Open Shortest Path First IGP P. Psenak, Ed. Internet-Draft S. Previdi, Ed. Intended status: Standards Track C. Filsfils Expires: January 7, 2017 Cisco Systems, Inc. H. Gredler Individual R. Shakir Jive Communications, Inc. W. Henderickx Nokia J. Tantsura Individual July 6, 2016 OSPF Extensions for Segment Routing draft-ietf-ospf-segment-routing-extensions-09 Abstract Segment Routing (SR) allows a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological sub-paths, called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This draft describes the OSPF extensions required for Segment Routing. 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/. 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." Psenak, et al. Expires January 7, 2017 [Page 1] Internet-Draft OSPF Extensions for Segment Routing July 2016 This Internet-Draft will expire on January 7, 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 2. Segment Routing Identifiers . . . . . . . . . . . . . . . . . 3 2.1. SID/Label Sub-TLV . . . . . . . . . . . . . . . . . . . . 4 3. Segment Routing Capabilities . . . . . . . . . . . . . . . . 4 3.1. SR-Algorithm TLV . . . . . . . . . . . . . . . . . . . . 4 3.2. SID/Label Range TLV . . . . . . . . . . . . . . . . . . . 6 4. OSPF Extended Prefix Range TLV . . . . . . . . . . . . . . . 7 5. Prefix SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 9 6. SID/Label Binding Sub-TLV . . . . . . . . . . . . . . . . . . 13 6.1. ERO Metric Sub-TLV . . . . . . . . . . . . . . . . . . . 14 6.2. ERO Sub-TLVs . . . . . . . . . . . . . . . . . . . . . . 15 6.2.1. IPv4 ERO Sub-TLV . . . . . . . . . . . . . . . . . . 15 6.2.2. Unnumbered Interface ID ERO Sub-TLV . . . . . . . . . 16 6.2.3. IPv4 Backup ERO Sub-TLV . . . . . . . . . . . . . . . 17 6.2.4. Unnumbered Interface ID Backup ERO Sub-TLV . . . . . 18 7. Adjacency Segment Identifier (Adj-SID) . . . . . . . . . . . 19 7.1. Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . . . 20 7.2. LAN Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 21 8. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 23 8.1. Intra-area Segment routing in OSPFv2 . . . . . . . . . . 23 8.2. Inter-area Segment routing in OSPFv2 . . . . . . . . . . 23 8.3. SID for External Prefixes . . . . . . . . . . . . . . . . 25 8.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . 25 8.4.1. Advertisement of Adj-SID on Point-to-Point Links . . 25 8.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 25 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 26 9.1. OSPF OSPF Router Information (RI) TLVs Registry . . . . . 26 9.2. OSPF Extended Prefix LSA TLV Registry . . . . . . . . . . 26 9.3. OSPF Extended Prefix LSA Sub-TLV Registry . . . . . . . . 26 Psenak, et al. Expires January 7, 2017 [Page 2] Internet-Draft OSPF Extensions for Segment Routing July 2016 9.4. OSPF Extended Link LSA Sub-TLV Registry . . . . . . . . . 26 10. Implementation Status . . . . . . . . . . . . . . . . . . . . 27 11. Security Considerations . . . . . . . . . . . . . . . . . . . 28 12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 28 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 28 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 29 14.1. Normative References . . . . . . . . . . . . . . . . . . 29 14.2. Informative References . . . . . . . . . . . . . . . . . 30 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 30 1. Introduction Segment Routing (SR) allows a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological sub-paths, called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). Prefix segments represent an ECMP-aware shortest-path to a prefix (or a node), as per the state of the IGP topology. Adjacency segments represent a hop over a specific adjacency between two nodes in the IGP. A prefix segment is typically a multi-hop path while an adjacency segment, in most cases, is a one-hop path. SR's control-plane can be applied to both IPv6 and MPLS data-planes, and does not require any additional signalling (other than IGP extensions). The IPv6 data plane is out of the scope of this specification - it is not applicable to OSPFv2 which only supports the IPv4 address-family. For example, when used in MPLS networks, SR paths do not require any LDP or RSVP-TE signalling. However, SR can interoperate in the presence of LSPs established with RSVP or LDP. This draft describes the OSPF extensions required for Segment Routing. Segment Routing architecture is described in [I-D.ietf-spring-segment-routing]. Segment Routing use cases are described in [I-D.filsfils-spring-segment-routing-use-cases]. 