Representing the Prefix Length of an Address
IPv6 uses a mask concept, called the prefix length, similar to IPv4 subnet masks. Similar to the IPv4 prefix-style mask, the IPv6 prefix length is written as a /, followed by a decimal number. The prefix length defines how many bits of the IPv6 address define the IPv6 prefix, which is basically the same concept as the IPv4 subnet ID.
When writing IPv6 addresses, if the prefix length matters, the prefix length follows the IPv6 address. When writing documentation, you can leave a space between the address and the /, but when typing the values into a Cisco router, you might need to configure with or without the space. For example, use either of these for an address with a 64-bit prefix length:
2222:1111:0:1:A:B:C:D/64 ...
Get CCENT/CCNA ICND1 100-101 Official Cert Guide now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
