Question 1

How does IPv6 subnetting work?

Accepted Answer

IPv6 uses 128-bit addresses and CIDR notation, e.g. 2001:db8::/32. The prefix length is the count of leading network bits. Everything after the prefix is the host portion. Unlike IPv4, IPv6 subnets typically use /64 per LAN (64 network bits + 64 host bits), giving 18.4 quintillion addresses per subnet.

Question 2

How many addresses are in an IPv6 /64 subnet?

Accepted Answer

An IPv6 /64 subnet contains 2^64 = 18,446,744,073,709,551,616 addresses (about 18.4 quintillion). All of them are usable for hosts — unlike IPv4, IPv6 has no network/broadcast address reservation.

Question 3

What is the difference between compressed and expanded IPv6?

Accepted Answer

Compressed (canonical) form removes leading zeros in each 16-bit block and replaces the longest run of all-zero blocks with ::, e.g. 2001:db8::1. Expanded form writes all 8 blocks with 4 hex digits each, e.g. 2001:0db8:0000:0000:0000:0000:0000:0001. Both refer to the same address.

Question 4

What is the ::1 IPv6 address?

Accepted Answer

::1 is the IPv6 loopback address, equivalent to 127.0.0.1 in IPv4. It always points back to the local host. Other special addresses include fe80::/10 (link-local), fc00::/7 (ULA / unique local), ff00::/8 (multicast) and 2001:db8::/32 (documentation).