--- 1/draft-ietf-mpls-sr-over-ip-02.txt 2019-03-03 11:13:09.558150896 -0800 +++ 2/draft-ietf-mpls-sr-over-ip-03.txt 2019-03-03 11:13:09.594151774 -0800 @@ -1,27 +1,27 @@ Network Working Group X. Xu Internet-Draft Alibaba, Inc Intended status: Standards Track S. Bryant -Expires: June 21, 2019 Huawei +Expires: September 4, 2019 Huawei A. Farrel Old Dog Consulting S. Hassan Cisco W. Henderickx Nokia Z. Li Huawei - December 18, 2018 + March 3, 2019 SR-MPLS over IP - draft-ietf-mpls-sr-over-ip-02 + draft-ietf-mpls-sr-over-ip-03 Abstract MPLS Segment Routing (SR-MPLS) is an MPLS data plane-based source routing paradigm in which the sender of a packet is allowed to partially or completely specify the route the packet takes through the network by imposing stacked MPLS labels on the packet. SR-MPLS could be leveraged to realize a source routing mechanism across MPLS, IPv4, and IPv6 data planes by using an MPLS label stack as a source routing instruction set while preserving backward compatibility with @@ -39,25 +39,25 @@ Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. 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." - This Internet-Draft will expire on June 21, 2019. + This Internet-Draft will expire on September 4, 2019. Copyright Notice - Copyright (c) 2018 IETF Trust and the persons identified as the + Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as @@ -74,35 +74,36 @@ 3.2.1. Packet Forwarding with Penultimate Hop Popping . . . 8 3.2.2. Packet Forwarding without Penultimate Hop Popping . . 9 3.2.3. Additional Forwarding Procedures . . . . . . . . . . 10 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 5. Security Considerations . . . . . . . . . . . . . . . . . . . 12 6. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 12 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 13 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 13 8.1. Normative References . . . . . . . . . . . . . . . . . . 13 8.2. Informative References . . . . . . . . . . . . . . . . . 14 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16 1. Introduction MPLS Segment Routing (SR-MPLS) [I-D.ietf-spring-segment-routing-mpls] is an MPLS data plane-based source routing paradigm in which the sender of a packet is allowed to partially or completely specify the route the packet takes through the network by imposing stacked MPLS - labels on the packet. SR-MPLS could be leveraged to realize a source - routing mechanism across MPLS, IPv4, and IPv6 data planes by using an - MPLS label stack as a source routing instruction set while preserving - backward compatibility with SR-MPLS. More specifically, the source - routing instruction set information contained in a source routed - packet could be uniformly encoded as an MPLS label stack no matter - whether the underlay is IPv4, IPv6, or MPLS. + labels on the packet. SR-MPLS uses an MPLS label stack to encode a + source routing instruction set. This can be used to realize a source + routing mechanism that can operate across MPLS, IPv4, and IPv6 data + planes. This approach preserves backward compatibility with SR-MPLS. + More specifically, the source routing instruction set information + contained in a source routed packet could be uniformly encoded as an + MPLS label stack no matter whether the underlay is IPv4, IPv6, or + MPLS. This document describes how SR-MPLS capable routers and IP-only routers can seamlessly co-exist and interoperate through the use of SR-MPLS label stacks and IP encapsulation/tunneling such as MPLS-in- UDP [RFC7510]. Section 2 describes various use cases for the tunneling SR-MPLS over IP. Section 3 describes a typical application scenario and how the packet forwarding happens. @@ -118,48 +119,50 @@ capitals, as shown here. 2. Use Cases Tunneling SR-MPLS using IPv4 and/or IPv6 tunnels is useful at least in the following use cases: o Incremental deployment of the SR-MPLS technology may be facilitated by tunneling SR-MPLS packets across parts of a network that are not SR-MPLS enabled using an IP tunneling mechanism such - as MPLS-in-UDP [RFC7510]. The tunnel destination address is the - address of the next SR-MPLS capable node along the path (i.e., the - egress of the active node segment). This is shown in Figure 1. + as