Network & IP Tools
Subnet and CIDR calculators, IPv4/IPv6 converters and validators, DNS record builders and bandwidth calculators — pure math, computed locally in your browser.
48 free tools
Subnet Calculator
Calculate network address, broadcast, usable host range and subnet mask from any IPv4 address and CIDR prefix. Free, instant and 100% in your browser.
CIDR to IP Range Converter
Convert CIDR notation like 192.168.1.0/26 into its first and last IP address and total address count. Handles many blocks at once, free and in-browser.
IP Range to CIDR Converter
Convert any start–end IP range into the smallest possible set of CIDR blocks. Ideal for firewall rules and route summaries — free and fully in-browser.
VLSM Subnet Calculator
Plan variable-length subnets from one parent network and a list of host requirements. Largest-first allocation with masks, ranges and waste — in-browser.
Subnet Mask Converter
Convert between CIDR prefix, dotted subnet mask, wildcard mask, hex and binary — with a full /0–/32 reference table. Free and 100% in your browser.
Wildcard Mask Calculator
Convert a subnet mask or CIDR prefix to a Cisco wildcard mask and back, with a ready-to-paste ACL line and binary view. Free, private, in-browser.
IP to Binary Converter
Convert IPv4 and IPv6 addresses to binary with a per-octet bit table, and turn 32-bit binary back into an IP. Free, instant and fully in your browser.
IP to Decimal Converter
Convert an IPv4 address to its 32-bit decimal, hex and octal forms and back, with the positional math shown step by step. Free and fully in-browser.
IP in Subnet Checker
Check whether IP addresses fall inside one or more CIDR subnets. Batch-check whole lists with a per-IP match table — free, private and in-browser.
IP Address Validator
Validate lists of IPv4, IPv6 and CIDR entries with the exact failure reason per line — compressed ::, IPv4-mapped forms and prefixes included. Free.
Private IP Address Checker
Check if an IPv4 or IPv6 address is private, loopback, link-local, CGNAT or otherwise special — with the matching RFC and public-routability verdict.
CIDR to IP List Generator
Expand a CIDR block into a downloadable list of every IP address it contains, up to /16. Include or exclude network and broadcast — free and in-browser.
IP Address Sorter
Sort IPv4 and IPv6 address lists in true numeric order — not alphabetical — with de-duplication and invalid-line reporting. Free and 100% in-browser.
IPv6 Subnet Calculator
Calculate IPv6 subnets online: network prefix, first and last address, total addresses and expanded/compressed forms for any /0–/128 prefix. 100% in-browser.
IPv6 Expander & Compressor
Expand a compressed IPv6 address to its full 8-group form, or compress it to the RFC 5952 canonical short form — instantly and 100% in your browser.
IPv4 to IPv6 Converter
Convert an IPv4 address to its IPv4-mapped (::ffff:), IPv4-compatible and 6to4 IPv6 forms — or extract the IPv4 hidden inside an IPv6 address. Free and private.
CIDR Aggregator
Aggregate a list of IPs and CIDR blocks into the minimal covering set. Merges overlapping and adjacent IPv4 ranges into clean summary routes — 100% offline.
MAC Address Formatter
Convert MAC addresses between colon, hyphen, Cisco dotted and bare-hex notation in bulk, with case control and U/L + multicast bit decoding. 100% in-browser.
PTR Record Generator
Build reverse-DNS PTR records for IPv4 and IPv6: in-addr.arpa and ip6.arpa names plus the ready-to-paste zone-file line. Pure formatting, no lookups.
SPF Record Generator
Create a valid SPF TXT record from your sending IPs, includes and mail servers — with live DNS-lookup counting against the 10-lookup limit. Free and private.
DMARC Record Generator
Generate a DMARC TXT record with policy, subdomain policy, pct, rua/ruf reporting and alignment options — each tag explained in plain English. 100% in-browser.
DNS Record Generator
Generate correctly formatted zone-file lines for A, AAAA, CNAME, MX, TXT, NS, SRV and CAA records — with FQDN dots, priorities and TXT chunking handled for you.
Port Number Lookup
Look up what a TCP or UDP port is used for — search 150+ common well-known and registered ports by number, service name or protocol. Instant and offline.
Download Time Calculator
Calculate how long a download takes from file size and connection speed, with correct Mbps vs MB/s handling, overhead allowance and the speed you need.
