Subject: [Tsvwg] update on ECN

From: Sally Floyd <[email-masked]>
Date: Sat, 04 Nov 2000 14:32:27 -0800

KK and I have submitted a new internet draft on "TCP with ECN: The
Treatment of Retransmitted Data Packets".  This specifies that the
TCP data sender should not set the ECT bit on retransmitted packets,
for greater robustness against denial of service attacks.

A local copy of the draft is available at:
 http://www.aciri.org/floyd/papers/draft-ietf-tsvwg-tcp-ecn-00.txt
or:
 http://www.aciri.org/floyd/papers/draft-ietf-tsvwg-tcp-ecn-00.ps

We would welcome any feedback on this.  This will be discussed at
the TSVWG at the San Diego IETF.  Any discussion of this draft
should take place on the TSVWG mailing list.

We have also talked with Scott Bradner and Allison Mankin, the
Transport Area ADs, and they are agreed that it is time to put all
of the ECN material into a single internet-draft, and then last-call
that document for Proposed Standard.  So hopefully we will soon
have a single internet-draft incorporating RFC 2481, the relevant
new language from draft-ietf-tsvwg-tcp-ecn-00.txt, and some paragraphs
about SYN and SYN-ACK packets, into a single internet-draft to
submit for Proposed Standard.

Many thanks,
- Sally
--------------------------------
http://www.aciri.org/floyd/
--------------------------------

Abstract of draft-ietf-tsvwg-tcp-ecn-00.txt:

   This document makes recommendations for the use of ECN with
   retransmitted data packets, for an ECN-capable TCP connection.  This
   document supplements RFC 2481 [RFC2481], which did not address the
   issue of retransmitted data packets.  This document recommends that
   for ECN-capable TCP implementations, the ECT bit (ECN-Capable
   Transport) in the IP header SHOULD NOT be set on retransmitted data
   packets, and that the TCP data receiver SHOULD ignore the ECN field
   on arriving data packets that are outside of the receiver's current
   window.  This is for greater security against denial-of-service
   attacks.

   In addition, this document recommends that the CWR bit (Congestion
   Window Reduced) in the TCP header SHOULD NOT be set on retransmitted
   packets.  When the TCP data sender is ready to set the CWR bit after
   reducing the congestion window, it SHOULD set the CWR bit on the
   first new data packet that it transmits.

------- End of Forwarded Message

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