Network Working Group C. Filsfils, Ed. Internet-Draft S. Previdi, Ed. Intended status: Informational Cisco Systems, Inc. Expires: March 17, 2017 E. Aries Facebook D. Ginsburg D. Afanasiev Yandex September 13, 2016 Segment Routing Centralized BGP Peer Engineering draft-ietf-spring-segment-routing-central-epe-02 Abstract Segment Routing (SR) leverages source routing. A node steers a packet through a controlled set of instructions, called segments, by prepending the packet with an SR header. A segment can represent any instruction topological or service-based. SR allows to enforce a flow through any topological path and service chain while maintaining per-flow state only at the ingress node of the SR domain. The Segment Routing architecture can be directly applied to the MPLS dataplane with no change on the forwarding plane. It requires minor extension to the existing link-state routing protocols. This document illustrates the application of Segment Routing to solve the BGP Peer Engineering (BGP-PE) requirement. The SR-based BGP-PE solution allows a centralized (SDN) controller to program any egress peer policy at ingress border routers or at hosts within the domain. This document is on the informational track. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. 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 http://datatracker.ietf.org/drafts/current/. Filsfils, et al. Expires March 17, 2017 [Page 1] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 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 March 17, 2017. Copyright Notice Copyright (c) 2016 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 (http://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 described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Segment Routing Documents . . . . . . . . . . . . . . . . 3 1.2. Problem Statement . . . . . . . . . . . . . . . . . . . . 4 2. BGP Peering Segments . . . . . . . . . . . . . . . . . . . . 6 3. Distribution of External Topology and TE Information using BGP-LS . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 3.1. BGP-PE Router advertising the Peer D and its PeerNode SID 7 3.2. BGP-PE Router advertising the Peer E and its PeerNode SID 7 3.3. BGP-PE Router advertising the Peer F and its PeerNode SID 8 3.4. BGP-PE Router advertising a first PeerAdj to Peer F . . . 8 3.5. BGP-PE Router advertising a second PeerAdj to Peer F . . 9 3.6. Fast Reroute (FRR) . . . . . . . . . . . . . . . . . . . 9 4. BGP-PE Controller . . . . . . . . . . . . . . . . . . . . . . 10 4.1. Valid Paths From Peers . . . . . . . . . . . . . . . . . 10 4.2. Intra-Domain Topology . . . . . . . . . . . . . . . . . . 11 4.3. External Topology . . . . . . . . . . . . . . . . . . . . 11 4.4. SLA characteristics of each peer . . . . . . . . . . . . 11 4.5. Traffic Matrix . . . . . . . . . . . . . . . . . . . . . 12 4.6. Business Policies . . . . . . . . . . . . . . . . . . . . 12 4.7. BGP-PE Policy . . . . . . . . . . . . . . . . . . . . . . 12 5. Programming an input policy . . . . . . . . . . . . . . . . . 13 5.1. At a Host . . . . . . . . . . . . . . . . . . . . . . . . 13 5.2. At a router - SR Traffic Engineering tunnel . . . . . . . 13 5.3. At a Router - RFC3107 policy route . . . . . . . . . . . 13 Filsfils, et al. Expires March 17, 2017 [Page 2] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 5.4. At a Router - VPN policy route . . . . . . . . . . . . . 14 5.5. At a Router - Flowspec route . . . . . . . . . . . . . . 14 6. IPv6 . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 7. Benefits . . . . . . . . . . . . . . . . . . . . . . . . . . 15 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 9. Manageability Considerations . . . . . . . . . . . . . . . . 15 10. Security Considerations . . . . . . . . . . . . . . . . . . . 16 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 16 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 16 12.1. Normative References . . . . . . . . . . . . . . . . . . 16 12.2. Informative References . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 1. Introduction The document is structured as follows: o Section 1 states the BGP-PE problem statement and provides the key references. o Section 2 defines the different BGP Peering Segments and the semantic associated to them. o Section 3 describes the automated allocation of BGP Peering SID's by the BGP-PE enabled egress border router and the automated signaling of the external peering topology and the related BGP Peering SID's to the collector [I-D.ietf-idr-bgpls-segment-routing-epe]. o Section 4 overviews the components of a centralized EPE controller. The definition of the EPE controller is outside the scope of this document. o Section 5 overviews the methods that could be used by the centralized BGP-PE controller to implement a BGP-PE policy at an ingress border router or at a source host within the domain. The exhaustive definition of all the means to program an BGP-PE input policy is outside the scope of this document. For editorial reasons, the solution is described for IPv4. A later section describes how the same solution is applicable to IPv6. 