In, Server Message Block ( SMB), one version of which was also known as Common Internet File System ( CIFS, ), operates as an mainly used for providing to, and and miscellaneous communications between nodes on a network. It also provides an authenticated mechanism. Most usage of SMB involves computers running, where it was known as 'Microsoft Windows Network' before the introduction of. Corresponding are LAN Manager Server (for the server component) and LAN Manager Workstation (for the client component). Contents. Features SMB can run on top of the (and lower) network layers in several ways:. Directly over, 445;.

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Via the API, which in turn can run on several:. On ports 137, 138 & TCP ports 137, 139 ;. On several legacy protocols such as,.

The SMB 'Inter-Process Communication' (IPC) system provides and was one of the first inter-process mechanisms commonly available to programmers that provides a means for services to inherit the authentication carried out when a client first connects to an SMB server. Some services that operate over named pipes, such as those which use Microsoft's own implementation of over SMB, known as over SMB, also allow MSRPC client programs to perform authentication, which overrides the authorization provided by the SMB server, but only in the context of the MSRPC client program that successfully makes the additional authentication.

Hopefully I can figure this out with your guys' help. When I send a text to some place like the radio station or a Taco Bell's number they say to text a code in, I receive a text back saying this: 'Free Msg: Unable to send message - Message Blocking is active'. But my phone settings are NOT rejecting anything. Most usage of SMB involves computers running Microsoft Windows, where it was known as 'Microsoft Windows Network' before the introduction of Active Directory. Corresponding Windows services are LAN Manager Server (for the server component) and LAN Manager Workstation (for the client component).

SMB signing: Windows NT 4.0 Service Pack 3 and upwards have the capability to use cryptography to SMB connections. The most common official term is 'SMB signing'. Other terms that have been used officially are 'SMB Security Signatures', 'SMB sequence numbers' and 'SMB Message Signing'. SMB signing may be configured individually for incoming SMB connections (handled by the 'LanManServer' service) and outgoing SMB connections (handled by the 'LanManWorkstation' service). The default setting from Windows 98 and upwards is to outgoing connections whenever the server also supports this. And to to unsigned SMB if both partners allow this.

The default setting for Windows from and upwards is to not allow fall back for incoming connections. The feature can also be turned on for any server running Windows NT 4.0 Service Pack 3 or later. This protects from against the Clients retrieving their from domain controllers at login. The design of Server Message Block version 2 (SMB2) aims to mitigate this performance limitation by coalescing SMB signals into single packets.

SMB supports —a special type of locking-mechanism—on files in order to improve performance. SMB serves as the basis for Microsoft's implementation. History SMB / CIFS / SMB1 Barry Feigenbaum originally designed SMB at with the aim of turning local file access into a networked file system. Has made considerable modifications to the most commonly used version.

Microsoft merged the SMB protocol with the product which it had started developing for with around 1990, and continued to add features to the protocol in ( c. 1992) and in later versions of Windows. SMB was originally designed to run on top of the /NetBEUI (typically implemented with, NetBIOS over, or ). Since, SMB runs, by default, with a thin layer, similar to the Session Message packet of NBT's Session Service, on top of, using TCP port 445 rather than TCP port 139—a feature known as 'direct host SMB'. Windows Server 2003, and older devices use SMB1/CIFS natively.

SMB1/CIFS is an extremely chatty protocol, in that it makes inefficient use of networking resources, particularly when transported over expensive WAN links. While Microsoft estimates that SMB1/CIFS comprises less than 10% of network traffic in the average Enterprise network, that is still a significant amount of traffic. One approach to mitigating the inefficiencies in the protocol is to use WAN Acceleration products such as those provided by Riverbed, Silver Peak, or Cisco Systems. A better approach is simply to eliminate SMB1/CIFS by upgrading the server infrastructure that uses it. This includes both NAS devices as well as Windows Server 2003. The most effective method in use currently to identify SMB1/CIFS traffic is to use a network analyzer tool such as Wireshark, etc., to identify SMB1/CIFS 'talkers' and then decommission or upgrade them over time.

