Subnet Expert

Visual Subnet Calculator

Plan, visualize, and manage IP subnets with an interactive tool for network engineers and IT professionals.

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Select a network type to customize IP address calculations for specific cloud providers.

Understanding IP Subnets

What is Subnetting?

Subnetting is the process of dividing a single network into smaller network segments. It helps optimize network performance, improve security, and manage IP address allocation.

CIDR Notation

CIDR (Classless Inter-Domain Routing) notation uses a suffix like /24 to indicate the number of bits in the network portion of an IP address.

For example, 192.168.1.0/24 indicates that the first 24 bits (three octets) define the network, leaving 8 bits for host addresses.

Reserved IPs by Cloud Providers

AWS

AWS reserves the first 4 IP addresses and the last IP address in each subnet:

  • The first address is the network address
  • The second address (.1) is used for the VPC router
  • The third address (.2) is for AWS DNS
  • The fourth address (.3) is reserved for future use
  • The last address is the broadcast address

For example, in a /24 subnet with 256 total addresses, AWS provides 251 usable IP addresses for resources.

Azure

Azure reserves the first 5 IP addresses and the last IP address in each subnet:

  • The first address is the network address
  • The second address (.1) is reserved for the default gateway
  • The third and fourth addresses (.2, .3) are reserved for Azure DNS
  • The fifth address (.4) is reserved for future use
  • The last address is the broadcast address

For example, in a /24 subnet with 256 total addresses, Azure provides 250 usable IP addresses for resources.

Google Cloud

Google Cloud Platform reserves 4 IP addresses in each subnet:

  • The first address is the network address
  • The second address (.1) is reserved as the default gateway
  • The second-to-last address is for future use
  • The last address is the broadcast address

For example, in a /29 subnet with 8 total addresses, GCP provides 4 usable IP addresses for resources.

Complete Subnet Mask Reference

Reference table for all CIDR notations and their corresponding values

View detailed CIDR reference →
CIDR (View Details)Subnet MaskUsable HostsAWS IPsAzure IPsGCP IPs
/00.0.0.04,294,967,2944,294,967,2894,294,967,2894,294,967,290
/1128.0.0.02,147,483,6462,147,483,6412,147,483,6412,147,483,642
/2192.0.0.01,073,741,8221,073,741,8171,073,741,8171,073,741,818
/3224.0.0.0536,870,910536,870,905536,870,905536,870,906
/4240.0.0.0268,435,454268,435,449268,435,449268,435,450
/5248.0.0.0134,217,726134,217,721134,217,721134,217,722
/6252.0.0.067,108,86267,108,85767,108,85767,108,858
/7254.0.0.033,554,43033,554,42533,554,42533,554,426
/8255.0.0.016,777,21416,777,20916,777,20916,777,210
/9255.128.0.08,388,6068,388,6018,388,6018,388,602
/10255.192.0.04,194,3024,194,2974,194,2974,194,298
/11255.224.0.02,097,1502,097,1452,097,1452,097,146
/12255.240.0.01,048,5741,048,5691,048,5691,048,570
/13255.248.0.0524,286524,281524,281524,282
/14255.252.0.0262,142262,137262,137262,138
/15255.254.0.0131,070131,065131,065131,066
/16255.255.0.065,53465,52965,52965,530
/17255.255.128.032,76632,76132,76132,762
/18255.255.192.016,38216,37716,37716,378
/19255.255.224.08,1908,1858,1858,186
/20255.255.240.04,0944,0894,0894,090
/21255.255.248.02,0462,0412,0412,042
/22255.255.252.01,0221,0171,0171,018
/23255.255.254.0510505505506
/24255.255.255.0254249249250
/25255.255.255.128126121121122
/26255.255.255.19262575758
/27255.255.255.22430252526
/28255.255.255.240149910
/29255.255.255.2486112
/30255.255.255.2522000
/31255.255.255.2540 (point-to-point)000
/32255.255.255.2551 (single host)000