Subnets·IPv6 /99
IPv6
/99
536,870,912

IPv6 /99 prefix

/99 means the first 99 bits are the network and 29 are left for hosts. That is 536,870,912 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
/99
Host bits
29
Addresses
536,870,912
Usable hosts
536,870,912
/64 networks inside
None
Nibble boundary
No

Prefixes either side

/964,294,967,2964,294,967,296/972,147,483,6482,147,483,648/981,073,741,8241,073,741,824/100268,435,456268,435,456/101134,217,728134,217,728/10267,108,86467,108,864

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 /99?

536,870,912, of which 536,870,912 can actually be handed out.

Q. How is a /99 written?

IPv6 uses no mask — you simply write /99.

Q. How many /64 networks fit in a /99?

None — it is narrower than a /64.

Q. How many host bits are there?

29. Each extra network bit halves the addresses.