mrnx/network

Subnet cheat sheet

Every IPv4 prefix length with netmask, wildcard and host counts, the reserved address ranges, well-known multicast groups and common IPv6 prefix sizes. Click any value to copy it.

IPv4 prefix lengths

PrefixNetmask / wildcardWildcardAddressesUsable hostsIn /24 terms
/00.0.0.0255.255.255.255255.255.255.2554,294,967,2964,294,967,29416,777,216 × /24
/1128.0.0.0127.255.255.255127.255.255.2552,147,483,6482,147,483,6468,388,608 × /24
/2192.0.0.063.255.255.25563.255.255.2551,073,741,8241,073,741,8224,194,304 × /24
/3224.0.0.031.255.255.25531.255.255.255536,870,912536,870,9102,097,152 × /24
/4240.0.0.015.255.255.25515.255.255.255268,435,456268,435,4541,048,576 × /24
/5248.0.0.07.255.255.2557.255.255.255134,217,728134,217,726524,288 × /24
/6252.0.0.03.255.255.2553.255.255.25567,108,86467,108,862262,144 × /24
/7254.0.0.01.255.255.2551.255.255.25533,554,43233,554,430131,072 × /24
/8255.0.0.00.255.255.2550.255.255.25516,777,21616,777,21465,536 × /24
/9255.128.0.00.127.255.2550.127.255.2558,388,6088,388,60632,768 × /24
/10255.192.0.00.63.255.2550.63.255.2554,194,3044,194,30216,384 × /24
/11255.224.0.00.31.255.2550.31.255.2552,097,1522,097,1508,192 × /24
/12255.240.0.00.15.255.2550.15.255.2551,048,5761,048,5744,096 × /24
/13255.248.0.00.7.255.2550.7.255.255524,288524,2862,048 × /24
/14255.252.0.00.3.255.2550.3.255.255262,144262,1421,024 × /24
/15255.254.0.00.1.255.2550.1.255.255131,072131,070512 × /24
/16255.255.0.00.0.255.2550.0.255.25565,53665,534256 × /24
/17255.255.128.00.0.127.2550.0.127.25532,76832,766128 × /24
/18255.255.192.00.0.63.2550.0.63.25516,38416,38264 × /24
/19255.255.224.00.0.31.2550.0.31.2558,1928,19032 × /24
/20255.255.240.00.0.15.2550.0.15.2554,0964,09416 × /24
/21255.255.248.00.0.7.2550.0.7.2552,0482,0468 × /24
/22255.255.252.00.0.3.2550.0.3.2551,0241,0224 × /24
/23255.255.254.00.0.1.2550.0.1.2555125102 × /24
/24255.255.255.00.0.0.2550.0.0.2552562541 per /24
/25255.255.255.1280.0.0.1270.0.0.1271281262 per /24
/26255.255.255.1920.0.0.630.0.0.6364624 per /24
/27255.255.255.2240.0.0.310.0.0.3132308 per /24
/28255.255.255.2400.0.0.150.0.0.15161416 per /24
/29255.255.255.2480.0.0.70.0.0.78632 per /24
/30255.255.255.2520.0.0.30.0.0.34264 per /24
/31255.255.255.2540.0.0.10.0.0.122 p2p128 per /24
/32255.255.255.2550.0.0.00.0.0.011256 per /24

Usable = addresses − 2 (network and broadcast), except /31 (point-to-point, RFC 3021) and /32 (single host).

Reserved IPv4 ranges

RangePurposeDefined in
0.0.0.0/8"This network" · RFC 791RFC 791
10.0.0.0/8Private · RFC 1918RFC 1918
100.64.0.0/10Shared address space (CGNAT) · RFC 6598RFC 6598
127.0.0.0/8Loopback · RFC 1122RFC 1122
169.254.0.0/16Link-local (APIPA) · RFC 3927RFC 3927
172.16.0.0/12Private (172.16.0.0 – 172.31.255.255) · RFC 1918RFC 1918
192.0.0.0/24IETF protocol assignments · RFC 6890RFC 6890
192.0.2.0/24Documentation (TEST-NET-1) · RFC 5737RFC 5737
192.168.0.0/16Private · RFC 1918RFC 1918
198.18.0.0/15Benchmarking · RFC 2544RFC 2544
198.51.100.0/24Documentation (TEST-NET-2) · RFC 5737RFC 5737
203.0.113.0/24Documentation (TEST-NET-3) · RFC 5737RFC 5737
224.0.0.0/4Multicast · RFC 5771RFC 5771
240.0.0.0/4Reserved · RFC 1112RFC 1112
255.255.255.255/32Limited broadcast · RFC 919RFC 919

IPv6 prefix sizes

PrefixTypical useHolds
/32Typical allocation to an ISP / LIR65,536 × /48
/48Typical site (business) assignment65,536 × /64
/56Typical home / small-site assignment256 × /64
/64One LAN segment (SLAAC requires /64)2⁶⁴ addresses
/127Point-to-point link (RFC 6164)2 addresses
/128Single host / loopback1 address

Special IPv6 ranges

RangePurpose
::/128Unspecified
::1/128Loopback
::ffff:0:0/96IPv4-mapped
64:ff9b::/96NAT64 well-known prefix
2000::/3Global unicast
2001:db8::/32Documentation
fc00::/7Unique local (ULA, use fd00::/8)
fe80::/10Link-local
ff00::/8Multicast

