ff00::/8 is the IPv6 multicast prefix. Addresses starting with ff are multicast — they identify a group of interfaces rather than a single host. IPv6 has no broadcast; multicast fills that role.

What is the difference between /8 and /9?

A /8 is twice as large as /9. /8 has 2¹²⁰ addresses; /9 has 2¹¹⁹. Each step down the prefix number doubles the address count.

How does /8 compare to /7?

A /7 is twice as large as /8. Moving from /8 to /7 adds one more fixed network bit, halving the host portion from 2¹²⁰ to 2¹²¹ addresses.

How do I calculate an IPv6 /8 subnet?

Enter an IPv6 address and select prefix /8 in the calculator above — or paste full CIDR notation like 2001::/8. The tool instantly returns the network address, address range, prefix mask, reverse DNS, and total count of 2¹²⁰ addresses.

IPv6 /8 Subnet Calculator

Results update as you type

A /8 at ff00::/8 is the entire IPv6 multicast range. Multicast replaces IPv4 broadcast — devices join groups to receive traffic destined for specific multicast addresses. This /8 is reserved by the IETF and is not used for unicast allocations.

Prefix length

/128

/8 = 2¹²⁰ addresses (≈ 1.33 × 10³⁶)

Results for 2000::/8

Global UnicastGlobal scope

Network / prefixThe first address — identifies the subnet itself

First addressSubnet-router anycast; first address in the block

Last addressThe highest address in this block

Prefix maskEquivalent to /8

Total addresses≈ 1.33 × 10³⁶ addresses

Address typeGlobally routable scope

More detailsNeighboring subnets, expanded address, reverse DNS, and hextet breakdown

Neighboring /8 subnets

Expanded address
Compressed address
Network (expanded)
Last address (expanded)
Prefix mask
Total addresses (exact)
Reverse DNS (PTR)
Host bits / network bits

Hextet breakdown

20010000000000000000000000000000

NetworkSplit groupHost

Quick facts for IPv6 /8

Prefix mask: ff00::
Total addresses: 2¹²⁰
Approx. count: 1.33 × 10³⁶
/64 subnets: 2⁵⁶

IPv6 /8 reference guideBit split, overview, key facts, sizing tables, design notes, standards, and FAQ

Network / host bit split

mixhosthosthosthosthosthosthost

Network bits (8)Split hextetHost bits (120)

Network bits: 8
Host bits: 120
Prefix mask: ff00::
Total addresses: 2¹²⁰
Approx. count: 1.33 × 10³⁶
/64 subnets: 2⁵⁶
Addresses formula: 2^120
/64 relationship: 2⁵⁶ × /64 subnets

Overview

Common use cases

IPv6 multicast group addressing
Service discovery and streaming protocols
Understanding multicast vs unicast in IPv6

Key facts

A /8 fixes 8 network bits and leaves 120 host bits — 2¹²⁰ total addresses.
In network design terms, /8 is typically a IANA reserved / special-purpose block.
You can subnet a /8 into about 2⁵⁶ /64 LANs.
At site scale, /8 equals about 2⁴⁰ /48 allocations.
At ISP scale, /8 contains about 2²⁴ /32 blocks.

Design guidance

A /8 is not a size you assign to a LAN or site. Treat it as documentation of how the IPv6 address space is carved at the top of the hierarchy. When studying for certifications, focus on which well-known ranges (2000::/3, fe80::/10, fc00::/7, ff00::/8) live inside or beside this block.

Practical example

Addresses like 2001::/8 fall in reserved or special-purpose space. They illustrate how a /8 boundary groups addresses for routing policy, not how you would number a home LAN.

Related RFCs and standards

RFC 4291IPv6 Addressing Architecture
RFC 3849IPv6 Documentation Address Prefix (2001:db8::/32)
RFC 4193Unique Local IPv6 Unicast Addresses (ULA)

Prefix sizing reference

Divide /8 into…

Prefix	Subnets	Addresses each
/9	2	2¹¹⁹
/10	4	2¹¹⁸
/12	16	2¹¹⁶
/16	256	2¹¹²

/8 fits inside…

Supernet	Addresses	/8s inside
/7	2¹²¹	2
/6	2¹²²	4
/4	2¹²⁴	16
/0	2¹²⁸	256

Notable /8 networks

ff00::/8IPv6 multicast
2001:db8::/32Documentation prefix (RFC 3849)

Frequently asked questions

Common questions about IPv6 /8 blocks, prefix sizes, and use cases.

Common IPv6 prefix sizes

/3 /12 /16 /20 /24 /28 /32 /36 /40 /44 /48 /52 /56 /60 /64 /80 /96 /112 /120 /124 /126 /127 /128