1.1. Segment Routing Documents The main references for this document are: o SR Problem Statement: [I-D.ietf-spring-problem-statement]. Filsfils, et al. Expires March 17, 2017 [Page 3] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 o SR Architecture: [I-D.ietf-spring-segment-routing]. o Distribution of External Topology and TE Information using BGP: [I-D.ietf-idr-bgpls-segment-routing-epe]. The SR instantiation in the MPLS dataplane is described in [I-D.ietf-spring-segment-routing-mpls]. The SR IGP protocol extensions are defined in [I-D.ietf-isis-segment-routing-extensions], [I-D.ietf-ospf-segment-routing-extensions] and [I-D.ietf-ospf-ospfv3-segment-routing-extensions]. The Segment Routing PCE protocol extensions are defined in [I-D.ietf-pce-segment-routing]. 1.2. Problem Statement The BGP-PE problem statement is defined in [I-D.ietf-spring-problem-statement]. A centralized controller should be able to instruct an ingress Provider Edge router (PE) or a content source within the domain to use a specific egress PE and a specific external interface/neighbor to reach a particular destination. We call this solution "BGP-PE" for "BGP Peer Engineering". The centralized controller is called the "BGP-PE Controller". The egress border router where the BGP-PE traffic-steering functionality is implemented is called a BGP-PE-enabled border router. The input policy programmed at an ingress border router or at a source host is called a BGP-PE policy. The requirements that have motivated the solution described in this document are listed here below: o The solution MUST apply to the Internet use-case where the Internet routes are assumed to use IPv4 unlabeled or IPv6 unlabeled. It is not required to place the Internet routes in a VRF and allocate labels on a per route, or on a per-path basis. o The solution MUST NOT make any assumption on the currently deployed iBGP schemes (RRs, confederations or iBGP full meshes) and MUST be able to support all of them. o The solution MUST be applicable to iBGP as well as eBGP peerings. Filsfils, et al. Expires March 17, 2017 [Page 4] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 o The solution SHOULD minimize the need for new BGP capabilities at the ingress PEs. o The solution MUST accommodate an ingress BGP-PE policy at an ingress PE or directly at an source host within the domain. o The solution MUST support automated Fast Reroute (FRR) and fast convergence mechanisms. The following reference diagram is used throughout this document. +---------+ +------+ | | | | | H B------D G | | +---/| AS 2 |\ +------+ | |/ +------+ \ | |---L/8 A AS1 C---+ \| | | |\\ \ +------+ /| AS 4 |---M/8 | | \\ +-E |/ +------+ | X | \\ | K | | +===F AS 3 | +---------+ +------+ Figure 1: Reference Diagram IPv4 addressing: o C's interface to D: 198.51.100.1/30, D's interface: 198.51.100.2/30 o C's interface to E: 198.51.100.5/30, E's interface: 198.51.100.6/30 o C's upper interface to F: 198.51.100.9/30, F's interface: 198.51.100.10/30 o C's lower interface to F: 198.51.100.13/30, F's interface: 198.51.100.14/30 o Loopback of F used for eBGP multi-hop peering to C: 192.0.2.2/32 o C's loopback is 203.0.113.3/32 with SID 64 C's BGP peering: o Single-hop eBGP peering with neighbor 198.51.100.2 (D) o Single-hop eBGP peering with neighbor 198.51.100.6 (E) Filsfils, et al. Expires March 17, 2017 [Page 5] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 o Multi-hop eBGP peering with F on IP address 192.0.2.2 (F) C's resolution of the multi-hop eBGP session to F: o Static route 192.0.2.2/32 via 198.51.100.10 o Static route 192.0.2.2/32 via 198.51.100.14 C is configured with local policy that defines a BGP PeerSet as the set of peers (198.51.100.6 and 192.0.2.2) X is the BGP-PE controller within AS1 domain. H is a content source within AS1 domain. 