Subnet Splitter
Split any IPv4 CIDR block into equal-sized subnets by new prefix length or subnet count, with network, broadcast, host range and CSV export.
CIDR Overlap Checker
Paste a list of IPv4 or IPv6 CIDR blocks and instantly see which ones overlap, which contain another, which are duplicates and where the gaps are.
Subnetting Practice Questions Generator
Generate unlimited CCNA-style subnetting practice questions with a seeded worksheet and a full answer key that shows the binary AND working.
EUI-64 Calculator
Convert a 48-bit MAC address to its modified EUI-64 IPv6 interface identifier and link-local address, or work backwards from an IPv6 address to the MAC.
IPv6 Address Compressor
Shorten any IPv6 address to its canonical RFC 5952 form, see the fully expanded version beside it, and compress a whole list at once.
IPv6 to IPv4 Converter
Pull the IPv4 address out of an IPv6 address and name the mechanism — IPv4-mapped, 6to4, Teredo, NAT64, ISATAP — or explain when there is none.
IPv6 ULA Generator
Generate a random RFC 4193 unique local IPv6 prefix (fd00::/8) with a 40-bit global ID, plus a table of /64 subnets ready to assign.
DHCP Scope Calculator
Plan a DHCP scope from a subnet: pool start and end, exclusions, lease count, T1/T2 renewal timers and ready-to-paste dhcpd.conf and netsh config.
MTU and MSS Calculator
Work out the TCP MSS for any path MTU, subtract PPPoE, GRE, IPsec, VXLAN or WireGuard overhead, and get the exact clamp value to configure.
TCP Window Size Calculator
Calculate the bandwidth-delay product, the receive window needed to saturate a link, the TCP window scale factor and the throughput a given window allows.
IPv4 Header Decoder
Paste an IPv4 header hex dump and decode every field — version, IHL, DSCP, flags, TTL, protocol — and recompute the header checksum to verify it.
TCP Header Decoder
Decode a TCP header hex dump: ports, sequence and ack numbers, all nine flag bits, window size, and every option including MSS, SACK and timestamps.
DNS Zone File Generator
Build a complete BIND zone file online: $ORIGIN, $TTL, a full SOA record with date-based serial, plus NS, A, AAAA, CNAME, MX, TXT and SRV rows.
DNS Zone File Parser
Paste a BIND zone file and see every record normalised to a full name with its effective TTL, plus duplicate, CNAME-clash and missing-dot warnings.
DKIM Record Generator
Generate a DKIM TXT record from your public key, or create a fresh 2048-bit RSA key pair in the browser. Output as one flat line and as BIND chunks.
MTA-STS Policy Generator
Generate both halves of RFC 8461 MTA-STS: the mta-sts.txt policy file with mode, mx and max_age, plus the _mta-sts TXT record with a fresh id.
BIMI Record Generator
Build the default._bimi TXT record for Brand Indicators for Message Identification, with URL checks for your SVG logo and Verified Mark Certificate.
TLSA Record Generator
Paste a certificate and get its DANE TLSA record: pick usage, selector and matching type, and the SHA-256 or SHA-512 hash is computed in your browser.
Email Header Analyzer
Paste raw email headers to trace the delivery path hop by hop, see where mail stalled, and read the SPF, DKIM and DMARC verdicts — all offline.
SMTP Status Code Lookup
Look up any SMTP reply code and decode RFC 3463 enhanced status codes like 5.7.1 field by field into class, subject and detail meanings.
IP Blocklist Generator
Turn a list of IPs and CIDR ranges into nginx, Apache, iptables, ufw, netsh or plain CIDR rules, with duplicates removed and ranges merged.
DSCP to ToS Converter
Convert between DSCP values, the legacy ToS byte, IP Precedence and PHB names like EF, AF31 and CS5, in decimal, hex and binary side by side.
VoIP Bandwidth Calculator
Work out VoIP bandwidth per call for G.711, G.729, Opus and more, including RTP/UDP/IP, Ethernet, PPP and IPsec overhead, with and without cRTP.
WiFi Channel to Frequency Converter
Convert WiFi channel numbers to centre frequencies and back for 2.4, 5 and 6 GHz, with band, DFS status, channel width spans and 2.4 GHz overlap.