MPLS-in-UDP [RFC7510]. The tunnel selected MUST have its + remote end point (destination) address equal to the address of the + next SR-MPLS capable node along the path (i.e., the egress of the + active node segment). This is shown in Figure 1. ________________________ _______ ( ) _______ ( ) ( IP Network ) ( ) ( SR-MPLS ) ( ) ( SR-MPLS ) ( Network ) ( ) ( Network ) ( -------- -------- ) ( | Border | SR-in-UDP Tunnel | Border | ) ( | Router |========================| Router | ) ( | R1 | | R2 | ) ( -------- -------- ) ( ) ( ) ( ) ( ) ( ) ( ) (_______) ( ) (_______) (________________________) Figure 1: SR-MPLS in UDP to Tunnel Between SR-MPLS Sites - o If encoding of entropy is desired, IP tunneling mechanisms that - allow encoding of entropy, such as MPLS-in-UDP encapsulation - [RFC7510] where the source port of the UDP header is used as an - entropy field, may be used to maximize the utilization of ECMP - and/or LAG, especially when it is difficult to make use of entropy - label mechanism. Refer to [I-D.ietf-mpls-spring-entropy-label]) - for more discussion about using entropy label in SR-MPLS. + o If encoding of entropy ([RFC6790] is desired, IP tunneling + mechanisms that allow encoding of entropy, such as MPLS-in-UDP + encapsulation [RFC7510] where the source port of the UDP header is + used as an entropy field, may be used to maximize the utilization + of ECMP and/or LAG, especially when it is difficult to make use of + the entropy label mechanism. Refer to + [I-D.ietf-mpls-spring-entropy-label]) for more discussion about + using entropy labels in SR-MPLS. o Tunneling MPLS into IP provides a technology that enables SR in an IPv4 and/or IPv6 network where the routers do not support SRv6 capabilities [I-D.ietf-6man-segment-routing-header] and where MPLS forwarding is not an option. This is shown in Figure 2. __________________________________ __( IP Network )__ __( )__ ( -- -- -- ) @@ -197,21 +200,22 @@ or all of the next-hops along the shortest path towards a prefix Segment Identifier (prefix-SID) are IP-only routers. Consider router A that receives a labeled packet with top label L(E) that corresponds to the prefix-SID SID(E) of prefix P(E) advertised by router E. Suppose the i-th next-hop router (termed NHi) along the shortest path from router A toward SID(E) is not SR-MPLS capable while both routers A and E are SR-MPLS capable. The following processing steps apply: - o Router E is SR-MPLS capable so it advertises the SRGB as described + o The Segment Routing Global Block (SRGB) is defined in [RFC8402]. + Router E is SR-MPLS capable, so it advertises an SRGB as described in [I-D.ietf-ospf-segment-routing-extensions] and [I-D.ietf-isis-segment-routing-extensions]. o When Router E advertises the prefix-SID SID(E) of prefix P(E) it MUST also advertise the encapsulation endpoint and the tunnel type of any tunnel used to reach E. It does this using the mechanisms described in [I-D.ietf-isis-encapsulation-cap] or [I-D.ietf-ospf-encapsulation-cap]. o If A and E are in different IGP areas/levels, then: @@ -250,40 +254,40 @@ * If the NP flag in OSPF or the P flag in ISIS is clear: pop the top label * If the NP flag in OSPF or the P flag in ISIS is set: swap the top label to a value equal to SID(E) plus the lower bound of the SRGB of E - * Encapsulate the packet according to the encapsulation + Once constructed, the FIB can be used to tell a router how to process + packets. It encapsulates the packets according to the encapsulation advertised in [I-D.ietf-isis-encapsulation-cap] or - [I-D.ietf-ospf-encapsulation-cap] - - * Send the packet towards the next hop NHi. + [I-D.ietf-ospf-encapsulation-cap]. Then it sends the packets towards + the next hop NHi. 3.2. Packet Forwarding Procedures [RFC7510] specifies an IP-based encapsulation for MPLS, i.e., MPLS- - in-UDP, which is applicable in some circumstances where IP-based - encapsulation for MPLS is required and further fine-grained load - balancing of MPLS packets over IP networks over Equal-Cost Multipath - (ECMP) and/or Link Aggregation Groups (LAGs) is required as well. - This section provides details about the forwarding procedure when - when UDP encapsulation is adopted for SR-MPLS over IP. + in-UDP. This approach is applicable where IP-based