How to use a CIDR netmask to block an IP address range using .htaccess

This article explains why you must sometimes use CIDR netmask notation to ban an IP address range using Apache .htaccess, and how to do it. It is intended to supplement the basic Apache information about mod_access in the documentation at http://httpd.apache.org/docs/1.3/mod/mod_access.html.

An IP address is a 32-bit binary number that uniquely identifies a computer on the internet

32-bit binary is hard to remember : 11000000010000000000000000000000

Decimal notation isn't much easier: 3225419776

So it is usually written like this     : 192.64.0.0

You get this "dotted-quad notation" by breaking the 32 bits into 4 groups of 8 and then converting each group to decimal:

11000000	01000000	00000000	00000000
192	64	0	0

192.64.0.0

That makes it easier to remember, but it creates problems if you try to use it for calculations.

An IP address contains two pieces of information:

1. The leftmost binary digits are the unique ID of the network (usually your Internet Service Provider, ISP) through which you are connected to the internet.


2. The remaining binary digits are your unique ID as an individual user on that network.

The number of leftmost digits used for network ID is not the same for every network. In CIDR notation, the /nn part says how many of the leftmost bits indicate the network.

If the network uses exactly the leftmost 8, 16, or 24 bits for its ID, then the dividing line between network and user falls on one of the period boundaries of the dotted-quad notation, and one of the partial IP notations will work:

.htaccess partial IP address	Equivalent CIDR
deny from 192	deny from 192.0.0.0/8
deny from 192.64	deny from 192.64.0.0/16
deny from 192.64.0	deny from 192.64.0.0/24

Each quad that you don't specify is treated as a wildcard that can take any value from 0 to 255. So the first example bans any IP address that starts with 192., followed by anything.

When to use CIDR notation

If the network doesn't use exactly 8, 16, or 24 bits for the network part of the IP address, the dividing line between network and user does not fall on a period boundary of dotted-quad notation, and you need to use a CIDR netmask.

Example CIDR/netmask:

192.64.0.0/10

This says the base address of the network is 192.64.0.0 and the first 10 bits are the network:

192 64 0 0 = 11000000 01000000 00000000 00000000

192 is the first 8 bits, but two more bits are part of the network ID, too. The 9th bit is 0 and the 10th is 1, and that is where the 64 comes from.

The full range of this network in quad notation is 192.64.0.0 - 192.127.255.255. Note that the 64 in the second position doesn't remain constant. The first 2 bits are always the same, but the righthand 6 will be different for different users.

The simple notations for an .htaccess ban won't work. Why not?

• deny from 192 would ban the range 192.0.0.0 - 192.255.255.255, which will ban some users that are not coming from this network.


• deny from 192.64 would ban the range 192.64.0.0 - 192.64.255.255, which is insufficient to ban all the users that are coming from this network.

So the answer is CIDR notation and an .htaccess line that says:

deny from 192.64.0.0/10

This says the base address is 192.64.0.0, and the first 10 bits identify the network (those are always the same for all users who are on that network).

To ban a specific IP range in htaccess

1. Figure out, from your website access logs or elsewhere, the IP addresses you want to ban. Look them up in a WhoIs database such as http://whois.domaintools.com/.
   
   


2. Determine whether you need to use a CIDR netmask. If the IP address range in the report looks like one of these, with each quad after the leading one(s) showing a rull range of 0-255, then you can use one of the simpler methods:
   
   
   
   192.0.0.0 - 192.255.255.255   -- Use deny from 192
   
   192.64.0.0 - 192.64.255.255   -- Use deny from 192.64
   
   192.64.128.0 - 192.64.128.255 -- Use deny from 192.64.128
   
   


3. For anything else, you need CIDR. At Domain Tools, the CIDR netmask is sometimes shown in the report for that IP address, several lines down in the report. If it is, that's all you need. You're ready to create the line in your .htaccess file. Go to Step 5.
   
   


4. If the CIDR wasn't given, you can calculate it yourself with a netmask calculator such as http://jodies.de/ipcalc.
   
   
   
   a) Enter the base (lowest) address. 
   
   
   
   b) You can simply determine the netmask (the /nn part) by trial and error, or you can calculate the minimum size to start with: take the rightmost nonzero quad of the base address and convert it to binary in your head or in Windows Calculator. Find the rightmost "1". The netmask will have to be sufficient to include all of the previous quads (at 8 bits each), plus all the digits in this quad up to its rightmost "1". That's the minimum. But it might include some of the trailing zeroes, too.
   
