1 ## This file is part of Scapy 2 ## See http://www.secdev.org/projects/scapy for more informations 3 ## Copyright (C) Philippe Biondi <phil (at] secdev.org> 4 ## This program is published under a GPLv2 license 5 6 """ 7 L2TP (Layer 2 Tunneling Protocol) for VPNs. 8 9 [RFC 2661] 10 """ 11 12 import struct 13 14 from scapy.packet import * 15 from scapy.fields import * 16 from scapy.layers.inet import UDP 17 from scapy.layers.ppp import PPP 18 19 20 class L2TP(Packet): 21 name = "L2TP" 22 fields_desc = [ 23 FlagsField("hdr", 0, 12, ['res00', 'res01', 'res02', 'res03', 'priority', 'offset', 24 'res06', 'sequence', 'res08', 'res09', 'length', 'control']), 25 BitEnumField("version", 2, 4, {2: 'L2TPv2'}), 26 27 ConditionalField(ShortField("len", 0), 28 lambda pkt: pkt.hdr & 'control+length'), 29 ShortField("tunnel_id", 0), 30 ShortField("session_id", 0), 31 ConditionalField(ShortField("ns", 0), 32 lambda pkt: pkt.hdr & 'sequence+control'), 33 ConditionalField(ShortField("nr", 0), 34 lambda pkt: pkt.hdr & 'sequence+control'), 35 ConditionalField( 36 PadField(ShortField("offset", 0), 4, b"\x00"), 37 lambda pkt: not (pkt.hdr & 'control') and pkt.hdr & 'offset' 38 ) 39 ] 40 41 def post_build(self, pkt, pay): 42 if self.len is None: 43 l = len(pkt)+len(pay) 44 pkt = pkt[:2]+struct.pack("!H", l)+pkt[4:] 45 return pkt+pay 46 47 48 bind_layers( UDP, L2TP, sport=1701, dport=1701) 49 bind_layers( L2TP, PPP, ) 50
