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Forum Replies

  1. ibmufa says:

    When looking at an IPv6 address assignment of say for example /64. is there an assumption we should make. Reason for question is that in an example, you advised
    IPv6 Global Unicast Subnet Assignments

    Our customer received prefix 2001:41f0:4060::/48 and they want to use it to configure IPv6 on their entire network. Where do we start?

    Then on the address assignments, we are using a /64. Do we have to have been given the information above 1st - the /48. It appears we are using 2 prefixes but only referencing the /64 at the customer end. What would be a typical test question look like given/or not given this information? looks like I need 1 on 1 :slight_smile:

  2. Hi Itai,

    It’s probably best to stick to use “A” instead of “10” as it can be confusing. It’s easy to read it as 10 while in reality it’s one, zero.

    About the subnets…the ISP will give you a /48 global prefix that you can use for your network. You should use /64 subnets since it’s convenient for autoconfiguration which leaves you with 16 bits you can use to create different subnets.

    A typical exam question could be something like:

    “The ISP has given you global prefix 2001:41f0:4060::/48. You have five VLANs that require connectivity. What subnets will you use? Also, for each subnet what IPv6 address will you assign to your default gateway?”


  3. Hello Willie.

    You got it, that’s exactly right!


  4. Hi I had a question. we are always told no more than 500 IP addresses in a subnet yet here we have 18,446,744,073,709,551,616.00 IP addresses. whats the idea on how this should be handled?

    great IPv6 lesson I’m actually enjoying IPv6 for first time in my studies. in past years I actually cringed learning it now im having fun!

  5. Hello Brian

    Yes, I understand your concern. After spending years (and some of us decades) learning and understanding IPv4 with both its strengths and its limitations, it is very often hard to avoid viewing IPv6 in a similar manner.

    Now if you have a prefix length of 48, 64 or even 96 bits which are all very common in IPv6, then of course you will have a subnet capable of supporting an ridiculously enormous number of hosts. Although IPv6 can actually handle a greater number of hosts per subnet than IPv4 (because there are no broadcasts and because it handles addressing differently) it would not be wise to actually use all those addresses.

    With IPv4, in order to conserve addresses, we subnetted our scopes to sizes comparable to what we need. With IPv6 you don’t need to do that because there are just so many addresses available there is no concern for address exhaustion. So, in order to simplify addressing, just make all your subnets with a /64 prefix and be done with it. Just don’t actually physically place more than 500 devices within a subnet.

    I hope this has been helpful!


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