## This file is part of Scapy
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## See http://www.secdev.org/projects/scapy for more informations
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## Copyright (C) Philippe Biondi <phil@secdev.org>
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## This program is published under a GPLv2 license
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"""
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L2TP (Layer 2 Tunneling Protocol) for VPNs.
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[RFC 2661]
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"""
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import struct
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from scapy.packet import *
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from scapy.fields import *
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from scapy.layers.inet import UDP
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from scapy.layers.ppp import PPP
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class L2TP(Packet):
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name = "L2TP"
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fields_desc = [
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FlagsField("hdr", 0, 12, ['res00', 'res01', 'res02', 'res03', 'priority', 'offset',
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'res06', 'sequence', 'res08', 'res09', 'length', 'control']),
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BitEnumField("version", 2, 4, {2: 'L2TPv2'}),
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ConditionalField(ShortField("len", 0),
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lambda pkt: pkt.hdr & 'control+length'),
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ShortField("tunnel_id", 0),
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ShortField("session_id", 0),
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ConditionalField(ShortField("ns", 0),
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lambda pkt: pkt.hdr & 'sequence+control'),
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ConditionalField(ShortField("nr", 0),
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lambda pkt: pkt.hdr & 'sequence+control'),
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ConditionalField(
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PadField(ShortField("offset", 0), 4, b"\x00"),
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lambda pkt: not (pkt.hdr & 'control') and pkt.hdr & 'offset'
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)
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]
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def post_build(self, pkt, pay):
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if self.len is None:
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l = len(pkt)+len(pay)
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pkt = pkt[:2]+struct.pack("!H", l)+pkt[4:]
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return pkt+pay
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bind_layers( UDP, L2TP, sport=1701, dport=1701)
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bind_layers( L2TP, PPP, )
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