Network Working Group Toerless Eckert Internet Draft Eric C. Rosen (editor) Expiration Date: August 2007 Cisco Systems, Inc. Updates RFCs 3032 and 4023 Rahul Aggarwal Yakov Rekhter Juniper Networks, Inc. February 2007 MPLS Multicast Encapsulations draft-ietf-mpls-multicast-encaps-03.txt Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. Abstract RFC 3032 established two data link layer codepoints for MPLS: one to indicate that the data link layer frame is carrying an MPLS unicast packet, and the other to indicate that the data link layer frame is carrying an MPLS multicast packet. This specification updates RFC3032 by redefining the meaning of these two codepoints. The former "multicast codepoint" is now to be used only on multiaccess media, and it is to mean "the top label of the following label stack is an upstream-assigned label". The former "unicast codepoint" is to Eckert, et al. [Page 1] Internet Draft draft-ietf-mpls-multicast-encaps-03.txt February 2007 be used in all other cases. Whether the data link layer payload is a unicast MPLS packet or a multicast MPLS packet is now to be determined by looking up the top label, rather than by the codepoint. RFC3032 does not specify the destination address to be placed in the "MAC DA" field of an ethernet frame which carries an MPLS multicast packet. This document provides that specification. This document updates RFC 3032 and RFC 4023. Contents 1 Introduction ......................................... 2 2 Upstream-Assigned vs. Downstream-Assigned ............ 3 3 Ethernet Codepoints .................................. 5 4 PPP Protocol Field ................................... 6 5 GRE Protocol Type .................................... 6 6 IP Protocol Number ................................... 6 7 Ethernet MAC DA for Multicast MPLS ................... 7 8 IANA Considerations .................................. 7 9 Security Considerations .............................. 7 10 Normative References ................................. 7 11 Informative References ............................... 8 12 Authors' Addresses ................................... 8 13 Full Copyright Statement ............................. 8 14 Intellectual Property ................................ 9 1. Introduction RFC 3031 defines the "Next Hop Label Forwarding Entry" (NHLFE). The NHLFE for a particular label maps the label into a next hop (among other things). When an MPLS packet is received, its top label is mapped to an NHLFE, and the packet is sent to the next hop specified by the NHLFE. We define a particular MPLS label to be a "multicast label" in a particular context if the NHLFE to which it is mapped in that context specifies a set of next hops, with the semantics that the packet is to be replicated, and a copy of the packet sent to each of the specified next hops. Note that this definition accommodates the case where the set of next hops contains a single member. What makes a Eckert, et al. [Page 2] Internet Draft draft-ietf-mpls-multicast-encaps-03.txt February 2007 label a multicast label in a particular context is the semantics attached to the set, i.e., the intention to replicate the packet and transmit to all members of the set if the set has more than one member. RFC 3032 established two data link layer codepoints for MPLS: one to indicate that the data link layer frame is carrying an MPLS unicast packet, and the other to indicate that the data link layer frame is carrying an MPLS multicast packet. The term "multicast packet" is not precisely defined in RFC 3032, though one may presume that the "multicast" codepoint is intended to identify the packet's top label as a multicast label. However, the multicast codepoint has never been deployed, and further development of the procedures for MPLS multicast have shown that, while there is a need for two codepoints, the use of the two codepoints is not properly captured by RFC3032. In particular, there is no need for the codepoint to indicate whether the top MPLS label is a multicast label. When the receiver of an MPLS packet looks up the top label, the NHLFE will specify whether the label is a multicast label or not. This document updates RFC 3032 and RFC 4023 by re-specifying the use of the codepoints. While RFC 3032 allows an MPLS packet to be carried in an ethernet multicast frame, it fails to specify how the Medium Access Layer Destination Address (MAC DA) field is to be set in that case. This document provides that specification. 