diff --git a/staticlibs/testutils/devicetests/com/android/testutils/ConnectivityDiagnosticsCollector.kt b/staticlibs/testutils/devicetests/com/android/testutils/ConnectivityDiagnosticsCollector.kt
index ea86281..9e63910 100644
--- a/staticlibs/testutils/devicetests/com/android/testutils/ConnectivityDiagnosticsCollector.kt
+++ b/staticlibs/testutils/devicetests/com/android/testutils/ConnectivityDiagnosticsCollector.kt
@@ -76,11 +76,13 @@
         private const val MAX_DUMPS = 20
 
         private val TAG = ConnectivityDiagnosticsCollector::class.simpleName
+        @JvmStatic
         var instance: ConnectivityDiagnosticsCollector? = null
     }
 
     private var failureHeader: String? = null
     private val buffer = ByteArrayOutputStream()
+    private val failureHeaderExtras = mutableMapOf<String, Any>()
     private val collectorDir: File by lazy {
         createAndEmptyDirectory(COLLECTOR_DIR)
     }
@@ -218,6 +220,8 @@
         val canUseShell = !isAtLeastS() ||
                 instr.uiAutomation.getAdoptedShellPermissions().isNullOrEmpty()
         val headerObj = JSONObject()
+        failureHeaderExtras.forEach { (k, v) -> headerObj.put(k, v) }
+        failureHeaderExtras.clear()
         if (canUseShell) {
             runAsShell(READ_PRIVILEGED_PHONE_STATE, NETWORK_SETTINGS) {
                 headerObj.apply {
@@ -332,6 +336,15 @@
         }
     }
 
+    /**
+     * Add a key->value attribute to the failure data, to be written to the diagnostics file.
+     *
+     * <p>This is to be called by tests that know they will fail.
+     */
+    fun addFailureAttribute(key: String, value: Any) {
+        failureHeaderExtras[key] = value
+    }
+
     private fun maybeWriteExceptionContext(writer: PrintWriter, exceptionContext: Throwable?) {
         if (exceptionContext == null) return
         writer.println("At: ")
diff --git a/tests/cts/net/jni/NativeMultinetworkJni.cpp b/tests/cts/net/jni/NativeMultinetworkJni.cpp
index f2214a3..1d848ec 100644
--- a/tests/cts/net/jni/NativeMultinetworkJni.cpp
+++ b/tests/cts/net/jni/NativeMultinetworkJni.cpp
@@ -415,9 +415,17 @@
     strlcpy(dst, buf, size);
 }
 
+static jobject create_query_test_result(JNIEnv* env, uint16_t src_port, int attempts, int errnum) {
+    jclass clazz = env->FindClass(
+        "android/net/cts/MultinetworkApiTest$QueryTestResult");
+    jmethodID ctor = env->GetMethodID(clazz, "<init>", "(III)V");
+
+    return env->NewObject(clazz, ctor, src_port, attempts, errnum);
+}
+
 extern "C"
-JNIEXPORT jint Java_android_net_cts_MultinetworkApiTest_runDatagramCheck(
-        JNIEnv*, jclass, jlong nethandle) {
+JNIEXPORT jobject Java_android_net_cts_MultinetworkApiTest_runDatagramCheck(
+        JNIEnv* env, jclass, jlong nethandle, jint src_port) {
     const struct addrinfo kHints = {
         .ai_flags = AI_ADDRCONFIG,
         .ai_family = AF_UNSPEC,
@@ -433,7 +441,7 @@
         LOGD("android_getaddrinfofornetwork(%llu, %s) returned rval=%d errno=%d",
               handle, kHostname, rval, errno);
         freeaddrinfo(res);
-        return -errno;
+        return create_query_test_result(env, 0, 0, errno);
     }
 
     // Rely upon getaddrinfo sorting the best destination to the front.
@@ -442,7 +450,7 @@
         LOGD("socket(%d, %d, %d) failed, errno=%d",
               res->ai_family, res->ai_socktype, res->ai_protocol, errno);
         freeaddrinfo(res);
-        return -errno;
+        return create_query_test_result(env, 0, 0, errno);
     }
 
