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An IPv6 allocation size is the prefix length of the address block you receive, and it decides how you can subnet and route that space. A /64 is one LAN segment and is the normal unit for SLAAC and neighbor discovery. A /48 is what you want when you plan to carve many /64 networks under one site. LogicWeb leases IPv6 from a /48 up through a /29 for larger designs. The length you choose also affects what other networks will accept from the global table.
What /64, /48, and /29 mean in practice
A /64 is one link or LAN. Give every segment its own /64 so hosts can use SLAAC and find neighbors without odd failures. A VPS that receives a single /64 for its IPv6 address is a normal setup for one server.
A /48 is a site-sized block you can split into many /64 networks. You will not use all of them, and that is fine. Choose a /48 when you expect growth or want separate subnets for different services.
A /29 is a large allocation for operators who announce aggregates and still need spare room. Most customers never need one. It fits serious multi-network designs rather than a single host or small site.
Routing length and what others will accept
Many networks filter IPv6 prefixes longer than a /48 at the default-free zone. If you announce only a /64, some paths may never install your route even when a nearby peer can reach you with ping6. Plan the length with the same care you would give an IPv4 announcement size, using the IPv6 numbers instead.
Announcing a more-specific /64 from inside a leased /48 can work inside a direct relationship. It can also vanish at someone else’s border filter. Confirm acceptance before you design traffic engineering on a length that may not travel globally.
Number each LAN, then create the ROA
A routed /48 does not replace numbering the link. Hosts still need a /64 on the segment. A host that only has a /128, with no /64 on the LAN, is a common reason NDP and SLAAC turn into a support ticket.
Draw the covering aggregate, any more-specifics, the ROA maxLength, and your LAN /64s on paper first. Then create the objects and announce. Set maxLength so it allows what you will really send; a loose maxLength of 128 can authorize longer prefixes you did not mean to use. Check a looking glass for the length you intended. A working ping6 from one neighbor is not proof of global reachability.
When you open a ticket about IPv6 reachability, include the prefix length, the ROA, and a looking-glass result. Say whether SLAAC or neighbor discovery is failing on the LAN, because that is a local numbering issue rather than a global routing one. Canceling a lease when you are done with a block is a separate request from simply shrinking a mask.
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