CORD-354 OF-DPA support for link-failures.

Bug fix in flowObjectives store. Adding a removeNextGroup API to the store. Change-Id: I5890411e5b4eabdc057402687ada26e539500f8f

CORD-354 OF-DPA support for link-failures.
Bug fix in flowObjectives store. Adding a removeNextGroup API to the store. Change-Id: I5890411e5b4eabdc057402687ada26e539500f8f
Saurav Das · Gerrit Code Review
Commit 423fe2b48751d3c740937b06cdf4fd19571c8cfd 423fe2b4 1 parent 1cd641be
Showing 7 changed files with 496 additions and 230 deletions
apps/segmentrouting/src/main/java/org/onosproject/segmentrouting/SegmentRoutingManager.java
apps/segmentrouting/src/main/java/org/onosproject/segmentrouting/grouphandler/DefaultGroupHandler.java
core/api/src/main/java/org/onosproject/net/flowobjective/FlowObjectiveStore.java
core/net/src/main/java/org/onosproject/net/flowobjective/impl/FlowObjectiveManager.java
core/store/dist/src/main/java/org/onosproject/store/flowobjective/impl/DistributedFlowObjectiveStore.java
drivers/src/main/java/org/onosproject/driver/pipeline/CpqdOFDPA2Pipeline.java
drivers/src/main/java/org/onosproject/driver/pipeline/OFDPA2Pipeline.java
--- a/apps/segmentrouting/src/main/java/org/onosproject/segmentrouting/SegmentRoutingManager.java
View file @423fe2b
+++ b/apps/segmentrouting/src/main/java/org/onosproject/segmentrouting/SegmentRoutingManager.java
View file @423fe2b
@@ -597,11 +597,20 @@ public class SegmentRoutingManager implements SegmentRoutingService {
                     } else if (event.type() == DeviceEvent.Type.DEVICE_ADDED ||
                             event.type() == DeviceEvent.Type.DEVICE_AVAILABILITY_CHANGED ||
                             event.type() == DeviceEvent.Type.DEVICE_UPDATED) {
-                        if (deviceService.isAvailable(((Device) event.subject()).id())) {
+                        DeviceId deviceId = ((Device) event.subject()).id();
+                        if (deviceService.isAvailable(deviceId)) {
                             log.info("Processing device event {} for available device {}",
                                      event.type(), ((Device) event.subject()).id());
                             processDeviceAdded((Device) event.subject());
-                        }
+                        } /* else {
+                            if (event.type() == DeviceEvent.Type.DEVICE_AVAILABILITY_CHANGED) {
+                                // availability changed and not available - dev gone
+                                DefaultGroupHandler groupHandler = groupHandlerMap.get(deviceId);
+                                if (groupHandler != null) {
+                                    groupHandler.removeAllGroups();
+                                }
+                            }
+                        }*/
                     } else if (event.type() == DeviceEvent.Type.PORT_REMOVED) {
                         processPortRemoved((Device) event.subject(),
                                            ((DeviceEvent) event).port());
@@ -655,7 +664,8 @@ public class SegmentRoutingManager implements SegmentRoutingService {
         log.debug("A link {} was removed", link.toString());
         DefaultGroupHandler groupHandler = groupHandlerMap.get(link.src().deviceId());
         if (groupHandler != null) {
-            groupHandler.portDown(link.src().port());
+            groupHandler.portDown(link.src().port(),
+                                  mastershipService.isLocalMaster(link.src().deviceId()));
         }
         log.trace("Starting optimized route population process");
         defaultRoutingHandler.populateRoutingRulesForLinkStatusChange(link);
@@ -711,7 +721,8 @@ public class SegmentRoutingManager implements SegmentRoutingService {
         log.debug("Port {} was removed", port.toString());
         DefaultGroupHandler groupHandler = groupHandlerMap.get(device.id());
         if (groupHandler != null) {
-            groupHandler.portDown(port.number());
+            groupHandler.portDown(port.number(),
+                                  mastershipService.isLocalMaster(device.id()));
         }
     }
--- a/apps/segmentrouting/src/main/java/org/onosproject/segmentrouting/grouphandler/DefaultGroupHandler.java
View file @423fe2b
+++ b/apps/segmentrouting/src/main/java/org/onosproject/segmentrouting/grouphandler/DefaultGroupHandler.java
View file @423fe2b
@@ -32,11 +32,13 @@ import org.onlab.packet.Ip4Prefix;
 import org.onlab.packet.IpPrefix;
 import org.onlab.packet.MacAddress;
 import org.onlab.packet.MplsLabel;
+import org.onlab.packet.VlanId;
 import org.onlab.util.KryoNamespace;
 import org.onosproject.core.ApplicationId;
 import org.onosproject.net.DeviceId;
 import org.onosproject.net.Link;
 import org.onosproject.net.PortNumber;
+import org.onosproject.net.flow.DefaultTrafficSelector;
 import org.onosproject.net.flow.DefaultTrafficTreatment;
 import org.onosproject.net.flow.TrafficSelector;
 import org.onosproject.net.flow.TrafficTreatment;
@@ -49,6 +51,7 @@ import org.onosproject.net.flowobjective.ObjectiveError;
 import org.onosproject.net.group.DefaultGroupKey;
 import org.onosproject.net.group.GroupKey;
 import org.onosproject.net.link.LinkService;
+import org.onosproject.segmentrouting.SegmentRoutingManager;
 import org.onosproject.segmentrouting.config.DeviceConfigNotFoundException;
 import org.onosproject.segmentrouting.config.DeviceProperties;
 import org.onosproject.store.service.EventuallyConsistentMap;
@@ -71,9 +74,11 @@ public class DefaultGroupHandler {
     protected MacAddress nodeMacAddr = null;
     protected LinkService linkService;
     protected FlowObjectiveService flowObjectiveService;
-
+    // local store for neighbor-device-ids and the set of ports on this device
+    // that connect to the same neighbor
     protected ConcurrentHashMap<DeviceId, Set<PortNumber>> devicePortMap =
             new ConcurrentHashMap<>();
+    //local store for ports on this device connected to neighbor-device-id
     protected ConcurrentHashMap<PortNumber, DeviceId> portDeviceMap =
             new ConcurrentHashMap<>();
     protected EventuallyConsistentMap<
@@ -225,26 +230,33 @@ public class DefaultGroupHandler {
                 deviceId,
                 nsSet);
         for (NeighborSet ns : nsSet) {
-            // Create the new bucket to be updated
+            Integer nextId = nsNextObjStore.
