The [[Windows domain]] logon protocols initially used [[40-bit encryption]] outside of the [[United States]], because of export restrictions on stronger 128-bit encryption<ref>{{cite web|date=November 1, 2006|title=Description of Microsoft Windows Encryption Pack 1|url=http://support.microsoft.com/kb/159709|url-status=live|archive-url=https://web.archive.org/web/20091002075623/http://support.microsoft.com/kb/159709|archive-date=October 2, 2009|access-date=November 1, 2009|publisher=[[Microsoft]]}}</ref> (subsequently lifted in 1996 when President [[Bill Clinton]] signed {{Ws2|Executive Order 13026}}<ref>{{cite web|year=1996|title=US Executive Order 13026|url=http://www.gpo.gov/fdsys/pkg/WCPD-1996-11-18/pdf/WCPD-1996-11-18-Pg2399.pdf|url-status=live|archive-url=https://web.archive.org/web/20091010125029/http://www.gpo.gov/fdsys/pkg/WCPD-1996-11-18/pdf/WCPD-1996-11-18-Pg2399.pdf|archive-date=October 10, 2009|access-date=November 1, 2009|publisher=[[United States Government]]}}</ref>).

SMB 1.0 (or SMB1) was originally designed to run on [[NetBIOS Frames]] (NetBIOS over [[IEEE 802.2]]). Since then, it has been adapted to NetBIOS over [[IPX/SPX]] (NBX), and [[NetBIOS over TCP/IP]] (NetBT). Also, since [[Windows 2000]], SMB runs on [[Transmission Control Protocol|TCP]] using TCP port 445, a feature known as "direct host SMB".<ref name="direct">{{cite web|url=http://support.microsoft.com/kb/204279|title=Direct hosting of SMB over TCP/IP|date=October 11, 2007|publisher=[[Microsoft]]|access-date=November 1, 2009|archive-url=https://web.archive.org/web/20110326164716/http://support.microsoft.com/kb/204279|archive-date=March 26, 2011|url-status=live}}</ref> There is still a thin layer (similar to the Session Message packet of NetBT's Session Service) between SMB and TCP.<ref name="direct" /> Windows Server 2003, and legacy [[Network-attached storage|NAS]] devices use SMB1 natively.

SMB1 is an extremely chatty protocol, which is not such an issue on a [[local area network]] (LAN) with low latency.  It becomes very slow on [[Wide area network|wide area networks]] (WAN) as the back and forth handshake of the protocol magnifies the inherent high latency of such a network. Later versions of the protocol reduced the high number of handshake exchanges. One approach to mitigating the inefficiencies in the protocol is to use [[WAN optimization]] products such as those provided by [[Riverbed Technology|Riverbed]], [[Silver Peak Systems|Silver Peak]], or [[Cisco Systems|Cisco]]. A better approach is to upgrade to a later version of SMB. This includes upgrading both NAS devices as well as Windows Server 2003. The most effective method to identify SMB1 traffic is with a network analyzer tool, such as [[Wireshark]].  Microsoft also provides an auditing tool in [[Windows Server 2016]] to track down devices that use SMB1.<ref name="messageanalyzer">{{cite web |last1=Kyttle |first1=Ralph |title=SMB1 – Audit Active Usage using Message Analyzer |url=https://blogs.technet.microsoft.com/ralphkyttle/2017/05/13/smb1-audit-active-usage-using-message-analyzer/ |website=Microsoft TechNet |publisher=Microsoft |access-date=28 March 2019 |date=13 May 2017 |archive-url=https://web.archive.org/web/20190328223802/https://blogs.technet.microsoft.com/ralphkyttle/2017/05/13/smb1-audit-active-usage-using-message-analyzer/ |archive-date=March 28, 2019 |url-status=live }}</ref>

Microsoft marked SMB1 as [[deprecation|deprecated]] in June 2013.<ref>{{Cite web|title=The Deprecation of SMB1 – You should be planning to get rid of this old SMB dialect – Jose Barreto's Blog|url=https://blogs.technet.microsoft.com/josebda/2015/04/21/the-deprecation-of-smb1-you-should-be-planning-to-get-rid-of-this-old-smb-dialect/|url-status=live|archive-url=https://web.archive.org/web/20170521154946/https://blogs.technet.microsoft.com/josebda/2015/04/21/the-deprecation-of-smb1-you-should-be-planning-to-get-rid-of-this-old-smb-dialect/|archive-date=May 21, 2017|access-date=2019-10-09|website=blogs.technet.microsoft.com|date=21 April 2015 }}</ref> Windows Server 2016 and [[Windows 10 version 1709]] do not have SMB1 installed by default.<ref>{{Cite web|title=SMBv1 is not installed by default in Windows 10 Fall Creators Update and Windows Server, version 1709 and later versions|url=https://support.microsoft.com/en-us/help/4034314/smbv1-is-not-installed-by-default-in-windows|url-status=live|archive-url=https://web.archive.org/web/20191010052046/https://support.microsoft.com/en-us/help/4034314/smbv1-is-not-installed-by-default-in-windows|archive-date=October 10, 2019|access-date=2019-10-09|website=support.microsoft.com}}</ref>

