Question 1

How many usable hosts does a /16 subnet have?

Accepted Answer

A /16 subnet has 65,534 usable host addresses. The total address count is 65,536 (2^16), minus 2 reserved addresses: the network address and the broadcast address.

Question 2

Why is /16 the recommended VPC CIDR in AWS?

Accepted Answer

AWS recommends /16 as the VPC CIDR because it provides the maximum flexibility for subnet design. With 65,536 addresses you can create hundreds of subnets of varying sizes for different availability zones, tiers, and services, without running out of IP space.

Question 3

What RFC 1918 ranges contain /16 blocks?

Accepted Answer

All three RFC 1918 private ranges support /16 blocks: 10.0.0.0/8 (contains 256 /16 blocks from 10.0.0.0/16 to 10.255.0.0/16), 172.16.0.0/12 (contains 16 /16 blocks from 172.16.0.0/16 to 172.31.0.0/16), and 192.168.0.0/16 (is exactly one /16 block).

Property	Value
Prefix length	/16
Subnet mask	255.255.0.0
Wildcard mask	0.0.255.255
Total addresses	65,536
Usable host addresses	65,534
Network address	x.x.0.0
Broadcast address	x.x.255.255
Binary mask	11111111.11111111.00000000.00000000

Subnet Size	Number of Subnets in a /16	Hosts per Subnet
/17	2	32,766
/18	4	16,382
/20	16	4,094
/22	64	1,022
/24	256	254
/26	1,024	62
/28	4,096	14

CIDR	Subnet Mask	Total IPs	Usable Hosts	Typical Use
/8	255.0.0.0	16,777,216	16,777,214	ISP / Class A legacy
/12	255.240.0.0	1,048,576	1,048,574	172.16.0.0/12 RFC 1918 block
/14	255.252.0.0	262,144	262,142	Large enterprise aggregation
/16	255.255.0.0	65,536	65,534	VPC root CIDR, campus network
/18	255.255.192.0	16,384	16,382	Regional subnet block
/20	255.255.240.0	4,096	4,094	Large availability zone subnet
/24	255.255.255.0	256	254	Standard workload subnet

What is a /16 Subnet?

Full Breakdown

Common Use Cases for /16 Subnets

How Many Subnets Fit in a /16?

Comparison: /16 vs Nearby Prefix Lengths

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