Skip to content

ip.md

Latest commit

 

History

History
84 lines (64 loc) · 3.3 KB

ip.md

File metadata and controls

84 lines (64 loc) · 3.3 KB
Raw

JustIP

justip (or just ip) reports the public IP address this machine presents to the internet. Both IPv4 and IPv6 are reported together, so the common question needs no switch. Run it bare for the console UI; the footer shows the exact headless command.

justip                  # both families, labeled
justip -4               # IPv4 only
justip -6               # IPv6 only
justip --plain          # bare addresses, one per line
justip --json           # {"ipv4":"…","ipv6":"…"}
justip --timeout 15     # wait longer on a slow link

What the address is

The address comes from a public echo service, which reports the address it saw the request arrive from. That is the address the internet sees, which behind NAT, a VPN, or a mobile carrier is not any address configured on a local interface. Nothing is sent but the request itself; the reply is a single line.

Each family is pinned by hostname rather than by a socket option. The IPv4 services publish only A records and the IPv6 services only AAAA records, so a request can reach them over one family only. An answer that arrives in the wrong family is discarded rather than reported under the wrong label.

Family Services, in the order they are tried
IPv4 api.ipify.org, ipv4.icanhazip.com, v4.ident.me
IPv6 api6.ipify.org, ipv6.icanhazip.com, v6.ident.me

The next service is tried whenever one fails, times out, or answers with something that is not an address for the family being asked about, so a single operator's outage does not take the command down with it.

Output

The default labeled form is one line per requested family:

IPv4: 203.0.113.7
IPv6: 2001:db8::7

--plain prints only the addresses, one per line, for piping into another command. --json prints one object whose ipv4 and ipv6 keys hold the address or null. Both keep stdout free of anything but the answer and send every explanation to stderr.

Families that cannot be reached

Most networks still have no public IPv6 route. Rather than wait out a connection that cannot complete, justip reads the source address the routing table would choose and skips the lookup when there is no globally routable one. No packet is sent for this check. A machine holding only link-local or unique-local IPv6 addresses is reported immediately:

IPv4: 203.0.113.7
IPv6: unavailable (this machine has no public IPv6 route)

One family answering is still an answer, so that run succeeds. The command fails, with exit status 1 and nothing on stdout, only when no requested family answers at all — including justip -6 on a machine with no IPv6.

--timeout bounds each family's lookup separately, from 1 to 60 seconds, and defaults to 5. Both families are looked up at once, so reporting both costs one timeout rather than two.

Saved defaults

The launcher remembers the address family, the output format, and the timeout. Nothing else is stored, and no address is ever written to disk.

Testing without the network

JUSTIP_IPV4_URL and JUSTIP_IPV6_URL replace the service list for that family with their own semicolon-separated URLs. An overridden family skips the public-route check, since the override is not expected to be on the public internet. This exists for the test suite and for pointing the command at a private echo service.