-            TrafficTreatment.Builder tBuilder =
+                    get(new NeighborSetNextObjectiveStoreKey(deviceId, ns));
-                    DefaultTrafficTreatment.builder();
+            if (nextId != null && isMaster) {
-            tBuilder.setOutput(newLink.src().port())
+                // Create the new bucket to be updated
+                TrafficTreatment.Builder tBuilder =
+                        DefaultTrafficTreatment.builder();
+                tBuilder.setOutput(newLink.src().port())
                     .setEthDst(dstMac)
                     .setEthSrc(nodeMacAddr);
-            if (ns.getEdgeLabel() != NeighborSet.NO_EDGE_LABEL) {
+                if (ns.getEdgeLabel() != NeighborSet.NO_EDGE_LABEL) {
-                tBuilder.pushMpls()
+                    tBuilder.pushMpls()
                         .copyTtlOut()
                         .setMpls(MplsLabel.mplsLabel(ns.getEdgeLabel()));
-            }
+                }
-
+                // setup metadata to pass to nextObjective - indicate the vlan on egress
-            Integer nextId = nsNextObjStore.
+                // if needed by the switch pipeline. Since hashed next-hops are always to
-                    get(new NeighborSetNextObjectiveStoreKey(deviceId, ns));
+                // other neighboring routers, there is no subnet assigned on those ports.
-            if (nextId != null && isMaster) {
+                TrafficSelector.Builder metabuilder = DefaultTrafficSelector.builder();
-                NextObjective.Builder nextObjBuilder = DefaultNextObjective
+                metabuilder.matchVlanId(
-                        .builder().withId(nextId)
+                    VlanId.vlanId(SegmentRoutingManager.ASSIGNED_VLAN_NO_SUBNET));
-                        .withType(NextObjective.Type.HASHED).fromApp(appId);
+
-
+                NextObjective.Builder nextObjBuilder = DefaultNextObjective.builder()
-                nextObjBuilder.addTreatment(tBuilder.build());
+                        .withId(nextId)
+                        .withType(NextObjective.Type.HASHED)
+                        .addTreatment(tBuilder.build())
+                        .withMeta(metabuilder.build())
+                        .fromApp(appId);
                 log.info("**linkUp in device {}: Adding Bucket "
                         + "with Port {} to next object id {}",
                         deviceId,
@@ -253,6 +265,18 @@ public class DefaultGroupHandler {
                 NextObjective nextObjective = nextObjBuilder.
                         addToExisting(new SRNextObjectiveContext(deviceId));
                 flowObjectiveService.next(deviceId, nextObjective);
+
+                // the addition of a bucket may actually change the neighborset
+                // update the global store
+                /*
+                Set<DeviceId> neighbors = new HashSet<DeviceId>(ns.getDeviceIds());
+                boolean newadd = neighbors.add(newLink.dst().deviceId());
+                if (newadd) {
+                    NeighborSet nsnew = new NeighborSet(neighbors, ns.getEdgeLabel());
+                    nsNextObjStore.put(new NeighborSetNextObjectiveStoreKey(deviceId, nsnew),
+                                       nextId);
+                    nsNextObjStore.remove(new NeighborSetNextObjectiveStoreKey(deviceId, ns));
+                }*/
             } else if (isMaster) {
                 log.warn("linkUp in device {}, but global store has no record "
                         + "for neighbor-set {}", deviceId, ns);
@@ -265,7 +289,7 @@ public class DefaultGroupHandler {
      *
      * @param port port number that has gone down
      */
-    public void portDown(PortNumber port) {
+    public void portDown(PortNumber port, boolean isMaster) {
         if (portDeviceMap.get(port) == null) {
             log.warn("portDown: unknown port");
             return;
@@ -292,40 +316,50 @@ public class DefaultGroupHandler {
                 .filter((ns) -> (ns.getDeviceIds()
                         .contains(portDeviceMap.get(port))))
                 .collect(Collectors.toSet());
-        log.trace("portDown: nsNextObjStore contents for device {}:",
+        log.debug("portDown: nsNextObjStore contents for device {}:{}",
-                  deviceId,
+                  deviceId, nsSet);
-                  nsSet);
         for (NeighborSet ns : nsSet) {
-            // Create the bucket to be removed
-            TrafficTreatment.Builder tBuilder = DefaultTrafficTreatment
-                    .builder();
-            tBuilder.setOutput(port)
-                    .setEthDst(dstMac)
-                    .setEthSrc(nodeMacAddr);
-            if (ns.getEdgeLabel() != NeighborSet.NO_EDGE_LABEL) {
-                tBuilder.pushMpls()
-                        .copyTtlOut()
-                        .setMpls(MplsLabel.mplsLabel(ns.getEdgeLabel()));
-            }
-
             Integer nextId = nsNextObjStore.
                     get(new NeighborSetNextObjectiveStoreKey(deviceId, ns));
-            if (nextId != null) {
+            if (nextId != null && isMaster) {
-                NextObjective.Builder nextObjBuilder = DefaultNextObjective
-                        .builder().withType(NextObjective.Type.SIMPLE).withId(nextId).fromApp(appId);
-
-                nextObjBuilder.addTreatment(tBuilder.build());
-
                 log.info("**portDown in device {}: Removing Bucket "
                         + "with Port {} to next object id {}",
                         deviceId,
                         port,
                         nextId);
-                // should do removefromexisting and only if master
+                // Create the bucket to be removed
-                /*NextObjective nextObjective = nextObjBuilder.
+                TrafficTreatment.Builder tBuilder = DefaultTrafficTreatment
-                        remove(new SRNextObjectiveContext(deviceId));
+                        .builder();
+                tBuilder.setOutput(port)
+                    .setEthDst(dstMac)
+                    .setEthSrc(nodeMacAddr);
+                if (ns.getEdgeLabel() != NeighborSet.NO_EDGE_LABEL) {
+                    tBuilder.pushMpls()
+                        .copyTtlOut()
+                        .setMpls(MplsLabel.mplsLabel(ns.getEdgeLabel()));
+                }
+                NextObjective.Builder nextObjBuilder = DefaultNextObjective
+                        .builder()
+                        .withType(NextObjective.Type.HASHED) //same as original
+                        .withId(nextId)
+                        .fromApp(appId)
+                        .addTreatment(tBuilder.build());
+                NextObjective nextObjective = nextObjBuilder.