2. Upstream-Assigned vs. Downstream-Assigned According to RFC 3031, if two MPLS Label Switching Routers (LSRs) are adjacent in a label switched path (LSP), with respect to that LSP, one of them may be called the "upstream" LSR and the other the "downstream" LSR. Call these Ru and Rd respectively. Before Ru can send an MPLS packet to Rd with label L at the top of the label stack, Ru and Rd must agree on the Forwarding Equivalence Class (FEC) which is bound to L. A particular binding of L to FEC F is called a "downstream-assigned" binding if the binding is first made by Rd and then advertised to Ru. If the binding is first made by Ru and then advertised to Rd, it is called an "upstream-assigned" binding. If Ru and RD are LSP adjacencies, then they transmit a MPLS packet to each other through one of the following mechanisms: Eckert, et al. [Page 3] Internet Draft draft-ietf-mpls-multicast-encaps-03.txt February 2007 1. by putting the MPLS packet in a data link layer frame and transmitting the frame 2. by transmitting the MPLS packet through an MPLS tunnel, i.e., by pushing an additional label (or labels) onto the label stack, and then invoking mechanism 1, 3. by transmitting the MPLS packet through an IP-based tunnel (e.g., via RFC 4023), and then invoking mechanisms 1 and/or 2. In short, an MPLS packet is transmitted either through a data link or through an MPLS tunnel or through an IP tunnel. In any of those cases, when the packet emerges through the tunnel, the downstream LSR must know whether the label that now appears at the top of the label stack has an upstream-assigned label binding or a downstream-assigned label binding. For convenience, we will speak of a label with an upstream-assigned label binding as an "upstream-assigned label". Unicast labels MUST be downstream-assigned. Under certain conditions, specified below, multicast labels MAY be upstream-assigned. The ability to use upstream-assigned labels is an OPTIONAL feature. Upstream-assigned labels MUST NOT be used unless it is known that the downstream LSR supports them. How this is known is outside the scope of this document. We discuss three different types of data link or tunnel: - Point-to-Point. A point-to-point data link or tunnel associates two systems, such that transmissions on that link or tunnel made by the one are received by the other, and only by the other. When an MPLS packet is transmitted on a point-to-point data link or tunnel, its top label (before applying the data link or tunnel encapsulation) MUST be a downstream-assigned label. - Point-to-Multipoint. A point-to-multipoint link or tunnel associates n systems, such that only one of them can transmit onto the link or tunnel, and the transmissions may be received by the other n-1 systems. The top labels (before applying the data link or tunnel encapsulation) of all MPLS packets which are transmitted on a particular point-to-multipoint data link or tunnel MUST be of the same type; either all upstream-assigned or all downstream- assigned. This means that all the receivers on the MPLS or IP tunnel must know a priori whether upstream-assigned or downstream-assigned labels are being used in the tunnel. How Eckert, et al. [Page 4] Internet Draft draft-ietf-mpls-multicast-encaps-03.txt February 2007 this is known is outside the scope of this document. - Multipoint-to-Multipoint. A multipoint-to-multipoint link or tunnel associates n systems, such that any of them can transmit on the link or tunnel, and the transmissions may be received by the other n-1 systems. If MPLS packets are transmitted on a particular multipoint-to- multipoint link or tunnel, one of the following scenarios applies: 1. It is known (by methods outside the scope of this document) that the top label of every MPLS packet on the link or tunnel is downstream-assigned 2. It is known (by methods outside the scope of this document) that the top label of every MPLS packet on the link or tunnel is upstream-assigned 3. Some MPLS packets on the link may have upstream-assigned top labels while some may have downstream-assigned top labels If (and only if) the third scenario applies, the data link or tunnel encapsulation MUST provide a codepoint which specifies whether the top label of the encapsulated MPLS packet is upstream-assigned or downstream-assigned. If a particular type of data link or tunnel does not provide such a codepoint, then the third scenario MUST NOT be used. The remainder of this document specifies procedures for setting the data link layer codepoints and address fields. 3. Ethernet Codepoints Ethernet is an example of a multipoint-to-multipoint data link. Ethertype 0x8847 is used whenever a unicast ethernet frame carries an MPLS packet. Ethertype 0x8847 is also used whenever a multicast ethernet frame carries an MPLS packet, EXCEPT for the case where the top label of the MPLS packet has been upstream-assigned. Ethertype 0x8848, formerly known as the "MPLS multicast codepoint", is to be used only when an MPLS packet whose top label is upstream- assigned is carried in a multicast ethernet frame. Eckert, et al. [Page 5] Internet Draft draft-ietf-mpls-multicast-encaps-03.txt February 2007 4. PPP Protocol Field PPP is an example of a point-to-point data link. When a PPP frame is carrying an MPLS packet, the PPP Protocol field is always set to 0x0281. 