How configure the DHCP settings of WIFI Tethering (Hotspot) on Android?

Question

When connecting my PC to Android Wi-Fi hotspot, it assigned a 192.168.42.x address to my PC. I really need to change this as it conflicts with one of our work subnets - is this possible?

Answer 1

Unfortunately, there is no way to change the IP address range for the builtin tethering support, even in CyanogenMod. The Wi-Fi hotspot IP is hardcoded in android.net.wifi.WifiStateMachine.startTethering(); the USB tethering IP is hardcoded in com.android.server.connectivity.Tethering.

However, if your phone is rooted, you can try using third-party apps for tethering which have the option to change the IP address range. E.g., when the builtin USB tethering was broken in CyanogenMod alphas for Samsung Galaxy W, I used Wired Tether for Root Users, which has such option. For Wi-Fi tethering you can try the Wireless Tether for Root Users app from the same authors, which also has the option to change the IP address range.

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Because Google Code was shut down, the above links no longer work. Some people exported the source code from those repositories to GitHub:

• https://github.com/luftreich/android-wired-tether
• https://github.com/mmorciegov/android-wifi-tether

However, there was no further development activity, and the apps probably no longer work on recent Android versions.

Just in case someone wants to try those obsolete apps, I have been able to find some APK files in the Google Code Archive:

• wired_tether_1_4.apk
• wifi_tether_v3_4-experimental1.apk

Answer 2

The Android builtin wifi tethering is designed to use 192.168.43.1/24 as the server, with netd handling the tethering, using dnsmasq. First DNS range is 192.168.42.1-254 and and 2nd DNS range is 192.168.43.1-254.

Netd is not easy to change. It requires a socket to communicate with it, and that socket is taken when android starts tethering. But going through the source files for Tethering.java (I used Froyo) we see:

// usb client will be provided 192.168.42.129
private static final String USB_NEAR_IFACE_ADDR      = "192.168.42.129";
private static final String USB_NETMASK              = "255.255.255.0";

// FYI - the default wifi is 192.168.43.1 and 255.255.255.0

private String[] mDhcpRange;
private static final String DHCP_DEFAULT_RANGE1_START = "192.168.42.2";
private static final String DHCP_DEFAULT_RANGE1_STOP  = "192.168.42.254";
private static final String DHCP_DEFAULT_RANGE2_START = "192.168.43.2";
private static final String DHCP_DEFAULT_RANGE2_STOP  = "192.168.43.254";

And Later on we see those ranges used, AS BACKUPS.

    mDhcpRange = context.getResources().getStringArray(
            com.android.internal.R.array.config_tether_dhcp_range);
    if ((mDhcpRange.length == 0) || (mDhcpRange.length % 2 ==1)) {
        mDhcpRange = new String[4];
        mDhcpRange[0] = DHCP_DEFAULT_RANGE1_START;
        mDhcpRange[1] = DHCP_DEFAULT_RANGE1_STOP;
        mDhcpRange[2] = DHCP_DEFAULT_RANGE2_START;
        mDhcpRange[3] = DHCP_DEFAULT_RANGE2_STOP;
    }

The main source for the dhcp ranges is not the hardcoded 42 and 43, but read from array.config_tether_dhcp_range, an internal string array. But it is currently empty.

You could edit the android framework. On my phone, it is /system/framework/framework-res.apk. There are a ton of tutorials online for editing framework-res.apk, from simple strings to full theming. Find one for your phone and android version.

Main thing you want to change is the /res/values/arrays.xml

Look for <array name="config_tether_dhcp_range" />

Change to:

<string-array name="config_tether_dhcp_range">
     <item>192.168.x.y</item>
     <item>192.168.x.z</item>
</string-array>

compile/zip/sign as needed (follow a tutorial), then reinstall.

If you want more than one range, just copy the two items over and over. You always need to provide a start and a stop for each range. Try to keep it in the same /24, ie 192.168.50.5 and 192.168.50.99 or whatever. You can confirm it is working with busybox ps | grep dnsmasq or if you don't have busybox ps dnsmasq then use the pid in cat /proc/pid/cmdline. You should get (or similar):

/system/bin/dnsmasq --no-daemon --no-poll -no-resolv --dhcp-range=192.168.50.5,192.168.50.99,1h

FWIW, my WIFI tethering uses the default dnsmasq ranges, yet my computer was assigned 192.168.43.147/24 and gateway 192.168.43.1/24. Not sure why yours defaulted to a 42.x address.

Answer 3

I know this is an old post, but thought I would provide an update. It appears some manufacturers and versions of Android now DO allow for the changing of the IP subnet range for the DHCP server through the UI when using WiFi hotspot feature. Here's where to find it on an HTC One M8 running Android 6.0. YMMV.

From the Mobile Hotspot screen, click the 3 dots icon (more), go to Advanced, then LAN settings. Under "Local IP" change the IP address to your desired IP. Under "Local DHCP" change the starting IP to match the subnet of your IP address.

Trent

Answer 4

Default DHCP IP address range is hard-coded, so you can't change it without rebuilding ROM with modified source code. Or use a little hack. Replace /system/bin/dnsmasq (the DHCP/DNS server up to Android 9) with a custom shell script which replaces old subnet with new one before executing actual dnsmasq binary.

For detailed steps see How to change the default DHCP IP address range?

Answer 5

Now they're dynamic. I have a device that when connected to the phone hotspot gets the address 192.168.XXX.85 where XXX changes all the time, possibly daily or with every reboot.