+                        removeFromExisting(new SRNextObjectiveContext(deviceId));
-                flowObjectiveService.next(deviceId, nextObjective);*/
+                flowObjectiveService.next(deviceId, nextObjective);
+
+                // the removal of a bucket may actually change the neighborset
+                // update the global store
+                /*
+                Set<DeviceId> neighbors = new HashSet<DeviceId>(ns.getDeviceIds());
+                boolean removed = neighbors.remove(portDeviceMap.get(port));
+                if (removed) {
+                    NeighborSet nsnew = new NeighborSet(neighbors, ns.getEdgeLabel());
+                    nsNextObjStore.put(new NeighborSetNextObjectiveStoreKey(deviceId, nsnew),
+                                       nextId);
+                    nsNextObjStore.remove(new NeighborSetNextObjectiveStoreKey(deviceId, ns));
+                }*/
             }
         }
@@ -718,6 +752,22 @@ public class DefaultGroupHandler {
         return false;
     }
+    public void removeAllGroups() {
+        for (Map.Entry<NeighborSetNextObjectiveStoreKey, Integer> entry:
+                nsNextObjStore.entrySet()) {
+            removeGroup(entry.getValue());
+        }
+        for (Map.Entry<PortNextObjectiveStoreKey, Integer> entry:
+                portNextObjStore.entrySet()) {
+            removeGroup(entry.getValue());
+        }
+        for (Map.Entry<SubnetNextObjectiveStoreKey, Integer> entry:
+                subnetNextObjStore.entrySet()) {
+            removeGroup(entry.getValue());
+        }
+        // should probably clean local stores port-neighbor
+    }
+
     protected static class SRNextObjectiveContext implements ObjectiveContext {
         final DeviceId deviceId;
--- a/core/api/src/main/java/org/onosproject/net/flowobjective/FlowObjectiveStore.java
View file @423fe2b
+++ b/core/api/src/main/java/org/onosproject/net/flowobjective/FlowObjectiveStore.java
View file @423fe2b
@@ -27,7 +27,8 @@ public interface FlowObjectiveStore
         extends Store<ObjectiveEvent, FlowObjectiveStoreDelegate> {
     /**
-     * Adds a NextGroup to the store.
+     * Adds a NextGroup to the store, by mapping it to the nextId as key,
+     * and replacing any previous mapping.
      *
      * @param nextId an integer
      * @param group a next group opaque object
@@ -36,12 +37,22 @@ public interface FlowObjectiveStore
     /**
      * Fetch a next group from the store.
-     * @param nextId an integer
+     *
-     * @return a next group
+     * @param nextId an integer used as key
+     * @return a next group, or null if group was not found
      */
     NextGroup getNextGroup(Integer nextId);
     /**
+     * Remove a next group mapping from the store.
+     *
+     * @param nextId  the key to remove from the store.
+     * @return the next group which mapped to the nextId and is now removed, or
+     *          null if no group mapping existed in the store
+     */
+    NextGroup removeNextGroup(Integer nextId);
+
+    /**
      * Allocates a next objective id. This id is globally unique
      *
      * @return an integer
--- a/core/net/src/main/java/org/onosproject/net/flowobjective/impl/FlowObjectiveManager.java
View file @423fe2b
+++ b/core/net/src/main/java/org/onosproject/net/flowobjective/impl/FlowObjectiveManager.java
View file @423fe2b
@@ -48,6 +48,7 @@ import org.onosproject.net.flowobjective.NextObjective;
 import org.onosproject.net.flowobjective.Objective;
 import org.onosproject.net.flowobjective.ObjectiveError;
 import org.onosproject.net.flowobjective.ObjectiveEvent;
+import org.onosproject.net.flowobjective.ObjectiveEvent.Type;
 import org.onosproject.net.group.GroupService;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
@@ -381,19 +382,19 @@ public class FlowObjectiveManager implements FlowObjectiveService {
     private class InternalStoreDelegate implements FlowObjectiveStoreDelegate {
         @Override
         public void notify(ObjectiveEvent event) {
-            log.debug("Received notification of obj event {}", event);
+            if (event.type() == Type.ADD) {
-            Set<PendingNext> pending = pendingForwards.remove(event.subject());
+                log.debug("Received notification of obj event {}", event);
+                Set<PendingNext> pending = pendingForwards.remove(event.subject());
-            if (pending == null) {
+                if (pending == null) {
-                log.debug("Nothing pending for this obj event");
+                    log.debug("Nothing pending for this obj event");
-                return;
+                    return;
-            }
+                }
-
-            log.debug("Processing pending forwarding objectives {}", pending.size());
-
-            pending.forEach(p -> getDevicePipeliner(p.deviceId())
-                    .forward(p.forwardingObjective()));
+                log.debug("Processing pending forwarding objectives {}", pending.size());
+                pending.forEach(p -> getDevicePipeliner(p.deviceId())
+                                .forward(p.forwardingObjective()));
+            }
         }
     }
--- a/core/store/dist/src/main/java/org/onosproject/store/flowobjective/impl/DistributedFlowObjectiveStore.java
View file @423fe2b
+++ b/core/store/dist/src/main/java/org/onosproject/store/flowobjective/impl/DistributedFlowObjectiveStore.java
View file @423fe2b
@@ -79,10 +79,9 @@ public class DistributedFlowObjectiveStore
         log.info("Stopped");
     }
-
     @Override
     public void putNextGroup(Integer nextId, NextGroup group) {
-        nextGroups.putIfAbsent(nextId, group.data());
+        nextGroups.put(nextId, group.data());
         notifyDelegate(new ObjectiveEvent(ObjectiveEvent.Type.ADD, nextId));
     }
@@ -96,6 +95,16 @@ public class DistributedFlowObjectiveStore
     }
     @Override
+    public NextGroup removeNextGroup(Integer nextId) {
+        Versioned<byte[]> versionGroup = nextGroups.remove(nextId);
+        if (versionGroup != null) {
+            notifyDelegate(new ObjectiveEvent(ObjectiveEvent.Type.REMOVE, nextId));
+            return new DefaultNextGroup(versionGroup.value());
+        }
+        return null;
+    }
+
+    @Override
     public int allocateNextId() {
         return (int) nextIds.incrementAndGet();
     }
--- a/drivers/src/main/java/org/onosproject/driver/pipeline/CpqdOFDPA2Pipeline.java
View file @423fe2b
+++ b/drivers/src/main/java/org/onosproject/driver/pipeline/CpqdOFDPA2Pipeline.java
View file @423fe2b
@@ -71,7 +71,6 @@ public class CpqdOFDPA2Pipeline extends OFDPA2Pipeline {
      * (non-Javadoc)
      * @see org.onosproject.driver.pipeline.OFDPA2Pipeline#processVlanIdFilter
      */
-
     @Override
     protected List<FlowRule> processVlanIdFilter(PortCriterion portCriterion,
                                                  VlanIdCriterion vidCriterion,
@@ -267,16 +266,18 @@ public class CpqdOFDPA2Pipeline extends OFDPA2Pipeline {
         }
         if (fwd.nextId() != null) {
-            NextGroup next = flowObjectiveStore.getNextGroup(fwd.nextId());
+            NextGroup next = getGroupForNextObjective(fwd.nextId());
-            List<Deque<GroupKey>> gkeys = appKryo.deserialize(next.data());
+            if (next != null) {
-            // we only need the top level group's key to point the flow to it
+                List<Deque<GroupKey>> gkeys = appKryo.deserialize(next.data());
-            Group group = groupService.getGroup(deviceId, gkeys.get(0).peekFirst());
+                // we only need the top level group's key to point the flow to it
-            if (group == null) {
+                Group group = groupService.getGroup(deviceId, gkeys.get(0).peekFirst());
-                log.warn("The group left!");
+                if (group == null) {
