Filter Files

Filter configuration (ctrl/*.cfg) and trash can (text/*.can) files allow the sysop to specify words (or any sequence of characters) that will be used to disallow clients, users, or their content.

Each line in a filter file may contain a comparison sequence. Blank lines and lines beginning with a semicolon are ignored.

Note: Prior to v3.17c, leading white-space in filter file lines was ignored. As of v3.17c, leading white-space *is* significant and can be used for filters such “ *” to filter (reject) any matches that begin with a leading space character.

• Sequences of alphabetic letters are treated case-insensitively
• Sequences beginning with an exclamation mark (!) negate the match logic for that sequence
• Sequences beginning with an asterisk (*) match only if the characters following the * are found at the end of the comparison string
• Sequences ending with an asterisk (*) or caret (^) match only if the characters preceding are found at the beginning of the comparison string
• Sequences ending with a tilde (~) match when the preceding string of characters are found anywhere within the comparison string
• All other sequences are “exact match” string comparisons

Examples:

• sysop in the name.can file would mean users could not use the name “sysop”.
• sysop* would mean users could not use names beginning with the word “sysop”, like “sysopa” or “sysops” etc.
• sysop~ would mean users could not use names that have the word “sysop” anywhere in them, like “imthesysop” or “Joe Sysop”.

An additional comparison format was introduced in v3.17 (Feb-9-2017) specifically for partial (ranges of) IPv4 address matching following standard Classless_Inter-Domain_Routing (CIDR) notation. For example, rather than using the comparison string “192.168.1.*” to match all IP addresses that begin with the first 3 octets of 192, 168, and 1, you could specify the same thing using CIDR notation:

192.168.1.0/24

This enables the flexibility of filtering ranges of IP addresses based on sub-networks that are not multiples of 8-bits (e.g. “192.168.1.33/30”) and the format is compatible with commonly available regional block lists.

All 4 octets of the IPv4 address must be specified in the CIDR comparison string (i.e. “192.168.1/24” is not a valid CIDR comparison string).

CIDR comparisons beginning with the negation prefix (!) are supported (reverses the IP address comparison logic).

IPv6 CIDR notation is not supported at this time.

The following table lists the supported trash can files, a description of their use, and optional rejection message (.msg) files that may be displayed to users that are (or have their content) filtered. Trash can files and their respective optional rejection message files are located in the text directory:

The following table lists other supported filter files and a description of their use. These filter files are located in the ctrl directory and do not have a respective response message file:

The following table lists supported filter exemption files and a description of their use. These filter exemption files are located in the ctrl directory:

• Configuration