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+OpenStreetMap DNS
+======================================
+
+This repository contains the DNS zonefiles and related code for managing OpenStreetMap.org and other domains. A full list of the managed domains available in [Makefile](Makefile).
+
+The authoritative DNS nameservers we use are kindly run by [Bytemark](https://docs.bytemark.co.uk/article/content-dns/). We would like to thank [Bytemark](https://www.bytemark.co.uk/) for their many years of support.
+
+## Standard DNS Zone Files
+
+The [zone files](src/) are templated [tinydns-data](http://cr.yp.to/djbdns/tinydns-data.html) syntax and are written out by the [Makefile](Makefile).
+
+On commit of a DNS update, a git [post-receive](https://github.com/openstreetmap/chef/blob/master/cookbooks/dns/files/default/post-receive) runs `make update` via a [script](https://github.com/openstreetmap/chef/blob/master/cookbooks/dns/templates/default/dns-update.erb`) which then pushes the updated zonefiles to the authoritative DNS nameservers.
+
+## GeoDNS Zones
+
+The GeoDNS zones are handled differently.
+
+### tile.openstreetmap.org (mkgeo Generated)
+
+The `tile.openstreetmap.org` and `[a|b|c].tile.openstreetmap.org` are CNAME'ed to `tile.geo.openstreetmap.org` zone.
+
+The `tile.openstreetmap.org` zone file is written by [mkgeo](bin/mkgeo) which attempts to match the [estimated country bandwidth requirements](bandwidth/tile.openstreetmap.yml) to the nearest [running](https://uptime.openstreetmap.org/) [tile cache server](src/tile.openstreetmap) with available capacity.
+
+Example `tile.openstreetmap.org` zone file snippet in [tinydns-data](http://cr.yp.to/djbdns/tinydns-data.html) syntax as generated by [mkgeo](bin/mkgeo):
+
+```
+# Afghanistan
+Caf.tile.openstreetmap.org:baku.tile.openstreetmap.org:600
+# Albania
+Cal.tile.openstreetmap.org:osijek.tile.openstreetmap.org:600
+# Algeria
+Cdz.tile.openstreetmap.org:zaragoza.tile.openstreetmap.org:600
+# American Samoa
+Cas.tile.openstreetmap.org:sanfrancisco.tile.openstreetmap.org:600
+...
+# Servers
++aalborg.tile.openstreetmap.org:130.225.254.123:600
++amsterdam.tile.openstreetmap.org:134.90.146.26:600
++baku.tile.openstreetmap.org:94.20.20.55:600
+```
+
+The current tile.openstreetmap.org matching is here: https://dns.openstreetmap.org/tile.openstreetmap.org.html
+
+### tile.geo.openstreetmap.org (GeoIP)
+
+The `tile.geo.openstreetmap.org` zone uses authoritative [gdnsd](https://gdnsd.org/) DNS nameservers (`a.ns.openstreetmap.org`, `b.ns.openstreetmap.org`, etc ).
+
+The gdnsd config is managed using a [chef cookbook](https://github.com/openstreetmap/chef/tree/master/cookbooks/geodns).
+
+The DNS responses from `tile.geo.openstreetmap.org` are CNAMEs to XX.tile.openstreetmap.org, where XX is the ISO 3166-1 alpha-2 country code from the [client subnet if supplied by EDNS0](https://tools.ietf.org/html/rfc7871) or the IP address of the resolving DNS if the client subnet is not supplied by EDNS0.
+
+A typical DNS query flow example: `a.tile.openstreetmap.org -> CNAME tile.geo.openstreetmap.org -> CNAME gb.tile.openstreetmap.org. -> CNAME aalborg.tile.openstreetmap.org. -> A aaa.bbb.ccc.ddd`
+
+### render.openstreetmap.org (mkgeo Generated)
+
+The `render.openstreetmap.org` zone is a DNS zone used internally by the tile.openstreetmap.org cache servers and ***SHOULD NOT BE BE USED BY OTHERS***.
+
+The `render.openstreetmap.org` zone file is written by [mkgeo](bin/mkgeo) which attempts to match the estimated caches' bandwidth requirement (dynamically generated above tile.openstreetmap.org mkgeo) to the nearest [running](https://uptime.openstreetmap.org/) [render server](src/render.openstreetmap) with available capacity.
+
+Example `tile.openstreetmap.org` zone file snippet in [tinydns-data](http://cr.yp.to/djbdns/tinydns-data.html) syntax as generated by [mkgeo](bin/mkgeo):
+
+```
+# aalborg
+Caalborg.render.openstreetmap.org:vial.render.openstreetmap.org:600
+# amsterdam
+Camsterdam.render.openstreetmap.org:yevaud.render.openstreetmap.org:600
+# baku
+Cbaku.render.openstreetmap.org:vial.render.openstreetmap.org:600
+...
+# Servers
++orm.render.openstreetmap.org:193.63.75.98:600
++vial.render.openstreetmap.org:138.201.195.31:600
++yevaud.render.openstreetmap.org:128.40.45.208:600
+```
+
+The current render.openstreetmap.org matching is here: https://dns.openstreetmap.org/render.openstreetmap.org.html