RFC 6040 on Tunnelling of Explicit Congestion Notification

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        RFC 6040

        Title:      Tunnelling of Explicit Congestion Notification 
        Author:     B. Briscoe
        Status:     Standards Track
        Stream:     IETF
        Date:       November 2010
        Mailbox:    [e-mail]
        Pages:      35
        Characters: 89412
        Updates:    RFC3168, RFC4301, RFC4774

        I-D Tag:    draft-ietf-tsvwg-ecn-tunnel-10.txt

        URL:        http://www.rfc-editor.org/rfc/rfc6040.txt

This document redefines how the explicit congestion notification
(ECN) field of the IP header should be constructed on entry to and
exit from any IP-in-IP tunnel.  On encapsulation, it updates RFC 3168
to bring all IP-in-IP tunnels (v4 or v6) into line with RFC 4301
IPsec ECN processing.  On decapsulation, it updates both RFC 3168 and
RFC 4301 to add new behaviours for previously unused combinations of
inner and outer headers.  The new rules ensure the ECN field is
correctly propagated across a tunnel whether it is used to signal one
or two severity levels of congestion; whereas before, only one
severity level was supported.  Tunnel endpoints can be updated in any
order without affecting pre-existing uses of the ECN field, thus
ensuring backward compatibility.  Nonetheless, operators wanting to
support two severity levels (e.g., for pre-congestion notification --
PCN) can require compliance with this new specification.  A thorough
analysis of the reasoning for these changes and the implications is
included.  In the unlikely event that the new rules do not meet a
specific need, RFC 4774 gives guidance on designing alternate ECN
semantics, and this document extends that to include tunnelling
issues.  [STANDARDS-TRACK]

This document is a product of the Transport Area Working Group Working Group of the IETF.

This is now a Proposed Standard Protocol.

STANDARDS TRACK: This document specifies an Internet standards track
protocol for the Internet community,and requests discussion and suggestions
for improvements.  Please refer to the current edition of the Internet
Official Protocol Standards (STD 1) for the standardization state and
status of this protocol.  Distribution of this memo is unlimited.

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