---
name: "flow-mask"
section: "1"
platform: "linux"
package: "flow-tools"
version: "1:0.68-12.5+b3"
release: "Debian 10 (Buster)"
platforms: ["linux"]
url: "https://new.carta.tech/flow-mask"
---

# flow-mask(1)

Apply tags to flow files.

## NAME

**flow-mask** — Apply tags to flow files.

## SYNOPSIS

**flow-mask** \[-hk\]  \[-b *big*\|*little*\]  \[-C *comment*\]  \[-d *debug\_level*\]  \[-m *mask\_fname*\]  \[-M *active\_def* ...\]

## DESCRIPTION

The **flow-mask** utility is used to modify the source and destination mask length's in flow records.

## OPTIONS

- \-b *big*\|*little*

  Byte order of output.

- \-C *Comment*

  Add a comment.

- \-d *debug\_level*

  Enable debugging.

- \-h

  Display help.

- \-k

  Keep time from input.

- \-m *mask\_fname*

  Load masks from **mask\_name**.  Defaults to  **/etc/flow-tools/cfg/mask**

- \-M *mask\_def*

  Use *active\_def* as the active tag definition(s).

The configuration file is a collection of definitions.  A definition lists a sequence of prefixes and the mask length to replace the matching prefix with. Lines begining with # are treated as comments and ignored.

```
mask-definition command             Description
----------------------------------------------------------------------
mask-definition                     Begin mask-definition section
                                    mask-definition foo
prefix                              List the prefix to match on and the
                                    replacement mask.
                                    prefix 128.146/16 24
```

## EXAMPLES

```
#
#file: masks
#
mask-definition foo
# All networks in 128.146/16 are /24's.
 prefix 128.146/16 24
# except for 128.146.214/24, which are /32's.
 prefix 128.146.214/24 32
```

**flow-cat flows \| flow-mask -mfoo -Fmasks \| flow-print -f4**

## FILES

  **Configuration files:**\
     **Mask - /etc/flow-tools/cfg/mask.cfg.**

## BUGS

**None known.**

## AUTHOR

**Mark Fullmer maf@splintered.net**

## SEE ALSO

**[flow-tools(1)](/flow-tools/1.md)**