If a direct connection can't be made to a peer over the original or default port, match the peer's host with any entries in knownPeers and try connecting to each of those until one succeeds.

src/main/java/org/qortal/controller/arbitrary/ArbitraryDataFileManager.java

@@ -5,6 +5,7 @@ import org.apache.logging.log4j.Logger;
 import org.qortal.arbitrary.ArbitraryDataFile;
 import org.qortal.controller.Controller;
 import org.qortal.data.network.ArbitraryPeerData;
+import org.qortal.data.network.PeerData;
 import org.qortal.data.transaction.ArbitraryTransactionData;
 import org.qortal.data.transaction.TransactionData;
 import org.qortal.network.Network;
@@ -20,6 +21,7 @@ import org.qortal.utils.Triple;
 
 import java.security.SecureRandom;
 import java.util.*;
+import java.util.stream.Collectors;
 
 public class ArbitraryDataFileManager {
 
@@ -258,21 +260,49 @@ public class ArbitraryDataFileManager {
             String peerAddressString = arbitraryPeerData.getPeerAddress();
             boolean success = Network.getInstance().requestDataFromPeer(peerAddressString, signature);
 
-            // If using a non-standard port, try a second connection with the default listen port, since almost all nodes use that
-            // This is a workaround to account for any ephemeral ports that may have made it into the dataset
-            boolean success2 = false;
+            // Parse the peer address to find the host and port
+            String host = null;
+            int port = -1;
             String[] parts = peerAddressString.split(":");
             if (parts.length > 1) {
-                String host = parts[0];
-                int port = Integer.parseInt(parts[1]);
-                int defaultPort = Settings.getInstance().getDefaultListenPort();
-                if (port != defaultPort) {
-                    String newPeerAddressString = String.format("%s:%d", host, defaultPort);
-                    success2 = Network.getInstance().requestDataFromPeer(newPeerAddressString, signature);
+                host = parts[0];
+                port = Integer.parseInt(parts[1]);
+            }
+
+            // If unsuccessful, and using a non-standard port, try a second connection with the default listen port,
+            // since almost all nodes use that. This is a workaround to account for any ephemeral ports that may
+            // have made it into the dataset.
+            if (!success) {
+                if (host != null && port > 0) {
+                    int defaultPort = Settings.getInstance().getDefaultListenPort();
+                    if (port != defaultPort) {
+                        String newPeerAddressString = String.format("%s:%d", host, defaultPort);
+                        success = Network.getInstance().requestDataFromPeer(newPeerAddressString, signature);
+                    }
+                }
+            }
+
+            // If _still_ unsuccessful, try matching the peer's IP address with some known peers, and then connect
+            // to each of those in turn until one succeeds.
+            if (!success) {
+                if (host != null) {
+                    final String finalHost = host;
+                    List<PeerData> knownPeers = Network.getInstance().getAllKnownPeers().stream()
+                            .filter(knownPeerData -> knownPeerData.getAddress().getHost().equals(finalHost))
+                            .collect(Collectors.toList());
+                    // Loop through each match and attempt a connection
+                    for (PeerData matchingPeer : knownPeers) {
+                        String matchingPeerAddress = matchingPeer.getAddress().toString();
+                        success = Network.getInstance().requestDataFromPeer(matchingPeerAddress, signature);
+                        if (success) {
+                            // Successfully connected, so stop making connections
+                            break;
+                        }
+                    }
                 }
             }
 
-            return success || success2;
+            return success;
 
         } catch (DataException e) {
             LOGGER.debug("Unable to fetch peer list from repository");