--- 1/draft-ietf-mpls-explicit-null-01.txt 2006-02-05 00:38:30.000000000 +0100 +++ 2/draft-ietf-mpls-explicit-null-02.txt 2006-02-05 00:38:30.000000000 +0100 @@ -1,26 +1,27 @@ - Network Working Group Eric C. Rosen Internet Draft Cisco Systems, Inc. -Expiration Date: October 2004 +Expiration Date: August 2005 Updates RFC 3032 - April 2004 + February 2005 Removing a Restriction on the use of MPLS Explicit NULL - draft-ietf-mpls-explicit-null-01.txt + draft-ietf-mpls-explicit-null-02.txt Status of this Memo - This document is an Internet-Draft and is in full conformance with - all provisions of Section 10 of RFC2026. + By submitting this Internet-Draft, I certify that any applicable + patent or other IPR claims of which I am aware have been disclosed, + or will be disclosed, and any of which I become aware will be + disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet-Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." @@ -32,32 +33,35 @@ Abstract The label stack encoding for MPLS (Multi-protocol Label Switching) defines a reserved label value known as "IPv4 Explicit NULL" and a reserved label value known as "IPv6 Explicit NULL". Previously, these labels were only legal when they occurred at the bottom of the MPLS label stack. This restriction is now removed, so that these label values may legally occur anywhere in the stack. + This document updates RFC 3032. + Contents 1 Introduction ......................................... 2 2 Detail of Change ..................................... 2 3 Reasons for Change ................................... 4 - 4 Security Considerations .............................. 5 - 5 Acknowledgments ...................................... 5 - 6 Normative References ................................. 6 - 7 Informative References ............................... 6 - 8 Author's Address ..................................... 6 - 9 Intellectual Property Notice ......................... 6 - 10 Copyright Notice ..................................... 7 + 4 Deployment Considerations ............................ 5 + 5 Security Considerations .............................. 6 + 6 Acknowledgments ...................................... 6 + 7 Normative References ................................. 6 + 8 Informative References ............................... 6 + 9 Author's Address ..................................... 6 + 10 Intellectual Property Statement ...................... 6 + 11 Full Copyright Statement ............................. 7 1. Introduction RFC 3032 defines a reserved label value known as "IPv4 Explicit NULL" and a reserved label value known as "IPv6 Explicit NULL". It states that these label values are only legal at the bottom of the MPLS label stack. However, no reason is given for this restriction. It has turned out that in practice there are some situations in which it is useful to send MPLS packets which have Explicit NULL occur @@ -171,105 +175,116 @@ of the Explicit Null label stack entry, and the tunneled Diff-Serv information will be carried in whatever is "below" the Explicit Null label stack entry, i.e., in the IP header DS bits or in the EXP bits of the next entry on the MPLS label stack. Naturally, this practice causes a problem if the Pipe Model LSP is being used to tunnel MPLS packets (i.e., if Condition L does not hold). With strict adherence to RFCs 3031 and 3036, this practice results in an MPLS packet where Explicit NULL is at the top of the label stack, even though it is not the only entry in the label - stack. However, RFC 3032 makes this packet illegal. Some - implementations simply transmit the illegal packet. Others try to - convert it to a legal packet by stripping off the Explicit NULL + stack. However, RFC 3032 makes this packet illegal. + + Some implementations simply transmit the illegal packet. Others try + to convert it to a legal packet by stripping off the Explicit NULL before transmitting it. However, that breaks the Pipe Model by - discarding the LSP Diff-Serv information. + discarding the LSP Diff-Serv information. It is conceivable that + there may be an implementation which drops the illegal packet + entirely; this would also break the Pipe Model, as it would lose not + only the LSP Diff-Serv information but the entire packet. Of course the LSP egress is not compelled to bind Explicit NULL to the tunnel's FEC; an ordinary label could be used instead. However, using Explicit NULL enables the egress to determine immediately (i.e., without need for lookup in the Label Information Base) that the further forwarding of the packet is to be determined by whatever is below the label. Avoiding this lookup can have favorable implications on forwarding performance. Removing the restriction that Explicit Null only occur at the bottom of the stack is the simplest way to facilitate the proper operation of the Pipe Model. -4. Security Considerations +4. Deployment Considerations + + Implementations which adhere to this specification will interoperate + correctly, and will correctly support the Pipe Model. + + Implementations which do not adhere to this specification may not + interoperate. In particular if a router advertises a binding of + Explicit NULL, and if that router has an upstream LDP peer which will + not transmit a packet that has multiple label stack entries with + Explicit Null at top of the stack, then it will not be possible to + use Explicit NULL to support the Pipe Model until the upstream LDP + peer is brought into compliance with this specification. + + It is possible that there may be a router implementation, preceding + this specification, which will discard any received packet with + multiple label stack entries and a top label value of Explicit Null. + It is advisable to configure any such routers so that they do not + advertise any bindings to Explicit Null. + +5. Security Considerations This document updates RFC 3032 by allowing Explicit NULL to occur at any position in the label stack. This modification does not impose any new security considerations beyond those discussed in RFC 3032. -5. Acknowledgments +6. Acknowledgments Thanks to Rahul Aggarwal, Francois LeFaucheur, Yakov Rekhter, and Dan Tappan for their helpful comments. -6. Normative References +7. Normative References [RFC3032] "MPLS Label Stack Encoding", Rosen, et. al., January 2001 -7. Informative References +8. Informative References [RFC3270] "Multi-Protocol Label Switching (MPLS) Support of Differentiated Services", Le Faucheur, et. al., May 2002 -8. Author's Address +9. Author's Address Eric C. Rosen Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough, MA 01719 Email: erosen@cisco.com -9. Intellectual Property Notice +10. 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