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Old 08-18-2009, 07:36 AM   #1
qwertyjjj
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Registered: Jul 2009
Location: UK
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CIDR explanantion?


I've been looking up CIDR but can't really get an explanation on anything that isn't 8bit, 24, etc.
I currently use this rule in a .htaccess file to restrict logins to the admin pages from my ISPs range:
Order Deny,Allow
Deny from all
Allow from 81.128.0.0/11

It works but my IP address is 81.159.xxx.xxx
I'm not really sure how the 11 factors into the equation?

I was going to use the same in iptables
 
Old 08-18-2009, 07:54 AM   #2
centosboy
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Registered: May 2009
Location: london
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Quote:
Originally Posted by qwertyjjj View Post
I've been looking up CIDR but can't really get an explanation on anything that isn't 8bit, 24, etc.
I currently use this rule in a .htaccess file to restrict logins to the admin pages from my ISPs range:
Order Deny,Allow
Deny from all
Allow from 81.128.0.0/11

It works but my IP address is 81.159.xxx.xxx
I'm not really sure how the 11 factors into the equation?

I was going to use the same in iptables
there is a short but sweet explanation on wiki
Code:
en.wikipedia.org/wiki/CIDR_notation
loads of detailed explanations too on the web. i didnt really understand it properly until i did the ccna.. so you may have to read up some good books for a 'proper' understanding


even shorter and sweeter is the iptab command or ipcalc which will work it all out for you if you give the relevant flags
 
Old 08-18-2009, 08:02 AM   #3
timvandijk039
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Registered: Jul 2009
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Distribution: Debian/Ubuntu and RHEL/CentOS
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Hi qwertyjjj,

The 11 points out how many bits of the subnet is reserved for the subnet. In your case that would be 11 bits. The decimal subnet-notation of an 11 bit subnetmask would be 255.224.0.0.

With a network-id of 81.128.0.0 and an 11 bits subnet, the host range will be from 81.128.0.1 until 81.159.255.254. Your IP number (81.159.xxx.xxx) should fit fine within these boundaries. So everything is peachy indeed :-)

Cheers...
 
  


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