What is the netmask for a /16 prefix length?

The netmask for a /16 prefix length is indeed 255.255.0.0. This is because in CIDR (Classless Inter-Domain Routing) notation, a prefix length of /16 indicates that the first 16 bits of the IP address are used for the network part, while the remaining bits are used for host addresses.

When translating the /16 prefix into a subnet mask, we turn the first 16 bits into ones (indicating the network portion), which corresponds to 255.255.0.0 in decimal format. Each octet in the subnet mask is represented by 8 bits. Thus, the first two octets (16 bits) being all ones yields 255 for each, while the remaining two octets (8 bits each) are all zeros, resulting in 0 for each, forming 255.255.0.0.

This specific netmask allows for a large number of host addresses (65,536 addresses), making it suitable for larger networks. Understanding subnetting and the relationship between CIDR notation and subnet masks is crucial for network design, availability, and efficient IP address utilization in routing protocols and network configuration.