Question 1

How is IPv6 subnetting different from IPv4?

Accepted Answer

IPv6 addresses are 128 bits instead of 32, written in hexadecimal groups rather than dotted decimal. There is no broadcast address and no network/broadcast pair to subtract, so you do not lose two addresses per subnet. Almost all LANs are /64, and you allocate space from large blocks like /48 and /56 rather than worrying about running out of hosts.

Question 2

Why is /64 the standard IPv6 subnet size?

Accepted Answer

Stateless address autoconfiguration (SLAAC) and several other IPv6 mechanisms assume exactly 64 host bits. Using a /64 per LAN keeps autoconfiguration, privacy addresses, and EUI-64 interface identifiers working. You should not make a normal LAN smaller than /64.

Question 3

How many addresses are in an IPv6 /64?

Accepted Answer

A /64 contains 2^64 addresses — 18,446,744,073,709,551,616, or about 18.4 quintillion. That single subnet holds far more addresses than the entire IPv4 internet.

Question 4

What is the difference between a /48, /56, and /64?

Accepted Answer

A /64 is one LAN subnet. A /56 contains 256 /64 subnets and is common for homes and small sites. A /48 contains 65,536 /64 subnets and is the standard allocation for a business or larger site. You subnet a /48 or /56 into many /64s.

Question 5

Does IPv6 have a broadcast address?

Accepted Answer

No. IPv6 removed broadcast entirely and replaced it with multicast. The all-zeros host address in a subnet is reserved as the subnet-router anycast address, but there is no broadcast address to set aside, so a subnet’s addresses are effectively all usable.

Question 6

What does "::" mean in an IPv6 address?

Accepted Answer

The double colon "::" represents one or more consecutive groups of all-zero hextets, and it can appear only once in an address. For example, 2001:db8::1 is shorthand for 2001:0db8:0000:0000:0000:0000:0000:0001. This calculator expands and compresses addresses for you.

Question 7

What are private (non-routable) IPv6 ranges?

Accepted Answer

Unique Local Addresses (ULA) in fc00::/7 (commonly fd00::/8) are the IPv6 equivalent of RFC 1918 private space — they are used inside a network and are not globally routed. Link-local addresses in fe80::/10 are valid only on a single link. Global unicast addresses in 2000::/3 are the routable public internet.

Question 8

What prefix should I use for point-to-point links?

Accepted Answer

RFC 6164 recommends /127 for links between two routers, which provides exactly two addresses and avoids a neighbor-discovery exhaustion attack. A /126 (four addresses) was common historically. Even though you could use a /64, /127 is the modern best practice for router interconnects.

Prefix	Addresses	/64 subnets	Typical use
/32	2⁹⁶	2³²	ISP allocation
/36	2⁹²	2²⁸	Regional block
/40	2⁸⁸	2²⁴	Large organization
/44	2⁸⁴	2²⁰	Large site
/48	2⁸⁰	2¹⁶	Site allocation
/52	2⁷⁶	2¹²	Medium business
/56	2⁷²	2⁸	Home / small site
/60	2⁶⁸	2⁴	Small delegation
/64	2⁶⁴	2⁰	Standard LAN subnet
/96	2³²	—	NAT64 / IPv4-mapped
/112	2¹⁶	—	Constrained segment
/126	2²	—	Point-to-point (legacy)
/127	2¹	—	Point-to-point (RFC 6164)
/128	2⁰	—	Single host

IPv6 Subnet Calculator

Results for 2001:db8::/64

Neighboring /64 subnets

Hextet breakdown

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