[e2e] 64-bit timestamps?

William Allen Simpson william.allen.simpson at gmail.com
Wed Sep 9 01:18:50 PDT 2009

Lars Eggert wrote:
> On 2009-9-9, at 1:24, David P. Reed wrote:
>> In regard to DNS security issues, I suggest reading Appendix B of RFC 
>> 1323 on whether PAWS helps. (I quote B.2 below).
> FYI, the TCPM working group is currently working on an update to RFC 
> 1323 (http://tools.ietf.org/html/draft-ietf-tcpm-1323bis) and would be 
> interested in receiving feedback on the current draft.
Thank you, I've already indicated that I'm aware of that draft
(although the other poster apparently was not).

Nothing there discusses 64-bit timestamps.

Anyway, looking at the existing code, it seems relatively easy expanding
to 64-bit timestamps by zeroing the first 32 bits.  Perhaps in the future
somebody will find the extension useful.

The negotiation is relatively straightforward.  <SYN> carries 32-bits
plus another 32-bits of zero (as usual).  <SYN,ACK> carries a full 64-bit
timestamp, and the original <SYN> sender merely calculates RTT from its
own saved timestamp in the old-fashioned way (Karn's algorithm).
<ACK>+data carries two full 64-bit timestamps, easily distinguished.

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