=== CIFS ===
In 1996, when Sun Microsystems announced [[WebNFS]],<ref name="WebNFS">{{cite web |title=WebNFS - Technical Overview |url=http://www.sun.com/software/webnfs/overview.xml |archive-url=https://web.archive.org/web/20070518204025/http://www.sun.com/software/webnfs/overview.xml |archive-date=2007-05-18}}</ref> Microsoft launched an initiative to rename SMB to Common Internet File System (CIFS)<ref name="tridgemyths" /> and added more features, including support for [[symbolic link]]s, [[hard link]]s, larger file sizes, and an initial attempt at supporting direct connections over TCP port 445 without requiring [[NetBIOS]] as a transport (a largely experimental effort that required further refinement). Microsoft submitted some partial specifications as [[Internet Draft]]s to the [[Internet Engineering Task Force|IETF]].<ref name="IETF">See:
* {{cite web|first1=I.|last1=Heizer|first2=P.|last2=Leach|first3=D.|last3=Perry|date=June 13, 1996|title=Common Internet File System Protocol (CIFS/1.0)|url=https://tools.ietf.org/html/draft-heizer-cifs-v1-spec-00|url-status=dead|archive-url=https://web.archive.org/web/20190808115512/https://tools.ietf.org/html/draft-heizer-cifs-v1-spec-00|archive-date=August 8, 2019}}
* {{cite web|first1=Paul J.|last1=Leach|first2=Dilip C.|last2=Naik|date=January 3, 1997|title=CIFS Logon and Pass Through Authentication|url=https://tools.ietf.org/html/draft-leach-cifs-logon-spec|access-date=December 10, 2017|archive-date=May 31, 2024|archive-url=https://web.archive.org/web/20240531142914/https://datatracker.ietf.org/doc/html/draft-leach-cifs-logon-spec|url-status=live}}
* {{cite web|first1=Paul J.|last1=Leach|first2=Dilip C.|last2=Naik|date=January 10, 1997|title=CIFS/E Browser Protocol|url=https://tools.ietf.org/html/draft-leach-cifs-browser-spec|access-date=December 10, 2017|archive-date=May 31, 2024|archive-url=https://web.archive.org/web/20240531142914/https://datatracker.ietf.org/doc/html/draft-leach-cifs-browser-spec|url-status=live}}
* {{cite web|first1=Paul J.|last1=Leach|first2=Dilip C.|last2=Naik|date=January 31, 1997|title=CIFS Printing Specification|url=https://tools.ietf.org/html/draft-leach-cifs-print-spec|access-date=December 10, 2017|archive-date=May 31, 2024|archive-url=https://web.archive.org/web/20240531142916/https://datatracker.ietf.org/doc/html/draft-leach-cifs-print-spec|url-status=live}}
* {{cite web|first1=Paul J.|last1=Leach|first2=Dilip C.|last2=Naik|date=February 26, 1997|title=CIFS Remote Administration Protocol|url=https://tools.ietf.org/html/draft-leach-cifs-rap-spec|access-date=December 10, 2017|archive-date=May 31, 2024|archive-url=https://web.archive.org/web/20240531142915/https://datatracker.ietf.org/doc/html/draft-leach-cifs-rap-spec|url-status=live}}
* {{cite web|first1=Paul J.|last1=Leach|first2=Dilip C.|last2=Naik|date=December 19, 1997|title=A Common Internet File System (CIFS/1.0) Protocol|url=https://tools.ietf.org/html/draft-leach-cifs-v1-spec|access-date=December 10, 2017|archive-date=May 31, 2024|archive-url=https://web.archive.org/web/20240531142916/https://datatracker.ietf.org/doc/html/draft-leach-cifs-v1-spec|url-status=live}}</ref> These submissions have since expired.

=== SMB 2.0 ===
Microsoft introduced a new version of the protocol (SMB 2.0 or SMB2) in 2006 with [[Windows Vista]] and [[Windows Server 2008]].<ref name="smb2">{{cite web | url=http://blogs.msdn.com/chkdsk/archive/2006/03/10/548787.aspx | title=What's new in SMB in Windows Vista | date=March 10, 2006 | access-date=May 1, 2006 | author=Navjot Virk and Prashanth Prahalad | work=Chk Your Dsks | publisher=[[Microsoft]] | url-status=dead | archive-url=https://web.archive.org/web/20060505005515/http://blogs.msdn.com/chkdsk/archive/2006/03/10/548787.aspx | archive-date=May 5, 2006 | df=mdy-all }}</ref> Although the protocol is proprietary, its specification has been published to allow other systems to interoperate with Microsoft operating systems that use the new protocol.<ref>{{cite tech report |url=https://docs.microsoft.com/openspecs/windows_protocols/ms-smb2 |title=Server Message Block (SMB) Protocol Versions 2 and 3 |department=Windows Protocols |work=Open Specifications |series=[[Microsoft Docs]] |institution=[[Microsoft]] |number=MS-SMB2 |access-date=2020-11-29}}</ref>

SMB2 reduces the 'chattiness' of the SMB 1.0 protocol by reducing the number of commands and subcommands from over a hundred to just nineteen.<ref name="barreto"/> It has mechanisms for [[Pipeline (computing)|pipelining]], that is, sending additional requests before the response to a previous request arrives, thereby improving performance over high-[[Network latency|latency]] links. It adds the ability to compound multiple actions into a single request, which significantly reduces the number of [[round-trip delay time|round-trips]] the client needs to make to the server, improving performance as a result.<ref name="barreto"/> SMB1 also has a compounding mechanism—known as AndX—to compound multiple actions, but Microsoft clients rarely use AndX.{{Citation needed|date=November 2010}} It also introduces the notion of "durable file handles": these allow a connection to an SMB server to survive brief network outages, as are typical in a wireless network, without having to incur the overhead of re-negotiating a new session.