     rval = android_setsocknetwork(handle, fd);
@@ -451,7 +459,31 @@
     if (rval != 0) {
         close(fd);
         freeaddrinfo(res);
-        return -errno;
+        return create_query_test_result(env, 0, 0, errno);
+    }
+
+    sockaddr_storage src_addr;
+    socklen_t src_addrlen = sizeof(src_addr);
+    if (src_port) {
+        if (res->ai_family == AF_INET6) {
+            *reinterpret_cast<sockaddr_in6*>(&src_addr) = (sockaddr_in6) {
+                .sin6_family = AF_INET6,
+                .sin6_port = htons(src_port),
+                .sin6_addr = in6addr_any,
+            };
+        } else {
+            *reinterpret_cast<sockaddr_in*>(&src_addr) = (sockaddr_in) {
+                .sin_family = AF_INET,
+                .sin_port = htons(src_port),
+                .sin_addr = { .s_addr = INADDR_ANY },
+            };
+        }
+        if (bind(fd, (sockaddr *)&src_addr, src_addrlen) != 0) {
+            LOGD("Error binding to port %d", src_port);
+            close(fd);
+            freeaddrinfo(res);
+            return create_query_test_result(env, 0, 0, errno);
+        }
     }
 
     char addrstr[kSockaddrStrLen+1];
@@ -462,19 +494,28 @@
     if (rval != 0) {
         close(fd);
         freeaddrinfo(res);
-        return -errno;
+        return create_query_test_result(env, 0, 0, errno);
     }
     freeaddrinfo(res);
 
-    struct sockaddr_storage src_addr;
-    socklen_t src_addrlen = sizeof(src_addr);
     if (getsockname(fd, (struct sockaddr *)&src_addr, &src_addrlen) != 0) {
         close(fd);
-        return -errno;
+        return create_query_test_result(env, 0, 0, errno);
     }
     sockaddr_ntop((const struct sockaddr *)&src_addr, sizeof(src_addr), addrstr, sizeof(addrstr));
     LOGD("... from %s", addrstr);
 
+    uint16_t socket_src_port;
+    if (res->ai_family == AF_INET6) {
+        socket_src_port = ntohs(reinterpret_cast<sockaddr_in6*>(&src_addr)->sin6_port);
+    } else if (src_addr.ss_family == AF_INET) {
+        socket_src_port = ntohs(reinterpret_cast<sockaddr_in*>(&src_addr)->sin_port);
+    } else {
+        LOGD("Invalid source address family %d", src_addr.ss_family);
+        close(fd);
+        return create_query_test_result(env, 0, 0, EAFNOSUPPORT);
+    }
+
     // Don't let reads or writes block indefinitely.
     const struct timeval timeo = { 2, 0 };  // 2 seconds
     setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &timeo, sizeof(timeo));
@@ -503,7 +544,7 @@
             errnum = errno;
             LOGD("send(QUIC packet) returned sent=%zd, errno=%d", sent, errnum);
             close(fd);
-            return -errnum;
+            return create_query_test_result(env, socket_src_port, i + 1, errnum);
         }
 
         rcvd = recv(fd, response, sizeof(response), 0);
@@ -521,18 +562,19 @@
             LOGD("Does this network block UDP port %s?", kPort);
         }
         close(fd);
-        return -EPROTO;
+        return create_query_test_result(env, socket_src_port, i + 1,
+                rcvd <= 0 ? errnum : EPROTO);
     }
 
     int conn_id_cmp = memcmp(quic_packet + 6, response + 7, 8);
     if (conn_id_cmp != 0) {
         LOGD("sent and received connection IDs do not match");
         close(fd);
-        return -EPROTO;
+        return create_query_test_result(env, socket_src_port, i + 1, EPROTO);
     }
 
     // TODO: Replace this quick 'n' dirty test with proper QUIC-capable code.
 
     close(fd);
-    return 0;
+    return create_query_test_result(env, socket_src_port, i + 1, 0);
 }
diff --git a/tests/cts/net/src/android/net/cts/MultinetworkApiTest.java b/tests/cts/net/src/android/net/cts/MultinetworkApiTest.java
index 2c7d5c6..c67443e 100644
--- a/tests/cts/net/src/android/net/cts/MultinetworkApiTest.java
+++ b/tests/cts/net/src/android/net/cts/MultinetworkApiTest.java
@@ -39,10 +39,13 @@
 import android.system.ErrnoException;
 import android.system.OsConstants;
 import android.util.ArraySet;
+import android.util.Log;
 
 import androidx.test.platform.app.InstrumentationRegistry;
 
+import com.android.net.module.util.CollectionUtils;
 import com.android.testutils.AutoReleaseNetworkCallbackRule;
+import com.android.testutils.ConnectivityDiagnosticsCollector;
 import com.android.testutils.DevSdkIgnoreRunner;
 import com.android.testutils.DeviceConfigRule;
 
@@ -51,6 +54,8 @@
 import org.junit.Test;
 import org.junit.runner.RunWith;
 
+import java.util.ArrayList;
+import java.util.Arrays;
 import java.util.Set;
 