2. Segment Routing Identifiers Segment Routing defines various types of Segment Identifiers (SIDs): Prefix-SID, Adjacency-SID, LAN Adjacency SID and Binding SID. For the purpose of the advertisements of various SID values, new Opaque LSAs [RFC5250] are defined in [RFC7684]. These LSAs are generic containers that can be used to advertise any additional attributes associated with a prefix or link. These Opaque LSAs are Psenak, et al. Expires January 7, 2017 [Page 3] Internet-Draft OSPF Extensions for Segment Routing July 2016 complementary to the existing LSAs and are not aimed to replace any of the existing LSAs. 2.1. SID/Label Sub-TLV The SID/Label Sub-TLV appears in multiple TLVs or Sub-TLVs defined later in this document. It is used to advertise the SID or label associated with a prefix or adjacency. The SID/Label TLV has following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Label (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: Type: TBD, suggested value 1 Length: variable, 3 or 4 octet SID/Label: If length is set to 3, then the 20 rightmost bits represent a label. If length is set to 4, then the value represents a 32-bit SID. The receiving router MUST ignore SID/Label Sub-TLV if the length is other then 3 or 4. 3. Segment Routing Capabilities Segment Routing requires some additional router capabilities to be advertised to other routers in the area. These SR capabilities are advertised in the Router Information Opaque LSA (defined in [RFC7770]). 3.1. SR-Algorithm TLV The SR-Algorithm TLV is a top-level TLV of the Router Information Opaque LSA (defined in [RFC7770]). The SR-Algorithm Sub-TLV is optional. It MAY only be advertised once in the Router Information Opaque LSA. If the SID/Label Range TLV, as defined in Section 3.2, is advertised, then the SR-Algorithm TLV MUST Psenak, et al. Expires January 7, 2017 [Page 4] Internet-Draft OSPF Extensions for Segment Routing July 2016 also be advertised. If the SR-Algorithm TLV is not advertised by the node, such node is considered as not being segment routing capable. An SR Router may use various algorithms when calculating reachability to OSPF routers or prefixes in an OSPF area. Examples of these algorithms are metric based Shortest Path First (SPF), various flavors of Constrained SPF, etc. The SR-Algorithm TLV allows a router to advertise the algorithms currently used by the router to other routers in an OSPF area. The SR-Algorithm TLV has following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Algorithm 1 | Algorithm... | Algorithm n | | +- -+ | | + + where: Type: TBD, suggested value 8 Length: variable Algorithm: Single octet identifying the algorithm. The following values are defined by this document: 0: Shortest Path First (SPF) algorithm based on link metric. This is the standard shortest path algorithm as computed by the OSPF protocol. Consistent with the deployed practice for link- state protocols, Algorithm 0 permits any node to overwrite the SPF path with a different path based on its local policy. If the SR-Algorithm Sub-TLV is advertised, Algorithm 0 MUST be included. 1: Strict Shortest Path First (SPF) algorithm based on link metric. The algorithm is identical to Algorithm 0 but Algorithm 1 requires that all nodes along the path will honor the SPF routing decision. Local policy at the node claiming support for Algorithm 1 MUST NOT alter the SPF paths computed by Algorithm 1. The RI LSA can be advertised at any of the defined opaque flooding scopes (link, area, or Autonomous System (AS)). For the purpose of SR-Algorithm TLV advertisement, area scope flooding is required. Psenak, et al. Expires January 7, 2017 [Page 5] Internet-Draft OSPF Extensions for Segment Routing July 2016 3.2. SID/Label Range TLV The SID/Label Range TLV is a top-level TLV of the Router Information Opaque LSA (defined in [RFC7770]). The SID/Label Range TLV MAY appear multiple times and has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Range Size | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs (variable) | +- -+ | | + + where: Type: TBD, suggested value 9 Length: variable Range Size: 3 octets of the SID/label range Initially, the only supported Sub-TLV is the SID/Label TLV as defined in Section 2.1. The SID/Label advertised in the SID/Label TLV represents the first SID/Label in the advertised range. Multiple occurrences of the SID/Label Range TLV MAY be advertised, in order to advertise multiple ranges. In such case: o The originating router MUST encode each range into a different SID/Label Range TLV. o The originating router decides the order in which the set of SID/ Label Range TLVs are advertised inside the Router Information Opaque LSA. The originating router MUST ensure the order is the same after a graceful restart (using checkpointing, non-volatile storage or any other mechanism) in order to assure the SID/label range and SID index correspondence is preserved across graceful restarts. o The receiving router must adhere to the order in which the ranges are advertised when calculating a SID/label from a SID index. Psenak, et al. Expires