IPv6 Address Block Calculator

About this interactive

Every kind of IPv6 address lives in a block you can write as a prefix: the block's first address, a slash, and how many leading bits every address in it shares. 2001:db8::/32, the block set aside for documentation, holds every address whose first two hextets are 2001:db8. The address types the lesson covers work the same way: global unicast, unique local, link-local and multicast each have a block of their own, and the first hextet tells you which one an address is in. Three special values stand apart: the loopback address, the unspecified address and the default route, the prefix that matches every destination. Only the first hextet counts: fe80 or ff further along an address means nothing. A company's ISP usually gives it a /48, it numbers its subnets in the fourth hextet, and each LAN is a /64 with 64 bits left for the interface. For example, 2001:db8:42::/48 holds the LAN 2001:db8:42:7::/64. Seven of the sixteen questions are drawn each run. Any you miss shows the answer and how to work it out.

What you'll learn

Write the prefix for each IPv6 address block the lesson names: global unicast, unique local, multicast, the link-local network, the default route, the unspecified address and loopback
Pick out the addresses of one type from a list by their first hextet alone, and work out where a block's addresses begin and end

Aligned to

Cisco CCNA

1.9 Describe IPv6 address types

1.8 Configure and verify IPv6 addressing and prefix

Cisco CCST Networking

2.3 Identify IPv6 addresses and prefix formats

CompTIA Network+

3.4 Given a scenario, implement IPv4 and IPv6 network services

Key terms

Global Unicast Address: A publicly routable IPv6 unicast address beginning with the prefix 2000::/3, equivalent in role to a public IPv4 address, used to identify a device uniquely across the internet. GUAs are assigned by ISPs and regional internet registries and are the addresses used for internet-facing communication in IPv6.
Unique Local Address: An IPv6 address in the FC00::/7 range (most commonly FD00::/8) used for private internal network communication, analogous to IPv4 private address ranges like 192.168.0.0/16. Unique local addresses are not routable on the public internet but can be routed within an organization's own network.
Link-Local Address: An IPv6 address in the FE80::/10 range that is automatically assigned to every IPv6-enabled interface and used only for communication within a single network link. It cannot be routed beyond the local Layer 2 segment and is required for Neighbor Discovery and router communication.
IPv6 Multicast Address: An IPv6 address in the FF00::/8 range used to deliver packets to multiple subscribed interfaces simultaneously.
Default Route: A catch-all routing entry represented as 0.0.0.0/0 (IPv4) or ::/0 (IPv6) that a router uses to forward packets when no more specific matching route exists in the routing table. It is typically configured to point toward the next-hop router or ISP connection.
Unspecified Address: The IPv6 address ::/128 (all zeros), used to indicate the absence of an address, typically before a device has been assigned one.
IPv6 Loopback Address: The reserved IPv6 address ::1/128 that a device uses to send traffic to itself, allowing the local network stack to be tested without sending packets onto a physical network. It is the IPv6 counterpart of IPv4's 127.0.0.1, but reserves a single address rather than the whole 127.0.0.0/8 range, and a packet addressed to ::1 never leaves the device.

Topics

Ipv6 Address Types Prefix Global Unicast Unique Local Link Local Multicast Interactive Calculation

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