Tunnelling of Explicit Congestion Notification (RFC6040)
Original Publication Date: 2010-Nov-01
Included in the Prior Art Database: 2010-Dec-01
Internet Society Requests For Comment (RFCs)
Explicit congestion notification (ECN [RFC3168]) allows a forwarding element (e.g., a router) to notify the onset of congestion without having to drop packets. Instead, it can explicitly mark a proportion of packets in the two-bit ECN field in the IP header (Table 1 recaps the ECN codepoints).
Internet Engineering Task Force (IETF) B. Briscoe Request for Comments: 6040 BT Updates: 3168, 4301, 4774 November 2010 Category: Standards Track ISSN: 2070-1721
Tunnelling of Explicit Congestion Notification
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
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at http://www.rfc-editor.org/info/rfc6040.
Briscoe Standards Track [Page 1]
RFC 6040 ECN Tunnelling November 2010
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