Microsoft also provides an auditing tool in Microsoft Server 2016, which can be used to track down SMB1/CIFS talkers. In 1996 when Sun Microsystems announced, Microsoft launched an initiative to rename SMB to Common Internet File System (CIFS), and added more features, including support for, larger file sizes, and an initial attempt at supporting direct connections over TCP port 445 without requiring as a transport (a largely experimental effort that required further refinement). Microsoft submitted some partial specifications as to the, though these submissions have expired. SMB 2.0 Microsoft introduced a new version of the protocol (SMB 2.0 or SMB2) with in 2006. 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.

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. It has mechanisms for, that is, sending additional requests before the response to a previous request arrives, thereby improving performance over high links. It adds the ability to compound multiple actions into a single request, which significantly reduces the number of the client needs to make to the server, improving performance as a result. SMB1 also has a compounding mechanism—known as AndX—to compound multiple actions, but Microsoft clients rarely use AndX. 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. Other improvements include caching of file properties, improved message signing with hashing algorithm and better scalability by increasing the number of users, shares and open files per server among others.

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, thereby removing previous constraints on block sizes, which improves performance with large file transfers over fast networks. Windows Vista/ 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' solutions. Samba 3.5 also includes experimental support for SMB2.

Samba 3.6 fully supports SMB2, except the modification of user quotas using the Windows quota management tools. When SMB2 was introduced it brought a number of benefits over SMB1 for third party implementers of SMB protocols. SMB1, originally designed by, was, and later became part of a wide variety of non-Windows operating systems such as, and. Standardized it partially; it also had draft standards which lapsed. (See 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 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 is also migrating to SMB2 (from their own, now legacy) with OS X 10.9. This transition was fraught with compatibility problems though. 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.

Apple switched to its own SMBX implementation after Samba adopted. The 's CIFS client file system has SMB2 support since version 3.7.

SMB 2.1 SMB 2.1, introduced with Windows 7 and Server 2008 R2, introduced minor performance enhancements with a new opportunistic locking mechanism. SMB 3.0 SMB 3.0 (previously named SMB 2.2) was introduced with and. It brought several significant changes that are intended to add functionality and improve SMB2 performance, notably in virtualized:. the SMB Direct Protocol (SMB over (RDMA)).

SMB Multichannel (multiple connections per SMB session),. SMB Transparent Failover It also introduces several security enhancements, such as and a new based signing algorithm.

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; in those and later releases, the earlier SMB version 1 can be optionally disabled to increase security. SMB 3.1.1 SMB 3.1.1 was introduced with and. This version supports encryption in addition to AES 128 encryption added in SMB3, and implements pre-authentication integrity check using hash. SMB 3.1.1 also makes secure negotiation mandatory when connecting to clients using SMB 2.x and higher. Implementation Client-server approach SMB works through a approach, where a makes specific requests and the server responds accordingly. One section of the SMB protocol specifically deals with access to, such that clients may make requests to a; but some other sections of the SMB protocol specialize in (IPC).

The Inter-Process Communication (IPC) share, or ipc$, is a network share on computers running Microsoft Windows. This virtual share is used to facilitate communication between processes and computers over SMB, often to exchange data between computers that have been authenticated. Developers have optimized the SMB protocol for local usage, but users have also put SMB to work to access different subnets across the Internet— involving file-sharing or print-sharing in MS Windows environments usually focus on such usage. SMB servers make their file systems and other available to clients on the network. Client computers may want access to the shared file systems and printers on the server, and in this primary functionality SMB has become best-known and most heavily used. However, the SMB file-server aspect would count for little without the suite of protocols, which provide NT-style domain-based at the very least.

Almost all implementations of SMB servers use NT Domain authentication to validate user-access to resources. This section needs to be updated. Please update this article to reflect recent events or newly available information. (April 2016) In 1991 started the development of Samba, a re-implementation (using ) of the SMB/CIFS networking protocol for systems, initially to implement an SMB server to allow PC clients running the client to access files on machines. Because of the importance of the SMB protocol in interacting with the widespread platform, Samba became a popular implementation of a compatible SMB client and server to allow non-Windows operating systems, such as 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 server domain, either as a (PDC) or as a domain member.

Samba4 installations can act as an domain controller or member server, at Windows 2008 domain and functional levels. Note in relation to Samba the use of the Linux cifs-utils package. NQ NQ is portable SMB client and server implementations developed by, an Israel-based company established in 1998 by Sam Widerman, formerly the CEO of Data Communications. The NQ family comprises an Embedded SMB stack (written in C and Java) and a Storage SMB implementation, all support the latest SMB3.1.1 dialect.

