RFC 1876 / START HERE
DNS LOC, before the details
LOC means location. RFC1876 defines an Experimental DNS location record; it is not an Internet Standard.
A LOC record attaches a geographic center, an enclosing size and uncertainty values to a DNS name. Latitude and longitude are angles; altitude is height relative to the WGS84 mathematical Earth model. The record reports coordinates rather than sensing a device.
The idea in one picture
Name a place
Encode its center
Show uncertainty
A simplified picture of the idea; the chapters explain the actual mechanisms.
Why it exists
Location-aware network maps need a way to read location data associated with hosts or networks. RFC1876 adds type29 and a sixteen-octet wire format to DNS, plus a historical IPv4 lookup/fallback procedure. It formally updates RFC1034 and RFC1035.
A familiar example
A fictional picnic.example.org record can describe an approximate area. Its horizontal precision is a diameter, not a plus-or-minus radius. A network-level fallback is less specific than a host location, and publishing precise data can expose physical details.
Helpful background
You can start here without reading another RFC. If these ideas are unfamiliar, these short introductions may help.
What you’ll learn next
Begin with chapter one, or choose a topic.
- Read the sixteen-byte location recordA LOC resource record stores a location, its size and its uncertainty. Type 29 identifies LOC; the version-zero record data has sixteen octets.→
- Offset latitude and longitude from a shared midpointCoordinates are angles. One degree contains sixty minutes; one minute contains sixty seconds of arc. LOC stores thousandths of an arcsecond around an unsigned midpoint.→
- Measure altitude from the reference spheroidAltitude is height relative to the WGS84 reference spheroid, a mathematical Earth model used by GPS. The stored integer uses centimeters and an offset.→
- Distinguish size from precision and radiusSIZE describes a sphere enclosing the entity. Horizontal and vertical precision describe uncertainty in the reported center; neither is an authentication guarantee.→
- Apply master-file units and defaultsA zone master file is human-readable DNS data. LOC writes latitude, hemisphere, longitude, hemisphere, altitude and optional size/precision values.→
- Search a name or an IPv4 address in orderA location-aware application can begin with a domain name or an IPv4 address. These are alternative starting points, not a single mandatory pipeline.→
- Search the most specific recorded network firstThe historical IPv4 fallback discovers network/subnet names into a stack, then checks the most specific name first. This is not a modern CIDR or IPv6 geolocation algorithm.→
- Keep scope and location-disclosure limits visiblePublishing a location can expose physical details. A LOC record reports data; it neither measures a device’s current position nor grants permission to find or approach it.→
This introduction explains RFC 1876 (1996). Read the original RFC ↗