IIS FTP log analysis is not complicated, the key is to understand the meaning of the field and the status code. The log is in W3C format by default. Each row of records contains fields such as date, time, c-ip, cs-username, s-ip, s-port, cs-method, cs-uri-stem, sc-status, sc-win32-status, etc., which are used to describe an FTP operation. Common cs-method commands include USER (login), PASS (password verification), RETR (download), STOR (upload), LIST (column directory), etc. These commands can determine user behavior. The sc-status status code is used to judge the operation result. For example, 226 indicates that the transmission is successful, 530 indicates that the login failed, 550 indicates that the file is unavailable, and 425 indicates that the data connection has failed. During analysis, you can use Excel to open the logs, filter by IP or username, and pay attention to frequent failed logins or large number of file transfers. Combined with Windows event logs, you can further troubleshoot the root cause of the problem. After mastering these key points, you can quickly locate FTP connection exceptions, permission issues, or potential attacks.

Interpreting IIS FTP log files is actually not complicated, but for those who are new to it, they may find the information messy and the format difficult to understand. IIS FTP logs use W3C extended log format by default. Each record contains multiple fields, indicating client IP, operation type, file path, status code, etc. Understanding these contents can help troubleshoot connection problems, analyze access behavior, and even detect abnormal activities.

1. Understand the basic structure of log files

Each line of the IIS FTP log represents an operation and consists of multiple fields. The common fields are as follows:

• date : date
• time : time
• c-ip : client IP address
• cs-username : login username
• s-ip : Server IP address
• s-port : server port
• cs-method : FTP commands (such as USER, PASS, RETR, STOR, LIST, etc.)
• cs-uri-stem : the requested file or path
• sc-status : response status code
• sc-win32-status : Windows system error code (if any)

For example, a line of logs might look like this:

 2024-03-15 10:23:45 192.168.1.100 21 FTP - - 192.168.1.101 50000 RETR /files/report.txt 226 0

This means that the client IP is 192.168.1.101 /files/report.txt was downloaded from the server at a specified time, and the operation was successful (status code 226).

2. Common FTP operations and corresponding commands (cs-method)

Understanding cs-method field is very important for judging user behavior. Here are some common FTP commands and their meanings:

• USER / PASS : User login attempt
• RETR : Download the file
• STOR : Upload file
• LIST : List the contents of the directory
• DELE : Delete the file
• MKD : Create a directory
• RMD : Delete the directory
• CWD : Switch the current directory

If you see a large number of RETR or STOR operations in the log, it means that the user is frequently transferring files. And if you see a lot of USER and failed PASS , you may be trying to brute force.

3. Status code interpretation (sc-status)

The status code is the key to determining whether the operation is successful:

• 226 : Transmission completed (download or upload successfully)
• 230 : Login successfully
• 530 : Login failed
• 550 : File is unavailable or has insufficient permissions (such as trying to download a non-existent file or no read permission)
• 425 : Unable to open data connection (commonly related to firewall or NAT configuration issues)
• 421 : Service is unavailable or disconnected from timeout

If you see a lot of 550 or 425 , you need to check the permission settings or network configuration.

4. Log analysis tips and tool suggestions

• Open logs using Excel or text editor : The log is in plain text format and can be opened in Notepad, but it is more convenient to view field columns with Excel.
• Filter a specific IP or operation : For example, to find an operation of a certain user, it can be filtered through cs-username or c-ip .
• Pay attention to abnormal login behavior : If a large number of failed logins appear in the log (status code 530) and multiple user names are tried, it may be a brute-force attack.
• Analyze with system logs : FTP logs do not record detailed error reasons, but there may be more detailed error information in Windows Event Viewer.

Basically that's it. After mastering these key points, you will no longer be confused when reading the IIS FTP log. As long as you are familiar with the meaning of the field and common status codes, you can quickly locate problems, such as user login failures, file download exceptions, etc.

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