-                fail(fwd, ObjectiveError.GROUPMISSING);
+                    log.warn("The group left!");
-                return Collections.emptySet();
+                    fail(fwd, ObjectiveError.GROUPMISSING);
+                    return Collections.emptySet();
+                }
+                tb.deferred().group(group.id());
             }
-            tb.deferred().group(group.id());
         }
         tb.transition(ACL_TABLE);
         FlowRule.Builder ruleBuilder = DefaultFlowRule.builder()
--- a/drivers/src/main/java/org/onosproject/driver/pipeline/OFDPA2Pipeline.java
View file @423fe2b
+++ b/drivers/src/main/java/org/onosproject/driver/pipeline/OFDPA2Pipeline.java
View file @423fe2b
@@ -94,7 +94,6 @@ import org.onosproject.net.group.GroupEvent;
 import org.onosproject.net.group.GroupKey;
 import org.onosproject.net.group.GroupListener;
 import org.onosproject.net.group.GroupService;
-import org.onosproject.net.packet.PacketService;
 import org.onosproject.store.serializers.KryoNamespaces;
 import org.slf4j.Logger;
@@ -149,7 +148,6 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
     protected FlowObjectiveStore flowObjectiveStore;
     protected DeviceId deviceId;
     protected ApplicationId driverId;
-    protected PacketService packetService;
     protected DeviceService deviceService;
     protected KryoNamespace appKryo = new KryoNamespace.Builder()
         .register(KryoNamespaces.API)
@@ -174,6 +172,10 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
     Map<VlanId, Set<PortNumber>> vlan2Port = new ConcurrentHashMap<VlanId,
                                                         Set<PortNumber>>();
+    // local store for pending bucketAdds - by design there can only be one
+    // pending bucket for a group
+    ConcurrentHashMap<Integer, NextObjective> pendingBuckets = new ConcurrentHashMap<>();
+
     // index number for group creation
     AtomicInteger l3vpnindex = new AtomicInteger(0);
@@ -202,7 +204,6 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
         flowRuleService = serviceDirectory.get(FlowRuleService.class);
         groupService = serviceDirectory.get(GroupService.class);
         flowObjectiveStore = context.store();
-        packetService = serviceDirectory.get(PacketService.class);
         deviceService = serviceDirectory.get(DeviceService.class);
         groupService.addListener(new InnerGroupListener());
@@ -293,10 +294,13 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
             if (nextGroup != null) {
                 log.debug("Processing NextObjective id{} in dev{} - add bucket",
                           nextObjective.id(), deviceId);
-                addBucketToGroup(nextObjective);
+                addBucketToGroup(nextObjective, nextGroup);
             } else {
                 // it is possible that group-chain has not been fully created yet
-                waitToAddBucketToGroup(nextObjective);
+                log.debug("Waiting to add bucket to group for next-id:{} in dev:{}",
+                          nextObjective.id(), deviceId);
+                // by design only one pending bucket is allowed for the group
+                pendingBuckets.put(nextObjective.id(), nextObjective);
             }
             break;
         case REMOVE:
@@ -307,7 +311,7 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
             }
             log.debug("Processing NextObjective id{}  in dev{} - remove group",
                       nextObjective.id(), deviceId);
-            removeGroup(nextObjective);
+            removeGroup(nextObjective, nextGroup);
             break;
         case REMOVE_FROM_EXISTING:
             if (nextGroup == null) {
@@ -317,7 +321,7 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
             }
             log.debug("Processing NextObjective id{} in dev{} - remove bucket",
                       nextObjective.id(), deviceId);
-            removeBucketFromGroup(nextObjective);
+            removeBucketFromGroup(nextObjective, nextGroup);
             break;
         default:
             log.warn("Unsupported operation {}", nextObjective.op());
@@ -791,17 +795,19 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
                 return Collections.emptySet();
             }
-            NextGroup next = flowObjectiveStore.getNextGroup(fwd.nextId());
+            NextGroup next = getGroupForNextObjective(fwd.nextId());
-            List<Deque<GroupKey>> gkeys = appKryo.deserialize(next.data());
+            if (next != null) {
-            // we only need the top level group's key to point the flow to it
+                List<Deque<GroupKey>> gkeys = appKryo.deserialize(next.data());
-            Group group = groupService.getGroup(deviceId, gkeys.get(0).peekFirst());
+                // we only need the top level group's key to point the flow to it
-            if (group == null) {
+                Group group = groupService.getGroup(deviceId, gkeys.get(0).peekFirst());
-                log.warn("Group with key:{} for next-id:{} not found in dev:{}",
+                if (group == null) {
-                         gkeys.get(0).peekFirst(), fwd.nextId(), deviceId);
+                    log.warn("Group with key:{} for next-id:{} not found in dev:{}",
-                fail(fwd, ObjectiveError.GROUPMISSING);
+                             gkeys.get(0).peekFirst(), fwd.nextId(), deviceId);
-                return Collections.emptySet();
+                    fail(fwd, ObjectiveError.GROUPMISSING);
+                    return Collections.emptySet();
+                }
+                tb.deferred().group(group.id());
             }
-            tb.deferred().group(group.id());
         }
         tb.transition(ACL_TABLE);
         FlowRule.Builder ruleBuilder = DefaultFlowRule.builder()
@@ -868,7 +874,7 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
         TrafficTreatment.Builder treatmentBuilder = DefaultTrafficTreatment.builder();
         if (fwd.nextId() != null) {
-            NextGroup next = flowObjectiveStore.getNextGroup(fwd.nextId());
+            NextGroup next = getGroupForNextObjective(fwd.nextId());
             if (next != null) {
                 List<Deque<GroupKey>> gkeys = appKryo.deserialize(next.data());
                 // we only need the top level group's key to point the flow to it
@@ -903,6 +909,23 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
         return rules;
     }
+    protected NextGroup getGroupForNextObjective(Integer nextId) {
+        NextGroup next = flowObjectiveStore.getNextGroup(nextId);
+        if (next != null) {
+            List<Deque<GroupKey>> gkeys = appKryo.deserialize(next.data());
+            if (gkeys != null && !gkeys.isEmpty()) {
+                return next;
+            } else {
+               log.warn("Empty next group found in FlowObjective store for "
+                       + "next-id:{} in dev:{}", nextId, deviceId);
+            }
+        } else {
+            log.warn("next-id {} not found in Flow objective store for dev:{}",
+                     nextId, deviceId);
+        }
+        return null;
+    }
+
     private void pass(Objective obj) {
         if (obj.context().isPresent()) {
             obj.context().get().onSuccess(obj);
@@ -1013,6 +1036,16 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
         }
     }
+    private void updatePendingGroups(GroupKey gkey, GroupChainElem gce) {
+        Set<GroupChainElem> gceSet = Collections.newSetFromMap(
+                                         new ConcurrentHashMap<GroupChainElem, Boolean>());
+        gceSet.add(gce);
+        Set<GroupChainElem> retval = pendingGroups.putIfAbsent(gkey, gceSet);
+        if (retval != null) {
+            retval.add(gce);
+        }
+    }
+
     /**
      * Creates a simple L2 Interface Group.
