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This might sound like a stupid question but I would really like to know how I would work out how many IP's I've got available on this network range:

196.44.198.32/29

Can someone explain it to me, what the /29 means and how you calculate it. The amount of IP's you've got available, the one that would be use to broadcast ect.

Kind regards Conrad

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1  
See serverfault.com/questions/49765/… –  Zoredache Sep 23 '09 at 16:54
    
Seems a little homeworkish –  MDMarra Sep 23 '09 at 22:23

5 Answers 5

up vote 10 down vote accepted

For such use you may use a pretty tool named ipcalc


Address:   196.44.198.32        11000100.00101100.11000110.00100 000
Netmask:   255.255.255.248 = 29 11111111.11111111.11111111.11111 000
Wildcard:  0.0.0.7              00000000.00000000.00000000.00000 111
=>
Network:   196.44.198.32/29     11000100.00101100.11000110.00100 000
HostMin:   196.44.198.33        11000100.00101100.11000110.00100 001
HostMax:   196.44.198.38        11000100.00101100.11000110.00100 110
Broadcast: 196.44.198.39        11000100.00101100.11000110.00100 111
Hosts/Net: 6                     Class C

Also you can use this simple way to calculate :
2^(32-29) - 2 = 6 hosts

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To explain what it actually is:

/29 means that 29 of the 32 bits of the address are the netmask, therefore, only 3 bits are available for differentiating between computers. However, you always lose 2 addresses from the block for broadcast and loopback, so your result is:

2**(32-29) - 2 = 2**3 - 2 = 8 - 2 = 6

The broadcast would always be the top of the range (setting all of the bits that aren't netmask to '1').

For more details, read up on "CIDR notation"

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29 is the number of bits placed to 1 on the netmask in binary. You can make a logical AND with these 1 and your IP to see the network.

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/29 means 6 usable addresses:

196.44.198.32 - 196.44.198.39

Typically, 196.44.198.33 would be your gateway.

See this CIDR calculator.

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2  
.32 would be the network address (which is unusable). The gateway is whatever you define it to be, but the first usable is a common one, which would be .33 in this case –  jj33 Sep 23 '09 at 17:19
    
Thanks - fat fingered the 33. –  Christopher_G_Lewis Sep 25 '09 at 19:39
    
No idea why this was downvoted. It's a perfectly correct answer. –  JamesBarnett Jan 15 '11 at 18:45

or,

nmap -sP 196.44.198.32/29
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2  
-1 for potentially harmful suggestion. Not everyone has the authority to scan a portion of the network at their workplace. calculate number of available host != scan available host. –  JamesBarnett Jan 15 '11 at 18:44

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