Set up Android Emulator networking

The emulator provides versatile networking capabilities that you can use toset up complex modeling and testing environments for your app. The followingsections introduce the emulator network architecture and capabilities.

Network address space

Each instance of the emulator runs behind a virtual router/firewall servicethat isolates it from your development machine network interfaces and settingsand from the internet. An emulated device can't see your development machineor other emulator instances on the network. Instead, it sees only that it isconnected through Ethernet to a router/firewall.

The virtual router for each instance manages the 10.0.2/24 network addressspace — all addresses managed by the router are in the form of 10.0.2.xx, where xx is a number. Addresses within this space arepre-allocated by the emulator/router as follows:

Note that the same address assignments are used by all running emulatorinstances. That means that if you have two instances running concurrently onyour machine, each will have its own router and, behind that, each will have anIP address of 10.0.2.15. The instances are isolated by a router and cannot see each other on the same network. For information about how tolet emulator instances communicate over TCP/UDP, see Interconnecting Emulator Instances.

Also note that the address 127.0.0.1 on your development machine correspondsto the emulator's own loopback interface. If you want to access services runningon your development machine loopback interface (a.k.a. 127.0.0.1 on yourmachine), you should use the special address 10.0.2.2 instead.

Finally, note that the pre-allocated addresses of an emulated device arespecific to the Android Emulator and will probably be very different on realdevices (which are also very likely to be NAT-ed, specifically, behind arouter/firewall).

Local networking limitations

Android apps running in an emulator can connect to the network available on yourworkstation. However, apps connect through the emulator, not directly to hardware, and the emulatoracts like a normal app on your workstation. This can cause some limitations:

• Communication with the emulated device may be blocked by a firewallprogram running on your machine.
• Communication with the emulated device may be blocked by another(physical) firewall/router to which your machine is connected.
  The emulator virtual router should be able to handle all outbound TCP andUDP connections/messages on behalf of the emulated device, provided yourdevelopment machine network environment allows it to do so. There are nobuilt-in limitations on port numbers or ranges except the one imposed by yourhost operating system and network.

Depending on the environment, the emulator might not be able to support otherprotocols (such as ICMP, used for "ping"). Currently, theemulator does not support IGMP or multicast.

Using network redirection

To communicate with an emulator instance behind its virtual router, you needto set up network redirection on the virtual router. Clients can then connectto a specified guest port on the router, while the router directs trafficto/from that port to the emulated device host port.

To set up the network redirection, you create a mapping of host and guestports/addresses on the emulator instance. There are two ways to set upnetwork redirection: using emulator console commands and using the adb tool, asdescribed below.

Setting up redirection through the Emulator Console

Each emulator instance provides a control console that you can connect to, toissue commands that are specific to that instance. You can use theredir console command to set up redirection as needed for anemulator instance.

First, determine the console port number for the target emulator instance.For example, the console port number for the first emulator instance launched is5554. Next, connect to the console of the target emulator instance, specifyingits console port number, as follows:

telnet localhost 5554

Once connected, use the redir command to work with redirection.To add a redirection, use:

add <protocol>:<host-port>:<guest-port>

where <protocol> is either tcp or udp,and <host-port> and <guest-port> set themapping between your own machine and the emulated system, respectively.

For example, the following command sets up a redirection that handles allincoming TCP connections to your host (development) machine on 127.0.0.1:5000and will pass them through to the emulated system on 10.0.2.15:6000:

redir add tcp:5000:6000

To delete a redirection, you can use the redir del command. Tolist all redirection for a specific instance, you can use redir
list. For more information about these and other console commands, seeUsing the Emulator Console.

Note that port numbers are restricted by your local environment. This typicallymeans that you cannot use host port numbers under 1024 without specialadministrator privileges. Also, you won't be able to set up a redirection for ahost port that is already in use by another process on your machine. In thatcase, redir generates an error message to that effect.

Setting up redirection through adb

The Android Debug Bridge (adb) tool provides port forwarding, an alternateway for you to set up network redirection. For more information, see Forwarding Ports in the adbdocumentation.

Note that adb does not currently offer any way to remove a redirection,except by killing the adb server.