January 7, 2017 [Page 6] Internet-Draft OSPF Extensions for Segment Routing July 2016 The following example illustrates the advertisement of multiple ranges: The originating router advertises following ranges: Range 1: [100, 199] Range 2: [1000, 1099] Range 3: [500, 599] The receiving routers concatenate the ranges and build the Segment Routing Global Block (SRGB) as follows: SRGB = [100, 199] [1000, 1099] [500, 599] The indexes span multiple ranges: index=0 means label 100 ... index 99 means label 199 index 100 means label 1000 index 199 means label 1099 ... index 200 means label 500 ... The RI LSA can be advertised at any of the defined flooding scopes (link, area, or autonomous system (AS)). For the purpose of SID/ Label Range TLV advertisement, area scope flooding is required. 4. OSPF Extended Prefix Range TLV In some cases it is useful to advertise attributes for a range of prefixes. The Segment Routing Mapping Server, which is described in [I-D.filsfils-spring-segment-routing-ldp-interop], is an example where we need a single advertisement to advertise SIDs for multiple prefixes from a contiguous address range. The OSPF Extended Prefix Range TLV, which is a new top level TLV of the Extended Prefix LSA described in [RFC7684] is defined for this purpose. Multiple OSPF Extended Prefix Range TLVs MAY be advertised in each OSPF Extended Prefix Opaque LSA, but all prefix ranges included in a single OSPF Extended Prefix Opaque LSA MUST have the same flooding scope. The OSPF Extended Prefix Range TLV has the following format: Psenak, et al. Expires January 7, 2017 [Page 7] Internet-Draft OSPF Extensions for Segment Routing July 2016 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Prefix Length | AF | Range Size | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Prefix (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs (variable) | +- -+ | | where: Type: TBD, suggested value 2. Length: Variable Prefix length: Length of the prefix AF: 0 - IPv4 unicast Range size: Represents the number of prefixes that are covered by the advertisement. The Range Size MUST NOT exceed the number of prefixes that could be satisfied by the prefix length without including the IPv4 multicast address range (224.0.0.0/3). Flags: Single octet field. The following flags are defined: 0 1 2 3 4 5 6 7 +--+--+--+--+--+--+--+--+ |IA| | | | | | | | +--+--+--+--+--+--+--+--+ where: IA-Flag: Inter-Area flag. If set, advertisement is of inter- area type. The ABR that is advertising the OSPF Extended Prefix Range TLV between areas MUST set this bit. This bit is used to prevent redundant flooding of Prefix Range TLVs between areas as follows: Psenak, et al. Expires January 7, 2017 [Page 8] Internet-Draft OSPF Extensions for Segment Routing July 2016 An ABR always prefers intra-area Prefix Range advertisements over inter-area advertisements. An ABR does not consider inter-area Prefix Range advertisements coming from non-backbone areas. An ABR only propagates an inter-area Prefix Range advertisement from the backbone area to connected non- backbone areas if the advertisement is considered to be the best one. Address Prefix: The prefix, encoded as an even multiple of 32-bit words, padded with zero bits as necessary. This encoding consumes ((PrefixLength + 31) / 32) 32-bit words. The Address Prefix represents the first prefix in the prefix range. 5. Prefix SID Sub-TLV The Prefix SID Sub-TLV is a Sub-TLV of the OSPF Extended Prefix TLV described in [RFC7684] and the OSPF Extended Prefix Range TLV described in Section 4. It MAY appear more than once in the parent TLV and has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Reserved | MT-ID | Algorithm | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Index/Label (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: Type: TBD, suggested value 2. Length: Variable Flags: Single octet field. The following flags are defined: 0 1 2 3 4 5 6 7 +--+--+--+--+--+--+--+--+ | |NP|M |E |V |L | | | +--+--+--+--+--+--+--+--+ where: Psenak, et al. Expires January 7, 2017 [Page 9] Internet-Draft OSPF Extensions for Segment Routing July 2016 NP-Flag: No-PHP flag. If set, then the penultimate hop MUST NOT pop the Prefix-SID before delivering packets to the node that advertised the Prefix-SID. M-Flag: Mapping Server Flag. If set, the SID was advertised by a Segment Routing Mapping Server as described in [I-D.filsfils-spring-segment-routing-ldp-interop]. E-Flag: Explicit-Null Flag. If set, any upstream neighbor of the Prefix-SID originator MUST replace the Prefix-SID with the Explicit-NULL label (0 for IPv4) before forwarding the packet. V-Flag: Value/Index Flag. If set, then the Prefix-SID carries an absolute value. If not set, then the Prefix-SID carries an index. L-Flag: Local/Global Flag. If set, then the value/index carried by the Prefix-SID has local