NQ is to any non-Windows platform such as, and all other. MoSMB MoSMB is a proprietary SMB implementation for Linux and other systems, developed by Ryussi Technologies. It supports only SMB 2.x and SMB 3.x.

Tuxera SMB Tuxera SMB is a proprietary SMB server implementation developed by that can be run either in kernel. It supports SMB 3.0 and previous versions. Likewise Likewise developed a CIFS/SMB implementation (versions 1.0, 2.0, 2.1 and NFS 3.0) back in 2009 that provided a multiprotocol, identity-aware platform for network access to files used in 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 in 2012.

CIFSD is an open source In-kernel CIFS/SMB server implemenation for Linux kernel. It has the following advantages over user-space implementations: It provides better performance, and it's easier to implement some features like SMB Direct. It supports SMB 3.1.1 and previous versions. Performance issues The use of the SMB protocol has often correlated with a significant increase in 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. By default, a 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 (WINS) or (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 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. Have found that has a significant impact on the performance of the SMB 1.0 protocol, that it performs more poorly than other protocols like. Monitoring reveals a high degree of 'chattiness' and a disregard of network latency between hosts. For example, a connection over the 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 protocol, that was originally designed for small; it has a block size that is limited to 64K, SMB signing creates an additional overhead and the is not optimized for WAN links. Solutions to this problem include the updated SMB 2.0 protocol, and devices from various network vendors that cache and optimize SMB 1.0 and 2.0.

Microsoft's modifications Microsoft added several extensions to its own SMB implementation. For example, it added, then NTLMv2 authentication protocols in order to address security weakness in the original. LAN Manager authentication was implemented based on the original legacy SMB specification's requirement to use IBM 'LAN Manager' passwords, but implemented in a that allowed passwords to be cracked. Later, authentication was also added. The logon protocols initially used outside of the, because of export restrictions on stronger 128-bit encryption (subsequently lifted in 1996 when President signed ). Opportunistic locking support has changed with each server release.

Opportunistic locking In the SMB protocol, opportunistic locking is a mechanism designed to improve performance by controlling of network files by the client. Unlike traditional, OpLocks are not strictly 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 MS-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.

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 2 OpLock' from the server. A Level 2 OpLock allows the caching of read requests but excludes write caching. Filter OpLocks Added in NT 4.0., Filter Oplocks are similar to Level 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 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. Security Over the years, there have been many security vulnerabilities in Microsoft's implementation of the protocol or components on which it directly relies. Other vendors' security vulnerabilities lie primarily in a lack of support for newer like and in favor of protocols like NTLMv1, or plaintext passwords. Real-time attack tracking shows that SMB is one of the primary attack vectors for intrusion attempts, for example the, and the of 2017.

Specifications. This section needs expansion with: WSPP, PFIF. You can help. (January 2014) The specifications for the SMB are proprietary and were originally closed, thereby forcing other vendors and projects to reverse-engineer the protocol in order 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 MSDN Open Specifications Developer Center from the outset. There are a number of specifications that are relevant to the SMB protocol:. MS-CIFS is a recent replacement (2007) for the draft-leach-cifs-v1-spec-02.txt a document widely used to implement SMB clients, but also known to have errors of omission and commission. Specification for Microsoft Extensions to. Specification for the SMB 2 and SMB 3 protocols. Describes the intended functionality of the Windows File Access Services System, how it interacts with systems and applications that need file services, and how it interacts with administrative clients to configure and manage the system.

SMB2 Remote Direct Memory Access (RDMA) Transport Protocol Specification See also. Microsoft TechNet Library. Retrieved August 20, 2013.

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The Common Internet File System (CIFS) is the standard way that computer users share files across corporate intranets and the Internet. An enhanced version of the Microsoft open, cross-platform Server Message Block (SMB) protocol, CIFS is a native file-sharing protocol in Windows 2000. Microsoft MSDN Library. July 25, 2013. Retrieved August 20, 2013. The Server Message Block (SMB) Protocol is a network file sharing protocol, and as implemented in Microsoft Windows is known as Microsoft SMB Protocol.

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