      *
@@ -1242,14 +1275,8 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
         }
         // store l2groupkey with the groupChainElem for the outer-group that depends on it
-        GroupChainElem gce = new GroupChainElem(outerGrpDesc, 1);
+        GroupChainElem gce = new GroupChainElem(outerGrpDesc, 1, false);
-        Set<GroupChainElem> gceSet = Collections.newSetFromMap(
+        updatePendingGroups(l2groupkey, gce);
-                                         new ConcurrentHashMap<GroupChainElem, Boolean>());
-        gceSet.add(gce);
-        Set<GroupChainElem> retval = pendingGroups.putIfAbsent(l2groupkey, gceSet);
-        if (retval != null) {
-            retval.add(gce);
-        }
         // create group description for the inner l2interfacegroup
         GroupBucket l2interfaceGroupBucket =
@@ -1376,7 +1403,8 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
                                         l2floodgroupId,
                                         nextObj.appId());
         GroupChainElem gce = new GroupChainElem(l2floodGroupDescription,
-                                                l2interfaceGroupDescs.size());
+                                                l2interfaceGroupDescs.size(),
+                                                false);
         log.debug("Trying L2-Flood: device:{} gid:{} gkey:{} nextid:{}",
                   deviceId, Integer.toHexString(l2floodgroupId),
                   l2floodgroupkey, nextObj.id());
@@ -1392,16 +1420,8 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
         for (GroupDescription l2intGrpDesc : l2interfaceGroupDescs) {
             // store all l2groupkeys with the groupChainElem for the l2floodgroup
             // that depends on it
-            Set<GroupChainElem> gceSet = Collections.newSetFromMap(
+            updatePendingGroups(l2intGrpDesc.appCookie(), gce);
-                                             new ConcurrentHashMap<GroupChainElem, Boolean>());
+            // send groups for all l2 interface groups
-            gceSet.add(gce);
-            Set<GroupChainElem> retval = pendingGroups.putIfAbsent(
-                                             l2intGrpDesc.appCookie(), gceSet);
-            if (retval != null) {
-                retval.add(gce);
-            }
-
-            // create and send groups for all l2 interface groups
             groupService.addGroup(l2intGrpDesc);
         }
     }
@@ -1430,17 +1450,81 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
      * <p>
      * NOTE: We do not create MPLS ECMP groups as they are unimplemented in
      *       OF-DPA 2.0 (even though it is in the spec). Therefore we do not
-     *       check the nextObjective meta.
+     *       check the nextObjective meta to see what is matching before being
+     *       sent to this nextObjective.
      *
      * @param nextObj  the nextObjective of type HASHED
      */
     private void processHashedNextObjective(NextObjective nextObj) {
-        // break up hashed next objective to multiple groups
-        Collection<TrafficTreatment> buckets = nextObj.next();
-
         // storage for all group keys in the chain of groups created
         List<Deque<GroupKey>> allGroupKeys = new ArrayList<>();
         List<GroupInfo> unsentGroups = new ArrayList<>();
+        createHashBucketChains(nextObj, allGroupKeys, unsentGroups);
+
+        // now we can create the outermost L3 ECMP group
+        List<GroupBucket> l3ecmpGroupBuckets = new ArrayList<>();
+        for (GroupInfo gi : unsentGroups) {
+            // create ECMP bucket to point to the outer group
+            TrafficTreatment.Builder ttb = DefaultTrafficTreatment.builder();
+            ttb.group(new DefaultGroupId(gi.outerGrpDesc.givenGroupId()));
+            GroupBucket sbucket = DefaultGroupBucket
+                    .createSelectGroupBucket(ttb.build());
+            l3ecmpGroupBuckets.add(sbucket);
+        }
+        int l3ecmpGroupId = L3ECMPMASK | nextObj.id() << 12;
+        GroupKey l3ecmpGroupKey = new DefaultGroupKey(appKryo.serialize(l3ecmpGroupId));
+        GroupDescription l3ecmpGroupDesc =
+                new DefaultGroupDescription(
+                        deviceId,
+                        GroupDescription.Type.SELECT,
+                        new GroupBuckets(l3ecmpGroupBuckets),
+                        l3ecmpGroupKey,
+                        l3ecmpGroupId,
+                        nextObj.appId());
+        GroupChainElem l3ecmpGce = new GroupChainElem(l3ecmpGroupDesc,
+                                                      l3ecmpGroupBuckets.size(),
+                                                      false);
+
+        // create objects for local and distributed storage
+        allGroupKeys.forEach(gkeyChain -> gkeyChain.addFirst(l3ecmpGroupKey));
+        OfdpaNextGroup ofdpaGrp = new OfdpaNextGroup(allGroupKeys, nextObj);
+
+        // store l3ecmpGroupKey with the ofdpaGroupChain for the nextObjective
+        // that depends on it
+        updatePendingNextObjective(l3ecmpGroupKey, ofdpaGrp);
+
+        log.debug("Trying L3ECMP: device:{} gid:{} gkey:{} nextId:{}",
+                  deviceId, Integer.toHexString(l3ecmpGroupId),
+                  l3ecmpGroupKey, nextObj.id());
+        // finally we are ready to send the innermost groups
+        for (GroupInfo gi : unsentGroups) {
+            log.debug("Sending innermost group {} in group chain on device {} ",
+                      Integer.toHexString(gi.innerGrpDesc.givenGroupId()), deviceId);
+            updatePendingGroups(gi.outerGrpDesc.appCookie(), l3ecmpGce);
+            groupService.addGroup(gi.innerGrpDesc);
+        }
+
+    }
+
+    /**
+     * Creates group chains for all buckets in a hashed group, and stores the
+     * GroupInfos and GroupKeys for all the groups in the lists passed in, which
+     * should be empty.