significance. If not set, then the value/index carried by this Sub-TLV has global significance. Other bits: Reserved. These MUST be zero when sent and are ignored when received. MT-ID: Multi-Topology ID (as defined in [RFC4915]). Algorithm: Single octet identifying the algorithm the Prefix-SID is associated with as defined in Section 3.1. SID/Index/Label: According to the V and L flags, it contains either: A 32-bit index defining the offset in the SID/Label space advertised by this router. A 24-bit label where the 20 rightmost bits are used for encoding the label value. If multiple Prefix-SIDs are advertised for the same prefix, the receiving router MUST use the first encoded SID and MAY use the subsequent SIDs. When propagating Prefix-SIDs between areas, if multiple prefix-SIDs are advertised for a prefix, an implementation SHOULD preserve the original order when advertising prefix-SIDs to other areas. This allows implementations that only support a single Prefix-SID to have a consistent view across areas. Psenak, et al. Expires January 7, 2017 [Page 10] Internet-Draft OSPF Extensions for Segment Routing July 2016 When calculating the outgoing label for the prefix, the router MUST take into account the E and P flags advertised by the next-hop router if that router advertised the SID for the prefix. This MUST be done regardless of whether the next-hop router contributes to the best path to the prefix. The NP-Flag (No-PHP) MUST be set for Prefix-SIDs allocated to inter- area prefixes that are originated by the ABR based on intra-area or inter-area reachability between areas. When the inter-area prefix is generated based on a prefix which is directly attached to the ABR, the NP-Flag SHOULD NOT be set. The NP-Flag (No-PHP) MUST be be set for the Prefix-SIDs allocated to redistributed prefixes, unless the redistributed prefix is directly attached to the ASBR, in which case the NP-flag SHOULD NOT be set. If the NP-Flag is not set, then any upstream neighbor of the Prefix- SID originator MUST pop the Prefix-SID. This is equivalent to the penultimate hop popping mechanism used in the MPLS dataplane. In such case, MPLS EXP bits of the Prefix-SID are not preserved for the final destination (the Prefix-SID being removed). If the NP-flag is not set then the received E-flag is ignored. If the NP-flag is set then: If the E-flag is not set, then any upstream neighbor of the Prefix-SID originator MUST keep the Prefix-SID on top of the stack. This is useful when the originator of the Prefix-SID must stitch the incoming packet into a continuing MPLS LSP to the final destination. This could occur at an Area Border Router (prefix propagation from one area to another) or at an AS Boundary Router (prefix propagation from one domain to another). If the E-flag is set, then any upstream neighbor of the Prefix-SID originator MUST replace the Prefix-SID with an Explicit-NULL label. This is useful, e.g., when the originator of the Prefix- SID is the final destination for the related prefix and the originator wishes to receive the packet with the original EXP bits. When the M-Flag is set, the NP-flag and the E-flag MUST be ignored at reception. As the Mapping Server does not specify the originator of a prefix advertisement, it is not possible to determine PHP behavior solely based on the Mapping Server advertisement. However, PHP behavior may safely be done in following cases: Psenak, et al. Expires January 7, 2017 [Page 11] Internet-Draft OSPF Extensions for Segment Routing July 2016 The Prefix is intra-area type and the downstream neighbor is the originator of the prefix. The Prefix is inter-area type and downstream neighbor is an ABR, which is advertising the prefix reachability and is also generating the Extended Prefix TLV with the A-flag set for this prefix as described in section 2.1 of [RFC7684]. The Prefix is external type and downstream neighbor is an ASBR, which is advertising the prefix reachability and is also generating the Extended Prefix TLV with the A-flag set for this prefix as described in section 2.1 of [RFC7684]. When a Prefix-SID is advertised in an Extended Prefix Range TLV, then the value advertised in Prefix SID Sub-TLV is interpreted as a starting SID value. Example 1: If the following router addresses (loopback addresses) need to be mapped into the corresponding Prefix SID indexes: Router-A: 192.0.2.1/32, Prefix-SID: Index 1 Router-B: 192.0.2.2/32, Prefix-SID: Index 2 Router-C: 192.0.2.3/32, Prefix-SID: Index 3 Router-D: 192.0.2.4/32, Prefix-SID: Index 4 then the Prefix field in the Extended Prefix Range TLV would be set to 192.0.2.1, Prefix Length would be set to 32, Range Size would be set to 4, and the Index value in the Prefix-SID Sub-TLV would be set to 1. Example 2: If the following prefixes need to be mapped into the corresponding Prefix-SID indexes: 