2. BGP Peering Segments As defined in [I-D.ietf-spring-segment-routing], certain segments are defined by BGP-PE capable node and corresponding to its attached peers. These segments are called BGP peering segments or BGP Peering SIDs. They enable the expression of source-routed inter-domain paths. An ingress border router of an AS may compose a list of segments to steer a flow along a selected path within the AS, towards a selected egress border router C of the AS and through a specific peer. At minimum, a BGP Peering Engineering policy applied at an ingress PE involves two segments: the Node SID of the chosen egress PE and then the BGP Peering Segment for the chosen egress PE peer or peering interface. [I-D.ietf-spring-segment-routing] defines three types of BGP peering segments/SID's: PeerNodeSID, PeerAdjSID and PeerSetSID. The BGP extensions to signal these BGP peering segments are outlined in the following section. 3. Distribution of External Topology and TE Information using BGP-LS In ships-in-the-night mode with respect to the pre-existing iBGP design, a BGP-LS session is established between the BGP-PE enabled border router and the BGP-PE controller. As a result of its local configuration and according to the behavior described in [I-D.ietf-idr-bgpls-segment-routing-epe], node C allocates the following BGP Peering Segments ([I-D.ietf-spring-segment-routing]): Filsfils, et al. Expires March 17, 2017 [Page 6] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 o A PeerNode segment for each of its defined peer (D, E and F). o A PeerAdj segment for each recursing interface to a multi-hop peer (e.g.: the upper and lower interfaces from C to F in figure 1). o A PeerSet segment to the set of peers (E and F). C programs its forwarding table accordingly: Incoming Outgoing Label Operation Interface ------------------------------------ 1012 POP link to D 1022 POP link to E 1032 POP upper link to F 1042 POP lower link to F 1052 POP load balance on any link to F 1060 POP load balance on any link to E or to F C signals the related BGP-LS NLRI's to the BGP-PE controller. Each such BGP-LS route is described in the following subsections according to the encoding details defined in [I-D.ietf-idr-bgpls-segment-routing-epe]. 3.1. BGP-PE Router advertising the Peer D and its PeerNode SID Descriptors: o Node Descriptors (router-ID, ASN): 203.0.113.3 , AS1 o Peer Descriptors (peer ASN): AS2 o Link Descriptors (IPv4 interface address, neighbor IPv4 address): 198.51.100.1, 198.51.100.2 Attributes: o PeerNode-SID: 1012 3.2. BGP-PE Router advertising the Peer E and its PeerNode SID Descriptors: o Node Descriptors (router-ID, ASN): 203.0.113.3 , AS1 o Peer Descriptors (peer ASN): AS3 Filsfils, et al. Expires March 17, 2017 [Page 7] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 o Link Descriptors (IPv4 interface address, neighbor IPv4 address): 198.51.100.5, 198.51.100.6 Attributes: o PeerNode-SID: 1022 o PeerSetSID: 1060 o Link Attributes: see section 3.3.2 of [RFC7752] 3.3. BGP-PE Router advertising the Peer F and its PeerNode SID Descriptors: o Node Descriptors (router-ID, ASN): 203.0.113.3 , AS1 o Peer Descriptors (peer ASN): AS3 o Link Descriptors (IPv4 interface address, neighbor IPv4 address): 203.0.113.3, 192.0.2.2 Attributes: o PeerNode-SID: 1052 o PeerSetSID: 1060 3.4. BGP-PE Router advertising a first PeerAdj to Peer F Descriptors: o Node Descriptors (router-ID, ASN): 203.0.113.3 , AS1 o Peer Descriptors (peer ASN): AS3 o Link Descriptors (IPv4 interface address, neighbor IPv4 address): 198.51.100.9, 198.51.100.10 Attributes: o PeerAdj-SID: 1032 o LinkAttributes: see section 3.3.2 of [RFC7752] Filsfils, et al. Expires March 17, 2017 [Page 8] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 3.5. BGP-PE Router advertising a second PeerAdj to Peer F Descriptors: o Node Descriptors (router-ID, ASN): 203.0.113.3 , AS1 o Peer Descriptors (peer ASN): AS3 o Link Descriptors (IPv4 interface address, neighbor IPv4 address): 198.51.100.13, 198.51.100.14 Attributes: o PeerAdj-SID: 1042 o LinkAttributes: see section 3.3.2 of [RFC7752] 3.6. Fast Reroute (FRR) An BGP-PE enabled border router should allocate a FRR backup entry on a per BGP Peering SID basis: o PeerNode SID 1. If multi-hop, backup via the remaining PeerADJ SIDs to the same peer. 2. Else backup via local PeerNode SID to the same AS. 3. Else pop the PeerNode SID and perform an IP lookup. o PeerAdj SID 1. If to a multi-hop peer, backup via the remaining PeerADJ SIDs to the same peer. 2. Else backup via PeerNode SID to the same AS. 3. Else pop the PeerNode SID and perform an IP lookup. o PeerSet SID 1. Backup via remaining PeerNode SIDs in the same PeerSet. 