IPv6
/120
256
IPv6 /120 prefix
/120 means the first 120 bits are the network and 8 are left for hosts. That is 256 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
- /120
- Host bits
- 8
- Addresses
- 256
- Usable hosts
- 256
- /64 networks inside
- None
- Nibble boundary
- Yes
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 /120?
256, of which 256 can actually be handed out.
Q. How is a /120 written?
IPv6 uses no mask — you simply write /120.
Q. How many /64 networks fit in a /120?
None — it is narrower than a /64.
Q. How many host bits are there?
8. Each extra network bit halves the addresses.