+     * <p>
+     * Does not create the top level ECMP group. Does not actually send the
+     * groups to the groupService.
+     *
+     * @param nextObj  the Next Objective with buckets that need to be converted
+     *                  to group chains
+     * @param allGroupKeys  a list to store groupKey for each bucket-group-chain
+     * @param unsentGroups  a list to store GroupInfo for each bucket-group-chain
+     */
+    private void createHashBucketChains(NextObjective nextObj,
+                                        List<Deque<GroupKey>> allGroupKeys,
+                                        List<GroupInfo> unsentGroups) {
+        // break up hashed next objective to multiple groups
+        Collection<TrafficTreatment> buckets = nextObj.next();
+
         for (TrafficTreatment bucket : buckets) {
             //figure out how many labels are pushed in each bucket
             int labelsPushed = 0;
@@ -1508,15 +1592,8 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
                                 l3vpngroupkey,
                                 l3vpngroupId,
                                 nextObj.appId());
-                GroupChainElem l3vpnGce = new GroupChainElem(l3vpnGroupDesc, 1);
+                GroupChainElem l3vpnGce = new GroupChainElem(l3vpnGroupDesc, 1, false);
-                Set<GroupChainElem> gceSet = Collections.newSetFromMap(
+                updatePendingGroups(onelabelGroupInfo.outerGrpDesc.appCookie(), l3vpnGce);
-                                                 new ConcurrentHashMap<GroupChainElem, Boolean>());
-                gceSet.add(l3vpnGce);
-                Set<GroupChainElem> retval = pendingGroups
-                        .putIfAbsent(onelabelGroupInfo.outerGrpDesc.appCookie(), gceSet);
-                if (retval != null) {
-                    retval.add(l3vpnGce);
-                }
                 gkeyChain.addFirst(onelabelGroupInfo.innerGrpDesc.appCookie());
                 gkeyChain.addFirst(onelabelGroupInfo.outerGrpDesc.appCookie());
@@ -1535,80 +1612,186 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
             } else {
                 log.warn("Driver currently does not handle more than 1 MPLS "
-                        + "labels. Not processing nextObjective {}", nextObj);
+                        + "labels. Not processing nextObjective {}", nextObj.id());
                 return;
             }
             // all groups in this chain
             allGroupKeys.add(gkeyChain);
         }
+    }
-        // now we can create the outermost L3 ECMP group
+    /**
-        List<GroupBucket> l3ecmpGroupBuckets = new ArrayList<>();
+     *  Adds a bucket to the top level group of a group-chain, and creates the chain.
-        for (GroupInfo gi : unsentGroups) {
+     *
-            // create ECMP bucket to point to the outer group
+     * @param nextObjective the next group to add a bucket to
-            TrafficTreatment.Builder ttb = DefaultTrafficTreatment.builder();
+     * @param next the representation of the existing group-chain for this next objective
-            ttb.group(new DefaultGroupId(gi.outerGrpDesc.givenGroupId()));
+     */
-            GroupBucket sbucket = DefaultGroupBucket
+    private void addBucketToGroup(NextObjective nextObjective, NextGroup next) {
-                    .createSelectGroupBucket(ttb.build());
+        if (nextObjective.type() != NextObjective.Type.HASHED) {
-            l3ecmpGroupBuckets.add(sbucket);
+            log.warn("AddBuckets not applied to nextType:{} in dev:{} for next:{}",
+                     nextObjective.type(), deviceId, nextObjective.id());
+            return;
         }
-        int l3ecmpGroupId = L3ECMPMASK | nextObj.id() << 12;
+        if (nextObjective.next().size() > 1) {
+            log.warn("Only one bucket can be added at a time");
+            return;
+        }
+        // storage for all group keys in the chain of groups created
+        List<Deque<GroupKey>> allGroupKeys = new ArrayList<>();
+        List<GroupInfo> unsentGroups = new ArrayList<>();
+        createHashBucketChains(nextObjective, allGroupKeys, unsentGroups);
+
+        // now we can create the outermost L3 ECMP group bucket to add
+        GroupInfo gi = unsentGroups.get(0); // only one bucket, so only one group-chain
+        TrafficTreatment.Builder ttb = DefaultTrafficTreatment.builder();
+        ttb.group(new DefaultGroupId(gi.outerGrpDesc.givenGroupId()));
+        GroupBucket sbucket = DefaultGroupBucket.createSelectGroupBucket(ttb.build());
+
+        // recreate the original L3 ECMP group id and description
+        int l3ecmpGroupId = L3ECMPMASK | nextObjective.id() << 12;
         GroupKey l3ecmpGroupKey = new DefaultGroupKey(appKryo.serialize(l3ecmpGroupId));
+
+        // Although GroupDescriptions are not necessary for adding buckets to
+        // existing groups, we use one in the GroupChainElem. When the latter is
+        // processed, the info will be extracted for the bucketAdd call to groupService
         GroupDescription l3ecmpGroupDesc =
                 new DefaultGroupDescription(
                         deviceId,
                         GroupDescription.Type.SELECT,
-                        new GroupBuckets(l3ecmpGroupBuckets),
+                        new GroupBuckets(Collections.singletonList(sbucket)),
                         l3ecmpGroupKey,
                         l3ecmpGroupId,
-                        nextObj.appId());
+                        nextObjective.appId());
-        GroupChainElem l3ecmpGce = new GroupChainElem(l3ecmpGroupDesc,
+        GroupChainElem l3ecmpGce = new GroupChainElem(l3ecmpGroupDesc, 1, true);
-                                                      l3ecmpGroupBuckets.size());
+
-
+        // update original NextGroup with new bucket-chain
-        // create objects for local and distributed storage
+        // don't need to update pendingNextObjectives -- group already exists
-        allGroupKeys.forEach(gkeyChain -> gkeyChain.addFirst(l3ecmpGroupKey));
+        Deque<GroupKey> newBucketChain = allGroupKeys.get(0);
-        OfdpaNextGroup ofdpaGrp = new OfdpaNextGroup(allGroupKeys, nextObj);
+        newBucketChain.addFirst(l3ecmpGroupKey);
-
+        List<Deque<GroupKey>> allOriginalKeys = appKryo.deserialize(next.data());
-        // store l3ecmpGroupKey with the ofdpaGroupChain for the nextObjective
+        allOriginalKeys.add(newBucketChain);
-        // that depends on it
+        flowObjectiveStore.putNextGroup(nextObjective.id(),
-        updatePendingNextObjective(l3ecmpGroupKey, ofdpaGrp);
+                                        new OfdpaNextGroup(allOriginalKeys, nextObjective));
-
+
-        log.debug("Trying L3ECMP: device:{} gid:{} gkey:{} nextId:{}",
+        log.debug("Adding to L3ECMP: device:{} gid:{} gkey:{} nextId:{}",
                   deviceId, Integer.toHexString(l3ecmpGroupId),
-                  l3ecmpGroupKey, nextObj.id());
+                  l3ecmpGroupKey, nextObjective.id());
-        // finally we are ready to send the innermost groups
+        // send the innermost group
-        for (GroupInfo gi : unsentGroups) {
+        log.debug("Sending innermost group {} in group chain on device {} ",
-            log.debug("Sending innermost group {} in group chain on device {} ",
+                  Integer.toHexString(gi.innerGrpDesc.givenGroupId()), deviceId);
-                      Integer.toHexString(gi.innerGrpDesc.givenGroupId()), deviceId);
+        updatePendingGroups(gi.outerGrpDesc.appCookie(), l3ecmpGce);
-            Set<GroupChainElem> gceSet = Collections.newSetFromMap(
+        groupService.addGroup(gi.innerGrpDesc);
-                                             new ConcurrentHashMap<GroupChainElem, Boolean>());
-            gceSet.add(l3ecmpGce);
-            Set<GroupChainElem> retval = pendingGroups
-                    .putIfAbsent(gi.outerGrpDesc.appCookie(), gceSet);
-            if (retval != null) {
-                retval.add(l3ecmpGce);
-            }
-
-            groupService.addGroup(gi.innerGrpDesc);
-        }
     }
-    private void addBucketToGroup(NextObjective nextObjective) {
+    /**
-        // TODO Auto-generated method stub
+     * Removes the bucket in the top level group of a possible group-chain. Does
-    }
+     * not remove the groups in a group-chain pointed to by this bucket, as they
-
+     * may be in use (referenced by other groups) elsewhere.
