Subnet Calculator + Common Ports Reference
Two tools in one: an IPv4 / IPv6 subnet calculator (enter 10.0.0.0/24 and get network, broadcast, usable range, host count, wildcard mask) and a searchable reference of common service ports (SSH 22, HTTP 80, HTTPS 443, MySQL 3306, Postgres 5432, Redis 6379, MongoDB 27017, RDP 3389, …). The ports list is the one every sysadmin keeps as a bookmark — built in.
Subnet calculator
Enter CIDR notation (e.g. 10.0.0.0/24, 172.16.5.0/22, 2001:db8::/64) and get: network address, broadcast address, usable host range (first to last), total + usable host counts, subnet mask (dotted decimal + binary), wildcard mask. Reverse direction: enter IP + mask, get the CIDR. Plus "split" mode: divide a larger subnet into smaller ones.
Common ports reference
Searchable table: type "ssh" to find SSH ports, type "5432" to identify the service. Covers ~200 common services. 1-1023: well-known (system) ports — SSH 22, DNS 53, HTTP 80, HTTPS 443, FTP 20/21, SMTP 25/465/587, IMAP 143/993, POP3 110/995, NTP 123, LDAP 389/636. 1024-49151: registered — MySQL 3306, Postgres 5432, Redis 6379, MongoDB 27017, Elasticsearch 9200, Docker 2375/2376, Kubernetes 6443. 49152+: ephemeral.
How to use it
- Open Tools → Network → Ports and Addresses.
- For subnet calc: enter CIDR (or IP + mask). Result shown immediately.
- For port lookup: type service name or port number in the search. Filter live.
- Click any row to copy the value.
Questions and answers
What's the /31 special case?
/31 has 2 addresses, both usable (RFC 3021 — typically used for point-to-point links between routers, where there's no need for separate network and broadcast).
How big a subnet can it split into smaller subnets?
Any. /16 split into /24s gives you 256 subnets — listed in a paginated table.
IPv6 host counts are astronomical — what's shown?
For IPv6, the calculator shows the prefix length and the number of /64 subnets within it. /64 is the standard subnet size, with ~10^19 addresses each — too many to list usefully.
Is this the IANA registered ports list?
A curated subset (~200 of the most common). The full IANA list has thousands of entries, most never used. The reference covers what 99% of sysadmins look up.
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