10.1.1/24, Prefix-SID: Index 51 10.1.2/24, Prefix-SID: Index 52 10.1.3/24, Prefix-SID: Index 53 10.1.4/24, Prefix-SID: Index 54 10.1.5/24, Prefix-SID: Index 55 10.1.6/24, Prefix-SID: Index 56 10.1.7/24, Prefix-SID: Index 57 then the Prefix field in the Extended Prefix Range TLV would be set to 10.1.1.0, Prefix Length would be set to 24, Range Size would be 7, and the Index value in the Prefix-SID Sub-TLV would be set to 51. Psenak, et al. Expires January 7, 2017 [Page 12] Internet-Draft OSPF Extensions for Segment Routing July 2016 6. SID/Label Binding Sub-TLV The SID/Label Binding Sub-TLV is used to advertise a SID/Label mapping for a path to the prefix. The SID/Label Binding Sub-TLV MAY be originated by any router in an OSPF domain. The router may advertise a SID/Label binding to a FEC along with at least a single 'nexthop style' anchor. The protocol supports more than one 'nexthop style' anchor to be attached to a SID/Label binding, which results in a simple path description language. In analogy to RSVP, the terminology for this is called an 'Explicit Route Object' (ERO). Since ERO style path notation allows anchoring SID/label bindings to both link and node IP addresses, any Label Switched Path (LSP) can be described. Additionally, SID/Label Bindings from external protocols can be easily re-advertised. The SID/Label Binding Sub-TLV may be used for advertising SID/Label Bindings and their associated Primary and Backup paths. In a single TLV, a primary ERO Path, backup ERO Path, or both can be advertised. If a router wants to advertise multiple parallel paths, then it can generate several TLVs for the same Prefix/FEC. Each occurrence of a Binding TLV for a given FEC Prefix will add a new path. The SID/Label Binding Sub-TLV is a Sub-TLV of the OSPF Extended Prefix TLV described in [RFC7684] and the OSPF Extended Prefix Range TLV described in Section 4. Multiple SID/Label Binding TLVs can be present in their parent TLV. The SID/Label Binding Sub-TLV has following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Reserved | MT-ID | Weight | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs (variable) | +- -+ | | where: Type: TBD, suggested value 3 Length: Variable Flags: Single octet field containing the following flags: Psenak, et al. Expires January 7, 2017 [Page 13] Internet-Draft OSPF Extensions for Segment Routing July 2016 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |M| | +-+-+-+-+-+-+-+-+ where: M-bit - When the bit is set, the binding represents a mirroring context as defined in [I-D.minto-rsvp-lsp-egress-fast-protection]. MT-ID: Multi-Topology ID (as defined in [RFC4915]). Weight: Weight used for load-balancing purposes. The use of the weight is defined in [I-D.ietf-spring-segment-routing]. The SID/Label Binding Sub-TLV supports the following Sub-TLVs: SID/Label Sub-TLV as described in Section 2.1. This Sub-TLV MUST appear in the SID/Label Binding Sub-TLV and it SHOULD only appear once. If the SID/Label Sub-TLV is not included in the SID/Label Binding Sub-TLV, the SID/Label Binding Sub-TLV MUST be ignored. If the SID/Label Sub-TLV appears in the SID/Label Binding Sub-TLV more than once, instances other than the first will be ignored and the condition SHOULD be logged for possible action by the network operator. ERO Metric Sub-TLV as defined in Section 6.1. ERO Sub-TLVs as defined in Section 6.2. 6.1. ERO Metric Sub-TLV The ERO Metric Sub-TLV is a Sub-TLV of the SID/Label Binding TLV. The ERO Metric Sub-TLV advertises the cost of an ERO path. It is used to compare the cost of a given source/destination path. A router SHOULD advertise the ERO Metric Sub-TLV in an advertised ERO TLV. The cost of the ERO Metric Sub-TLV SHOULD be set to the cumulative IGP or TE path cost of the advertised ERO. Since manipulation of the Metric field may attract or repel traffic to and from the advertised segment, it MAY be manually overridden. Psenak, et al. Expires January 7, 2017 [Page 14] Internet-Draft OSPF Extensions for Segment Routing July 2016 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Metric (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ERO Metric Sub-TLV format where: Type: TBD, suggested value 8 Length: Always 4 Metric: A 4-octet metric representing the aggregate IGP or TE path cost. 6.2. ERO Sub-TLVs All ERO information represents an ordered set which describes the segments of a path. The first ERO Sub-TLV describes the first segment of a path. Similiarly, the last ERO Sub-TLV describes the segment closest to the egress point. If a router extends or stitches a path, it MUST prepend the new segment's path information to the ERO list. This applies equally to advertised backup EROs. All ERO Sub-TLVs must immediately follow the SID/Label Sub-TLV. All Backup ERO Sub-TLVs must immediately follow the last ERO Sub-TLV. 6.2.1. IPv4 ERO Sub-TLV The