Event logsīoth SMB Client and SMB Server have a detailed event log structure, as shown in the following screenshot. Optionally, you might also temporarily uninstall the antivirus program during troubleshooting. You contact the antivirus program manufactory to resolve the issue. Removing an antivirus program resolves the slow file transfers. The two-sided traces show that the SRV responds slowly to a READ request. You experience slow file transfers to a single file server. If all other options fail, collect a t.cmd if you suspect that the issue occurs within SMB itself, or if none of the other data is sufficient to identify a root cause. ![]() Run the netsh command to trace and gather details about whether there are issues in the network stack or drops in Windows Filtering Platform (WFP) applications, such as firewall or antivirus program. If it is not, collect data that is closer to or at a lower level to look for more information about the root cause. You can learn a lot about what the application is trying to do by examining the SMB commands.Ĭompare the commands and operations to the protocol specification to make sure that everything is operating correctly. Remember that SMB does only what it is told to do. Only Message Analyzer can parse SMBv3 and later version commands. ![]() Look at the actual SMB protocol details in the network trace to understand the exact commands and options that are used. If the connection ended prematurely, identify the last exchange communication between the client and server. This process might fail because a WAN optimizer is modifying the SMB Negotiate packet. The SMB session must be terminated (TCP reset) when the Validate Negotiate process fails on either the client or the server. If so, refer to the following information: The MS-SMB2 Server Processing topic details how the SMB server creates requests and responds to client requests.Ĭheck whether a TCP reset command is sent immediately after an FSCTL_VALIDATE_NEGOTIATE_INFO (validate negotiate) command. The MS-SMB2 Client Processing topic details how the SMB client creates requests and responds to server messages. The MS-SMB2 Message Syntax topic details each SMB command and its options. Refer to the following information to determine why SMB returned the error before you conclude that the error is related to any of the following issues: Many SMB errors are benign (not harmful). To do this, follow these steps:Īlways check SMB errors against the MS-SMB2 protocol specification. If there is no noticeable TCP/IP issue, look for SMB errors. This can be caused by slow storage or some other issue that prevents data from being retrieved from the Ancillary Function Driver (AFD) Winsock buffer. These can cause slow file transfers because of compound TCP congestion throttling.įive retransmits followed by a TCP reset could mean that the connection between systems was lost, or that one of the SMB services crashed or stopped responding. This typically indicates that there is a firewall block, or that the Server service is not running. The TCP three-way handshake does not finish. Therefore, an SMB issue can also be caused by TCP/IP issues.Ĭheck whether TCP/IP experiences any of these issues: SMB is an application-level protocol that uses TCP/IP as the network transport protocol. For performance issues, always take both a good and bad trace, if the situation allows it. You should trace only a minimum amount of the data that's transferred. This section provides the steps for using netshell to collect network trace. To discover the source of the issue, you can check the two-sided traces: CLI, SRV, or somewhere in between. Stop collecting data by using Ctrl+C from keyboard. For example, if the SMB client or SMB server is a Unix host, you can collect data by running the following command: # tcpdump -s0 -n -i any -w /tmp/$(hostname)-smbtrace.pcap Third-party devices generally have an in-box packet capture tool, such as tcpdump (Linux/FreeBSD/Unix), or pktt (NetApp). On Windows systems, you can use netshell (netsh), Network Monitor, Message Analyser, or Wireshark to collect a network trace. Collect dataīefore you troubleshoot SMB issues, we recommend that you first collect a network trace on both the client and server sides. ![]() The SMB Client (CLI) refers to the system that is trying to access the file system, regardless of the OS version or edition.įor example, if you use Windows Server 2016 to reach an SMB share that is hosted on Windows 10, Windows Server 2016 is the SMB Client and Windows 10 the SMB Server. ![]() The SMB Server (SRV) refers to the system that is hosting the file system, also known as the file server.
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