IPv6 question

TechGromitTechGromit Member Posts: 2,156 ■■■■■■■■■□
in CCNA & CCENT
Hello, I was wondering if someone could explain to me the ipv6 address /# meaning. When an address says:

2000::/3 or

FE80::/10

what does the /number signify. I keep reading the CCNA routing and Switch guide I have and it's not clear what this number signifies. I looked at a couple videos on Youtube and they really don't clear up my confusion.

Thanks.
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Comments

  • PCTechLincPCTechLinc Member Posts: 646 ■■■■■■□□□□
    Subnetting in IPv6 is a bit different to understand than IPv4, since the first 64 bits are ALWAYS designated for the network portion.


    That being said, in your first example above, the prefix 2000::/3 means that the first 3 bits MUST be the same in order for the rest of the prefix to be considered as part of the same IPv6 subnet. If we break apart the hex digit 2, that gives us 0010. The /3 prefix says that it can be 0010 or 0011, which would be hex digit 2 or 3. SO, any prefix starting with the hex digit 2 or 3 would be on the same subnet. It gets a LITTLE more complicated as you "subnet" deeper, but with a little practice, it gets easier to understand.


    The second example, FE80::/10, that means the first 10 bits need to stay the same. That means that the first hex digit needs to be F, and break apart the second digit E, and you get 1110. The first two digits have to be 11, so anything after would be a part of the same subnet. That means that you can have 1100 (C), 1101 (D), 1110 (E), or 1111 (F).


    I really hope that makes sense.
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    Master of Science in Information Security and Assurance - Western Governors University
    Bachelor of Science in Network Administration - Western Governors University
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  • MAC_AddyMAC_Addy Member Posts: 1,740 ■■■■□□□□□□
    2000/3 is the global unicast address range. - First 3 bits.

    FE80::/10 is the link-local. - First 10 bits.

    It just shows you what the shortened version of the IPv6 address looks like.
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  • TechGromitTechGromit Member Posts: 2,156 ■■■■■■■■■□
    PCTechLinc wrote: »
    The second example, FE80::/10

    So with /10, 1111 1110 01xx must always be the same? but the other bits can be anything I want? That would make FE9x (0101), FEAx (0110), and FEBx (0111), part of the same IPv6 subnet?
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  • PCTechLincPCTechLinc Member Posts: 646 ■■■■■■□□□□
    Oops, you corrected my mistake. I didn't make the bits go far enough; they are supposed to go into the 3rd character. You are correct in your last sentence.
    Master of Business Administration in Information Technology Management - Western Governors University
    Master of Science in Information Security and Assurance - Western Governors University
    Bachelor of Science in Network Administration - Western Governors University
    Associate of Applied Science x4 - Heald College
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  • TechGromitTechGromit Member Posts: 2,156 ■■■■■■■■■□
    PCTechLinc wrote: »
    Oops, you corrected my mistake. I didn't make the bits go far enough; they are supposed to go into the 3rd character. You are correct in your last sentence.

    Thanks, this isn't adequately explained in my book, I have two other books at home, but I just assumed the 1050 page bible I have at work would be more than sufficient to explain everything I need to know about the CCNA.
    Still searching for the corner in a round room.
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