encapsulation for + MPLS is required and further fine-grained load balancing of MPLS + packets over IP networks over Equal-Cost Multipath (ECMP) and/or Link + Aggregation Groups (LAGs) is also required. This section provides + details about the forwarding procedure when when UDP encapsulation is + adopted for SR-MPLS over IP. Nodes that are SR-MPLS capable can process SR-MPLS packets. Not all of the nodes in an SR-MPLS domain are SR-MPLS capable. Some nodes may be "legacy routers" that cannot handle SR-MPLS packets but can - forward IP packets. An SR-MPLS-capable node may advertise its + forward IP packets. An SR-MPLS-capable node MAY advertise its capabilities using the IGP as described in Section 3. There are six types of node in an SR-MPLS domain: o Domain ingress nodes that receive packets and encapsulate them for transmission across the domain. Those packets may be any payload protocol including native IP packets or packets that are already MPLS encapsulated. o Legacy transit nodes that are IP routers but that are not SR-MPLS capable (i.e., are not able to perform segment routing). @@ -301,26 +305,26 @@ ultimate delivery. 3.2.1. Packet Forwarding with Penultimate Hop Popping The description in this section assumes that the label associated with each prefix-SID is advertised by the owner of the prefix-SID is a Penultimate Hop Popping (PHP) label. That is, the NP flag in OSPF or the P flag in ISIS associated with the prefix SID is not set. +-----+ +-----+ +-----+ +-----+ +-----+ - | A +-------+ B +-------+ C +--------+ D +--------+ H | + | A +-------+ B +-------+ C +-------+ D +-------+ H | +-----+ +--+--+ +--+--+ +--+--+ +-----+ | | | | | | +--+--+ +--+--+ +--+--+ - | E +-------+ F +--------+ G | + | E +-------+ F +-------+ G | +-----+ +-----+ +-----+ +--------+ |IP(A->E)| +--------+ +--------+ +--------+ | UDP | |IP(E->G)| |IP(G->H)| +--------+ +--------+ +--------+ | L(G) | | UDP | | UDP | +--------+ +--------+ +--------+ | L(H) | | L(H) | |Exp Null| @@ -341,26 +345,26 @@ Router A will impose an MPLS label stack on the packet that corresponds to that explicit path. Since the next hop toward router E is only IP-capable (B is a legacy transit node), router A replaces the top label (that indicated router E) with a UDP-based tunnel for MPLS (i.e., MPLS-over-UDP [RFC7510]) to router E and then sends the packet. In other words, router A pops the top label and then encapsulates the MPLS packet in a UDP tunnel to router E. When the IP-encapsulated MPLS packet arrives at router E (which is an SR-MPLS-capable transit node), router E strips the IP-based tunnel - header and then process the decapsulated MPLS packet. The top label - indicates that the packet must be forwarded toward router G. Since - the next hop toward router G is only IP-capable, router E replaces - the current top label with an MPLS-over-UDP tunnel toward router G - and sends it out. That is, router E pops the top label and then - encapsulates the MPLS packet in a UDP tunnel to router G. + header and then processes the decapsulated MPLS packet. The top + label indicates that the packet must be forwarded toward router G. + Since the next hop toward router G is only IP-capable, router E + replaces the current top label with an MPLS-over-UDP tunnel toward + router G and sends it out. That is, router E pops the top label and + then encapsulates the MPLS packet in a UDP tunnel to router G. When the packet arrives at router G, router G will strip the IP-based tunnel header and then process the decapsulated MPLS packet. The top label indicates that the packet must be forwarded toward router H. Since the next hop toward router H is only IP-capable (D is a legacy transit router), router G would replace the current top label with an MPLS-over-UDP tunnel toward router H and send it out. However, since router G reaches the bottom of the label stack (G is the penultimate SR-MPLS capable node on the path) this would leave the original packet that router A wanted to send to router H encapsulated in UDP @@ -438,26 +442,26 @@ the stack and an MPLS-over-UDP tunnel is preferred to an MPLS LSP according to local policies, router E would replace the current top label with an MPLS-over-UDP tunnel toward router G and send it out. IP Header