Unique local address

As explained in Acing the CCNA Exam: Volume 1 Fundamentals and Protocols

A unique local address is an IPv6 private unicast address intended for use within internal networks and not for communication over the public internet.

A unique local address (ULA) is a private IPv6 unicast address for internal networks. It identifies one host but cannot communicate across the public internet; ISPs drop traffic sourced from or destined for ULAs. section 20.5.2

Use these properties to recognize and plan ULAs:

• Use the active fd00::/8 range; fc00::/8 remains reserved, so ULAs should begin with fd. section 20.5.2
• Organize the address as a 40-bit randomly generated global ID, a 16-bit subnet identifier, and a 64-bit interface identifier. section 20.5.2
• Treat ULAs as the IPv6 equivalent of private IPv4 ranges 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. section 20.5.2
• Generate the global ID randomly even though global uniqueness is not required, reducing the chance of overlapping addresses between enterprises. section 20.5.2

Figure 20.8 The structure of an IPv6 unique local address. After the prefix fd, there is a 40-bit global ID, which should be randomly generated. The following 16 bits are the subnet identifier, and the remaining 64 bits are the interface identifier.

Use the address-structure diagram to distinguish the fd prefix, global ID, subnet identifier, and interface identifier. section 20.5.2

How Acing the CCNA Exam: Volume 1 Fundamentals and Protocols covers it

How deep it goes

Explains ranges, packet restrictions, address fields, and random-ID rationale, but does not provide configuration commands.

Examples

Uses the fd00::/8 and fc00::/8 ranges alongside the three familiar private IPv4 ranges as recognition examples.

What it assumes

Assumes basic IPv6 addressing and unicast concepts while relating ULAs to familiar private IPv4 addressing.

What you can do after

Evaluate whether an IPv6 address is suitable for internal use and identify its ULA fields and internet limitations.

How it connects

Connects ULAs with global unicast, unicast communication, private IPv4 addresses, subnet identifiers, and interface identifiers.

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Related concepts

• private ipv4 addressequivalent to · A private IPv4 address is an address from a designated range intended for communication within private networks rather than direct routing on the public Internet.
• unicast frameuses · A unicast frame is a link-layer frame addressed to one destination host's MAC address.
• interface identifierhas part · An interface identifier is the portion of an IPv6 address that identifies a specific network interface within its address prefix.
• IPv6kind of · IPv6 is the sixth version of the Internet Protocol, using 128-bit network addresses for packet-based communication.

This explainer was generated by Manning's knowledge graph from the text of Acing the CCNA Exam: Volume 1 Fundamentals and Protocols. The section links point to the parts of the book it draws on.