On Thu, Jul 30, 2020 at 10:05:46AM +0100, antlists wrote in
<b11e9eef-08e5-7e2a-ff35-2a118dbb8...@youngman.org.uk>:
From what little I understand, IPv6 *enforces* CIDR. So, of the 64
network bits, maybe the first 16 bits are allocated to each high level
allocator eg RIPE, ARIN etc. An ISP will then be allocated the next 16
bits, giving them a 32-bit address space to allocate to their
customers - each ISP will have an address space the size of IPv4?!
Each customer is then given one of these 64-bit address spaces for
their local network. So routing tables suddenly become extremely
simple - eactly the way IPv4 was intended to be.
An IPv6 address is 128 bits in length. Usually an ISP allocates 64
bits to a single customer, allowing the systems on/behind that
connection to automatically assign themselves an address based on
their MAC address for example. Note that also allocations bigger than
64 bits are common so customers get 70 or 76 bits to use and can use
multiple subnets on their home/business networks.
Point is though, with IPv6 addresses are no longer a scarce
commodity. The cost to an ISP to give you one IPv6 address (/128) is
just the same as given you enough room for your own IPv4 internet
(/64). Whether they make them static or dynamic depends on their
policy and what their customers are willing to put up with / pay for.
