IPv6
/8
2^120
IPv6 /8 prefix
/8 means the first 8 bits are the network and 120 are left for hosts. That is 2^120 addresses.
Addresses are 128 bits, so nobody writes a mask — only the prefix length. A home gets a /56, a single network a /64.
- Prefix
- /8
- Host bits
- 120
- Addresses
- 2^120
- Usable hosts
- 2^120
- /64 networks inside
- 2^120
- Nibble boundary
- Yes
Blocks reserved at this length
Blocks the standards set aside. The addresses themselves are the same everywhere, so they are left as they are.
ff00::/8
Prefixes either side
How to read this
- /24 means the first 24 bits are the network; the remaining 8 hold the addresses inside it.
- Each extra bit splits the network in two and halves the addresses.
- Usable addresses are normally the total minus two — the network and broadcast addresses.
- IPv6 has no broadcast, so nothing is subtracted. One network is conventionally a /64.
Frequently asked questions
Q. How many addresses are in a /8?
2^120, of which 2^120 can actually be handed out.
Q. How is a /8 written?
IPv6 uses no mask — you simply write /8.
Q. How many /64 networks fit in a /8?
2^120.
Q. How many host bits are there?
120. Each extra network bit halves the addresses.