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On the generation of TCP timestamps (draft-gont-tcpm-tcp-timestamps)

On the generation of TCP timestamps (draft-gont-tcpm-tcp-timestamps). Fernando Gont on behalf of UK CPNI 73 rd IETF meeting, November 16-21, 2008 Minneapolis, MN, USA. Overview. RFC1323 describes the generation of TCP timestamps

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On the generation of TCP timestamps (draft-gont-tcpm-tcp-timestamps)

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  1. On the generation of TCP timestamps(draft-gont-tcpm-tcp-timestamps) Fernando Gont on behalf of UK CPNI 73rd IETF meeting, November 16-21, 2008 Minneapolis, MN, USA

  2. Overview • RFC1323 describes the generation of TCP timestamps • It states that they must be monotonicaly-increasing for a given connections • However, it does not require timestamps to be monotonically-increasing accross TCP connections (protection against stale segments from previous connections is provided by the TIME-WAIT state and the quiet-time concept). • However, timestamps that are monotonically-increasing accross TCP connections can be useful: • They allow the implementation of heuristics for handling incomming connection request when there’s a previous incarnation of the same connection in the TIME-WAIT state • This is similar to what BSD-derived implementations have done with TCP ISNs, but probably works better than the TCP SEQ hack.

  3. So… what is this document about? • It describes an algorithm for selecting TCP timestamps such that • The TCP timestamps are monotonically-increasing accross TCP connections • The chances of an off-path attacker for guessing the TCP timestamps used for future connections are reduced • It describes the heuristics that can be implemented based on the TCP timestamps when processing incoming connection requests. • This already ships with Linux

  4. Moving forward Should we adopt this document as a wg item?

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