add support for encapsulating Ethernet frame in MPLS (#1047)

* add support for encapsulating Ethernet frame in MPLS with optional
control word per rfc 4448

* add import of ShortField in mpls.py to fix a ut failure

* add MPLS tests in test/regression.uts

* revert indentation fixes in mpls.py to perserve clean histry

scapy/contrib/mpls.py

@@ -16,12 +16,22 @@
 # scapy.contrib.status = loads
 
 from scapy.packet import Packet, bind_layers, Padding
-from scapy.fields import BitField,ByteField
+from scapy.fields import BitField,ByteField,ShortField
 from scapy.layers.inet import IP
 from scapy.layers.inet6 import IPv6
 from scapy.layers.l2 import Ether, GRE
 from scapy.compat import orb
 
+class EoMCW(Packet):
+    name = "EoMCW"
+    fields_desc = [ BitField("zero", 0, 4),
+                    BitField("reserved", 0, 12),
+                    ShortField("seq", 0) ]
+    def guess_payload_class(self, payload):
+        if len(payload) >= 1:
+            return Ether
+        return Padding
+
 class MPLS(Packet):
    name = "MPLS"
    fields_desc =  [ BitField("label", 3, 20),
@@ -38,8 +48,15 @@ class MPLS(Packet):
                return IP
            elif ip_version == 6:
                return IPv6
+           else:
+               if orb(payload[0]) == 0 and orb(payload[1]) == 0:
+                   return EoMCW
+               else:
+                   return Ether
        return Padding
 
 bind_layers(Ether, MPLS, type=0x8847)
 bind_layers(GRE, MPLS, proto=0x8847)
 bind_layers(MPLS, MPLS, s=0)
+bind_layers(MPLS, EoMCW)
+bind_layers(EoMCW, Ether, zero=0, reserved=0)

test/regression.uts

@@ -9492,7 +9492,7 @@ assert(pkt.ByteCount == 1)
 + MPLS tests
 
 = MPLS - build/dissection
-from scapy.contrib.mpls import MPLS
+from scapy.contrib.mpls import EoMCW, MPLS
 p1 = MPLS()/IP()/UDP()
 assert(p1[MPLS].s == 1)
 p2 = MPLS()/MPLS()/IP()/UDP()
@@ -9504,6 +9504,56 @@ p2[MPLS]
 p2[MPLS:1]
 p2[IP]
 
+= MPLS encapsulated Ethernet with CW - build/dissection
+p = Ether(dst="11:11:11:11:11:11", src="22:22:22:22:22:22")
+p /= MPLS(label=1)/EoMCW(seq=1234)
+p /= Ether(dst="33:33:33:33:33:33", src="44:44:44:44:44:44")/IP()
+p = Ether(raw(p))
+assert(p[EoMCW].zero == 0)
+assert(p[EoMCW].reserved == 0)
+assert(p[EoMCW].seq == 1234)
+
+=  MPLS encapsulated Ethernet without CW - build/dissection
+p = Ether(dst="11:11:11:11:11:11", src="22:22:22:22:22:22")
+p /= MPLS(label=2)/MPLS(label=1)
+p /= Ether(dst="33:33:33:33:33:33", src="44:44:44:44:44:44")/IP()
+p = Ether(raw(p))
+assert(p[Ether:2].type == 0x0800)
+
+try:
+    p[EoMCW]
+except IndexError:
+    ret = True
+else:
+    ret = False
+
+assert(ret)
+assert(p[Ether:2].type == 0x0800)
+
+= MPLS encapsulated IP - build/dissection
+p = Ether(dst="11:11:11:11:11:11", src="22:22:22:22:22:22")
+p /= MPLS(label=1)/IP()
+p = Ether(raw(p))
+
+try:
+    p[EoMCW]
+except IndexError:
+    ret = True
+else:
+    ret = False
+
+assert(ret)
+
+try:
+    p[Ether:2]
+except IndexError:
+    ret = True
+else:
+    ret = False
+
+assert(ret)
+
+p[IP]
 
 + Restore normal routes & Ifaces