SMB2 includes support for [[symbolic link]]s. Other improvements include caching of file properties, improved message signing with [[HMAC]] [[SHA-256]] hashing algorithm and better scalability by increasing the number of users, shares and open files per server among others.<ref name="barreto"/> The SMB1 protocol uses 16-bit data sizes, which amongst other things, limits the maximum block size to 64K. SMB2 uses 32- or 64-bit wide storage fields, and 128 bits in the case of [[file handle|file-handle]]s, thereby removing previous constraints on block sizes, which improves performance with large file transfers over fast networks.<ref name="barreto"/>

Windows Vista/[[Server 2008]] and later operating systems use SMB2 when communicating with other machines also capable of using SMB2. SMB1 continues in use for connections with older versions of Windows, as well various vendors' [[Network-attached storage|NAS]] solutions. Samba 3.5 also includes experimental support for SMB2.<ref>{{Cite web |url=http://www.samba.org/samba/history/samba-3.5.0.html |title=Samba 3.5.0 Available for Download |access-date=July 8, 2011 |archive-url=https://web.archive.org/web/20110724051402/http://www.samba.org/samba/history/samba-3.5.0.html |archive-date=July 24, 2011 |url-status=live }}</ref> Samba 3.6 fully supports SMB2, except the modification of user quotas using the Windows quota management tools.<ref>{{Cite web |url=http://samba.org/samba/history/samba-3.6.0.html |title=Samba 3.6.0 Available for Download |access-date=August 10, 2011 |archive-url=https://web.archive.org/web/20110924042737/http://www.samba.org/samba/history/samba-3.6.0.html |archive-date=September 24, 2011 |url-status=live }}</ref>

When SMB2 was introduced it brought a number of benefits over SMB1 for third party implementers of SMB protocols. SMB1, originally designed by [[IBM]], was [[reverse engineering|reverse engineered]], and later became part of a wide variety of non-Windows operating systems such as [[Xenix]], [[OS/2]] and [[OpenVMS|VMS]] ([[Pathworks]]). [[X/Open]] standardized it partially; Microsoft had submitted Internet-Drafts describing SMB2 to the [[Internet Engineering Task Force|IETF]], partly in response to formal IETF standardization of version 4 of the [[Network File System]] in December 2000 as IETF RFC 3010;<ref>{{cite IETF|rfc=3010|title=NFS version 4 Protocol|date=December 2000}}</ref> however, those SMB-related Internet-Drafts expired without achieving any IETF standards-track approval or any other IETF endorsement. (See http://ubiqx.org/cifs/Intro.html for historical detail.) SMB2 is also a relatively clean break with the past. Microsoft's SMB1 code has to work with a large variety of SMB clients and servers. SMB1 features many versions of information for commands (selecting what structure to return for a particular request) because features such as [[Unicode]] support were retro-fitted at a later date. SMB2 involves significantly reduced compatibility-testing for implementers of the protocol. SMB2 code has considerably less complexity since far less variability exists (for example, non-Unicode code paths become redundant as SMB2 requires Unicode support).

Apple migrated to SMB2 (from their own [[Apple Filing Protocol]], now legacy) starting with [[OS X Mavericks|OS X 10.9 "Mavericks"]].<ref name="ai2013">{{cite web |last=Eran |first=Daniel |url=http://appleinsider.com/articles/13/06/11/apple-shifts-from-afp-file-sharing-to-smb2-in-os-x-109-mavericks |title=Apple shifts from AFP file sharing to SMB2 in OS X 10.9 Mavericks |publisher=Appleinsider.com |date=June 11, 2013 |access-date=January 12, 2014 |archive-url=https://web.archive.org/web/20170212162139/http://appleinsider.com/articles/13/06/11/apple-shifts-from-afp-file-sharing-to-smb2-in-os-x-109-mavericks |archive-date=February 12, 2017 |url-status=live }}</ref> This transition was fraught with compatibility problems though.<ref>{{cite web |last=Vaughan |first=Steven J. |url=https://www.zdnet.com/article/mavericks-smb2-problem-and-fixes/ |title=Mavericks' SMB2 problem and fixes |publisher=ZDNet |date=October 28, 2013 |access-date=January 12, 2014 |archive-url=https://web.archive.org/web/20140105011410/http://www.zdnet.com/mavericks-smb2-problem-and-fixes-7000022519/ |archive-date=January 5, 2014 |url-status=live }}</ref><ref>{{cite web |author=MacParc |url=http://hints.macworld.com/article.php?story=20131122083837447 |title=10.9: Switch the SMB stack to use SMB1 as default |work=Mac OS X Hints |publisher=macworld.com |access-date=January 12, 2014 |archive-url=https://web.archive.org/web/20140112051604/http://hints.macworld.com/article.php?story=20131122083837447 |archive-date=January 12, 2014 |url-status=live }}</ref> Non-default support for SMB2 appeared in fact in OS X 10.7, when Apple abandoned Samba in favor of its own SMB implementation called SMBX<ref name="ai2013"/> after Samba adopted [[GPLv3]].<ref>{{cite web|url=http://reviews.cnet.com/8301-13727_7-20046383-263.html|title=Say adios to Samba in OS X|author=Topher Kessler|date=March 23, 2011|publisher=CNET|access-date=January 12, 2014|archive-url=https://web.archive.org/web/20140115220216/http://reviews.cnet.com/8301-13727_7-20046383-263.html|archive-date=January 15, 2014|url-status=live}}</ref><ref>{{cite web|url=http://www.osnews.com/story/24572/Apple_Ditches_SAMBA_in_Favour_of_Homegrown_Replacement|title=Apple Ditches SAMBA in Favour of Homegrown Replacement|author=Thom Holwerda|date=March 26, 2011|access-date=January 12, 2014|archive-url=https://web.archive.org/web/20131102235327/http://www.osnews.com/story/24572/Apple_Ditches_SAMBA_in_Favour_of_Homegrown_Replacement|archive-date=November 2, 2013|url-status=live}}</ref>