IPv4 ERO Sub-TLV is a Sub-TLV of the SID/Label Binding Sub-TLV. The IPv4 ERO Sub-TLV describes a path segment using IPv4 Address style encoding. Its semantics have been borrowed from [RFC3209]. Psenak, et al. Expires January 7, 2017 [Page 15] Internet-Draft OSPF Extensions for Segment Routing July 2016 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Address (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv4 ERO Sub-TLV format where: Type: TBD, suggested value 4 Length: 8 octets Flags: Single octet field containing the following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |L| | +-+-+-+-+-+-+-+-+ where: L-bit - If the L-bit is set, then the segment path is designated as 'loose'. Otherwise, the segment path is designated as 'strict'. The terms 'loose' and 'strict' are defined for RSVP subobjects in [RFC3209]. IPv4 Address - The address of the explicit route hop. 6.2.2. Unnumbered Interface ID ERO Sub-TLV The Unnumbered Interface ID ERO Sub-TLV is a Sub-TLV of the SID/Label Binding Sub-TLV. The appearance and semantics of the 'Unnumbered Interface ID' have been borrowed from [RFC3477]. The Unnumbered Interface-ID ERO Sub-TLV describes a path segment that includes an unnumbered interface. Unnumbered interfaces are referenced using the interface index. Interface indices are assigned local to the router and therefore are not unique within a domain. All elements in an ERO path need to be unique within a domain and hence need to be disambiguated using a domain unique Router-ID. Psenak, et al. Expires January 7, 2017 [Page 16] Internet-Draft OSPF Extensions for Segment Routing July 2016 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: Unnumbered Interface ID ERO Sub-TLV format Type: TBD, suggested value 5 Length: 12 octets Flags: Single octet field containing the following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |L| | +-+-+-+-+-+-+-+-+ where: L-bit - If the L-bit is set, then the segment path is designated as 'loose'. Otherwise, the segment path is designated as 'strict'. The terms 'loose' and 'strict' are defined for RSVP subobjects in [RFC3209] Router-ID: Router-ID of the next-hop. Interface ID: The identifier assigned to the link by the router specified by the Router-ID. 6.2.3. IPv4 Backup ERO Sub-TLV IPv4 Prefix Backup ERO Sub-TLV is a Sub-TLV of the SID/Label Binding Sub-TLV. The IPv4 Backup ERO Sub-TLV describes a path segment using IPv4 Address style of encoding. Its semantics have been borrowed from [RFC3209]. Psenak, et al. Expires January 7, 2017 [Page 17] Internet-Draft OSPF Extensions for Segment Routing July 2016 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IPv4 Address (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ IPv4 Backup ERO Sub-TLV format where: Type: TBD, suggested value 6 Length: 8 octets Flags: Single octet field containing the following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |L| | +-+-+-+-+-+-+-+-+ where: L-bit - If the L-bit is set, then the segment path is designated as 'loose'. Otherwise, the segment path is designated as 'strict'. The terms 'loose' and 'strict' are defined for RSVP subobjects in [RFC3209] IPv4 Address - The address of the explicit route hop. 6.2.4. Unnumbered Interface ID Backup ERO Sub-TLV The Unnumbered Interface ID Backup ERO Sub-TLV is a Sub-TLV of the SID/Label Binding Sub-TLV. The appearance and semantics of the 'Unnumbered Interface ID' have been borrowed from [RFC3477]. The Unnumbered Interface-ID Backup ERO Sub-TLV describes a path segment that includes an unnumbered interface. Unnumbered interfaces are referenced using the interface index. Interface indices are assigned local to the router and are therefore not unique within a domain. All elements in an ERO path need to be unique within a Psenak, et al. Expires January 7, 2017 [Page 18] Internet-Draft OSPF Extensions for Segment Routing July 2016 domain and hence need to be disambiguated with specification of the domain unique Router-ID. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Router ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Interface ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Unnumbered Interface ID Backup ERO Sub-TLV format where: Type: TBD, suggested value 7 Length: 12 octets Flags: Single octet field containing the following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |L| | +-+-+-+-+-+-+-+-+ where: L-bit - If the L-bit is set, then the segment path is designated as 'loose'. Otherwise, the segment path is designated as 'strict'. Router-ID: Router-ID of the next-hop. Interface ID: The identifier assigned to the link by the router specified by the Router-ID. 7. Adjacency Segment Identifier (Adj-SID) An Adjacency Segment Identifier (Adj-SID) represents a router adjacency in Segment Routing. Psenak, et al. Expires January 7, 2017 [Page 19] Internet-Draft OSPF