Master Server Query Protocol

Client to master server

Send the following UDP query to a master server to get a list of Source host servers.

Format

Type	Field	Value
Byte	Message Type	0x31 - the character "1"
Byte	Region Code	See below
String Zero	IP:Port	See below
String Zero	Filter	See below

Region codes

The region of the world that you wish to find servers in.

Byte	Description	0x03	Europe IP:Port The first IP:Port you should send is "41.99.155.45" From then on, IP:Port becomes the last IP:Port received in the master servers reply. This allows steam to then grab another list of more servers. Terminate this with 0x00 Note that whenever you open a new socket (and thus get a new random client port), the Master Server will always send you the first batch of IPs even if you pass a valid game server IP. Do not close your socket between packets. Filter Allows you to restrict the results to servers running a certain game, map, etc. Send an empty string (0x00) to receive a list of all types of servers. Insert \ in between filter parameters \type\d Servers running dedicated \secure\1 Servers using anti-cheat technology (VAC, but potentially others as well) \gamedir\[mod] Servers running the specified modification (ex. cstrike) \map\[map] Servers running the specified map (ex. de_dust2) \linux\1 Servers running on a Linux platform \empty\1 Servers that are 7 empty \full\1 Servers that are not full \proxy\1 Servers that are spectator proxies \napp\[appid] Servers that are NOT running game [appid] (This was introduced to block Left 4 Dead games from the Steam Server Browser) \24\1 Servers that are empty \white\1 Servers that are whitelisted Sample query To get all servers everywhere: 0000 31 FF 30 2E 30 2E 30 2E 1.0.0.0. 0008 30 3A 30 00 00 0:0.. This is the default Steam Server Browser query to the Source Master Server. It uses the napp filter to filter out Left 4 Dead games (which are meant to be joined using the matchmaking feature). 31 ff 30 2e 30 2e 30 2e 30 3a 30 00 5c 6e 61 70 1.0.0.0.0:0.\nap 70 5c 35 30 30 00 p\500. Master servers Current master servers are: GoldSrc hl1master.steampowered.com:27010 (numeric IP may change) [1] Source hl2master.steampowered.com:27011 (numeric IP may change) Rag Doll Kung Fu 67.132.200.140:27012 Red Orchestra Unknown - same as Source? SiN 1 Multiplayer 69.28.151.162:27010 If you can, get your application to check the file Steam\config\masterservers.vdf to get the latest list of master servers. Reply format The reply always starts with FF FF FF FF 66 0A. The format is then a series of these server address blocks: Type Data Byte First octet of IP address Byte Second octet of IP address Byte Third octet of IP address Byte Fourth octet of IP address Unsigned Short Port number - usually 27015 (69 87) - this is network ordered, which is unlike every other Steam protocol. Some of the servers may be unreachable, so query each server directly to find out. Note also that this list is not exhaustive, so if you're looking for a particular type of server make sure that you specify a filter with the query, rather than filtering client side. End of IP address list The full requested IP list may not fit in 1 x packet. Subsequent packets must be requested by using the last received IP address and Port as the 'seed' in the next request. The end of the IP list is indicated by a received IP address of 0.0.0.0 Port:0. Game server to master server Join Shortly after a game server has been initialized, it picks two master servers to "join." In order for clients to see a particular game server when they click on the "Internet" tab, the game server must be present in the Steam master servers' records. The game server sends each master server "q" (71). The master servers each respond by sending FF FF FF FF 73 0A followed by a (relatively) unique 4-byte "challenge" number. If you send the master servers an invalid challenge, you will get another challenge as a response. Challenge response After receiving the challenge packet, the game server then sends its challenge information in the following format: Goldsource 002a 30 0a 5c 70 72 6f 0.