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CIDR Subnet Mask Cheat Sheet

Quickly look up subnet masks, wildcard masks, total IP capacities, and usable host counts for all prefixes from /0 to /32 with instant keyword filtering.

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CIDR PrefixSubnet MaskWildcard MaskTotal AddressesUsable HostsClass EquivalenceCommon Use Case
/32255.255.255.2550.0.0.011 (Host route)1 HostSingle host route, loopback interface, VPN client endpoint
/31255.255.255.2540.0.0.122 (RFC 3021)2 HostsPoint-to-point serial links (RFC 3021, saves IP address space)
/30255.255.255.2520.0.0.3421/64 Class CTraditional point-to-point WAN links between two routers
/29255.255.255.2480.0.0.7861/32 Class CSmall DMZ, multi-firewall gateway cluster, small branch office
/28255.255.255.2400.0.0.1516141/16 Class CServer farm tier, micro-services cluster, management VLAN
/27255.255.255.2240.0.0.3132301/8 Class CDepartmental subnet (e.g. Finance, HR), small office floor
/26255.255.255.1920.0.0.6364621/4 Class CMedium departmental subnet, database pool, staging environments
/25255.255.255.1280.0.0.1271281261/2 Class CHalf Class C network, large office department, corporate Wi-Fi
/24255.255.255.00.0.0.2552562541 Class CStandard LAN, home router subnet (192.168.1.0/24), cloud subnet
/23255.255.254.00.0.1.2555125102 Class CMid-sized business network, VoIP handset network
/22255.255.252.00.0.3.2551,0241,0224 Class CLarge enterprise branch, university building, AWS VPC subnets
/21255.255.248.00.0.7.2552,0482,0468 Class CHigh-density campus wireless network, convention center Wi-Fi
/20255.255.240.00.0.15.2554,0964,09416 Class CKubernetes Pod CIDR network, corporate campus network
/19255.255.224.00.0.31.2558,1928,19032 Class CRegional enterprise site, cloud availability zone network
/18255.255.192.00.0.63.25516,38416,38264 Class CLarge data center segment, enterprise multi-VPC hub
/17255.255.128.00.0.127.25532,76832,766128 Class CHalf Class B network, large ISP distribution network
/16255.255.0.00.0.255.25565,53665,5341 Class B (256 Class C)Standard AWS VPC / Azure VNet block (e.g. 10.0.0.0/16), Docker bridge
/15255.254.0.00.1.255.255131,072131,0702 Class BLarge enterprise corporate core, ISP subscriber block
/14255.252.0.00.3.255.255262,144262,1424 Class BRegional ISP allocation, multi-cloud core infrastructure
/13255.248.0.00.7.255.255524,288524,2868 Class BTelco subscriber network, cloud provider regional block
/12255.240.0.00.15.255.2551,048,5761,048,57416 Class BRFC 1918 Private Range (172.16.0.0/12), National ISP
/11255.224.0.00.31.255.2552,097,1522,097,15032 Class BMajor ISP routing pool, wholesale telecom block
/10255.192.0.00.63.255.2554,194,3044,194,30264 Class BCarrier-Grade NAT (RFC 6598: 100.64.0.0/10), broadband mobile networks
/9255.128.0.00.127.255.2558,388,6088,388,606128 Class BHalf Class A network, Tier 1 telecom provider backbone
/8255.0.0.00.255.255.25516,777,21616,777,2141 Class ARFC 1918 Private Range (10.0.0.0/8), DoD, Apple, IBM legacy allocations
/7254.0.0.01.255.255.25533,554,43233,554,4302 Class AGlobal internet routing aggregation
/6252.0.0.03.255.255.25567,108,86467,108,8624 Class ARIR continental block allocation (ARIN, RIPE, APNIC)
/5248.0.0.07.255.255.255134,217,728134,217,7268 Class AMajor internet registry allocation block
/4240.0.0.015.255.255.255268,435,456268,435,45416 Class AMulticast block (224.0.0.0/4), Experimental block (240.0.0.0/4)
/3224.0.0.031.255.255.255536,870,912536,870,91032 Class A1/8th of global IPv4 address space
/2192.0.0.063.255.255.2551,073,741,8241,073,741,82264 Class A1/4th of global IPv4 address space
/1128.0.0.0127.255.255.2552,147,483,6482,147,483,646128 Class AHalf of the entire global IPv4 internet space
/00.0.0.0255.255.255.2554,294,967,2964,294,967,294All IPv4Default route (0.0.0.0/0), Quad-Zero Internet Gateway

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Frequently Asked Questions

Clear answers to common questions about subnetting, CIDR notation, and network design.

What is a Subnet Mask Cheat Sheet?
A Subnet Mask Cheat Sheet is a reference chart mapping every CIDR prefix (/0 through /32) to its dotted-decimal subnet mask, inverted wildcard mask, total IP addresses, and usable host count. It is an essential quick-reference guide for CCNA exams, network engineering interviews, and cloud network provisioning.
Why do subnets like /30 and /31 exist?
A /30 subnet provides 2 usable hosts (out of 4 total addresses) and was traditionally used for point-to-point router links. Under RFC 3021, a /31 prefix provides 2 usable hosts (out of 2 total addresses) without wasting network or broadcast IDs, doubling the address efficiency for modern point-to-point links.
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