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Forum Replies

  1. Can you please elaborate on Anycast addresses? The concept is still pretty confusing.

  2. Hi Dhananjay,

    Anycast basically means that we configure the same address on multiple devices and then advertise the address in a routing protocol. For example, you could do this for a DNS server.

    Depending on where you are located, you will always be routed to the closest DNS server.

    You can even “try” this with IPv4. Configure two of your routers to advertise the same loopback interface. Depending on where you are in the network, you will always be routed to the closest loopback.



  3. Great post!

    I only had one question and its not really that important of a question but I was curious.

    If you have to change the L bit to a 1 making it FD then why do they say FC in the first place? why not just call all Unique Local FD which is what it really is anyway because of the rule.

  4. Hello Brian

    MAC addresses when configured have the U/L bit which is the 7th bit of the 48 bit address. This bit, when set to 0 when this address is locally administered and 1 if the address is globally unique. An example is the virtual MAC address that is created by HSRP. This MAC address will always have 0 in the seventh bit, while a hardwired MAC address on a switch or a PC will have the 7th bit 1.

    Now because there is a mechanism of EUI-64 which is used to assign an IPv6 address that is derived from a MAC addresses, this L bit seems to have migrated into the IPv6 format. According to most sources, (and @ReneMolenaar can correct me if I’m wrong), this bit isn’t actually taken into account in most IPv6 applications. Both the FC00 and FD00 blocks are considered unique local addresses.

    The reason why the L should be changed to 1 is because the block FC00 has not been defined yet. It has been proposed to be managed by an allocation authority, but this has not gained acceptance in the IETF.

    I hope this has been helpful!


  5. Hi Rene,
    I have a silly question running over my head. I see that we have Global unicast address, somewhere i read that the range for global unicast is from 2000::/16 to 3fff::/16.
    My question:

    1. is this correct?
    2. why such a small range of global unicast addresses from a massive IPv6 address? Your introduction to IPv6 course mentioned that there is no real requirement of NAT in IPv6. With this small range we might require NAT in future (please correct me if i am wrong)
    3. can’t we assign other addresses like 7000::/16 as global unicast ?
      I know that IANA does the address allocation, but as i said it’s just a silly question troubling me in this course.

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