 @DevSdkIgnoreRunner.RestoreDefaultNetwork
@@ -70,13 +75,34 @@
     private static final String TAG = "MultinetworkNativeApiTest";
     static final String GOOGLE_PRIVATE_DNS_SERVER = "dns.google";
 
+    public static class QueryTestResult {
+        public final int sourcePort;
+        public final int attempts;
+        public final int errNo;
+
+        public QueryTestResult(int sourcePort, int attempts, int errNo) {
+            this.sourcePort = sourcePort;
+            this.attempts = attempts;
+            this.errNo = errNo;
+        }
+
+        @Override
+        public String toString() {
+            return "QueryTestResult{"
+                    + "sourcePort=" + sourcePort
+                    + ", attempts=" + attempts
+                    + ", errNo=" + errNo
+                    + '}';
+        }
+    }
+
     /**
      * @return 0 on success
      */
     private static native int runGetaddrinfoCheck(long networkHandle);
     private static native int runSetprocnetwork(long networkHandle);
     private static native int runSetsocknetwork(long networkHandle);
-    private static native int runDatagramCheck(long networkHandle);
+    private static native QueryTestResult runDatagramCheck(long networkHandle, int sourcePort);
     private static native void runResNapiMalformedCheck(long networkHandle);
     private static native void runResNcancelCheck(long networkHandle);
     private static native void runResNqueryCheck(long networkHandle);
@@ -165,14 +191,69 @@
         }
     }
 
+    private void runNativeDatagramTransmissionDiagnostics(Network network,
+            QueryTestResult failedResult) {
+        final ConnectivityDiagnosticsCollector collector = ConnectivityDiagnosticsCollector
+                .getInstance();
+        if (collector == null) {
+            Log.e(TAG, "Missing ConnectivityDiagnosticsCollector, not adding diagnostics");
+            return;
+        }
+
+        final int numReruns = 10;
+        final ArrayList<QueryTestResult> reruns = new ArrayList<>(numReruns);
+        for (int i = 0; i < numReruns; i++) {
+            final QueryTestResult rerunResult =
+                    runDatagramCheck(network.getNetworkHandle(), 0 /* sourcePort */);
+            Log.d(TAG, "Rerun result " + i + ": " + rerunResult);
+            reruns.add(rerunResult);
+        }
+        // Rerun on the original port after trying the other ports, to check that the results are
+        // consistent, as opposed to the network recovering halfway through.
+        int originalPortFailedReruns = 0;
+        for (int i = 0; i < numReruns; i++) {
+            final QueryTestResult originalPortRerun = runDatagramCheck(network.getNetworkHandle(),
+                    failedResult.sourcePort);
+            Log.d(TAG, "Rerun result " + i + " with original port: " + originalPortRerun);
+            if (originalPortRerun.errNo != 0) {
+                originalPortFailedReruns++;
+            }
+        }
+
+        final int noRetrySuccessResults = reruns.stream()
+                .filter(result -> result.errNo == 0 && result.attempts == 1)
+                .mapToInt(result -> 1)
+                .sum();
+        final int failedResults = reruns.stream()
+                .filter(result -> result.errNo != 0)
+                .mapToInt(result -> 1)
+                .sum();
+        collector.addFailureAttribute("numReruns", numReruns);
+        collector.addFailureAttribute("noRetrySuccessReruns", noRetrySuccessResults);
+        collector.addFailureAttribute("failedReruns", failedResults);
+        collector.addFailureAttribute("originalPortFailedReruns", originalPortFailedReruns);
+    }
+
     @Test
     public void testNativeDatagramTransmission() throws Exception {
         for (Network network : getTestableNetworks()) {
-            int errno = runDatagramCheck(network.getNetworkHandle());
-            if (errno != 0) {
-                throw new ErrnoException(
-                        "DatagramCheck on " + mCM.getNetworkInfo(network), -errno);
+            final QueryTestResult result = runDatagramCheck(network.getNetworkHandle(),
+                    0 /* sourcePort */);
+            if (result.errNo == 0) {
+                continue;
             }
+            final NetworkCapabilities nc = mCM.getNetworkCapabilities(network);
+            final int[] transports = nc != null ? nc.getTransportTypes() : null;
+            if (CollectionUtils.contains(transports, TRANSPORT_WIFI)) {
+                runNativeDatagramTransmissionDiagnostics(network, result);
+            }
+
+            // Log the whole result (with source port and attempts) to logcat, but use only the
+            // errno and transport in the fail message so similar failures have consistent messages
+            final String error = "DatagramCheck on transport " + Arrays.toString(transports)
+                    + " failed: " + result.errNo;
+            Log.e(TAG, error + ", result: " + result);
+            fail(error);
         }
     }