networking addressing

IPv6

ipv6 networking addressing
Plain English

IPv6 is the newer internet address system. IPv4 ran out of addresses; IPv6 has so many that every device can have its own public address.

Technical Definition

IPv6 addresses are 128 bits, written as eight hex groups; :: compresses one run of zeros.

  • ::1 is loopback; fe80::/10 is link-local (every interface has one); 2000::/3 is global unicast; fd00::/8 is unique local (private).
  • Hosts usually configure themselves with SLAAC from router advertisements, or with DHCPv6.
  • No NAT needed, so the firewall matters more.
  • ARP is replaced by Neighbor Discovery (ICMPv6).

Source: RFC 8200; CompTIA Network+ N10-009 Exam Objectives v4.0

IPv6 in practice 

$ ip -6 addr show dev lo
    inet6 ::1/128 scope host noprefixroute

$ ping -6 -c1 ::1
In the Wild

Most home ISPs now hand out IPv6, so services you think are LAN-only may be reachable over v6. ufw writes rules for both by default. Network+ N10-009 objective 1.8 covers IPv6 addressing and 3.4 covers IPv6 services such as SLAAC.

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