The [[Linux kernel]]'s CIFS client file system has SMB2 support since version 3.7.<ref>{{cite web|url=https://kernelnewbies.org/Linux_3.7#head-7c9c911e4c41bcbc635cd8fa561278c833844bc2|title=Linux 3.7 - Linux Kernel Newbies|access-date=September 4, 2016|archive-url=https://web.archive.org/web/20160911130335/https://kernelnewbies.org/Linux_3.7#head-7c9c911e4c41bcbc635cd8fa561278c833844bc2|archive-date=September 11, 2016|url-status=live}}</ref>

=== SMB 2.1 ===
SMB 2.1, introduced with Windows 7 and Server 2008 R2, introduced minor performance enhancements with a new opportunistic locking mechanism.<ref>{{cite web|url=http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=d8541618-5c63-4c4d-a0fd-d942cd3d2ec6|publisher=[[Microsoft]]|access-date=November 2, 2009|date=October 21, 2009|title=Implementing an End-User Data Centralization Solution|pages=10–11|archive-url=https://web.archive.org/web/20100906141857/http://www.microsoft.com/downloads/details.aspx?displaylang=en&FamilyID=d8541618-5c63-4c4d-a0fd-d942cd3d2ec6|archive-date=September 6, 2010|url-status=live}}</ref>

=== SMB 3.0 ===
SMB 3.0 (previously named SMB 2.2)<ref name="smb3">{{cite web|url=https://cloudblogs.microsoft.com/windowsserver/2012/04/19/smb-2-2-is-now-smb-3-0/|work=Windows Server Blog|title=SMB 2.2 is now SMB 3.0|author=Jeffrey Snover|date=April 19, 2012|access-date=July 6, 2020|archive-date=July 8, 2020|archive-url=https://web.archive.org/web/20200708211728/https://cloudblogs.microsoft.com/windowsserver/2012/04/19/smb-2-2-is-now-smb-3-0/|url-status=live}}</ref> was introduced with [[Windows 8]]<ref name="smb3"/> and [[Windows Server 2012]].<ref name="smb3"/> It brought several significant changes that are intended to add functionality and improve SMB2 performance,<ref>{{cite web | url=http://www.chelsio.com/chelsio-to-demonstrate-40g-smb-direct-rdma-over-ethernet-for-windows-server-2012/ | title=40G SMB Direct | author=Chelsio Communications | date=2 April 2013 | access-date=June 18, 2013 | archive-url=https://web.archive.org/web/20130907065805/http://www.chelsio.com/chelsio-to-demonstrate-40g-smb-direct-rdma-over-ethernet-for-windows-server-2012/ | archive-date=September 7, 2013 | url-status=live }}</ref> notably in virtualized [[data center]]s:
* the SMB Direct Protocol (SMB over [[remote direct memory access]] [RDMA])
* SMB Multichannel (multiple connections per SMB session),<ref>{{cite web | url=https://www.eiseverywhere.com/file_uploads/b4f7436c4bc86fe545abe9fc042d4a7f_JoseBarreto_SMB3_Remote_File_Protocol_revision.pdf | title=SNIA Tutorial on the SMB Protocol | author=Jose Barreto | date=October 19, 2012 | access-date=November 28, 2012 | publisher=[[Storage Networking Industry Association]] | archive-url=https://web.archive.org/web/20130603133014/https://www.eiseverywhere.com/file_uploads/b4f7436c4bc86fe545abe9fc042d4a7f_JoseBarreto_SMB3_Remote_File_Protocol_revision.pdf | archive-date=June 3, 2013 | url-status=live }}</ref><ref>{{ cite web | url=http://www.snia.org/sites/default/files2/SDC2011/presentations/keynote/ThomasPfenning_The_Future_of_File_Protocols-final.pdf | title=The Future of File Protocols: SMB 2.2 in the Datacenter |archive-url=https://web.archive.org/web/20120720020805/http://www.snia.org/sites/default/files2/SDC2011/presentations/keynote/ThomasPfenning_The_Future_of_File_Protocols-final.pdf |archive-date=2012-07-20 | author=Thomas Pfenning }}</ref>
* SMB Transparent Failover<ref>{{cite web | url = https://blogs.technet.microsoft.com/clausjor/2012/06/07/smb-transparent-failover-making-file-shares-continuously-available/ | title = SMB Transparent Failover – making file shares continuously available | date = 2012-06-07 | first = Claus | last = Joergensen | work = Microsoft TechNet | access-date = February 1, 2017 | archive-url = https://web.archive.org/web/20190111144942/https://blogs.technet.microsoft.com/clausjor/2012/06/07/smb-transparent-failover-making-file-shares-continuously-available/ | archive-date = January 11, 2019 | url-status = live }}</ref><ref>{{cite web | url = http://windowsitpro.com/windows-server-2012/new-ways-enable-high-availability-file-shares | title = New Ways to Enable High Availability for File Shares | date = 2012-08-21 | first = John | last = Savill | work = Windows IT Pro | access-date = February 1, 2017 | archive-url = https://web.archive.org/web/20161127102639/http://windowsitpro.com/windows-server-2012/new-ways-enable-high-availability-file-shares | archive-date = November 27, 2016 | url-status = live }}</ref>

