README
1mod_limitipconn.c
2David Jao <djao@dominia.org>
3
4This is an Apache 2.4/2.2/2.0 C module whose purpose is to limit the
5maximum number of simultaneous connections per IP address. It supports
6IPv4 and IPv6 connections. The module allows inclusion and exclusion of
7files based on MIME type.
8
9This module is not designed to prevent denial-of-service attacks. Its
10function is only to deny users the ability to use large numbers of
11simultaneous connections.
12
13Tested with httpd-2.4.2 and httpd-2.2.17. Should work with httpd-2.0 but
14has not been tested.
15
16Example configuration:
17
18---------------------------------------------------------------------------
19
20# This command is always needed
21ExtendedStatus On
22
23# Only needed if the module is compiled as a DSO
24LoadModule limitipconn_module lib/apache/mod_limitipconn.so
25
26<IfModule mod_limitipconn.c>
27
28 # Set a server-wide limit of 10 simultaneous downloads per IP,
29 # no matter what.
30 MaxConnPerIP 10
31 <Location /somewhere>
32 # This section affects all files under http://your.server/somewhere
33 MaxConnPerIP 3
34 # exempting images from the connection limit is often a good
35 # idea if your web page has lots of inline images, since these
36 # pages often generate a flurry of concurrent image requests
37 NoIPLimit image/*
38 </Location>
39
40 <Directory /home/*/public_html>
41 # This section affects all files under /home/*/public_html
42 MaxConnPerIP 1
43 # In this case, all MIME types other than audio/mpeg and video*
44 # are exempt from the limit check
45 OnlyIPLimit audio/mpeg video
46 </Directory>
47</IfModule>
48
49---------------------------------------------------------------------------
50
51Notes:
52
531) This module will not function unless mod_status is loaded and the
54 "ExtendedStatus On" directive is set.
55
562) Server-wide access restrictions and per-directory access restrictions
57 are computed separately. In the above example, if someone is
58 downloading 11 images from http://your.server/somewhere
59 simultaneously, they WILL be denied on the 11th download, because the
60 server-wide limit of 10 downloads is not affected by the per-directory
61 NoIPLimit. If you want to set global settings which can be overruled
62 by per-directory settings, you will need something like
63
64 <Location />
65 # global per-directory settings here
66
67 <Location /somewhere>
68 # local per-directory settings here
69
70 </Location>
71
72 </Location>
73
743) If you are using any module based upon a quick handler hook (such as
75 mod_cache), mod_limitipconn will not be able to process any
76 per-directory configuration directives in time to affect the return
77 result of the other module. This is a technical limitation imposed
78 by Apache. In such a situation, you will have to use server-wide
79 configuration directives only.
80
81 Versions of mod_limitipconn prior to 0.23 did not allow any
82 server-wide configuration directives, and hence could not be used
83 with mod_cache at all.
84
854) The limits defined by mod_limitipconn.c apply to all IP addresses
86 connecting to your Apache server. Currently there is no way to set
87 different limits for different IP addresses. One workaround is to set
88 up two different URIs for the same content and use access control to
89 restrict which IP addresses can access which URIs.
90
915) Connections in excess of the limit result in a stock 503 Service
92 Temporarily Unavailable response. The job of returning a more useful
93 error message to the client is left as an exercise for the reader.
94
956) mod_limitipconn sets the LIMITIP environment variable to 1 whenever a
96 download is denied on the basis of too high an IP count. You can use
97 this variable to distinguish accesses that have been denied by this
98 module. For example, a line like
99
100 CustomLog /var/log/httpd/access_log common env=!LIMITIP
101
102 in httpd.conf can be used to suppress logging of denied connections
103 from /var/log/httpd/access_log. (Note that, if you really want to
104 suppress logging, you'll probably also want to comment out the
105 ap_log_rerror lines from mod_limitipconn.c as well.)
106
1077) By default, all clients behind a proxy are treated as coming from the
108 proxy server's IP address. If you wish to alter this behavior,
109 use the mod_remoteip module included in Apache 2.4.
110