2. Else pop the PeerNode SID and IP lookup. We illustrate the different types of possible backups using the reference diagram and considering the Peering SIDs allocated by C. Filsfils, et al. Expires March 17, 2017 [Page 9] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 PeerNode SID 1052, allocated by C for peer F: o Upon the failure of the upper connected link CF, C can reroute all the traffic onto the lower CF link to the same peer (F). PeerNode SID 1022, allocated by C for peer E: o Upon the failure of the connected link CE, C can reroute all the traffic onto the link to PeerNode SID 1052 (F). PeerNode SID 1012, allocated by C for peer D: o Upon the failure of the connected link CD, C can pop the PeerNode SID and lookup the IP destination address in its FIB and route accordingly. PeerSet SID 1060, allocated by C for the set of peers E and F: o Upon the failure of a connected link in the group, the traffic to PeerSet SID 1060 is rerouted on any other member of the group. For specific business reasons, the operator might not want the default FRR behavior applied to a PeerNode SID or any of its dependent PeerADJ SID. The operator should be able to associate a specific backup PeerNode SID for a PeerNode SID: e.g., 1022 (E) must be backed up by 1012 (D) which overrules the default behavior which would have preferred F as a backup for E. 4. BGP-PE Controller In this section, we provide a non-exhaustive set of inputs that an BGP-PE controller would likely collect such as to perform the BGP-PE policy decision. The exhaustive definition is outside the scope of this document. 4.1. Valid Paths From Peers The BGP-PE controller should collect all the paths advertised by all the engineered peers. This could be realized by setting an iBGP session with the BGP-PE enabled border router, with "add-path all" and the original next-hop preserved. Filsfils, et al. Expires March 17, 2017 [Page 10] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 In this case, C would advertise the following Internet routes to the BGP-PE controller: o NLRI , nhop 198.51.100.2, AS Path {AS 2, 4} * X (i.e.: the BGP-PE controller) knows that C receives a path to L/8 via neighbor 198.51.100.2 of AS2. o NLRI , nhop 198.51.100.6, AS Path {AS 3, 4} * X knows that C receives a path to L/8 via neighbor 198.51.100.6 of AS2. o NLRI , nhop 192.0.2.2, AS Path {AS 3, 4} * X knows that C has an eBGP path to L/8 via AS3 via neighbor 192.0.2.2 An alternative option would be for an BGP-PE collector to use BGP Monitoring Protocol (BMP) to track the Adj-RIB-In of BGP-PE enabled border routers. 4.2. Intra-Domain Topology The BGP-PE controller should collect the internal topology and the related IGP SIDs. This could be realized by collecting the IGP LSDB of each area or running a BGP-LS session with a node in each IGP area. 4.3. External Topology Thanks to the collected BGP-LS routes described in the section 2 (BGP-LS advertisements), the BGP-PE controller is able to maintain an accurate description of the egress topology of node C. Furthermore, the BGP-PE controller is able to associate BGP Peering SIDs to the various components of the external topology. 4.4. SLA characteristics of each peer The BGP-PE controller might collect SLA characteristics across peers. This requires an BGP-PE solution as the SLA probes need to be steered via non-best-path peers. Unidirectional SLA monitoring of the desired path is likely required. This might be possible when the application is controlled at the source and the receiver side. Unidirectional monitoring dissociates the SLA characteristic of the return path (which cannot usually be Filsfils, et al. Expires March 17, 2017 [Page 11] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 controlled) from the forward path (the one of interest for pushing content from a source to a consumer and the one which can be controlled). Alternatively, Extended Metrics, as defined in [I-D.ietf-isis-te-metric-extensions] could also be advertised using new BGP-LS attributes. 4.5. Traffic Matrix The BGP-PE controller might collect the traffic matrix to its peers or the final destinations. IPFIX is a likely option. An alternative option consists in collecting the link utilization statistics of each of the internal and external links, also available in the current definition of [RFC7752]. 4.6. Business Policies The BGP-PE controller should collect business policies. 