CompTIA Network+ (N10-009)
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Hi, I have a question for the "Examining IPv4 Address Classes" episode in Networking concepts.
In the episode at 10:20, the presenter talks about IPv4 Class A supports 128 networks. This number is from the default subnet mask 255.0.0.0/8. The size of network number bit field is 8 with the reserved highest order bits of 01 so instead of doing 2^8 to get 256 we do 2^6 to get 128 networks.
However this is wrong since 2^6 is 64, 2^7 is 128. I did some googleing and found out that the reserved leading bit(s) for class A is not 01 but only 0 and the network number is given by the next 7 bits. Which means 2^7.Also in the notes it has the range for IPv4 class A is 1.0.0.0 to 126.0.0.0 and that makes 128 networks which doesn't make sense since 1 to 126 counts 126 not 128.
From what I gathered from googleing, the range is 0.0.0.0 to 127.0.0.0 and that would make 128 networks. In octet it would be from 00000000 - 01111111 with the first 0 reserved to identify as Class A. However with 2 addresses being reserved for something (I'm asuming 0.0.0.0 - "This network" address and 127.0.0.0 - Loopback address) so there are only 126 available network.Am I mistaken?
Thank you.
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Great job here Henry! Mathematically, there are 128 networks available (2^7 = 128). But in reality, we cannot use the 0.0.0.0 network and we cannot use loopback 127.0.0.0. So while there are 128 available, there are only 126 usable. Keep up the great work in your studies.
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Thanks Wes for the reply. I was confused watching the episode when the math doesn't fit. I've watch latter episodes and it has become clearer for me. Just to confirm tho, in the video you show that the reserved leading bit(s) for Class A is 01 meaning the 1st octet would be 01000000 - 01111111 (or 64 - 127). But from googleing it seem to be the reserved leading bit(s) for class A is 0 instead of 01 meaning the 1st octet would be 00000000 - 01111111 (or 0 - 127). With 00000000 and 01111111 being reserved ofcourse. Is it 0 or 01?
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You are correct! The octet would be "0"
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Ok got it, thanks for you help.
