13

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

16

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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16

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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2

/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
  • No idea why this was downvoted. It's a perfectly correct answer. – JamesBarnett Jan 15 '11 at 18:45
0

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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-4

or,

nmap -sP 196.44.198.32/29
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  • 3
    -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