5. GRE Protocol Type RFC 4023 is modified as described below. If the IP destination address of the GRE encapsulation is a unicast IP address, then the ethertype value 0x8847 MUST be used in all cases for the MPLS-in-GRE encapsulation. If the IP destination address of the GRE encapsulation is a multicast IP address, then: - the ethertype value 0x8847 MUST be used when the top label of the encapsulated MPLS packet is downstream-assigned, - the ethertype value 0x8848 MUST be used when the top label of the encapsulated MPLS packet is upstream-assigned. Through procedures which are outside the scope of this specification, it may be known that if the destination address of a GRE packet is a multicast IP address, then the top label of the GRE payload is upstream-assigned. In such a case, the occurrence of the 8847 codepoint in a GRE packet with a multicast destination IP address MUST be considered an error, and the packet MUST be discarded. 6. IP Protocol Number RFC 4023 is modified as follows: the IPv4 Protocol Number field or the IPv6 Next Header field is always set to 137, whether or not the encapsulated MPLS packet is an MPLS multicast packet. If the IP destination address of the IP encapsulation is an IP multicast address, the IP tunnel may be considered to be a point-to- multipoint tunnel or a multipoint-to-multipoint tunnel. In either case, either all encapsulated MPLS packets in the particular tunnel have a downstream-assigned label at the top of the stack, or all encapsulated MPLS packets in that tunnel have an upstream-assigned label at the top of the stack. The means by which this is determined for a particular tunnel is outside the scope of this specification. Eckert, et al. [Page 6] Internet Draft draft-ietf-mpls-multicast-encaps-03.txt February 2007 7. Ethernet MAC DA for Multicast MPLS When a multicast MPLS packet is carried in a multicast ethernet frame, the Destination MAC Address shall be set to the value 01-00- 5e-8a-bc-de, where abcde is the twenty-bit (5-nibble) value of the topmost MPLS label of the MPLS packet. 8. IANA Considerations IANA already owns the set of ethernet multicast addresses in the range 01-00-5e-00-00-00 to 01-00-5e-ff-ff-ff. Addresses in the range 01-00-5e-00-00-00 to 01-00-5e-7f-ff-ff are reserved for use when an ethernet multicast frame carries an IP multicast packet. IANA shall reserve ethernet addresses in the range 01-00-5e-80-00-00 to 01-00- 5e-8f-ff-ff for use when an ethernet multicast frame carries an MPLS multicast packet. 9. Security Considerations The security considerations of RFC 3032 and RFC 4023 apply. Malicious changing of the codepoint may result in loss or misrouting of packets. However, altering the codepoint without also altering the label does not result in a predictable effect. Malicious alteration of the MAC DA on an ethernet can result in packets being received by a third party, rather than by the intended recipient. 10. Normative References [RFC3031] "Multiprotocol Label Switching Architecture", Rosen, Viswanathan, Callon, January 2001 [RFC3032] "MPLS Label Stack Encoding", Rosen, et. al., January 2001 [RFC4023] "Encapsulating MPLS in IP or GRE", Worster, Rekhter, Rosen, March 2005 Eckert, et al. [Page 7] Internet Draft draft-ietf-mpls-multicast-encaps-03.txt February 2007 11. Informative References 12. Authors' Addresses Toerless Eckert Cisco Systems, Inc. 170 Tasman Drive San Jose, CA, 95134 Email: eckert@cisco.com Eric C. Rosen Cisco Systems, Inc. 1414 Massachusetts Avenue Boxborough, MA 01719 Email: erosen@cisco.com Rahul Aggarwal Juniper Networks 1194 North Mathilda Ave. Sunnyvale, CA 94089 Email: rahul@juniper.net Yakov Rekhter Juniper Networks 1194 North Mathilda Ave. Sunnyvale, CA 94089 Email: yakov@juniper.net 13. Full Copyright Statement Copyright (C) The IETF Trust (2007). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. This document and the information contained herein are provided on an "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND Eckert, et al. [Page 8] Internet Draft draft-ietf-mpls-multicast-encaps-03.txt February 2007 THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. 14. Intellectual Property The IETF takes no position regarding the validity or scope of any Intellectual Property Rights or other rights that might be claimed to pertain to the implementation or use of the technology described in this document or the extent to which any license under such rights might or might not be available; nor does it represent that it has made any independent effort to identify any such rights. Information on the procedures with respect to rights in RFC documents can be found in BCP 78 and BCP 79. Copies of IPR disclosures made to the IETF Secretariat and any assurances of licenses to be made available, or the result of an attempt made to obtain a general license or permission for the use of such proprietary rights by implementers or users of this specification can be obtained from the IETF on-line IPR repository at http://www.ietf.org/ipr. The IETF invites any interested party to bring to its attention any copyrights, patents or patent applications, or other proprietary rights that may cover technology that may be required to implement this standard. Please address the information to the IETF at ietf- ipr@ietf.org. Eckert, et al. [Page 9]