It also introduces several security enhancements, such as [[end-to-end encryption]] and a new [[Advanced Encryption Standard|AES]] based signing algorithm.<ref>{{cite web | url=https://technet.microsoft.com/en-us/library/dn551363.aspx | title=SMB Security Enhancements | publisher=Microsoft Technet | date=January 15, 2014 | access-date=June 18, 2014 | archive-url=https://web.archive.org/web/20141009101031/http://technet.microsoft.com/en-us/library/dn551363.aspx | archive-date=October 9, 2014 | url-status=live }}</ref><ref>{{cite web|url=https://blogs.technet.microsoft.com/josebda/2013/05/05/updated-links-on-windows-server-2012-file-server-and-smb-3-0/|title=Updated Links on Windows Server 2012 File Server and SMB 3.0|author=Jose Barreto|date=May 5, 2013|publisher=[[Microsoft TechNet]] Server & Management Blogs|access-date=August 14, 2016|archive-url=https://web.archive.org/web/20160803070533/https://blogs.technet.microsoft.com/josebda/2013/05/05/updated-links-on-windows-server-2012-file-server-and-smb-3-0/|archive-date=August 3, 2016|url-status=live}}</ref>

=== SMB 3.0.2 ===
SMB 3.0.2 (known as 3.02 at the time) was introduced with Windows 8.1 and Windows Server 2012 R2;<ref>{{cite web|url=https://blogs.technet.microsoft.com/josebda/2014/07/07/updated-links-on-windows-server-2012-r2-file-server-and-smb-3-02/|title=Updated Links on Windows Server 2012 R2 File Server and SMB 3.02|author=Jose Barreto|date=July 7, 2014|publisher=[[Microsoft TechNet]] Server & Management Blogs|access-date=August 14, 2016|archive-url=https://web.archive.org/web/20160826110750/https://blogs.technet.microsoft.com/josebda/2014/07/07/updated-links-on-windows-server-2012-r2-file-server-and-smb-3-02/|archive-date=August 26, 2016|url-status=live}}</ref><ref>{{cite web|url=https://blogs.technet.microsoft.com/josebda/2013/12/12/storage-developer-conference-sdc-2013-slides-now-publicly-available-here-are-the-links-to-microsoft-slides/|title=Storage Developer Conference – SDC 2013 slides now publicly available. Here are the links to Microsoft slides…|author=Jose Barreto|date=December 12, 2013|publisher=[[Microsoft TechNet]] Server & Management Blogs|access-date=August 14, 2016|archive-url=https://web.archive.org/web/20160826113828/https://blogs.technet.microsoft.com/josebda/2013/12/12/storage-developer-conference-sdc-2013-slides-now-publicly-available-here-are-the-links-to-microsoft-slides/|archive-date=August 26, 2016|url-status=live}}</ref> in those and later releases, the earlier SMB version 1 can be optionally disabled to increase security.<ref>{{cite web|url=http://www.windowsnetworking.com/articles-tutorials/windows-server-2012/improvements-smb-30-and-302-protocol-updates.html|title=WindowsNetworking.com: Improvements in the SMB 3.0 and 3.02 Protocol Updates|author=Eric Geier|date=December 5, 2013|website=WindowsNetworking.com|access-date=April 6, 2015|archive-url=https://web.archive.org/web/20150409010758/http://www.windowsnetworking.com/articles-tutorials/windows-server-2012/improvements-smb-30-and-302-protocol-updates.html|archive-date=April 9, 2015|url-status=live}}</ref><ref name="barreto-smb3-links-ws2012r2">{{cite web|url=https://blogs.technet.microsoft.com/josebda/2015/04/30/smb3-networking-links-for-windows-server-2012-r2/|title=SMB3 Networking Links for Windows Server 2012 R2|author=Jose Barreto|date=April 30, 2015|publisher=[[Microsoft TechNet]] Server & Management Blogs|access-date=August 14, 2016|archive-url=https://web.archive.org/web/20160826115342/https://blogs.technet.microsoft.com/josebda/2015/04/30/smb3-networking-links-for-windows-server-2012-r2/|archive-date=August 26, 2016|url-status=live}}</ref>

=== SMB 3.1.1 ===
SMB 3.1.1 was introduced with [[Windows 10]] and [[Windows Server 2016]].<ref>{{cite web|url=https://blogs.technet.microsoft.com/josebda/2015/05/05/whats-new-in-smb-3-1-1-in-the-windows-server-2016-technical-preview-2/|title=What's new in SMB 3.1.1 in the Windows Server 2016 Technical Preview 2|author=Jose Barreto|date=May 5, 2015|publisher=[[Microsoft TechNet]] Server & Management Blogs|access-date=August 14, 2016|archive-url=https://web.archive.org/web/20161008054848/https://blogs.technet.microsoft.com/josebda/2015/05/05/whats-new-in-smb-3-1-1-in-the-windows-server-2016-technical-preview-2/|archive-date=October 8, 2016|url-status=live}}</ref> This version supports [[Advanced Encryption Standard|AES-128]] [[Galois/Counter Mode|GCM]] encryption in addition to AES-128 [[CCM mode|CCM]] encryption added in SMB3, and implements pre-authentication integrity check using [[SHA-512]] hash. SMB 3.1.1 also makes secure negotiation mandatory when connecting to clients using SMB versions that support it.<ref>{{Cite web|url=https://learn.microsoft.com/en-us/windows-server/storage/file-server/smb-security#smb-encryption|title=SMB security enhancements|publisher=Microsoft Learn|access-date=2023-04-10|archive-date=2023-04-10|archive-url=https://web.archive.org/web/20230410045614/https://learn.microsoft.com/en-us/windows-server/storage/file-server/smb-security#smb-encryption|url-status=live}}</ref>

