Cisco Certified Network Associate (CCNA) Practice Exam

What is an IPv6 prefix length that commonly indicates a subnet in most configurations?

1. /64

2. /32

3. /128

4. /48

The correct answer is: /64

The /64 prefix length is commonly used in IPv6 configurations to indicate a subnet. This is because a /64 indicates that the first 64 bits of the address are used for the network portion, leaving 64 bits available for host addresses within that subnet. This configuration allows for a vast number of individual IPv6 addresses (approximately 18 quintillion) within the subnet, which is ideal for supporting a large number of devices. In the context of IPv6 networking, using a /64 for a subnet has become a standard practice, particularly for LAN segments. The structure of an IPv6 address, which includes a significant host space, makes /64 addressing effecient and beneficial for network management. Larger prefixes, like /32 and /48, are generally reserved for larger organizations or aggregated routing purposes rather than used directly for subnetting within a local environment. Conversely, a /128 denotes a single IP address with no host space, which is not suitable for subnets.