Subnetting in Your Head: Class B Addresses
Written on 23:25 by Ahmet Emir
Are you nuts? Subnet Class B addresses in our heads? It’s absolutely easier than autograph it out—
I’m not kidding! Let me appearance you how:
Question: What subnet and advertisement abode is the IP abode 172.16.10.33
255.255.255.224 (/27) a affiliate of?
Answer: The absorbing octet is the fourth octet. 256 – 224 = 32. 32 + 32 = 64. Bingo: 33
is amid 32 and 64. However, bethink that the third octet is advised allotment of the
subnet, so the acknowledgment would be the 10.32 subnet. The advertisement is 10.63, back 10.64 is
the abutting subnet. That was a appealing accessible one.
Question: What subnet and advertisement abode is the IP abode 172.16.66.10
255.255.192.0 (/18) a affiliate of?
Answer: The absorbing octet is the third octet instead of the fourth octet. 256 – 192 = 64.
0, 64, 128. The subnet is 172.16.64.0. The advertisement charge be 172.16.127.255 since
128.0 is the abutting subnet.
Question: What subnet and advertisement abode is the IP abode 172.16.50.10
255.255.224.0 (/19) a affiliate of?
Answer: 256 – 224 = 0, 32, 64 (remember, we consistently alpha counting at aught (0)). The subnet
is 172.16.32.0, and the advertisement charge be 172.16.63.25 back 64.0 is the abutting subnet.
Question: What subnet and advertisement abode is the IP abode 172.16.46.255
255.255.240.0 (/20) a affiliate of?
Answer: 256 – 240 = 16. The third octet is absorbing to us. 0, 16, 32, 48. This subnet
address charge be in the 172.16.32.0 subnet, and the advertisement charge be 172.16.47.255
since 48.0 is the abutting subnet. So, yes, 172.16.46.255 is a accurate host.
Question: What subnet and advertisement abode is the IP abode 172.16.45.14
255.255.255.252 (/30) a affiliate of?
Answer: Where is the absorbing octet? 256 – 252 = 0, 4, 8, 12, 16 (in the fourth octet).
The subnet is 172.16.45.12, with a advertisement of 172.16.45.15 because the abutting subnet is
172.16.45.16.
Question: What is the subnet and advertisement abode of the host 172.16.88.255/20?
Answer: What is a /20? If you can’t acknowledgment this, you can’t acknowledgment this question, can you?
A /20 is 255.255.240.0, which gives us a block admeasurement of 16 in the third octet, and back no
subnet $.25 are on in the fourth octet, the acknowledgment is consistently 0 and 255 in the fourth octet.
0, 16, 32, 48, 64, 80, 96…bingo. 88 is amid 80 and 96, so the subnet is 80.0 and the
broadcast abode is 95.255.
Question: A router receives a packet on an interface with a destination abode of
172.16.46.191/26. What will the router do with this packet?
Answer: Abandon it. Do you apperceive why? 172.16.46.191/26 is a 255.255.255.192 mask,
which gives us a block admeasurement of 64. Our subnets are again 0, 64, 128, 192. 191 is the broadcast
address of the 128 subnet, so a router, by default, will abandon any advertisement packets.
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