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# MAC Address Numbers And Letters

January 1, 2016

January 1, 2016

Correct me if I'm wrong but MAC addresses start with 0-9 and A-F.
Not always. MAC addresses are made up of 6 hexadecimal numbers, so they can start with any permutation on 0-9 and A-F.
Sorry, I should have rephrased to say "can start with.." Either way you answered my question. I knew it was correct but one of the CCNA videos stated they can start with 1-9 and a-f. I just wanted to confirm.
Hello, I have watche Data link overview (https://www.cybrary.it/video/layer2-data-link-layer-overview/). Somewhere around the end Mr.Memon talks about MAC addresses and OUIF field. He says, that there is 7th bin from the left side. Mac address he has written is 0024.ABCD.1234 The first zero from the left is 4 bits as other letters in the MAC address, but why is the second zero from the left side taken az 7th bit? Can you please explain it to me? Thank you for any answers. Pinguin
To Pinguin - second zero from the left is't taken as "bit" as it is 4-bit hex number. But that number contains bits #5,6,7 and 8 (as bits 1...4 are used by the left most, or most significant number). Obviously, if you will manipulate one bit in the 4-bit "word" result will change. Say you had 0524.ABCD.1234 as your MAC, in binary it can be represented as 0000 0101 0010 0100 (that is just for 0524) and changed it from Universally unique to Local, i.e. changed 7-th bit from 0 to 1. Binary will look like 0000 0111 0010 0100, hex will change to 0724.
Ibrahimus TY 4 dat explanation. From watching the video I got the impression of that bit changing only from 0 -> 2 (0000 -> 0010) but from my binary accounting it can be activated as: 0010 - 2 0011 - 3 0110 - 6 0111 - 7 1010 - A 1011 - B 1110 - E 1111 - F So I went through this forum hoping someone had the same doubt as me. Again, TYVM Deniz