   
   
   c) Keep using trial and error for the netmask until HostMin and HostMax match the IP address range you saw in the Domain Tools report.

Note that final quads of 0 and 255 are reserved, so:



The calculated HostMin will be nnn.nnn.nnn.1,  not nnn.nnn.nnn.0

The calculated HostMax will be nnn.nnn.nnn.254 not nnn.nnn.nnn.255



The Hosts/Net line tells you how many users this network might have, which can help decide whether you really want to ban the entire range.

5. Edit your public_html/.htaccess file to add the "deny from" line:

1. Go to cPanel > File Manager.


2. Navigate to the file public_html/.htaccess.


3. Click on its file name (not the icon next to it).


4. In the upper right corner of the screen, click Edit File.


5. Make a backup copy: Copy all the text in the file, and save it into a file on your local computer so you can put it back into .htaccess if something goes wrong.


6. Backup made? Ok, now you can edit the file. On a blank line in a part of the file that is not between HTML-style tags like <tag></tag>, type the line:
   
   
   
   deny from nnn.nnn.nnn.nnn/nn
   
   
   
   Replace the nnn's with the IP/netmask you calculated for this range.
   
   
   
   Further explanation: some lines of your .htaccess file might be contained between tags that look like HTML tags where the opening tag looks like <tag> and the closing tag looks like </tag>. Insert this new line in a part of the file that is not between any of these pairs of tags.
   
   
   
   Depending on what is in your .htaccess, you might need to use your judgment whether to use the order and allow directives that are also provided by mod_access. See the link to Apache at the top of this article for more information. That is beyond the scope of this article, and it will require your judgment. I'd suggest adding only the "deny from" line at first and seeing if it works as expected. What is expected: you can access your website; most other people can, too; when the denied party tries, your logs will show a result code of 403 Forbidden.
   
   

Mod-Rewrite Tricks and Tips - .Htaccess rewrites rules

If you really want to take a look, check out the mod_rewrite.c and mod_rewrite.h files.

Be aware that mod_rewrite (RewriteRule, RewriteBase, and RewriteCond) code is executed for each and every HTTP request that accesses a file in or below the directory where the code resides, so it’s always good to limit the code to certain circumstances if readily identifiable.

For example, to limit the next 5 RewriteRules to only be applied to .html and .php files, you can use the following code, which tests if the url does not end in .html or .php and if it doesn’t, it will skip the next 5 RewriteRules.

---

RewriteRule !\.(html|php)$ - [S=5]  
RewriteRule ^.*-(vf12|vf13|vf5|vf35|vf1|vf10|vf33|vf8).+$ - [S=1]  

.htaccess rewrite examples should begin with:

Options +FollowSymLinks     
RewriteEngine On  RewriteBase /  

Require the www

Options +FollowSymLinks 
RewriteEngine On  
RewriteBase /  
RewriteCond %{HTTP_HOST} !^www\.yourdomain\.com$ [NC]  
RewriteRule ^(.*)$ http://www.yourdomain.com/$1 [R=301,L]  

Loop Stopping Code

Sometimes your rewrites cause infinite loops, stop it with one of these rewrite code snippets.

RewriteCond %{REQUEST_URI} ^/(stats/|missing\.html|failed_auth\.html|error/).* [NC]  
RewriteRule .* - [L]     
RewriteCond %{ENV:REDIRECT_STATUS} 200  
RewriteRule .* - [L]  

Cache-Friendly File Names

This is probably my favorite, and I use it on every site I work on. It allows me to update my javascript and css files in my visitors cache’s simply by naming them differently in the html, on the server they stay the same name. This rewrites all files for /zap/j/anything-anynumber.js to /zap/j/anything.js and /zap/c/anything-anynumber.css to /zap/c/anything.css

RewriteRule ^zap/(j|c)/([a-z]+)-([0-9]+)\.(js|css)$ /zap/$1/$2.$4 [L]  

SEO friendly link for non-flash browsers

When you use flash on your site and you properly supply a link to download flash that shows up for non-flash aware browsers, it is nice to use a shortcut to keep your code clean and your external links to a minimum. This code allows me to link to site.com/getflash/ for non-flash aware browsers.

