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admin
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Joined: 16 May 2006
Posts: 84
Location: NJ
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 Posted: Sun Sep 23, 2007 10:04 pm Post subject: Subnetting Tutorial |
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I created this for myself I figured it will be useful to others:
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1 2 3 4 5 6 7 8 _ 9 10 11 12 13 14 15 16 _ 17 18 19 20 21 22 23 24 _ 25 26 27 28 29 30 31 32
128 64 32 16 8 4 2 1
For CIDR - if it is /21, goto the 21st bit and look at the chart above where it stands. Now 21st bit is @ "8" so add the following: "128+64+32+16+8 = 248" so the subnetmask would be 255.255.248.0
Each Additional Bit Doubles the Available Addresses
n4 bits = 16 Addresses
n5 bits = 32 Addresses
nEach Bit Removed Halves the Available Addresses
n8 bits = 256 Addresses
n7 bits = 128 Addresses nNumber of Addresses = 2n where n is the number of bits available for addressing n2 8 = 2*2*2*2*2*2*2*2 = 256
Class A
nNetwork . Host . Host . Host
nClass B nNetwork . Network . Host . Host
nClass C nNetwork . Network . Network . Host
nClass D & E
Always Subtract 2 from the number of Host IDs nHost IDs cannot be all 1’s (reserved for broadcast address) nHost IDs cannot be all 0’s (reserved for “this network only” address)
Class D
Used by multicast
224.0.0.0 - 239.255.255.255
Class E
Experimental
240.0.0.0+
Subnetting a Class B:
128 64 32 16 8 4 2 1
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128 192 224 240 248 252 254 255
0 2 6 14 30 62 126 254 (Number of Subnet ID's)
- Start from left.
- Every time we take the bit away we are cutting the # of hosts into half
- So going from left look at the chart above
IPv4 = 32Bit
IPv6 (RFC 2373)= 128Bit
- Assigned to interfaces not nodes
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