Reported by Ovidiu Poncea on the ns-developers list:

-----

So, if you have the action OFPP_FLOOD and the received packet is not coming
into port 0 of the switch then the packet will be flooded on all ports
including the receiving port - which is very bad specially if you have
broadcasts as packets will get replicated indefinitely (ARP req for e.g.).
This is caused by a missing ntohs(). The ReceivePacketOut() gets 0 if the
input port is 0 and it works but 512 if the input port is 1 and we don't
have this port.

Oh, and I'm using 3.20 but it's still present in ns3-dev.

Here is my patch:

Fix flooding of packets on input port, for packets received on in!=0

Packets that were not received on port zero were also flooded on input.
Because htons(0) will return 0 it works for packets coming in on port 0.
Seems that someone encountered some issues and left a trail of 
commented modifications - I left some of them unmodified as they 
seems unrelated to this issue.

ns-3.20/src/openflow/model/openflow-switch-net-device.cc | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/ns-3.20/src/openflow/model/openflow-switch-net-device.cc
b/ns-3.20/src/openflow/model/openflow-switch-net-device.cc
index 9071ed1..65c4711 100644
--- a/ns-3.20/src/openflow/model/openflow-switch-net-device.cc
+++ b/ns-3.20/src/openflow/model/openflow-switch-net-device.cc
@@ -1164,7 +1164,7 @@ OpenFlowSwitchNetDevice::ReceivePacketOut (const void
*msg)
     }

   sw_flow_key key;
-  flow_extract (buffer, opo->in_port, &key.flow); // ntohs(opo->in_port)
+  flow_extract (buffer, ntohs(opo->in_port), &key.flow); //
ntohs(opo->in_port)

   uint16_t v_code = ofi::ValidateActions (&key, opo->actions, actions_len);
   if (v_code != ACT_VALIDATION_OK)
@@ -1307,7 +1307,7 @@ OpenFlowSwitchNetDevice::AddFlow (const ofp_flow_mod
*ofm)
         { 
           sw_flow_key key;
           flow_used (flow, buffer);
-          flow_extract (buffer, ofm->match.in_port, &key.flow); //
ntohs(ofm->match.in_port);
+          flow_extract (buffer, ntohs(ofm->match.in_port), &key.flow); //
ntohs(ofm->match.in_port);
           ofi::ExecuteActions (this, ofm->buffer_id, buffer, &key,
ofm->actions, actions_len, false);
           ofpbuf_delete (buffer);
         }
@@ -1348,7 +1348,7 @@ OpenFlowSwitchNetDevice::ModFlow (const ofp_flow_mod
*ofm)
       if (buffer)
         {
           sw_flow_key skb_key;
-          flow_extract (buffer, ofm->match.in_port, &skb_key.flow); //
ntohs(ofm->match.in_port);
+          flow_extract (buffer, ntohs(ofm->match.in_port), &skb_key.flow);
// ntohs(ofm->match.in_port);
           ofi::ExecuteActions (this, ofm->buffer_id, buffer, &skb_key,
ofm->actions, actions_len, false);
           ofpbuf_delete (buffer);
         }