RewriteRule ^getflash/?$ http://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=ShockwaveFlash [NC,L,R=307]  

Removing the Query_String

On many sites, the page will be displayed for both page.html and page.html?anything=anything, which hurts your SEO with duplicate content. An easy way to fix this issue is to redirect external requests containing a query string to the same uri without the query_string.

RewriteCond %{THE_REQUEST} ^GET\ /.*\;.*\ HTTP/  
RewriteCond %{QUERY_STRING} !^$  
RewriteRule .* http://www.askapache.com%{REQUEST_URI}? [R=301,L]  

Sending requests to a php script

This .htaccess rewrite example invisibly rewrites requests for all Adobe pdf files to be handled by /cgi-bin/pdf-script.php

RewriteRule ^(.+)\.pdf$  /cgi-bin/pdf-script.php?file=$1.pdf [L,NC,QSA]  

Setting the language variable based on Client

For sites using multiviews or with multiple language capabilities, it is nice to be able to send the correct language automatically based on the clients preferred language.

RewriteCond %{HTTP:Accept-Language} ^.*(de|es|fr|it|ja|ru|en).*$ [NC]  
RewriteRule ^(.*)$ - [env=prefer-language:%1]  

Deny Access To Everyone Except PHP fopen

This allows access to all files by php fopen, but denies anyone else.

RewriteEngine On  
RewriteBase /  
RewriteCond %{THE_REQUEST} ^.+$ [NC]  
RewriteRule .* - [F,L]  

If you are looking for ways to block or deny specific requests/visitors, then you should definately read Blacklist with mod_rewrite. I give it a 10/10

Deny access to anything in a subfolder except php fopen

This can be very handy if you want to serve media files or special downloads but only through a php proxy script.

RewriteEngine On  
RewriteBase /  
RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /([^/]+)/.*\ HTTP [NC]  
RewriteRule .* - [F,L]  

Require no www

Options +FollowSymLinks  
RewriteEngine On  
RewriteBase /  
RewriteCond %{HTTP_HOST} !^yourdomain\.com$ [NC]  
RewriteRule ^(.*)$ http://yourdomain.com/$1 [R=301,L]  

Check for a key in QUERY_STRING

Uses a RewriteCond Directive to check QUERY_STRING for passkey, if it doesn’t find it it redirects all requests for anything in the /logged-in/ directory to the /login.php script.

RewriteEngine On  RewriteBase /  
RewriteCond %{QUERY_STRING} !passkey  
RewriteRule ^/logged-in/(.*)$ /login.php [L]  

Removes the QUERY_STRING from the URL

If the QUERY_STRING has any value at all besides blank than the?at the end of /login.php? tells mod_rewrite to remove the QUERY_STRING from login.php and redirect.

RewriteEngine On  RewriteBase /  
RewriteCond %{QUERY_STRING} .  
RewriteRule ^login.php /login.php? [L]  

Fix for infinite loops

An error message related to this isRequest exceeded the limit of 10 internal redirects due to probable configuration error. Use 'LimitInternalRecursion' to increase the limit if necessary. Use 'LogLevel debug' to get a backtrace.or you may seeRequest exceeded the limit,probable configuration error,Use 'LogLevel debug' to get a backtrace, orUse 'LimitInternalRecursion' to increase the limit if necessary

RewriteCond %{ENV:REDIRECT_STATUS} 200  
RewriteRule .* - [L]  

External Redirect .php files to .html files (SEO friendly)

RewriteRule ^(.*)\.php$ /$1.html [R=301,L]  

Internal Redirect .php files to .html files (SEO friendly)

Redirects all files that end in .html to be served from filename.php so it looks like all your pages are .html but really they are .php

RewriteRule ^(.*)\.html$ $1.php [R=301,L]  

block access to files during certain hours of the day

Options +FollowSymLinks  
RewriteEngine On  
RewriteBase /  
# If the hour is 16 (4 PM) Then deny all access  
RewriteCond %{TIME_HOUR} ^16$  
RewriteRule ^.*$ - [F,L]  

