Adding in a P4 example that implements the Axon source-routed Ethernet protocol.

examples/axon/receive.py

@@ -0,0 +1,60 @@
+#!/usr/bin/python
+
+# Copyright 2013-present Barefoot Networks, Inc. 
+# 
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+# 
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+#
+# Author: Brent Stephens 
+#
+
+from scapy.all import sniff, sendp
+from scapy.all import Packet
+from scapy.all import ShortField, IntField, LongField, BitField
+
+import sys
+import struct
+
+def handle_pkt(pkt):
+    pkt = str(pkt)
+    if len(pkt) < 13: return
+    preamble = pkt[:8]
+    preamble_exp = "\x00" * 8
+    if preamble != preamble_exp: return
+    axonType = pkt[8]
+    if axonType != "\x00": return
+    axonLength = struct.unpack("!H", pkt[9:11])[0]
+    fwdHopCount = struct.unpack("B", pkt[11])[0]
+    revHopCount = struct.unpack("B", pkt[12])[0]
+    if fwdHopCount != 0:
+        print 'received a packet that has not been fully forwarded'
+    if revHopCount <= 0:
+        print 'received a packet that has no reverse hops'
+    if axonLength != 2 + fwdHopCount + revHopCount:
+        print 'received a packet with either an incorrect axonLength, fwdHopCount, or revHopCount'
+    msg = pkt[11 + axonLength:]
+    print msg
+    sys.stdout.flush()
+
+    # Optional debugging
+    #print 'axonLength:', axonLength
+    #print 'fwdHopCount:', fwdHopCount
+    #print 'revHopCount:', revHopCount
+    #print pkt
+
+def main():
+    sniff(iface = "eth0",
+          prn = lambda x: handle_pkt(x))
+
+if __name__ == '__main__':
+    main()