4.7. BGP-PE Policy On the basis of all these inputs (and likely others), the BGP-PE Controller decides to steer some demands away from their best BGP path. The BGP-PE policy is likely expressed as a two-entry segment list where the first element is the IGP prefix SID of the selected egress border router and the second element is a BGP Peering SID at the selected egress border router. A few examples are provided hereafter: o Prefer egress PE C and peer AS AS2: {64, 1012}. o Prefer egress PE C and peer AS AS3 via eBGP peer 198.51.100.6: {64, 1022}. o Prefer egress PE C and peer AS AS3 via eBGP peer 192.0.2.2: {64, 1052}. o Prefer egress PE C and peer AS AS3 via interface 198.51.100.14 of multi-hop eBGP peer 192.0.2.2: {64, 1042}. o Prefer egress PE C and any interface to any peer in the group 1060: {64, 1060}. Filsfils, et al. Expires March 17, 2017 [Page 12] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 Note that the first SID could be replaced by a list of segments. This is useful when an explicit path within the domain is required for traffic-engineering purposes. For example, if the Prefix SID of node B is 60 and the BGP-PE controller would like to steer the traffic from A to C via B then through the external link to peer D then the segment list would be {60, 64, 1012}. 5. Programming an input policy The detailed/exhaustive description of all the means to implement an BGP-PE policy are outside the scope of this document. A few examples are provided in this section. 5.1. At a Host A static IP/MPLS route can be programmed at the host H. The static route would define a destination prefix, a next-hop and a label stack to push. The global property of the IGP Prefix SID is particularly convenient: the same policy could be programmed across hosts connected to different routers. 5.2. At a router - SR Traffic Engineering tunnel The BGP-PE controller can configure the ingress border router with an SR traffic engineering tunnel T1 and a steering-policy S1 which causes a certain class of traffic to be mapped on the tunnel T1. The tunnel T1 would be configured to push the required segment list. The tunnel and the steering policy could be configured via PCEP according to [I-D.ietf-pce-segment-routing] and [I-D.ietf-pce-pce-initiated-lsp] or via Netconf ([RFC6241]). Example: at A Tunnel T1: push {64, 1042} IP route L/8 set nhop T1 5.3. At a Router - RFC3107 policy route The BGP-PE Controller could build a RFC3107 ([RFC3107]) route (from scratch) and send it to the ingress router: o NLRI: the destination prefix to engineer: e.g., L/8. o Next-Hop: the selected egress border router: C. o Label: the selected egress peer: 1042. Filsfils, et al. Expires March 17, 2017 [Page 13] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 o AS path: reflecting the selected valid AS path. o Some BGP policy to ensure it will be selected as best by the ingress router. This RFC3107 policy route "overwrites" an equivalent or less-specific "best path". As the best-path is changed, this EPE input policy option influences the path propagated to the upstream peer/customers. 5.4. At a Router - VPN policy route The EPE Controller could build a VPNv4 route (from scratch) and send it to the ingress router: o NLRI: the destination prefix to engineer: e.g., L/8. o Next-Hop: the selected egress border router: C. o Label: the selected egress peer: 1042. o Route-Target: selecting the appropriate VRF at the ingress router. o AS path: reflecting the selected valid AS path. o Some BGP policy to ensure it will be selected as best by the ingress router in the related VRF. The related VRF must be preconfigured. A VRF fallback to the main FIB might be beneficial to avoid replicating all the "normal" Internet paths in each VRF. 5.5. At a Router - Flowspec route An EPE Controller builds a FlowSpec route and sends it to the ingress router to engineer: o Dissemination of Flow Specification Rules ([RFC5575]. o Destination/Source IP Addresses, IP Protocol, Destination/Source port (+1 component). o ICMP Type/Code, TCP Flags, Packet length, DSCP, Fragment. 6. IPv6 The described solution is applicable to IPv6, either with MPLS-based or IPv6-Native segments. In both cases, the same three steps of the solution are applicable: Filsfils, et al. Expires March 17, 2017 [Page 14] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 o BGP-LS-based signaling of the external topology and BGP Peering Segments to the BGP-PE controller. o Collection of various inputs by the BGP-PE controller to come up with a policy decision. o Programming at an ingress router or source host of the desired BGP-PE policy which consists in a list of segments to push on a defined traffic class. 