Subnetting

Nelson2027

Which subnet does host 172.29.187.129 255.255.254.0 belong to?

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You can check it here - https://cidr.xyz

There are also other subnet calculators online you can use. However, if you are preparing for Net+, I suggest you understand the theory behind it.

kaiju

Flip the bits!

Translates to everything to binary. You will see you only have to deal with the last bit in the subnet mask.

172.29.187.129 = 10101100.00011101.10111011.10000001

255.255.255.254 = 11111111.11111111.11111111.11111110

Bits in the IP address that correspond to the "1" bits in the subnet mask cannot change so concentrate on the last octet.

The first 7 bits in the last octet are locked because of the corresponding "1" bits in the mask. Flip the last bit to "0" to get the subnet IP (first ip):

(1000000)1

(1111111)0

-------------

10000000 = 128

Flip the last bit to "1" to get the last IP:

10000001=129

Since this is a /31 for a point to point connection(p2p), you will not see the normal subnet and broadcast IP.

If the subnet mask was a /30 you would have seen four IPs: subnet IP, two usable IPs and a broadcast IP.

(100000)01 = 129

(111111)00 = 252

Flip the last two bits to "0" and you get a subnet ip of .128

10000000

Flip the last two bits to "1" and you get a broadcast ip of 131

10000011

With two usable IP of .129 and .130 (.10000001 and .10000010).

/30 and /31 are used for p2p connections with the /31 being used when IP space is scarce.