Question 1

What is an IPv6 address and how is it structured?

Accepted Answer

IPv6 (Internet Protocol version 6) uses 128-bit addresses written as 8 groups of 4 hexadecimal digits separated by colons: 2001:0db8:85a3:0000:0000:8a2e:0370:7334. Leading zeros in each group can be omitted: 2001:db8:85a3:0:0:8a2e:370:7334. One contiguous sequence of zero groups can be replaced with :: (double colon): 2001:db8:85a3::8a2e:370:7334. :: can only appear once in an address.

Question 2

What is the difference between IPv4 and IPv6?

Accepted Answer

IPv4 uses 32-bit addresses (4.3 billion addresses) written as four decimal octets (192.168.1.1). IPv6 uses 128-bit addresses (340 undecillion addresses) written in hexadecimal groups. IPv6 eliminates NAT (every device gets a globally unique address), has built-in IPsec support, simpler packet headers for faster routing, stateless address autoconfiguration (SLAAC), and mandatory support for multicast. IPv4 exhaustion since 2011 drives IPv6 adoption.

Question 3

What are the special IPv6 address ranges?

Accepted Answer

Key ranges: ::1/128 — loopback (localhost, equivalent to 127.0.0.1); fe80::/10 — link-local (auto-configured, not routable beyond the local link); fc00::/7 — unique local (private, like RFC 1918 in IPv4); 2001:db8::/32 — documentation examples (never routed); 2001::/32 — Teredo tunneling; ::ffff:0:0/96 — IPv4-mapped addresses (e.g. ::ffff:192.168.1.1); 2000::/3 — global unicast (routable public addresses).

Question 4

How do I use IPv6 addresses in URLs?

Accepted Answer

IPv6 addresses in URLs must be enclosed in square brackets to avoid ambiguity with the port colon separator: http://[2001:db8::1]:8080/path. Without brackets, the URL parser cannot distinguish between the address colons and the port colon. In curl: curl 'http://[::1]:3000/api'. In HTML: link. In /etc/hosts: 2001:db8::1 example.com (no brackets in hosts file — only in URLs).

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