[tor-bugs] #7228 [Ooni]: Detect if the client is behind NAT

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#7228: Detect if the client is behind NAT
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 Reporter:  hellais      |          Owner:  hellais
     Type:  enhancement  |         Status:  new    
 Priority:  minor        |      Milestone:         
Component:  Ooni         |        Version:         
 Keywords:  oonib        |         Parent:         
   Points:               |   Actualpoints:         
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 In #6074 we thought that it would be nice to be able to detect if the
 client running an OONI-probe test is behind NAT.

 Doing some very summary research a possible approach is detailed in
 RFC3947 (http://www.ietf.org/rfc/rfc3947.txt) section 3.2.
 The idea is that the client and server send the packets they send and
 receive. If there is a mismatch between these then somewhere along the
 path either the DST/SRC ip:port pair has changed and then NAT is present.

 This should be implemented in both the OONI client and the OONI backend.

 A technique that does not require having a backend would be ideal.

 Phrack #63 contains a technique for detecting NAT based on TCP timestamp
 fingerprints: http://www.phrack.org/issues.html?id=3&issue=63

 A tool that probably is not that relevant is masquet
 http://toxygen.net/misc/. It detects devices that may be natted on the
 local network based on the TTLs of packets and port numbers.

-- 
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/7228>
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