Rewrite underscores to hyphens for SEO URL

Options +FollowSymLinks  
RewriteEngine On  
RewriteBase /     
RewriteRule !\.(html|php)$ - [S=4]  
RewriteRule ^([^_]*)_([^_]*)_([^_]*)_([^_]*)_(.*)$ $1-$2-$3-$4-$5 [E=uscor:Yes]  
RewriteRule ^([^_]*)_([^_]*)_([^_]*)_(.*)$ $1-$2-$3-$4 [E=uscor:Yes]  
RewriteRule ^([^_]*)_([^_]*)_(.*)$ $1-$2-$3 [E=uscor:Yes]  
RewriteRule ^([^_]*)_(.*)$ $1-$2 [E=uscor:Yes]     
RewriteCond %{ENV:uscor} ^Yes$  
RewriteRule (.*) http://d.com/$1 [R=301,L]  

Require the www without hardcoding

Options +FollowSymLinks  
RewriteEngine On  RewriteBase /  
RewriteCond %{HTTP_HOST} !^www\.[a-z-]+\.[a-z]{2,6} [NC]  
RewriteCond %{HTTP_HOST} ([a-z-]+\.[a-z]{2,6})$     [NC]  
RewriteRule ^/(.*)$ http://%1/$1 [R=301,L]  

Require no subdomain

RewriteEngine On  
RewriteBase /  
RewriteCond %{HTTP_HOST} \.([a-z-]+\.[a-z]{2,6})$ [NC]  
RewriteRule ^/(.*)$ http://%1/$1 [R=301,L]  

Require no subdomain

RewriteEngine On  
RewriteBase /  
RewriteCond %{HTTP_HOST} \.([^\.]+\.[^\.0-9]+)$  
RewriteRule ^(.*)$ http://%1/$1 [R=301,L]

Redirecting Wordpress Feeds to Feedburner

RewriteEngine On  
RewriteBase /  
RewriteCond %{REQUEST_URI} ^/feed\.gif$  
RewriteRule .* - [L]     
RewriteCond %{HTTP_USER_AGENT} !^.*(FeedBurner|FeedValidator) [NC]  
RewriteRule ^feed/?.*$ http://feeds.feedburner.com/apache/htaccess [L,R=302]     
RewriteCond %{REQUEST_FILENAME} !-f  
RewriteCond %{REQUEST_FILENAME} !-d  
RewriteRule . /index.php [L] 

Only allow GET and PUT Request Methods

RewriteEngine On  
RewriteBase /  
RewriteCond %{REQUEST_METHOD} !^(GET|PUT)  
RewriteRule .* - [F]  

Prevent Files image/file hotlinking and bandwidth stealing

RewriteEngine On  
RewriteBase /  
RewriteCond %{HTTP_REFERER} !^$  
RewriteCond %{HTTP_REFERER} !^http://(www\.)?askapache.com/.*$ [NC]  
RewriteRule \.(gif|jpg|swf|flv|png)$ /feed/ [R=302,L]  

Stop browser prefetching

RewriteEngine On  
SetEnvIfNoCase X-Forwarded-For .+ proxy=yes  
SetEnvIfNoCase X-moz prefetch no_access=yes     
# block pre-fetch requests with X-moz headers  
RewriteCond %{ENV:no_access} yes  
RewriteRule .* - [F,L]  

Mod Rewrite Tips and Examples

For example, to limit the next 5 RewriteRules to only be applied to .html and .php files, you can use the following code, which tests if the url does not end in .html or .php and if it doesn’t, it will skip the next 5 RewriteRules.



RewriteRule !\.(html|php)$ - [S=5]

RewriteRule ^.*-(vf12|vf13|vf5|vf35|vf1|vf10|vf33|vf8).+$ - [S=1]



.htaccess rewrite examples should begin with:

Options +FollowSymLinks



RewriteEngine On

RewriteBase /

Require the www

Options +FollowSymLinks

RewriteEngine On

RewriteBase /

RewriteCond %{HTTP_HOST} !^www\.askapache\.com$ [NC]

RewriteRule ^(.*)$ http://www.askapache.com/$1 [R=301,L]

Loop Stopping Code

Sometimes your rewrites cause infinite loops, stop it with one of these rewrite code snippets.

