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POParsing PPPoE Tags with Scapy
 

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    <p>I am trying to correctly dissect PPPoE Discovery packets with Scapy. Here's how Scapy displays example PADI packet:</p> <pre><code>&gt;&gt;&gt; p = Ether("\xff\xff\xff\xff\xff\xff\x08\x00'\xf3&lt;5\x88c\x11\t\x00\x00\x00\x0c\x01\x01\x00\x00\x01\x03\x00\x04\xe0\x07\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00") &gt;&gt;&gt; p.show() ###[ Ethernet ]### dst= ff:ff:ff:ff:ff:ff src= 08:00:27:f3:3c:35 type= 0x8863 ###[ PPP over Ethernet Discovery ]### version= 1L type= 1L code= PADI sessionid= 0x0 len= 12 ###[ Raw ]### load= '\x01\x01\x00\x00\x01\x03\x00\x04\xe0\x07\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00' </code></pre> <p>I want to parse that Raw payload. This payload is just a list PPPoE tags. Each tags consists of two byte code field, two byte length field and a value (it's length given by previous field, of course).</p> <p>This is my attempt at representing all this:</p> <pre><code>from scapy.all import * class PPPoETag(Packet): name = "PPPoE Tag" fields_desc = [ ShortEnumField('tag_type', None, {0x0000: 'End-Of-List', 0x0101: 'Service-Name', 0x0102: 'AC-Name', 0x0103: 'Host-Uniq', 0x0104: 'AC-Cookie', 0x0105: 'Vendor-Specific', 0x0110: 'Relay-Session-Id', 0x0201: 'Service-Name-Error', 0x0202: 'AC-System-Error', 0x0203: 'Generic-Error'}), FieldLenField('tag_len', None, length_of='tag_value', fmt='H'), StrLenField('tag_value', '', length_from=lambda pkt:pkt.tag_len)] def extract_padding(self, s): return '', s class PPPoED_Tags(Packet): name = "PPPoE Tag List" fields_desc = [ PacketListField('tag_list', None, PPPoETag) ] bind_layers(PPPoED, PPPoED_Tags, type=1) </code></pre> <p>Not quite sure if it's the right and best way. Any advice on improving?</p>
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      1. USMike Pennington
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    1. CONot really worth providing this as an answer since it doesn't specifically apply to Scapy, but dpkt has a slightly different approach that might give you some ideas here.. http://code.google.com/p/dpkt/source/browse/trunk/dpkt/pppoe.py
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    2. COAre you asking for general advice or do you have a specific question?
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      1. USMoshe
    3. CO@Moshe: my specific question was how to correctly parse PPPoE tags with Scapy. But in the end I have switched to parsing all information from PPPoE packet manually without any libraries, as it turns out to be pretty simple.
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