MAXFWD module

Admin Guide

Overview

The module implements all the operations regarding MaX-Forward header field, like adding it (if not present) or decrementing and checking the value of the existent one.

Dependencies

OpenSIPS Modules

The following modules must be loaded before this module:

• No dependencies on other OpenSIPS modules.

External Libraries or Applications

The following libraries or applications must be installed before running OpenSIPS with this module loaded:

• None.

Exported Parameters

max_limit (integer)

Set an upper limit for the max-forward value in the outgoing requests. If the header is present, the decremented value is not allowed to exceed this max_limits - if it does, the header value will by decreased to “max_limit”.

Note: This check is done when calling the mf_process_maxfwd_header() header.

The range of values stretches from 1 to 256, which is the maximum MAX-FORWARDS value allowed by RFC 3261.

Default value is “256”.

Set max_limit parameter

...
modparam("maxfwd", "max_limit", 32)
...

Exported Functions

mf_process_maxfwd_header(max_value)

If no Max-Forward header is present in the received request, a header will be added having the original value equal with “max_value”. If a Max-Forward header is already present, its value will be decremented (if not 0).

Retuning codes:

• 2 (true) - header was not found and a new header was successfully added.
• 1 (true) - header was found and its value was successfully decremented (had a non-0 value).
• -1 (false) - the header was found and its value is 0 (cannot be decremented).
• -2 (false) - error during processing.

The return code may be extensivly tested via script variable “retcode” (or ”$?”).

Meaning of the parameters is as follows:

• max_value (int) - Value to be added if there is no Max-Forwards header field in the message.

This function can be used from REQUEST_ROUTE.

mx_process_maxfwd_header usage

...
# initial sanity checks -- messages with
# max_forwards==0, or excessively long requests
if (!mf_process_maxfwd_header(10) && $retcode==-1) {
  sl_send_reply(483,"Too Many Hops");
  exit;
};
...

is_maxfwd_lt(max_value)

Checks if the Max-Forward header value is less then the “max_value” parameter value. It considers also the value of the new inserted header (if locally added).

Retuning codes:

• 1 (true) - header was found or set and its value is strictly less than “max_value”.
• -1 (false) - the header was found or set and its value is greater or equal to “max_value”.
• -2 (false) - header was not found or not set.
• -3 (false) - error during processing.

The return code may be extensivly tested via script variable “retcode” (or ”$?”).

Meaning of the parameters is as follows:

• max_value (int) - value to check the Max-Forward.value against (as less than).

is_maxfwd_lt usage

...
# next hope is a gateway, so make no sens to
# forward if MF is 0 (after decrement)
if ( is_maxfwd_lt(1) ) {
  sl_send_reply(483,"Too Many Hops");
  exit;
};
...

Contributors

By Commit Statistics

Top contributors by DevScore⁽¹⁾, authored commits⁽²⁾ and lines added/removed⁽³⁾

#	Name	DevScore	Commits	Lines++	Lines—
1.	Bogdan-Andrei Iancu (@bogdan-iancu)	47	30	889	509
2.	Liviu Chircu (@liviuchircu)	12	10	26	53
3.	Jan Janak (@janakj)	11	9	58	38
4.	Daniel-Constantin Mierla (@miconda)	11	9	23	19
5.	Andrei Pelinescu-Onciul	10	8	31	26
6.	Jiri Kuthan (@jiriatipteldotorg)	9	7	93	7
7.	Razvan Crainea (@razvancrainea)	9	7	11	10
8.	Vlad Patrascu (@rvlad-patrascu)	6	4	37	46
9.	Stefan Darius (@dariusstefan)	6	3	190	26
10.	Henning Westerholt (@henningw)	4	2	3	3

All remaining contributors: Konstantin Bokarius, Peter Lemenkov (@lemenkov), Walter Doekes (@wdoekes), Andreas Heise, Edson Gellert Schubert, Nils Ohlmeier, Klaus Darilion, Elena-Ramona Modroiu.

(1) DevScore = author_commits + author_lines_added / (project_lines_added / project_commits) + author_lines_deleted / (project_lines_deleted / project_commits)

(2) including any documentation-related commits, excluding merge commits

(3) ignoring whitespace edits, renamed files and auto-generated files

By Commit Activity

#	Name	Commit Activity
1.	Stefan Darius (@dariusstefan)	Jun 2026 - Jul 2026
2.	Razvan Crainea (@razvancrainea)	Feb 2012 - Jun 2026
3.	Liviu Chircu (@liviuchircu)	Jan 2014 - May 2024
4.	Vlad Patrascu (@rvlad-patrascu)	May 2017 - Apr 2019
5.	Bogdan-Andrei Iancu (@bogdan-iancu)	Jan 2002 - Apr 2019
6.	Peter Lemenkov (@lemenkov)	Jun 2018 - Jun 2018
7.	Walter Doekes (@wdoekes)	May 2014 - May 2014
8.	Daniel-Constantin Mierla (@miconda)	Nov 2006 - Mar 2008
9.	Konstantin Bokarius	Mar 2008 - Mar 2008
10.	Edson Gellert Schubert	Feb 2008 - Feb 2008

All remaining contributors: Henning Westerholt (@henningw), Klaus Darilion, Andreas Heise, Elena-Ramona Modroiu, Jan Janak (@janakj), Andrei Pelinescu-Onciul, Nils Ohlmeier, Jiri Kuthan (@jiriatipteldotorg).

(1) including any documentation-related commits, excluding merge commits

Documentation

Contributors

Last edited by: Razvan Crainea (@razvancrainea), Vlad Patrascu (@rvlad-patrascu), Liviu Chircu (@liviuchircu), Peter Lemenkov (@lemenkov), Bogdan-Andrei Iancu (@bogdan-iancu), Daniel-Constantin Mierla (@miconda), Konstantin Bokarius, Edson Gellert Schubert, Klaus Darilion, Elena-Ramona Modroiu.

License

All documentation files (i.e. .md extension) are licensed under the Creative Common License 4.0