diff --git a/router/java/src/net/i2p/router/transport/udp/MTU.java b/router/java/src/net/i2p/router/transport/udp/MTU.java
index 9258043f6..9a8fd3601 100644
--- a/router/java/src/net/i2p/router/transport/udp/MTU.java
+++ b/router/java/src/net/i2p/router/transport/udp/MTU.java
@@ -72,11 +72,29 @@ abstract class MTU {
 
 /****
     public static void main(String args[]) {
+        System.out.println("Cmd line interfaces:");
+        for (int i = 0; i < args.length; i++) {
+            try {
+                InetAddress test = InetAddress.getByName(args[i]);
+                System.out.println("MTU of " + args[i] + " is " + getMTU(test));
+            } catch (Exception e) {
+                e.printStackTrace();
+            }
+        }
+        System.out.println("All interfaces:");
         try {
-            InetAddress test = InetAddress.getByName(args[0]);
-            System.out.println("MTU is " + getMTU(test));
-        } catch (Exception e) {
-            e.printStackTrace();
+            Enumeration<NetworkInterface> ifcs = NetworkInterface.getNetworkInterfaces();
+            if (ifcs != null) {
+                while (ifcs.hasMoreElements()) {
+                    NetworkInterface ifc = ifcs.nextElement();
+                    for(Enumeration<InetAddress> addrs =  ifc.getInetAddresses(); addrs.hasMoreElements();) {
+                        InetAddress addr = addrs.nextElement();
+                        System.out.println("MTU of " + addr.getHostAddress() + " is " + getMTU(addr));
+                    }
+                }
+            }
+        } catch (SocketException se) {
+             System.out.println("no interfaces");
         }
     }
 ****/
diff --git a/router/java/src/net/i2p/router/transport/udp/PeerState.java b/router/java/src/net/i2p/router/transport/udp/PeerState.java
index e04f3b531..04b944815 100644
--- a/router/java/src/net/i2p/router/transport/udp/PeerState.java
+++ b/router/java/src/net/i2p/router/transport/udp/PeerState.java
@@ -267,7 +267,8 @@ class PeerState {
      * and so PacketBuilder.buildPacket() works correctly.
      */
     public static final int MIN_MTU = 620;
-    public static final int MIN_IPV6_MTU = 1280;
+    /** 1276 */
+    public static final int MIN_IPV6_MTU = MTU.rectify(1280);
     private static final int DEFAULT_MTU = MIN_MTU;
 
     /* 
@@ -319,11 +320,12 @@ class PeerState {
         if (remoteIP.length == 4) {
             _mtu = DEFAULT_MTU;
             _mtuReceive = DEFAULT_MTU;
+            _largeMTU = transport.getMTU(false);
         } else {
             _mtu = MIN_IPV6_MTU;
             _mtuReceive = MIN_IPV6_MTU;
+            _largeMTU = transport.getMTU(true);
         }
-        _largeMTU = transport.getMTU();
         //_mtuLastChecked = -1;
         _lastACKSend = -1;
         _rto = INIT_RTO;
diff --git a/router/java/src/net/i2p/router/transport/udp/UDPTransport.java b/router/java/src/net/i2p/router/transport/udp/UDPTransport.java
index 339ea5cdf..ca05e879c 100644
--- a/router/java/src/net/i2p/router/transport/udp/UDPTransport.java
+++ b/router/java/src/net/i2p/router/transport/udp/UDPTransport.java
@@ -82,6 +82,8 @@ public class UDPTransport extends TransportImpl implements TimedWeightedPriority
     private long _lastInboundReceivedOn;
     private final DHSessionKeyBuilder.Factory _dhFactory;
     private int _mtu;
+    private int _mtu_ipv6;
+
     /**
      *  Do we have a public IPv6 address?
      *  TODO periodically update via CSFI.NetMonitor?
@@ -243,6 +245,7 @@ public class UDPTransport extends TransportImpl implements TimedWeightedPriority
         _introducersSelectedOn = -1;
         _lastInboundReceivedOn = -1;
         _mtu = PeerState.LARGE_MTU;
+        _mtu_ipv6 = PeerState.MIN_IPV6_MTU;
         setupPort();
         _needsRebuild = true;
         
@@ -552,20 +555,29 @@ public class UDPTransport extends TransportImpl implements TimedWeightedPriority
     /**
      *  Set the MTU for the socket interface at addr.
      *  @param addr null ok
+     *  @return the mtu
      *  @since 0.9.2
      */
-    private void setMTU(InetAddress addr) {
+    private int setMTU(InetAddress addr) {
         String p = _context.getProperty(PROP_DEFAULT_MTU);
         if (p != null) {
             try {
                 _mtu = MTU.rectify(Integer.parseInt(p));
-                return;
+                _mtu_ipv6 = Math.max(_mtu, PeerState.MIN_IPV6_MTU);
+                return _mtu;
             } catch (NumberFormatException nfe) {}
         }
         int mtu = MTU.getMTU(addr);
-        if (mtu <= 0)
-            mtu = PeerState.LARGE_MTU;
-        _mtu = mtu;
+        if (addr != null && addr.getAddress().length == 16) {
+            if (mtu <= 0)
+                mtu = PeerState.MIN_IPV6_MTU;
+            _mtu_ipv6 = mtu;
+        } else {
+            if (mtu <= 0)
+                mtu = PeerState.LARGE_MTU;
+            _mtu = mtu;
+        }
+        return mtu;
     }
 
     /**
@@ -574,8 +586,9 @@ public class UDPTransport extends TransportImpl implements TimedWeightedPriority
      * @return limited to range PeerState.MIN_MTU to PeerState.LARGE_MTU.
      * @since 0.9.2
      */
-    int getMTU() {
-        return _mtu;
+    int getMTU(boolean ipv6) {
+        // TODO multiple interfaces of each type
+        return ipv6 ? _mtu_ipv6 : _mtu;
     }
 
     /**
@@ -1751,11 +1764,23 @@ public class UDPTransport extends TransportImpl implements TimedWeightedPriority
             options.setProperty(UDPAddress.PROP_CAPACITY, ""+UDPAddress.CAPACITY_TESTING + UDPAddress.CAPACITY_INTRODUCER);
 
         // MTU since 0.9.2
-        if (_mtu < PeerState.LARGE_MTU)
-            options.setProperty(UDPAddress.PROP_MTU, Integer.toString(_mtu));
+        int mtu;
+        if (host == null) {
+            mtu = _mtu;
+        } else {
+            try {
+                InetAddress ia = InetAddress.getByName(host);
+                mtu = setMTU(ia);
+            } catch (UnknownHostException uhe) {
+                mtu = _mtu;
+            }
+        }
+        if (mtu < PeerState.LARGE_MTU)
+            options.setProperty(UDPAddress.PROP_MTU, Integer.toString(mtu));
 
         if (directIncluded || introducersIncluded) {
             // This is called via TransportManager.configTransports() before startup(), prevent NPE
+            // Note that peers won't connect to us without this - see EstablishmentManager
             if (_introKey != null)
                 options.setProperty(UDPAddress.PROP_INTRO_KEY, _introKey.toBase64());