Extensions for Segment Routing July 2016 7.1. Adj-SID Sub-TLV Adj-SID is an optional Sub-TLV of the Extended Link TLV defined in [RFC7684]. It MAY appear multiple times in the Extended Link TLV. Examples where more than one Adj-SID may be used per neighbor are described in section 4 of [I-D.filsfils-spring-segment-routing-use-cases]. The Adj-SID Sub-TLV has the following format: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Reserved | MT-ID | Weight | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Label/Index (variable) | +---------------------------------------------------------------+ where: Type: TBD, suggested value 2. Length: Variable. Flags: Single octet field containing the following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |B|V|L|G| | +-+-+-+-+-+-+-+-+ where: B-Flag: Backup Flag. If set, the Adj-SID refers to an adjacency that is eligible for protection (e.g.: using IPFRR or MPLS-FRR) as described in section 3.5 of [I-D.ietf-spring-segment-routing]. The V-Flag: Value/Index Flag. If set, then the Adj-SID carries an absolute value. If not set, then the Adj-SID carries an index. The L-Flag: Local/Global Flag. If set, then the value/index carried by the Adj-SID has local significance. If not set, then the value/index carried by this Sub-TLV has global significance. Psenak, et al. Expires January 7, 2017 [Page 20] Internet-Draft OSPF Extensions for Segment Routing July 2016 The G-Flag: Group Flag. When set, the G-Flag indicates that the Adj-SID refers to a group of adjacencies (and therefore MAY be assigned to other adjacencies as well). Other bits: Reserved. These MUST be zero when sent and are ignored when received. MT-ID: Multi-Topology ID (as defined in [RFC4915]. Weight: Weight used for load-balancing purposes. The use of the weight is defined in [I-D.ietf-spring-segment-routing]. SID/Index/Label: According to the V and L flags, it contains either: A 32-bit index defining the offset in the SID/Label space advertised by this router. A 24-bit label where the 20 rightmost bits are used for encoding the label value. An SR capable router MAY allocate an Adj-SID for each of its adjacencies and set the B-Flag when the adjacency is eligible for protection by an FRR mechanism (IP or MPLS) as described in section 3.5 of [I-D.ietf-spring-segment-routing]. 7.2. LAN Adj-SID Sub-TLV LAN Adj-SID is an optional Sub-TLV of the Extended Link TLV defined in [RFC7684]. It MAY appear multiple times in the Extended-Link TLV. It is used to advertise a SID/Label for an adjacency to a non-DR router on a broadcast, NBMA, or hybrid [RFC6845] network. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Reserved | MT-ID | Weight | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Neighbor ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Label/Index (variable) | +---------------------------------------------------------------+ where: Type: TBD, suggested value 3. Psenak, et al. Expires January 7, 2017 [Page 21] Internet-Draft OSPF Extensions for Segment Routing July 2016 Length: Variable. Flags: Single octet field containing the following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |B|V|L|G| | +-+-+-+-+-+-+-+-+ where: B-Flag: Backup-flag. If set, the LAN-Adj-SID refers to an adjacency that is eligible for protection (e.g.: using IPFRR or MPLS-FRR) as described in section 3.5 of [I-D.ietf-spring-segment-routing]. The V-Flag: Value/Index Flag. If set, then the Prefix-SID carries an absolute value. If not set, then the Prefix-SID carries an index. The L-Flag: Local/Global Flag. If set, then the value/index carried by the Prefix-SID has local significance. If not set, then the value/index carried by this Sub-TLV has global significance. The G-Flag: Group Flag. When set, the G-Flag indicates that the LAN-Adj-SID refers to a group of adjacencies (and therefore MAY be assigned to other adjacencies as well). Other bits: Reserved. These MUST be zero when sent and are ignored when received. MT-ID: Multi-Topology ID (as defined in [RFC4915]. Weight: Weight used for load-balancing purposes. The use of the weight is defined in [I-D.ietf-spring-segment-routing]. Neighbor ID: The Router ID of the neighbor for which the LAN-Adj- SID is advertised. SID/Index/Label: According to the V and L flags, it contains either: A 32-bit index defining the offset in the SID/Label space advertised by this router. A 24-bit label where the 20 rightmost bits are used for encoding the label value. Psenak, et al. Expires January 7, 2017 [Page 22] Internet-Draft OSPF Extensions for Segment Routing July 2016 8. Elements of Procedure 8.1. Intra-area Segment routing in OSPFv2 An OSPFv2 router that supports segment routing MAY advertise Prefix- SIDs for any prefix to which it is advertising reachability (e.g., a loopback IP address as described in Section 5). If multiple routers advertise a