To query the server list, your game asks Master Servers for a list of all Game Servers.
If the Master Server is down, your game won't list any Game Servers.
As a backup, some Game Servers uplink not only to the default Master Server (= master.gamespy.com) but also to other master servers.
So if you extend your client game configuration, you'll still get a list of Game Servers from other Master Servers.
[UBrowserAll]
ListFactories[0]=UBrowser.UBrowserGSpyFact,MasterServerAddress=master0.gamespy.com,MasterServerTCPPort=28900,Region=0,GameName=unreal
ListFactories[1]=UBrowser.UBrowserHTTPFact,MasterServerAddress=master.telefragged.com,MasterServerTCPPort=80,MasterServerURI=/servers.txt
ListFactories[2]=UBrowser.UBrowserGSpyFact,MasterServerAddress=hyper.dnsalias.net,MasterServerTCPPort=28900,Region=0,GameName=unreal
[Engine.GameEngine]
...
ServerActors=IpServer.UdpServerUplink MasterServerAddress=master0.gamespy.com MasterServerPort=27900
ServerActors=IpServer.UdpServerUplink MasterServerAddress=www.epicgames.com MasterServerPort=27900
ServerActors=IpServer.UdpServerUplink MasterServerAddress=master.telefragged.com MasterServerPort=27500
ServerActors=IpServer.UdpServerUplink MasterServerAddress=hyper.dnsalias.net MasterServerPort=27900
[Engine.GameEngine]
...
ServerActors=Nephthys.NptServerUplink MasterServerAddress=master0.gamespy.com MasterServerPort=27900
ServerActors=Nephthys.NptServerUplink MasterServerAddress=www.epicgames.com MasterServerPort=27900
ServerActors=Nephthys.NptServerUplink MasterServerAddress=master.telefragged.com MasterServerPort=27500
ServerActors=Nephthys.NptServerUplink MasterServerAddress=hyper.dnsalias.net MasterServerPort=27900
ListFactories[3]=UBrowser.UBrowserGSpyFact,MasterServerAddress=master.oldunreal.com,MasterServerTCPPort=28900,Region=0,GameName=unreal
ServerActors=Nephthys.NptServerUplink MasterServerAddress=master.oldunreal.com MasterServerPort=27900
ServerActors=Nephthys.NptServerUplink MasterServerAddress=master.qtracker.com MasterServerPort=27900