In message <596349CF.9000709@nsc.liu.se>, Thomas Bellman writes:
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On 2017-07-08 23:00, Radu-Adrian Feurdean wrote:
On Sat, Jul 8, 2017, at 19:13, Mel Beckman wrote:
That open atmosphere was by design. It's why IPv6 uses 128-bit addresses,
That's for hosts. When you care more about subnets, it's shortened to 64 bits.
Indeed. Especielly if you do hierarchical delegation within your organization, you will often have sparse allocations at several levels. A /48 for an organization might seem like reasonably lots with 65536 subnets, but if that organization in turn delegates to departments, and they have more than 16 departments, each department might only get a /56 (256 subnets).
If I had 32 departments and were wanting to give them equal sized allocations then I'd give them a /53 each which is 2064 subnets each. It isn't that hard to do 8 delegations in the reverse tree for each of the 32 departments. Delegation on nibble boundaries is for convience and nothing else. Or you could start with a /56 each and reserve the next 7 /56s for each department to grow into.
Try to delegate that one step further, and you can't do any reasonable allocation strategy, but have to allocate subnet by subnet.
Of which the only downside is that it is harder to do internal firewalls between departments or if you want to do cost recovery of external traffic to departments. The DHCPv6 servers also need to learn where to get additional subnets from to fulfill PD requests. Remember a site can have more than one /48. Thats just the recommended starting point.
I managed to get a full /52 from our host university, but they initially wanted to give us only a /56. Of course, they can only give out a few /52:s; other departments will have less structured address plans than us.
- -- Thomas Bellman, National Supercomputer Centre, Linköping Univ., Sweden "Life IS pain, highness. Anyone who tells ! bellman @ nsc . liu . se differently is selling something." ! Make Love -- Nicht Wahr!
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