IPv6 /48 Prefix ReferenceIPv6
The classic site allocation: a /48 wraps 65,536 /64 subnets into one block, historically the standard gift to any business that asked. Policy has loosened since, but the /48 remains the archetype of a company-sized prefix.
/48 facts at a glance
- Total addresses
- 1,208,925,819,614,629,174,706,176 (280)
- /64 subnets inside
- 65,536
- Host/interface bits
- 80
- Example network
- 2001:db8::/48
- First address
- 2001:db8::
- Last address
- 2001:db8:0:ffff:ffff:ffff:ffff:ffff
- Typical role
- Standard site allocation (routing prefix)
A /48 in documentation space
Using 2001:db8::/32 (RFC 3849 documentation space) aligned to its own boundary, a /48 occupies:
| Block | First address | Last address |
|---|---|---|
| 2001:db8::/48 | 2001:db8:: | 2001:db8:0:ffff:ffff:ffff:ffff:ffff |
How an IPv6 /48 prefix works
A /48 prefix pins the first 48 bits of a 128-bit address, leaving 80 bits free. That free portion holds 280 = 1,208,925,819,614,629,174,706,176 distinct addresses, and every such block begins at a multiple of that size. Because each subnet should be a /64, the 16 middle bits between the prefix and the /64 boundary give 65,536 subnets to hand out.
Where /48 is used
- Enterprise sites carrying their own /48 under one corporate aggregate.
- Hosting providers subdividing a /48 into customer /56s or /64s.
- Multi-VLAN campuses that want every segment routed without NAT.
Early guidance (RFC 3177) urged giving every site a /48; RFC 6177 relaxed that advice toward right-sizing, so businesses today commonly receive /48s or /56s depending on need.
Frequently asked questions
How many /64s fit in a /48?
65,536. Sixteen bits separate the prefixes, so a /48 also equals 256 blocks of /56.
Is a /48 still the standard business allocation?
It depends on the provider: since RFC 6177 replaced RFC 3177's one-size-fits-all stance, many assign /48s to larger sites and /56s or single /64s where demand is modest.
How many /48s are in a /32?
65,536, which is why one ISP aggregate comfortably serves thousands of business sites.
Should I request a /48 or a /56?
Size for the number of /64 segments you expect to route. Both are trivially large in absolute terms; pick whichever matches your VLAN count and growth plans.
Open this prefix in the calculator
Open 2001:db8::/48 in the IPv6 calculator