Support double-tagged host

Change-Id: Ie4041a0b5159e7a8b3a9ed82b55ce3c26b520a3b
diff --git a/core/api/src/main/java/org/onosproject/net/Host.java b/core/api/src/main/java/org/onosproject/net/Host.java
index b47f843..1c2e50a 100644
--- a/core/api/src/main/java/org/onosproject/net/Host.java
+++ b/core/api/src/main/java/org/onosproject/net/Host.java
@@ -15,6 +15,7 @@
  */
 package org.onosproject.net;
 
+import org.onlab.packet.EthType;
 import org.onlab.packet.IpAddress;
 import org.onlab.packet.MacAddress;
 import org.onlab.packet.VlanId;
@@ -77,6 +78,24 @@
     default boolean configured() {
         return false;
     }
+
+    /**
+     * Returns the inner VLAN ID tied to this host.
+     *
+     * @return VLAN ID value; VlanId.NONE if only one VLAN ID is tied to this host
+     */
+    default VlanId innerVlan() {
+        return VlanId.NONE;
+    }
+
+    /**
+     * Returns the TPID of the outermost VLAN associated with this host.
+     *
+     * @return TPID of the outermost VLAN header
+     */
+    default EthType tpid() {
+        return EthType.EtherType.UNKNOWN.ethType();
+    }
     // TODO: explore capturing list of recent locations to aid in mobility
 
 }