Updates to basic_tunnel and basic (#78)

* Adding initial implementation of basic_encap example

* Updated basic_encap example to count the number of valid packets

* Updated basic_encap example to put encapsulation layer after Ethernet
header.

* Added solution file for basic_encap example

* Changed the name of the basic_encap example to basic_tunnel and called
the new header myTunnel. Also changed the myTunnel field names slightly.

* Updated the README file for the basic_tunnel exercise. Also added topo.pdf
image to serve as a reference during implementation.

* Updated basic/README.md to point to basic_tunnel as the next exercise.

* Updated the README for basic to point to basic_tunnel.

Updated the starter code for basic_tunnel to look like basic
solution with todo comments.

Updated send.py and receive.py to be able to send both plain IP
packets and tunneled IP packets.

Updated basic_tunnel.p4 to have same control flow as p4runtime
exercise.

P4D2_2017_Fall/exercises/basic/receive.py

@@ -6,7 +6,7 @@ import os
 from scapy.all import sniff, sendp, hexdump, get_if_list, get_if_hwaddr
 from scapy.all import Packet, IPOption
 from scapy.all import ShortField, IntField, LongField, BitField, FieldListField, FieldLenField
-from scapy.all import IP, UDP, Raw
+from scapy.all import IP, TCP, UDP, Raw
 from scapy.layers.inet import _IPOption_HDR
 
 def get_if():
@@ -34,10 +34,11 @@ class IPOption_MRI(IPOption):
                                    IntField("", 0),
                                    length_from=lambda pkt:pkt.count*4) ]
 def handle_pkt(pkt):
-    print "got a packet"
-    pkt.show2()
-#    hexdump(pkt)
-    sys.stdout.flush()
+    if TCP in pkt and pkt[TCP].dport == 1234:
+        print "got a packet"
+        pkt.show2()
+    #    hexdump(pkt)
+        sys.stdout.flush()
 
 
 def main():
@@ -45,7 +46,7 @@ def main():
     iface = ifaces[0]
     print "sniffing on %s" % iface
     sys.stdout.flush()
-    sniff(filter="tcp", iface = iface,
+    sniff(iface = iface,
           prn = lambda x: handle_pkt(x))
 
 if __name__ == '__main__':