== Specifications ==

The specifications for the SMB are proprietary and were initially closed, thereby forcing other vendors and projects to reverse-engineer the protocol to interoperate with it. The SMB 1.0 protocol was eventually published some time after it was reverse engineered, whereas the SMB 2.0 protocol was made available from Microsoft's Open Specifications Developer Center from the outset.<ref>{{Cite web |url=https://msdn.microsoft.com/en-us/library/cc216517%28PROT.10%29.aspx |title=Windows Protocols<!-- Bot generated title --> |access-date=October 13, 2009 |archive-url=https://web.archive.org/web/20090926202714/http://msdn.microsoft.com/en-us/library/cc216517(PROT.10).aspx |archive-date=September 26, 2009 |url-status=live }}</ref>

== Third-party implementations ==

=== Samba ===
{{Main article|Samba (software)}}
{{Update section|date=April 2016}}

In 1991, [[Andrew Tridgell]] started the development of Samba, a [[free-software]] re-implementation (using [[reverse engineering]]) of the SMB/CIFS networking protocol for [[Unix-like]] systems,  initially to implement an SMB server to allow PC clients running the [[Digital Equipment Corporation|DEC]] [[Pathworks]] client to access files on [[SunOS]] machines.<ref name='tridgemyths' /><ref>{{cite web|url=http://www.rxn.com/services/faq/smb/samba.history.txt|title=A bit of history and a bit of fun|author=Tridgell, Andrew|author-link=Andrew Tridgell|date=June 27, 1997|access-date=July 26, 2011|archive-url=https://web.archive.org/web/20110717071846/http://www.rxn.com/services/faq/smb/samba.history.txt|archive-date=July 17, 2011|url-status=live}}</ref> Because of the importance of the SMB protocol in interacting with the widespread [[Microsoft Windows]] platform, Samba became a popular [[free software]] implementation of a compatible SMB client and server to allow non-Windows operating systems, such as [[Unix-like]] operating systems, to interoperate with Windows.

As of version 3 (2003), Samba provides file and print services for Microsoft Windows clients and can integrate with a [[Windows NT 4.0]] server domain, either as a [[Primary Domain Controller]] (PDC) or as a domain member. Samba4 installations can act as an [[Active Directory]] domain controller or member server, at Windows 2008 domain and [[Active Directory|forest]] functional levels.<ref>{{cite web |url=http://samba.2283325.n4.nabble.com/Samba-4-functional-levels-td3322760.html |title=Samba 4 functional levels <!--copy of Google Goups(?), not |publisher=Samba.2283325.n4.nabble.com --> |date=February 25, 2011 |access-date=January 12, 2014 |archive-url=https://web.archive.org/web/20140729014411/http://samba.2283325.n4.nabble.com/Samba-4-functional-levels-td3322760.html |archive-date=July 29, 2014 |url-status=live }}</ref>

Package managers in Linux distributions can search for the ''cifs-utils'' package.  The package is from the Samba maintainers.

=== Netsmb ===
NSMB (Netsmb and SMBFS) is a family of in-kernel SMB client implementations in BSD operating systems. It was first contributed to [[FreeBSD]] 4.4 by Boris Popov, and is now found in a wide range of other BSD systems including [[NetBSD]] and [[macOS]].<ref>{{cite web |title=netsmb(4) |url=https://man.netbsd.org/NetBSD-8.0/man4/netsmb.4 |website=NetBSD 8.0 manual pages |access-date=5 January 2020 |archive-date=17 November 2022 |archive-url=https://web.archive.org/web/20221117092107/https://man.netbsd.org/NetBSD-8.0/man4/netsmb.4 |url-status=live }}</ref> The implementations have diverged significantly ever since.<ref>{{man|5|nsmb.conf|FreeBSD}}.</ref>

The macOS version of NSMB is notable for its now-common scheme of representing symlinks. This "Minshall-French" format shows symlinks as textual files with a {{code|.symlink}} extension and a {{code|Xsym\n}} magic number, always 1067 bytes long. This format is also used for storing symlinks on native SMB servers or unsupported filesystems. Samba supports this format with an {{code|mfsymlink}} option.<ref>{{cite web |title=UNIX Extensions |url=https://wiki.samba.org/index.php/UNIX_Extensions#Storing_symlinks_on_Windows_servers |website=SambaWiki |access-date=March 15, 2020 |archive-url=https://web.archive.org/web/20200612000308/https://wiki.samba.org/index.php/UNIX_Extensions#Storing_symlinks_on_Windows_servers |archive-date=June 12, 2020 |url-status=live }}</ref> Docker on Windows also seems to use it.{{Citation needed|date=May 2020}}

=== NQ ===
NQ is a family of portable SMB client and server implementations developed by [https://www.visualitynq.com/ Visuality Systems], an Israel-based company established in 1998 by Sam Widerman, formerly the CEO of [[Siemens]] Data Communications. The NQ family comprises an embedded SMB stack (written in C), a Pure Java SMB Client, and a storage SMB Server implementation. All solutions support the latest SMB&nbsp;3.1.1 dialect. [https://visualitynq.com/resources/articles/smb3-for-linux NQ for Linux], [https://visualitynq.com/resources/articles/smb3-for-wince NQ for WinCE], iOS, Android, VxWorks and other real-time operating systems are all supported by the configurable NQ solution.