RewriteCond %{REQUEST_URI} ^/(stats/|missing\.html|failed_auth\.html|error/).* [NC]

RewriteRule .* - [L]



RewriteCond %{ENV:REDIRECT_STATUS} 200

RewriteRule .* - [L]

Cache-Friendly File Names

This is probably my favorite, and I use it on every site I work on. It allows me to update my javascript and css files in my visitors cache’s simply by naming them differently in the html, on the server they stay the same name. This rewrites all files for /zap/j/anything-anynumber.js to /zap/j/anything.js and /zap/c/anything-anynumber.css to /zap/c/anything.css

RewriteRule ^zap/(j|c)/([a-z]+)-([0-9]+)\.(js|css)$ /zap/$1/$2.$4 [L]



SEO friendly link for non-flash browsers

When you use flash on your site and you properly supply a link to download flash that shows up for non-flash aware browsers, it is nice to use a shortcut to keep your code clean and your external links to a minimum. This code allows me to link to site.com/getflash/ for non-flash aware browsers.

RewriteRule ^getflash/?$ http://www.adobe.com/shockwave/download/download.cgi?P1_Prod_Version=ShockwaveFlash [NC,L,R=307]



Removing the Query_String

On many sites, the page will be displayed for both page.html and page.html?anything=anything, which hurts your SEO with duplicate content. An easy way to fix this issue is to redirect external requests containing a query string to the same uri without the query_string.

RewriteCond %{THE_REQUEST} ^GET\ /.*\;.*\ HTTP/

RewriteCond %{QUERY_STRING} !^$

RewriteRule .* http://www.askapache.com%{REQUEST_URI}? [R=301,L]

Sending requests to a php script

This .htaccess rewrite example invisibly rewrites requests for all Adobe pdf files to be handled by /cgi-bin/pdf-script.php

RewriteRule ^(.+)\.pdf$ /cgi-bin/pdf-script.php?file=$1.pdf [L,NC,QSA]

Setting the language variable based on Client

For sites using multiviews or with multiple language capabilities, it is nice to be able to send the correct language automatically based on the clients preferred language.

RewriteCond %{HTTP:Accept-Language} ^.*(de|es|fr|it|ja|ru|en).*$ [NC]

RewriteRule ^(.*)$ - [env=prefer-language:%1]



Deny Access To Everyone Except PHP fopen

This allows access to all files by php fopen, but denies anyone else.

RewriteEngine On

RewriteBase /

RewriteCond %{THE_REQUEST} ^.+$ [NC]

RewriteRule .* - [F,L]

Deny access to anything in a subfolder except php fopen

This can be very handy if you want to serve media files or special downloads but only through a php proxy script.

RewriteEngine On

RewriteBase /

RewriteCond %{THE_REQUEST} ^[A-Z]{3,9}\ /([^/]+)/.*\ HTTP [NC]

RewriteRule .* - [F,L]

Require no www

Options +FollowSymLinks

RewriteEngine On

RewriteBase /

RewriteCond %{HTTP_HOST} !^askapache\.com$ [NC]

RewriteRule ^(.*)$ http://askapache.com/$1 [R=301,L]

Check for a key in QUERY_STRING

Uses a RewriteCond Directive to check QUERY_STRING for passkey, if it doesn’t find it it redirects all requests for anything in the /logged-in/ directory to the /login.php script.

RewriteEngine On

RewriteBase /

RewriteCond %{QUERY_STRING} !passkey

RewriteRule ^/logged-in/(.*)$ /login.php [L]

Removes the QUERY_STRING from the URL

If the QUERY_STRING has any value at all besides blank than the?at the end of /login.php? tells mod_rewrite to remove the QUERY_STRING from login.php and redirect.

RewriteEngine On

RewriteBase /

RewriteCond %{QUERY_STRING} .

RewriteRule ^login.php /login.php? [L]

Fix for infinite loops

An error message related to this isRequest exceeded the limit of 10 internal redirects due to probable configuration error. Use 'LimitInternalRecursion' to increase the limit if necessary. Use 'LogLevel debug' to get a backtrace.or you may seeRequest exceeded the limit,probable configuration error,Use 'LogLevel debug' to get a backtrace, orUse 'LimitInternalRecursion' to increase the limit if necessary

RewriteCond %{ENV:REDIRECT_STATUS} 200

RewriteRule .* - [L]

External Redirect .php files to .html files (SEO friendly)

RewriteRule ^(.*)\.php$ /$1.html [R=301,L]

Internal Redirect .php files to .html files (SEO friendly)

Redirects all files that end in .html to be served from filename.php so it looks like all your pages are .html but really they are .php

RewriteRule ^(.*)\.html$ $1.php [R=301,L]



block access to files during certain hours of the day

Options +FollowSymLinks

RewriteEngine On

RewriteBase /

# If the hour is 16 (4 PM) Then deny all access

RewriteCond %{TIME_HOUR} ^16$

RewriteRule ^.*$ - [F,L]



Rewrite underscores to hyphens for SEO URL

Converts all underscores “_” in urls to hyphens “-” for SEO benefits… See the full article for more info.