-    private void waitToAddBucketToGroup(NextObjective nextObjective) {
+     *
-        // TODO Auto-generated method stub
+     * @param nextObjective the next group to remove a bucket from
-    }
+     * @param next the representation of the existing group-chain for this next objective
+     */
+    private void removeBucketFromGroup(NextObjective nextObjective, NextGroup next) {
+        if (nextObjective.type() != NextObjective.Type.HASHED) {
+            log.warn("RemoveBuckets not applied to nextType:{} in dev:{} for next:{}",
+                     nextObjective.type(), deviceId, nextObjective.id());
+            return;
+        }
+        Collection<TrafficTreatment> treatments = nextObjective.next();
+        TrafficTreatment treatment = treatments.iterator().next();
+        // find the bucket to remove by noting the outport, and figuring out the
+        // top-level group in the group-chain that indirectly references the port
+        PortNumber outport = null;
+        for (Instruction ins : treatment.allInstructions()) {
+            if (ins instanceof OutputInstruction) {
+                outport = ((OutputInstruction) ins).port();
+                break;
+            }
+        }
+        if (outport == null) {
+            log.error("next objective {} has no outport", nextObjective.id());
+            return;
+        }
-    private void removeBucketFromGroup(NextObjective nextObjective) {
+        List<Deque<GroupKey>> allgkeys = appKryo.deserialize(next.data());
-        // TODO Auto-generated method stub
+        Deque<GroupKey> foundChain = null;
+        int index = 0;
+        for (Deque<GroupKey> gkeys : allgkeys) {
+            GroupKey groupWithPort = gkeys.peekLast();
+            Group group = groupService.getGroup(deviceId, groupWithPort);
+            if (group == null) {
+                log.warn("Inconsistent group chain");
+                continue;
+            }
+            // last group in group chain should have a single bucket pointing to port
+            List<Instruction> lastIns = group.buckets().buckets().iterator()
+                                            .next().treatment().allInstructions();
+            for (Instruction i : lastIns) {
+                if (i instanceof OutputInstruction) {
+                    PortNumber lastport = ((OutputInstruction) i).port();
+                    if (lastport.equals(outport)) {
+                        foundChain = gkeys;
+                        break;
+                    }
+                }
+            }
+            if (foundChain != null) {
+                break;
+            }
+            index++;
+        }
+        if (foundChain != null) {
+            //first groupkey is the one we want to modify
+            GroupKey modGroupKey = foundChain.peekFirst();
+            Group modGroup = groupService.getGroup(deviceId, modGroupKey);
+            //second groupkey is the one we wish to remove the reference to
+            GroupKey pointedGroupKey = null;
+            int i = 0;
+            for (GroupKey gk : foundChain) {
+                if (i++ == 1) {
+                    pointedGroupKey = gk;
+                    break;
+                }
+            }
+            Group pointedGroup = groupService.getGroup(deviceId, pointedGroupKey);
+            GroupBucket bucket = DefaultGroupBucket.createSelectGroupBucket(
+                                     DefaultTrafficTreatment.builder()
+                                         .group(pointedGroup.id())
+                                         .build());
+            GroupBuckets removeBuckets = new GroupBuckets(Collections
+                                                          .singletonList(bucket));
+            log.debug("Removing buckets from group id {} for next id {} in device {}",
+                      modGroup.id(), nextObjective.id(), deviceId);
+            groupService.removeBucketsFromGroup(deviceId, modGroupKey,
+                                                removeBuckets, modGroupKey,
+                                                nextObjective.appId());
+            //update store
+            allgkeys.remove(index);
+            flowObjectiveStore.putNextGroup(nextObjective.id(),
+                                            new OfdpaNextGroup(allgkeys, nextObjective));
+        } else {
+            log.warn("Could not find appropriate group-chain for removing bucket"
+                    + " for next id {} in dev:{}", nextObjective.id(), deviceId);
+        }
     }
-    private void removeGroup(NextObjective nextObjective) {
+    /**
-        // TODO Auto-generated method stub
+     * Removes all groups in multiple possible group-chains that represent the next
+     * objective.
+     *
+     * @param nextObjective the next objective to remove
+     * @param next the NextGroup that represents the existing group-chain for
+     *             this next objective
+     */
+    private void removeGroup(NextObjective nextObjective, NextGroup next) {
+        List<Deque<GroupKey>> allgkeys = appKryo.deserialize(next.data());
+        allgkeys.forEach(groupChain -> {
+            groupChain.forEach(groupKey ->
+            groupService.removeGroup(deviceId, groupKey, nextObjective.appId()));
+        });
+        flowObjectiveStore.removeNextGroup(nextObjective.id());
     }
     /**
@@ -1617,7 +1800,7 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
      * and this driver has received notification for it. A second assumption is
      * that if there is another group waiting for this group then the appropriate
      * stores already have the information to act upon the notification for the
-     * creating of this group.
+     * creation of this group.