=== MoSMB ===
MoSMB is a user space SMB implementation for Linux. It supports  SMB 2.x and SMB 3.x. Key features include Cloud-scale Active-Active Scale-out Clusters, SMB Direct (RDMA), SMB Multichannel, Transparent Failover and Continuous Availability. MoSMB also supports [[Amazon S3]] object storage as storage backend in addition to POSIX file systems such as [[ext4]], [[ZFS]], [[Lustre (file system)|Lustre]], [[Ceph (software)|Ceph]], etc.<ref>{{cite web|url=http://www.snia.org/sites/default/files/SDC/2016/presentations/smb/Sunu_Engineer_Building_Highly_Scalable_Performant_SMB_Protocol_Server.pdf|title=Building a Highly Scalable and Performant SMB Protocol Server|author=Sunu Engineer|access-date=September 25, 2016|archive-url=https://web.archive.org/web/20160927162136/http://www.snia.org/sites/default/files/SDC/2016/presentations/smb/Sunu_Engineer_Building_Highly_Scalable_Performant_SMB_Protocol_Server.pdf|archive-date=September 27, 2016|url-status=live}}</ref>

=== Fusion File Share by Tuxera ===
Fusion File Share by Tuxera is a proprietary SMB server implementation developed by [[Tuxera]] that can be run either in kernel or [[user space]].<ref>{{cite web|title=Microsoft and Tuxera strengthen partnership through Tuxera SMB Server|url=https://news.microsoft.com/2016/09/14/microsoft-and-tuxera-strengthen-partnership-through-tuxera-smb-server|website=Microsoft|date=14 September 2016|publisher=Microsoft News Center|access-date=6 February 2017|archive-url=https://web.archive.org/web/20161117044100/http://news.microsoft.com/2016/09/14/microsoft-and-tuxera-strengthen-partnership-through-tuxera-smb-server/|archive-date=November 17, 2016|url-status=live}}</ref> It supports SMB 3.1.1 and all previous versions, additionally advanced SMB features like continuous availability (persistent handles) scale-out, [[Remote direct memory access|RDMA]] (SMB Direct), SMB multichannel, transparent compression, [[shadow copy]].

=== Likewise ===

Likewise developed a CIFS/SMB implementation (versions 1.0, 2.0, 2.1 and SMB 3.0) in 2009 that provided a multiprotocol, identity-aware platform for network access to files used in [[Original equipment manufacturer|OEM]] storage products built on Linux/Unix based devices. The platform could be used for traditional NAS, Cloud Gateway, and Cloud Caching devices for providing secure access to files across a network.  Likewise was purchased by [[EMC Isilon]] in 2012.

=== KSMBD ===
[[KSMBD]] is an open source in-kernel CIFS/SMB server implementation for the Linux kernel. Compared to user-space implementations, it provides better performance and makes it easier to implement some features such as SMB Direct. It supports SMB 3.1.1 and previous versions.

== Security ==
Over the years, there have been many security vulnerabilities in Microsoft's implementation of the protocol or components on which it directly relies.<ref>{{cite web|url=http://support.microsoft.com/kb/329170|title=MS02-070: Flaw in SMB Signing May Permit Group Policy to Be Modified|publisher=[[Microsoft]]|access-date=November 1, 2009|date=December 1, 2007|archive-url=https://web.archive.org/web/20091008113615/http://support.microsoft.com/kb/329170|archive-date=October 8, 2009|url-status=live}}</ref><ref>{{cite web|url=http://support.microsoft.com/kb/958687|title=MS09-001: Vulnerabilities in SMB could allow remote code execution|publisher=[[Microsoft]]|access-date=November 1, 2009|date=January 13, 2009|archive-url=https://web.archive.org/web/20091005062727/http://support.microsoft.com/kb/958687|archive-date=October 5, 2009|url-status=live}},</ref> Other vendors' security vulnerabilities lie primarily in a lack of support for newer [[authentication protocol]]s like [[NTLMv2]] and [[Kerberos (protocol)|Kerberos]] in favor of protocols like NTLMv1, [[LM hash|LanMan]], or [[plaintext]] passwords. Real-time attack tracking<ref>{{cite web|url=http://www.sicherheitstacho.eu|title=Sicherheitstacho.eu|publisher=[[Deutsche Telekom]]|access-date=March 7, 2013|date=March 7, 2013|archive-url=https://web.archive.org/web/20130308043532/http://www.sicherheitstacho.eu/|archive-date=March 8, 2013|url-status=live}}</ref> shows that SMB is one of the primary attack vectors for intrusion attempts,<ref>{{cite web|url=https://www.us-cert.gov/ncas/alerts/TA14-353A|title=Alert (TA14-353A) Targeted Destructive Malware|publisher=[[US-CERT]]|access-date=December 20, 2014|archive-url=https://web.archive.org/web/20141220134115/https://www.us-cert.gov/ncas/alerts/TA14-353A|archive-date=December 20, 2014|url-status=live}}</ref> for example the [[Sony Pictures hack|2014 Sony Pictures attack]],<ref>{{cite web|url=http://www.securityweek.com/hackers-used-sophisticated-smb-worm-tool-attack-sony|title=Sony Hackers Used Server Message Block (SMB) Worm Tool|date=19 December 2014 |access-date=December 20, 2014|archive-url=https://web.archive.org/web/20141220134150/http://www.securityweek.com/hackers-used-sophisticated-smb-worm-tool-attack-sony|archive-date=December 20, 2014|url-status=live}}</ref> and the [[WannaCry ransomware attack]] of 2017.<ref>{{cite news|url=http://www.eweek.com/security/wannacry-ransomware-attack-hits-victims-with-microsoft-smb-exploit|title=WannaCry Ransomware Attack Hits Victims With Microsoft SMB Exploit|work=[[eWeek]]|access-date=13 May 2017}}</ref> In 2020, two SMB high-severity vulnerabilities were disclosed and dubbed as [[SMBGhost (security vulnerability)|SMBGhost]] ([https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-0796 CVE-2020-0796]) and [https://www.hackreports.com/smbleed-smbghost-latest-windows-smb-protocol-vulnerability-smbleedingghost/ SMBleed] ([https://portal.msrc.microsoft.com/en-US/security-guidance/advisory/CVE-2020-1206 CVE-2020-1206]), which when chained together can provide [[Remote code execution|RCE (Remote Code Execution)]] privilege to the attacker.<ref>{{Cite web|date=2020-06-09|title=SMBleedingGhost Writeup: Chaining SMBleed (CVE-2020-1206) with SMBGhost|url=https://blog.zecops.com/vulnerabilities/smbleedingghost-writeup-chaining-smbleed-cve-2020-1206-with-smbghost/|access-date=2020-11-19|website=ZecOps Blog|language=en|archive-date=2020-11-27|archive-url=https://web.archive.org/web/20201127202823/https://blog.zecops.com/vulnerabilities/smbleedingghost-writeup-chaining-smbleed-cve-2020-1206-with-smbghost/|url-status=live}}</ref>

