DNS: Difference between revisions
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At system start, FlightGear sends a query for the DNS name <code>terrasync.flightgear.org</code>. The URL for scenery download is encoded in the regex field between the last two exclamation marks. This string MUST start with <code>!^.*$!</code> and must end with <code>!</code>, the regex itself is not interpreted by the TerraSync client, only the fixed string is taken. | At system start, FlightGear sends a query for the DNS name <code>terrasync.flightgear.org</code>. The URL for scenery download is encoded in the regex field between the last two exclamation marks. This string MUST start with <code>!^.*$!</code> and must end with <code>!</code>, the regex itself is not interpreted by the TerraSync client, only the fixed string is taken. | ||
The | The DNS to query is currently not configurable at system start by setting a property. The version number can be changed by setting property /sim/terrasync/scenery-version to a value other than the default "ws20". | ||
Revision as of 19:26, 10 November 2016
Usage of DNS within FlightGear
The Domain Name System (DNS) is being used within FlightGear to look up resources providing several services. Its use started with release 2016.2.1 as an experimental feature to resolve the location of the TerraSync servers. This page documents the used services in detail[1].
Its creation was inspired by a discussion that took place on the FlightGear devel mailing list in 11/2016 to stop using a dedicated web service for retrieving a list of active multiplayer servers and instead use DNS [2].
FlightGear systems using DNS
Currently, (as of version 2016.4.0) these systems use DNS for service discovery:
- The TerraSync client to find a TerraSync server
- The multiplayer client to list multiplayer servers and retrieve information about each server
TerraSync
The TerraSync client queries NAPTR record s for the DNS name terrasync.flightgear.org
. As of version 2016.4, the configured entries are:
- terrasync.flightgear.org. IN NAPTR 100 100 "U" "ws20" "!^.*$!http://flightgear.sourceforge.net/scenery!" .
- terrasync.flightgear.org. IN NAPTR 100 50 "U" "ws20" "!^.*$!http://fgfs.goneabitbursar.com/terrascenery!" .
- terrasync.flightgear.org. IN NAPTR 100 50 "U" "ws20" "!^.*$!http://mpserver16.flightgear.org/scenery!" .
At system start, FlightGear sends a query for the DNS name terrasync.flightgear.org
. The URL for scenery download is encoded in the regex field between the last two exclamation marks. This string MUST start with !^.*$!
and must end with !
, the regex itself is not interpreted by the TerraSync client, only the fixed string is taken.
The DNS to query is currently not configurable at system start by setting a property. The version number can be changed by setting property /sim/terrasync/scenery-version to a value other than the default "ws20".
Multiplayer
The multiplayer client queries SRV record s for a list of multiplayer servers and TXT record s on each server for detailed information about the server.
The SRV record for a multiplayer server looks like this:
_fgms._udp IN SRV 10 20 5001 mpserver01
All entries currently use the same values for priority and weight. The port numbers for active servers are set to the port number of the running fgms instance. The port number is zero for inactive servers.
The TXT record for each referenced multiplayer server looks like this:
mpserver01 IN TXT "flightgear-mpserver=eyJuYW1lIjoibXBzZXJ2ZXIwMSIsImxvY2F0aW9uIjoiRnJhbmtmdXJ0LEdlcm1hbnkifQo="
with the text data used as in RFC 1464 - Using the Domain Name System To Store Arbitrary String Attributes. The attribute name flightgear-mpserver marks this entry as "ours" while it's attribute value is a base64 encoded json string containing additional attributes for the server not available within the SRV record. For the given example, the base64 string of
eyJuYW1lIjoibXBzZXJ2ZXIwMSIsImxvY2F0aW9uIjoiRnJhbmtmdXJ0LEdlcm1hbnkifQo=
decodes to
{"name":"mpserver01","location":"Frankfurt,Germany"}
References
References
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