diff --git a/Tethering/src/android/net/util/PrefixUtils.java b/Tethering/src/android/net/util/PrefixUtils.java
new file mode 100644
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+++ b/Tethering/src/android/net/util/PrefixUtils.java
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+/*
+ * Copyright (C) 2017 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.net.util;
+
+import android.net.IpPrefix;
+import android.net.LinkAddress;
+import android.net.LinkProperties;
+
+import java.net.Inet4Address;
+import java.net.InetAddress;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Set;
+
+
+/**
+ * @hide
+ */
+public class PrefixUtils {
+    private static final IpPrefix[] MIN_NON_FORWARDABLE_PREFIXES = {
+            pfx("127.0.0.0/8"),     // IPv4 loopback
+            pfx("169.254.0.0/16"),  // IPv4 link-local, RFC3927#section-8
+            pfx("::/3"),
+            pfx("fe80::/64"),       // IPv6 link-local
+            pfx("fc00::/7"),        // IPv6 ULA
+            pfx("ff02::/8"),        // IPv6 link-local multicast
+    };
+
+    public static final IpPrefix DEFAULT_WIFI_P2P_PREFIX = pfx("192.168.49.0/24");
+
+    /** Get non forwardable prefixes. */
+    public static Set<IpPrefix> getNonForwardablePrefixes() {
+        final HashSet<IpPrefix> prefixes = new HashSet<>();
+        addNonForwardablePrefixes(prefixes);
+        return prefixes;
+    }
+
+    /** Add non forwardable prefixes. */
+    public static void addNonForwardablePrefixes(Set<IpPrefix> prefixes) {
+        Collections.addAll(prefixes, MIN_NON_FORWARDABLE_PREFIXES);
+    }
+
+    /** Get local prefixes from |lp|. */
+    public static Set<IpPrefix> localPrefixesFrom(LinkProperties lp) {
+        final HashSet<IpPrefix> localPrefixes = new HashSet<>();
+        if (lp == null) return localPrefixes;
+
+        for (LinkAddress addr : lp.getAllLinkAddresses()) {
+            if (addr.getAddress().isLinkLocalAddress()) continue;
+            localPrefixes.add(asIpPrefix(addr));
+        }
+        // TODO: Add directly-connected routes as well (ones from which we did
+        // not also form a LinkAddress)?
+
+        return localPrefixes;
+    }
+
+    /** Convert LinkAddress |addr| to IpPrefix. */
+    public static IpPrefix asIpPrefix(LinkAddress addr) {
+        return new IpPrefix(addr.getAddress(), addr.getPrefixLength());
+    }
+
+    /** Convert InetAddress |ip| to IpPrefix. */
+    public static IpPrefix ipAddressAsPrefix(InetAddress ip) {
+        final int bitLength = (ip instanceof Inet4Address)
+                ? NetworkConstants.IPV4_ADDR_BITS
+                : NetworkConstants.IPV6_ADDR_BITS;
+        return new IpPrefix(ip, bitLength);
+    }
+
+    private static IpPrefix pfx(String prefixStr) {
+        return new IpPrefix(prefixStr);
+    }
+}