      * <p>
      * The processing of the GroupChainElement depends on the number of groups
      * this element is waiting on. For all group types other than SIMPLE, a
@@ -1632,7 +1815,15 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
             return;
         }
         log.debug("GCE: {} ready to be processed", gce);
-        groupService.addGroup(gce.groupDescription);
+        if (gce.addBucketToGroup) {
+            groupService.addBucketsToGroup(gce.groupDescription.deviceId(),
+                                           gce.groupDescription.appCookie(),
+                                           gce.groupDescription.buckets(),
+                                           gce.groupDescription.appCookie(),
+                                           gce.groupDescription.appId());
+        } else {
+            groupService.addGroup(gce.groupDescription);
+        }
     }
     private class GroupChecker implements Runnable {
@@ -1646,33 +1837,45 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
                     .collect(Collectors.toSet());
             keys.addAll(otherkeys);
-            keys.stream().forEach(key -> {
+            keys.stream().forEach(key ->
-                //first check for group chain
+                processPendingGroupsOrNextObjectives(key, false));
-                Set<GroupChainElem> gceSet = pendingGroups.remove(key);
+        }
-                if (gceSet != null) {
+    }
-                    for (GroupChainElem gce : gceSet) {
+
-                        log.info("Group service processed group key {} in device {}. "
+    private void processPendingGroupsOrNextObjectives(GroupKey key, boolean added) {
-                                + "Processing next group in group chain with group id {}",
+        //first check for group chain
-                                key, deviceId,
+        Set<GroupChainElem> gceSet = pendingGroups.remove(key);
-                                Integer.toHexString(gce.groupDescription.givenGroupId()));
+        if (gceSet != null) {
-                        processGroupChain(gce);
+            for (GroupChainElem gce : gceSet) {
-                    }
+                log.info("Group service {} group key {} in device {}. "
-                } else {
+                        + "Processing next group in group chain with group id {}",
-                    List<OfdpaNextGroup> objList = pendingNextObjectives.getIfPresent(key);
+                        (added) ? "ADDED" : "processed",
-                    if (objList != null) {
+                        key, deviceId,
-                        pendingNextObjectives.invalidate(key);
+                        Integer.toHexString(gce.groupDescription.givenGroupId()));
-                        objList.forEach(obj -> {
+                processGroupChain(gce);
-                            log.info("Group service processed group key {} in device:{}. "
+            }
-                                    + "Done implementing next objective: {} <<-->> gid:{}",
+        } else {
-                                    key, deviceId, obj.nextObjective().id(),
+            // otherwise chain complete - check for waiting nextObjectives
-                                    Integer.toHexString(groupService.getGroup(deviceId, key)
+            List<OfdpaNextGroup> nextGrpList = pendingNextObjectives.getIfPresent(key);
-                                                        .givenGroupId()));
+            if (nextGrpList != null) {
-                            pass(obj.nextObjective());
+                pendingNextObjectives.invalidate(key);
-                            flowObjectiveStore.putNextGroup(obj.nextObjective().id(), obj);
+                nextGrpList.forEach(nextGrp -> {
-                        });
+                    log.info("Group service {} group key {} in device:{}. "
+                            + "Done implementing next objective: {} <<-->> gid:{}",
+                            (added) ? "ADDED" : "processed",
+                            key, deviceId, nextGrp.nextObjective().id(),
+                            Integer.toHexString(groupService.getGroup(deviceId, key)
+                                                .givenGroupId()));
+                    pass(nextGrp.nextObjective());
+                    flowObjectiveStore.putNextGroup(nextGrp.nextObjective().id(), nextGrp);
+                    // check if addBuckets waiting for this completion
+                    NextObjective pendBkt = pendingBuckets
+                                                .remove(nextGrp.nextObjective().id());
+                    if (pendBkt != null) {
+                        addBucketToGroup(pendBkt, nextGrp);
                     }
-                }
+                });
-            });
+            }
         }
     }
@@ -1682,31 +1885,7 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
             log.trace("received group event of type {}", event.type());
             if (event.type() == GroupEvent.Type.GROUP_ADDED) {
                 GroupKey key = event.subject().appCookie();
-                // first check for group chain
+                processPendingGroupsOrNextObjectives(key, true);
-                Set<GroupChainElem> gceSet = pendingGroups.remove(key);
-                if (gceSet != null) {
-                    for (GroupChainElem gce : gceSet) {
-                        log.info("group ADDED with group key {} .. "
-                                + "Processing next group in group chain with group key {}",
-                                key,
-                                gce.groupDescription.appCookie());
-                        processGroupChain(gce);
-                    }
-                } else {
-                    List<OfdpaNextGroup> objList = pendingNextObjectives.getIfPresent(key);
-                    if (objList != null) {
-                        pendingNextObjectives.invalidate(key);
-                        objList.forEach(obj -> {
-                            log.info("group ADDED with key {} in dev {}.. Done implementing next "
-                                    + "objective: {} <<-->> gid:{}",
-                                    key, deviceId, obj.nextObjective().id(),
-                                    Integer.toHexString(groupService.getGroup(deviceId, key)
-                                                        .givenGroupId()));
-                            pass(obj.nextObjective());
-                            flowObjectiveStore.putNextGroup(obj.nextObjective().id(), obj);
-                        });
-                    }
-                }
             }
         }
     }
@@ -1714,7 +1893,7 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
     /**
      * Represents an entire group-chain that implements a Next-Objective from
      * the application. The objective is represented as a list of deques, where
-     * each deque can is a separate chain of groups.
+     * each deque is a separate chain of groups.
      * <p>
      * For example, an ECMP group with 3 buckets, where each bucket points to
      * a group chain of L3 Unicast and L2 interface groups will look like this:
@@ -1765,10 +1944,13 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
     private class GroupChainElem {
         private GroupDescription groupDescription;
         private AtomicInteger waitOnGroups;
+        private boolean addBucketToGroup;
-        GroupChainElem(GroupDescription groupDescription, int waitOnGroups) {
+        GroupChainElem(GroupDescription groupDescription, int waitOnGroups,
+                       boolean addBucketToGroup) {
             this.groupDescription = groupDescription;
             this.waitOnGroups = new AtomicInteger(waitOnGroups);
+            this.addBucketToGroup = addBucketToGroup;
         }
         /**
@@ -1788,6 +1970,7 @@ public class OFDPA2Pipeline extends AbstractHandlerBehaviour implements Pipeline
             return (Integer.toHexString(groupDescription.givenGroupId()) +
                     " groupKey: " + groupDescription.appCookie() +
                     " waiting-on-groups: " + waitOnGroups.get() +
+                    " addBucketToGroup: " + addBucketToGroup +
                     " device: " + deviceId);
         }
     }