7. Benefits The BGP-PE solutions described in this document have the following benefits: o No assumption on the iBGP design within AS1. o Next-Hop-Self on the Internet routes propagated to the ingress border routers is possible. This is a common design rule to minimize the number of IGP routes and to avoid importing external churn into the internal routing domain. o Consistent support for traffic-engineering within the domain and at the external edge of the domain. o Support both host and ingress border router BGP-PE policy programming. o BGP-PE functionality is only required on the BGP-PE enabled egress border router and the BGP-PE controller: an ingress policy can be programmed at the ingress border router without any new functionality. o Ability to deploy the same input policy across hosts connected to different routers (avail the global property of IGP prefix SIDs). 8. IANA Considerations This document does not request any IANA allocations. 9. Manageability Considerations TBD Filsfils, et al. Expires March 17, 2017 [Page 15] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 10. Security Considerations TBD 11. Acknowledgements The authors would like to thank Acee Lindem for his comments and contribution. 12. References 12.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3107] Rekhter, Y. and E. Rosen, "Carrying Label Information in BGP-4", RFC 3107, DOI 10.17487/RFC3107, May 2001, . [RFC5575] Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J., and D. McPherson, "Dissemination of Flow Specification Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009, . [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, . 12.2. Informative References [I-D.ietf-idr-bgpls-segment-routing-epe] Previdi, S., Filsfils, C., Ray, S., Patel, K., Dong, J., and M. Chen, "Segment Routing BGP Egress Peer Engineering BGP-LS Extensions", draft-ietf-idr-bgpls-segment-routing- epe-05 (work in progress), May 2016. [I-D.ietf-isis-segment-routing-extensions] Previdi, S., Filsfils, C., Bashandy, A., Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS Extensions for Segment Routing", draft-ietf-isis-segment- routing-extensions-07 (work in progress), June 2016. Filsfils, et al. Expires March 17, 2017 [Page 16] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 [I-D.ietf-isis-te-metric-extensions] Previdi, S., Giacalone, S., Ward, D., Drake, J., and W. Wu, "IS-IS Traffic Engineering (TE) Metric Extensions", draft-ietf-isis-te-metric-extensions-11 (work in progress), February 2016. [I-D.ietf-ospf-ospfv3-segment-routing-extensions] Psenak, P., Previdi, S., Filsfils, C., Gredler, H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPFv3 Extensions for Segment Routing", draft-ietf-ospf-ospfv3- segment-routing-extensions-06 (work in progress), July 2016. [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-09 (work in progress), July 2016. [I-D.ietf-pce-pce-initiated-lsp] Crabbe, E., Minei, I., Sivabalan, S., and R. Varga, "PCEP Extensions for PCE-initiated LSP Setup in a Stateful PCE Model", draft-ietf-pce-pce-initiated-lsp-07 (work in progress), July 2016. [I-D.ietf-pce-segment-routing] Sivabalan, S., Medved, J., Filsfils, C., Crabbe, E., Lopez, V., Tantsura, J., Henderickx, W., and J. Hardwick, "PCEP Extensions for Segment Routing", draft-ietf-pce- segment-routing-07 (work in progress), March 2016. [I-D.ietf-spring-problem-statement] Previdi, S., Filsfils, C., Decraene, B., Litkowski, S., Horneffer, M., and R. Shakir, "SPRING Problem Statement and Requirements", draft-ietf-spring-problem-statement-08 (work in progress), April 2016. [I-D.ietf-spring-segment-routing] Filsfils, C., Previdi, S., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", draft-ietf- spring-segment-routing-09 (work in progress), July 2016. [I-D.ietf-spring-segment-routing-mpls] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., Litkowski, S., Horneffer, M., Shakir, R., jefftant@gmail.com, j., and E. Crabbe, "Segment Routing with MPLS data plane", draft-ietf-spring-segment-routing- mpls-05 (work in progress), July 2016. Filsfils, et al. Expires March 17, 2017 [Page 17] Internet-DraftSegment Routing Centralized BGP Peer EngineeSeptember 2016 [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and S. Ray, "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, DOI 10.17487/RFC7752, March 2016, . Authors' Addresses Clarence Filsfils (editor) Cisco Systems, Inc. Brussels BE Email: cfilsfil@cisco.com Stefano Previdi (editor) Cisco Systems, Inc. Via Del Serafico, 200 Rome 00142 Italy Email: sprevidi@cisco.com Ebben Aries Facebook 1 Hacker Way Menlo Park, CA 94025 US Email: exa@fb.com Daniel Ginsburg Yandex RU Email: dbg@yandex-team.ru Dmitry Afanasiev Yandex RU Email: fl0w@yandex-team.ru Filsfils, et al. Expires March 17, 2017 [Page 18]