Fields: When encapsulating an MPLS packet in UDP, the resulting packet is further encapsulated in IP for transmission. IPv4 or IPv6 may be used according to the capabilities of the network. The address fields are set as described in Section 2. The other IP header fields (such as DSCP code point, or IPv6 Flow - Label) on each UDP-encapsulated segment can be set according to - the operator's policy: they may be copied from the header of the - incoming packet; they may be promoted from the header of the - payload packet; they may be set according to instructions - programmed to be associated with the SID; or they may be - configured dependent on the outgoing interface and payload. + Label) on each UDP-encapsulated segment SHOULD be configurable + according to the operator's policy: they may be copied from the + header of the incoming packet; they may be promoted from the + header of the payload packet; they may be set according to + instructions programmed to be associated with the SID; or they may + be configured dependent on the outgoing interface and payload. Entropy and ECMP: When encapsulating an MPLS packet with an IP tunnel header that is capable of encoding entropy (such as [RFC7510]), the corresponding entropy field (the source port in case UDP tunnel) MAY be filled with an entropy value that is generated by the encapsulator to uniquely identify a flow. However, what constitutes a flow is locally determined by the encapsulator. For instance, if the MPLS label stack contains at least one entropy label and the encapsulator is capable of reading that entropy label, the entropy label value could be directly @@ -545,22 +549,22 @@ Marvell Email: talmi@marvell.com Jeff Tantsura Individual Email: jefftant@gmail.com 7. Acknowledgements Thanks to Joel Halpern, Bruno Decraene, Loa Andersson, Ron Bonica, - Eric Rosen, Jim Guichard, and Gunter Van De Velde for their - insightful comments on this draft. + Eric Rosen, Jim Guichard, Gunter Van De Velde, Andy Malis, Robert + Sparks, and Al Morton for their insightful comments on this draft. 8. References 8.1. Normative References [I-D.ietf-spring-segment-routing-mpls] Bashandy, A., Filsfils, C., Previdi, S., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing with MPLS data plane", draft-ietf-spring-segment-routing-mpls-18 (work in progress), December 2018. @@ -601,27 +605,32 @@ [RFC7981] Ginsberg, L., Previdi, S., and M. Chen, "IS-IS Extensions for Advertising Router Information", RFC 7981, DOI 10.17487/RFC7981, October 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . + [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., + Decraene, B., Litkowski, S., and R. Shakir, "Segment + Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, + July 2018, . + 8.2. Informative References [I-D.ietf-6man-segment-routing-header] Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header - (SRH)", draft-ietf-6man-segment-routing-header-15 (work in - progress), October 2018. + (SRH)", draft-ietf-6man-segment-routing-header-16 (work in + progress), February 2019. [I-D.ietf-isis-encapsulation-cap] Xu, X., Decraene, B., Raszuk, R., Chunduri, U., Contreras, L., and L. Jalil, "Advertising Tunnelling Capability in IS-IS", draft-ietf-isis-encapsulation-cap-01 (work in progress), April 2017. [I-D.ietf-isis-segment-routing-extensions] Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A., Gredler, H., and B. Decraene, "IS-IS Extensions for @@ -639,20 +648,25 @@ Jalil, "The Tunnel Encapsulations OSPF Router Information", draft-ietf-ospf-encapsulation-cap-09 (work in progress), October 2017. [I-D.ietf-ospf-segment-routing-extensions] Psenak, P., Previdi, S., Filsfils, C., Gredler, H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF Extensions for Segment Routing", draft-ietf-ospf-segment- routing-extensions-27 (work in progress), December 2018. + [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and + L. Yong, "The Use of Entropy Labels in MPLS Forwarding", + RFC 6790, DOI 10.17487/RFC6790, November 2012, + . + [RFC8354] Brzozowski, J., Leddy, J., Filsfils, C., Maglione, R., Ed., and M. Townsley, "Use Cases for IPv6 Source Packet Routing in Networking (SPRING)", RFC 8354, DOI 10.17487/RFC8354, March 2018, . Authors' Addresses Xiaohu Xu Alibaba, Inc