\pro 0030 74 6f 63 6f 6c 5c 34 37 5c 63 68 61 6c 6c 65 6e tocol\47\challen 0040 67 65 5c 31 33 33 39 38 39 35 37 30 32 5c 70 6c ge\1339895702\pl 0050 61 79 65 72 73 5c 30 5c 6d 61 78 5c 32 5c 62 6f ayers\0\max\2\bo 0060 74 73 5c 30 5c 67 61 6d 65 64 69 72 5c 63 73 74 ts\0\gamedir\cst 0070 72 69 6b 65 5c 6d 61 70 5c 64 65 5f 64 75 73 74 rike\map\de_dust 0080 5c 74 79 70 65 5c 64 5c 70 61 73 73 77 6f 72 64 \type\d\password 0090 5c 30 5c 6f 73 5c 6c 5c 73 65 63 75 72 65 5c 30 \0\os\l\secure\0 00a0 5c 6c 61 6e 5c 30 5c 76 65 72 73 69 6f 6e 5c 31 \lan\0\version\1 00b0 2e 31 2e 32 2e 35 2f 53 74 64 69 6f 5c 72 65 67 .1.2.5/Stdio\reg 00c0 69 6f 6e 5c 32 35 35 5c 70 72 6f 64 75 63 74 5c ion\255\product\ 00d0 63 73 74 72 69 6b 65 0a cstrike. The challenge number is simply the challenge sent by the master server converted to an int. Source 002a 30 0a 5c 70 72 6f 0.\pro 0030 74 6f 63 6f 6c 5c 37 5c 63 68 61 6c 6c 65 6e 67 tocol\7\challeng 0040 65 5c 31 33 33 39 36 31 38 32 33 5c 70 6c 61 79 e\133961823\play 0050 65 72 73 5c 30 5c 6d 61 78 5c 32 5c 62 6f 74 73 ers\0\max\2\bots 0060 5c 30 5c 67 61 6d 65 64 69 72 5c 63 73 74 72 69 \0\gamedir\cstri 0070 6b 65 5c 6d 61 70 5c 64 65 5f 64 75 73 74 5c 70 ke\map\de_dust\p 0080 61 73 73 77 6f 72 64 5c 30 5c 6f 73 5c 6c 5c 6c assword\0\os\l\l 0090 61 6e 5c 30 5c 72 65 67 69 6f 6e 5c 32 35 35 5c an\0\region\255\ 00a0 74 79 70 65 5c 64 5c 73 65 63 75 72 65 5c 30 5c type\d\secure\0\ 00b0 76 65 72 73 69 6f 6e 5c 31 2e 30 2e 30 2e 32 38 version\1.0.0.28 00c0 5c 70 72 6f 64 75 63 74 5c 63 73 74 72 69 6b 65 \product\cstrike 00d0 0a . The challenge number is simply the challenge sent by the master server converted to an int. Orangebox 0000 30 0a 5c 70 72 6f 74 6f 63 6f 6c 5c 37 5c 63 68 0.\protocol\7\ch 0010 61 6c 6c 65 6e 67 65 5c 31 39 35 39 36 38 37 33 allenge\19596873 0020 39 39 5c 70 6c 61 79 65 72 73 5c 31 5c 6d 61 78 99\players\1\max 0030 5c 34 5c 62 6f 74 73 5c 30 5c 67 61 6d 65 64 69 \4\bots\0\gamedi 0040 72 5c 74 66 5c 6d 61 70 5c 61 72 65 6e 61 5f 62 r\tf\map\arena_b 0050 61 64 6c 61 6e 64 73 5c 70 61 73 73 77 6f 72 64 adlands\password 0060 5c 30 5c 6f 73 5c 77 5c 6c 61 6e 5c 31 5c 72 65 \0\os\w\lan\1\re 0070 67 69 6f 6e 5c 2d 31 5c 67 61 6d 65 74 79 70 65 gion\-1\gametype 0080 5c 61 72 65 6e 61 5c 74 79 70 65 5c 6c 5c 73 65 \arena\type\l\se 0090 63 75 72 65 5c 30 5c 76 65 72 73 69 6f 6e 5c 31 cure\0\version\1 00a0 2e 30 2e 34 2e 33 5c 70 72 6f 64 75 63 74 5c 74 .0.4.3\product\t 00b0 66 0a f. The challenge number is simply the challenge sent by the master server converted to an int. Differences The field order is a bit different with Source than with Goldsource. Goldsource protocol challenge players max bots gamedir map type password os secure lan version region product Source protocol challenge players max bots gamedir map password os lan region type secure version product Heartbeat A "heartbeat" occurs every five minutes in order to let the master servers know that a game server is still "alive". The game server simply goes through the process of "joining" the master server list again. Quit Goldsource The game server sends the master server 62 0A to signal that the game server has shut down. Source The game server sends the master server 62 0A 00 to signal that the game server has shut down. See also Server Queries Steam Condenser