== See also ==
{{Columns-list|colwidth=20em|
* [[List of products that support SMB]]
* [[Administrative share]]
* [[Shared file access]]
* [[AppleTalk]]
* [[Network File System (protocol)]]
* [[Remote File System]]
* [[WebDAV]]
* [[Uniform Naming Convention]]
* [[Network Neighborhood]]
}}

== References ==
{{reflist}}

== Further reading ==

=== SMB specifications ===
* {{Cite web |url=https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-cifs/d416ff7c-c536-406e-a951-4f04b2fd1d2b |title=[MS-CIFS<nowiki>]</nowiki>: Common Internet File System (CIFS) Protocol |website=Open Specifications |publisher=[[Microsoft]] |date=30 October 2020}}
** Specifies the Common Internet File System (CIFS) Protocol, a cross-platform, transport-independent protocol that provides a mechanism for client systems to use file and print services made available by server systems over a network
* {{Cite web |url=https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-smb/f210069c-7086-4dc2-885e-861d837df688 |title=[MS-SMB<nowiki>]</nowiki>: Server Message Block (SMB) Protocol |website=Open Specifications |publisher=[[Microsoft]] |date=25 June 2021}}
** Specifies the Server Message Block (SMB) Protocol, which defines extensions to the existing Common Internet File System (CIFS) specification that have been implemented by Microsoft since the publication of the CIFS specification.
* {{Cite web |url=https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-smb2/5606ad47-5ee0-437a-817e-70c366052962 |title=[MS-SMB2<nowiki>]</nowiki>: Server Message Block (SMB) Protocol Versions 2 and 3 |website=Open Specifications |publisher=[[Microsoft]] |date=14 December 2021}}
** Specifies the Server Message Block (SMB) Protocol Versions 2 and 3, which support the sharing of file and print resources between machines and extend the concepts from the Server Message Block Protocol.
* {{Cite web |url=https://docs.microsoft.com/en-us/openspecs/windows_protocols/ms-smbd/1ca5f4ae-e5b1-493d-b87d-f4464325e6e3 |title=[MS-SMBD<nowiki>]</nowiki>: SMB2 Remote Direct Memory Access (RDMA) Transport Protocol |website=Open Specifications |publisher=[[Microsoft]] |date=25 June 2021}}
** Specifies the SMB2 Remote Direct Memory Access (RDMA) Transport Protocol, a wrapper for the existing SMB2 protocol that allows SMB2 packets to be delivered over RDMA-capable transports such as iWARP or Infiniband while utilizing the direct data placement (DDP) capabilities of these transports. Benefits include reduced CPU overhead, lower latency, and improved throughput.

=== Miscellaneous ===
{{Refbegin}}
* Hertel, Christopher (2003). ''[http://www.ubiqx.org/cifs/Book.html Implementing CIFS{{snd}} The Common Internet FileSystem] {{Webarchive|url=https://web.archive.org/web/20040202181950/http://ubiqx.org/cifs/Book.html |date=2004-02-02 }}''. Prentice Hall. {{ISBN|0-13-047116-X}}. (Text licensed under the [[Open Publication License]], v1.0 or later, available from the link above.)
* Steven M. French, [https://www.kernel.org/doc/ols/2007/ols2007v1-pages-131-140.pdf A New Network File System is Born: Comparison of SMB2, CIFS, and NFS] {{Webarchive|url=https://web.archive.org/web/20120907100828/http://www.kernel.org/doc/ols/2007/ols2007v1-pages-131-140.pdf |date=2012-09-07 }}, [[Linux Symposium]] 2007
* Steve French, [http://www.samba.org/~sfrench/presentations/smf-linux-collab-summmit-future-of-file-protocols-smb2.2.pdf The Future of File Protocols: SMB2 Meets Linux] {{Webarchive|url=https://web.archive.org/web/20180817112740/https://www.samba.org/~sfrench/presentations/smf-linux-collab-summmit-future-of-file-protocols-smb2.2.pdf |date=2018-08-17 }}, Linux Collaboration Summit 2012
{{Refend}}

== External links ==
* [https://docs.microsoft.com/en-us/windows/win32/dfs/distributed-file-system DFS section in "Windows Developer" documentation]
* [http://www.samba.org/samba/ftp/specs/smb-nt01.doc the NT LM 0.12 dialect of SMB]. In [[Microsoft Word]] format

{{URI scheme}}
{{File systems}}

[[Category:Application layer protocols]]
[[Category:Inter-process communication]]
[[Category:Network file systems]]
[[Category:Network protocols]]
[[Category:Windows communication and services]]