Well-known multicast groups

IPv4 / IPv6Used byIPv6
224.0.0.1ff02::1All hostsff02::1
224.0.0.2ff02::2All routers (also HSRPv1, LDP hello)ff02::2
224.0.0.5ff02::5OSPF all routersff02::5
224.0.0.6ff02::6OSPF DR / BDRff02::6
224.0.0.9ff02::9RIPv2 (RIPng)ff02::9
224.0.0.10ff02::aEIGRPff02::a
224.0.0.13ff02::dPIMff02::d
224.0.0.18ff02::12VRRPff02::12
224.0.0.22ff02::16IGMPv3 reports (MLDv2)ff02::16
224.0.0.102ff02::66HSRPv2, GLBP (HSRP for IPv6)ff02::66
224.0.0.251ff02::fbmDNS (Bonjour, AirPlay)ff02::fb
224.0.0.252ff02::1:3LLMNRff02::1:3
224.0.1.1ff0x::101NTPff0x::101
224.0.1.129ff0x::181PTP (IEEE 1588)ff0x::181
239.255.255.250ff02::cSSDP / UPnPff02::c
—ff02::1:2DHCPv6 servers and relaysff02::1:2
—ff02::1:ff00:0/104Solicited-node (neighbour discovery)ff02::1:ff00:0/104
224.0.0.0/24ff02::/16Local network control: never routed, TTL 1ff02::/16
232.0.0.0/8ff3x::/32Source-specific multicast (SSM)ff3x::/32
239.0.0.0/8ff08::/16Administratively scoped (private use)ff08::/16

On the wire an IPv4 group maps to MAC 01:00:5e plus its low 23 bits, so 32 groups share each MAC; an IPv6 group maps to 33:33 plus its low 32 bits. In IPv6, x is the scope: 2 link, 5 site, 8 organisation, e global.

IPv4 subnet calculatorNetwork, broadcast, host range, binary view and subnet splitting.VLSM plannerCarve an address block into right-sized subnets from host counts.CIDR aggregationMerge and deduplicate prefix lists for ACLs, firewalls and route summaries.Wildcard mask calculatorConvert masks and wildcards, see exactly which addresses a wildcard matches and find one wildcard for a set of hosts.IPv6 calculatorCompress, expand, classify and subnet IPv6 prefixes.IP ↔ hex & DHCP option 43Convert IPs to hex, decimal and binary, build or decode option 43 for wireless controller discovery.
Domain health reportOne graded report for a domain: name servers, SOA, DNSSEC, CAA, MX, SPF, DMARC, DKIM and MTA-STS.DNS lookupAll common record types for a name in one go, with TTLs, DNSSEC status and reverse lookups.SPF / DMARC / DKIM checkerLook up or paste email authentication records and get them validated and explained.Email header analyzerTrace a message hop by hop with delays, see SPF/DKIM/DMARC results and spot spoofing signs.
What's my IPYour public IP address as the internet sees it, plus what your browser reveals.IP, ASN & WHOIS lookupOwner, prefix, origin AS, RPKI status and abuse contact for an IP; prefixes for an AS; registration for a domain.Bulk IP extractor & enrichmentPull every IP out of a log, count and classify them, then add owner, AS, country and Tor-exit status.Bulk MAC vendor lookupPaste a MAC/ARP table or any text; every MAC is found and matched to its vendor.
Config template generatorFill a config template with {{ placeholders }} from a spreadsheet: one block per port, VLAN, firewall object or switch.ACL builderBuild Cisco IOS access lists from plain input (CIDR, port lists, ranges) with correct wildcards, then send them to the tester.ACL testerPaste a Cisco IOS ACL, test a packet against it and find shadowed or redundant rules.Prefix list creator & testerTest which entry of a BGP prefix list a route hits, spot dead entries, or generate lists for IOS, IOS XR and Junos.BGP toolkitTest AS-path regexes, decode communities (no-export, blackhole, route targets) and convert or classify AS numbers.VLAN list calculatorCompare, compress and expand trunk VLAN lists and get the add / remove commands for each vendor.
Packet capture analyzerDrop a .pcap / .pcapng: talkers, TCP retransmissions and resets, DNS, DHCP, TLS, ARP and STP problems, analysed in your browser.Config & state diffCompare configs or full show-command backups: see interfaces that went down, lost neighbors, moved MACs, and get draft config commands.MTU & MSS calculatorStack tunnels (GRE, IPsec, VXLAN, WireGuard, PPPoE, MPLS) to get the inner MTU, TCP MSS clamp and DF ping tests.Bandwidth & throughputLive copy progress, transfer times, TCP window limits, TB vs TiB and latency from distance.Signal & link budgetdBm to mW, Wi-Fi signal through walls, free-space path loss and fibre optical power budget.
Certificate decoderDecode PEM certificates and chains: SANs, validity, key size, extensions and fingerprints.JWT decoderDecode a JSON Web Token, read its claims and expiry, spot risky settings and check HMAC signatures.Password & key generatorStrong random passwords, Wi-Fi keys, hex/base64 secrets and UUIDs, with entropy and crack-time estimates.Encoders & convertersBase64, URL and hex encoding, SHA hashes, Unix timestamps, punycode domains and a chmod calculator.
Subnet cheat sheetEvery prefix length with mask, wildcard and host count, plus reserved ranges and IPv6 sizes.Port referenceSearchable list of common ports and protocols with security notes.DSCP & QoS referenceDSCP, ToS byte, precedence, CoS and Wi-Fi classes side by side, with capture filters and marking commands.Network command referenceCommands by task for Cisco, Arista, Aruba, Juniper, Huawei, MikroTik, Fortinet (switch, FortiGate) and Palo Alto, side by side.

↑↓ move↵ openesc close