Options +FollowSymLinks

RewriteEngine On

RewriteBase /



RewriteRule !\.(html|php)$ - [S=4]

RewriteRule ^([^_]*)_([^_]*)_([^_]*)_([^_]*)_(.*)$ $1-$2-$3-$4-$5 [E=uscor:Yes]

RewriteRule ^([^_]*)_([^_]*)_([^_]*)_(.*)$ $1-$2-$3-$4 [E=uscor:Yes]

RewriteRule ^([^_]*)_([^_]*)_(.*)$ $1-$2-$3 [E=uscor:Yes]

RewriteRule ^([^_]*)_(.*)$ $1-$2 [E=uscor:Yes]



RewriteCond %{ENV:uscor} ^Yes$

RewriteRule (.*) http://d.com/$1 [R=301,L]



Require the www without hardcoding

Options +FollowSymLinks

RewriteEngine On

RewriteBase /

RewriteCond %{HTTP_HOST} !^www\.[a-z-]+\.[a-z]{2,6} [NC]

RewriteCond %{HTTP_HOST} ([a-z-]+\.[a-z]{2,6})$ [NC]

RewriteRule ^/(.*)$ http://%1/$1 [R=301,L]



Require no subdomain

RewriteEngine On

RewriteBase /

RewriteCond %{HTTP_HOST} \.([a-z-]+\.[a-z]{2,6})$ [NC]

RewriteRule ^/(.*)$ http://%1/$1 [R=301,L]

Require no subdomain

RewriteEngine On

RewriteBase /

RewriteCond %{HTTP_HOST} \.([^\.]+\.[^\.0-9]+)$

RewriteRule ^(.*)$ http://%1/$1 [R=301,L]



Redirecting Wordpress Feeds to Feedburner

Full article:Redirecting Wordpress Feeds to Feedburner

RewriteEngine On

RewriteBase /

RewriteCond %{REQUEST_URI} ^/feed\.gif$

RewriteRule .* - [L]



RewriteCond %{HTTP_USER_AGENT} !^.*(FeedBurner|FeedValidator) [NC]

RewriteRule ^feed/?.*$ http://feeds.feedburner.com/apache/htaccess [L,R=302]



RewriteCond %{REQUEST_FILENAME} !-f

RewriteCond %{REQUEST_FILENAME} !-d

RewriteRule . /index.php [L]



Only allow GET and PUT Request Methods

Article: Request Methods

RewriteEngine On

RewriteBase /

RewriteCond %{REQUEST_METHOD} !^(GET|PUT)

RewriteRule .* - [F]

Prevent Files image/file hotlinking and bandwidth stealing

RewriteEngine On

RewriteBase /

RewriteCond %{HTTP_REFERER} !^$

RewriteCond %{HTTP_REFERER} !^http://(www\.)?askapache.com/.*$ [NC]

RewriteRule \.(gif|jpg|swf|flv|png)$ /feed/ [R=302,L]

Stop browser prefetching

RewriteEngine On

SetEnvIfNoCase X-Forwarded-For .+ proxy=yes

SetEnvIfNoCase X-moz prefetch no_access=yes



# block pre-fetch requests with X-moz headers

RewriteCond %{ENV:no_access} yes

RewriteRule .* - [F,L]

Make a prefetching hint for Firefox.

Header append Link "

</index.htm>

; rel=prefetch"

This module uses a rule-based rewriting engine (based on a regular-expression parser) to rewrite requested URLs on the fly. It supports an unlimited number of rules and an unlimited number of attached rule conditions for each rule, to provide a really flexible and powerful URL manipulation mechanism. The URL manipulations can depend on various tests, of server variables, environment variables, HTTP headers, or time stamps. Even external database lookups in various formats can be used to achieve highly granular URL matching.

This module operates on the full URLs (including the path-info part) both in per-server context (httpd.conf) and per-directory context (.htaccess) and can generate query-string parts on result. The rewritten result can lead to internal sub-processing, external request redirection or even to an internal proxy throughput.

Further details, discussion, and examples, are provided in the detailed mod_rewrite documentation.

Agile web-crawler : design and implementation

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