Configuring the emulator DNS settings

At startup, the emulator reads the list of DNS servers that your system iscurrently using. It then stores the IP addresses of up to four servers on thislist and sets up aliases to them on the emulated addresses 10.0.2.3, 10.0.2.4,10.0.2.5 and 10.0.2.6 as needed.

On Linux and OS X, the emulator obtains the DNS server addresses by parsingthe file /etc/resolv.conf. On Windows, the emulator obtains theaddresses by calling the GetNetworkParams() API. Note that thisusually means that the emulator ignores the content of your "hosts" file(/etc/hosts on Linux/OS X, %WINDOWS%/system32/HOSTS on Windows).

When starting the emulator at the command line, you can also use the-dns-server <serverList> option to manually specify theaddresses of DNS servers to use, where <serverList> is a comma-separatedlist of server names or IP addresses. You might find this option useful if youencounter DNS resolution problems in the emulated network (for example, an"Unknown Host error" message that appears when using the web browser).

Using the emulator with a proxy

On many corporate networks, direct connections to the internet don't work (they're refused bythe network administrators), except if they happen through a specific proxy. Web browsers andother corporate apps are preconfigured to use the proxy, so you can browse the web. Forregular apps, like the emulator, they need to know that there's a proxy and that they need toconnect to it.

Due to the nature of HTTP, a direct web server connection and a connection througha proxy result in different GET requests. The emulator transparently rewrites theGET requests from the virtual device before talking to the proxy so it works.

If your emulator must access the internet through a proxy server, you can configure acustom HTTP proxy from the emulator's Extended controls screen. With the emulatoropen, click More, and then click Settings andProxy. From here, you can define your own HTTP proxy settings.

Alternatively, you can configure a proxy from the command line with the-http-proxy <proxy> option when starting the emulator.In this case, you specify proxy informationin <proxy> in one of these formats:

http://<machineName>:<port>

or

http://<username>:<password>@<machineName>:<port>

The -http-proxy option forces the emulator to use the specifiedHTTP/HTTPS proxy for all outgoing TCP connections. Redirection for UDP is notcurrently supported.

Alternatively, you can define the environment variablehttp_proxy to the value you want to use for<proxy>. In this case, you do not need to specify a value for<proxy> in the -http-proxy command — theemulator checks the value of the http_proxy environment variable atstartup and uses its value automatically, if defined.

You can use the -debug-proxy option to diagnose proxyconnection problems.

Interconnecting emulator instances

To allow one emulator instance to communicate with another, you must set upthe necessary network redirection as illustrated below.

Assume that your environment is

• A is your development machine
• B is your first emulator instance, running on A

• C is your second emulator instance, also running on A
  and you want to run a server on B, to which C will connect, here is how youcould set it up:

• Set up the server on B, listening to10.0.2.15:<serverPort>

• On the B console, set up a redirection fromA:localhost:<localPort> to
B:10.0.2.15:<serverPort>

• On C, have the client connect to 10.0.2.2:<localPort>
  For example, if you wanted to run an HTTP server, you can select<serverPort> as 80 and <localPort> as8080:

• B listens on 10.0.2.15:80

• On the B console, issue redir add tcp:8080:80
• C connects to 10.0.2.2:8080

Sending a voice call or SMS to another emulator instance

The emulator automatically forwards simulated voice calls and SMS messages from one instance toanother. To send a voice call or SMS, use the dialer app or SMS app, respectively,from one of the emulators.

To initiate a simulated voice call to another emulator instance:

• Launch the dialer app on the originating emulator instance.
• As the number to dial, enter the console port number of the instance you'd like to call. You can determine the console port number of the target instance by checking its window title, where the console port number is reported as "Android Emulator ().
• Press "Dial". A new inbound call appears in the target emulator instance.
  To send an SMS message to another emulator instance, launch the SMS app (if available). Specify the console port number of the target emulator instance as as the SMS address, enter the message text, and send the message. The message is delivered to the target emulator instance.

You can also connect to an emulator console to simulate an incoming voice call or SMS.For more information, seeTelephony Emulation and SMS Emulation.