Prefix-SID for the same prefix, then the Prefix-SID MUST be the same. This is required in order to allow traffic load-balancing when multiple equal cost paths to the destination exist in the OSPFv2 routing domain. Prefix-SID can also be advertised by the SR Mapping Servers (as described in [I-D.filsfils-spring-segment-routing-ldp-interop]). The Mapping Server advertises Prefix-SIDs for remote prefixes that exist in the OSPFv2 routing domain. Multiple Mapping Servers can advertise Prefix-SIDs for the same prefix, in which case the same Prefix-SID MUST be advertised by all of them. The flooding scope of the OSPF Extended Prefix Opaque LSA that is generated by the SR Mapping Server could be either area scoped or AS scoped and is determined based on the configuration of the SR Mapping Server. The SR Mapping Server MUST use OSPF Extended Prefix Range TLV when advertising SIDs for prefixes. Prefixes of different route-types can be combined in a single OSPF Extended Prefix Range TLV advertised by the SR Mapping Server. Area-scoped OSPF Extended Prefix Range TLV are propagated between areas. Similar to propagation of prefixes between areas, an ABR only propagates the OSPF Extended Prefix Range TLV that it considers to be the best from the set it received. The rules used to pick the best OSPF Extended Prefix Range TLV are described in Section 4. When propagating an OSPF Extended Prefix Range TLV between areas, ABRs MUST set the IA-Flag, that is used to prevent redundant flooding of the OSPF Extended Prefix Range TLV between areas as described in Section 4. If the Prefix-SID that is advertised in a Prefix SID Sub-TLV is also covered by the OSPF Extended Prefix Range TLV, the Prefix-SID advertised in Prefix SID Sub-TLV MUST be preferred. 8.2. Inter-area Segment routing in OSPFv2 In order to support SR in a multi-area environment, OSPFv2 must propagate Prefix-SID information between areas. The following procedure is used to propagate Prefix SIDs between areas. Psenak, et al. Expires January 7, 2017 [Page 23] Internet-Draft OSPF Extensions for Segment Routing July 2016 When an OSPF ABR advertises a Type-3 Summary LSA from an intra-area prefix to all its connected areas, it will also originate an Extended Prefix Opaque LSA, as described in [RFC7684]. The flooding scope of the Extended Prefix Opaque LSA type will be set to area-scope. The route-type in the OSPF Extended Prefix TLV is set to inter-area. The Prefix-SID Sub-TLV will be included in this LSA and the Prefix-SID value will be set as follows: The ABR will look at its best path to the prefix in the source area and find the advertising router associated with the best path to that prefix. The ABR will then determine if such router advertised a Prefix-SID for the prefix and use it when advertising the Prefix-SID to other connected areas. If no Prefix-SID was advertised for the prefix in the source area by the router that contributes to the best path to the prefix, the originating ABR will use the Prefix-SID advertised by any other router when propagating the Prefix-SID for the prefix to other areas. When an OSPF ABR advertises Type-3 Summary LSAs from an inter-area route to all its connected areas, it will also originate an Extended Prefix Opaque LSA, as described in [RFC7684]. The flooding scope of the Extended Prefix Opaque LSA type will be set to area-scope. The route-type in OSPF Extended Prefix TLV is set to inter-area. The Prefix-SID Sub-TLV will be included in this LSA and the Prefix-SID will be set as follows: The ABR will look at its best path to the prefix in the backbone area and find the advertising router associated with the best path to that prefix. The ABR will then determine if such router advertised a Prefix-SID for the prefix and use it when advertising the Prefix-SID to other connected areas. If no Prefix-SID was advertised for the prefix in the backbone area by the ABR that contributes to the best path to the prefix, the originating ABR will use the Prefix-SID advertised by any other router when propagating the Prefix-SID for the prefix to other areas. Psenak, et al. Expires January 7, 2017 [Page 24] Internet-Draft OSPF Extensions for Segment Routing July 2016 8.3. SID for External Prefixes Type-5 LSAs are flooded domain wide. When an ASBR, which supports SR, generates Type-5 LSAs, it should also originate Extended Prefix Opaque LSAs, as described in [RFC7684]. The flooding scope of the Extended Prefix Opaque LSA type is set to AS-scope. The route-type in the OSPF Extended Prefix TLV is set to external. The Prefix-SID Sub-TLV is included in this LSA and the Prefix-SID value will be set to the SID that has been reserved for that prefix. When an NSSA ABR translates Type-7 LSAs into Type-5 LSAs, it should also advertise the Prefix-SID for the prefix. The NSSA ABR determines its best path to the prefix advertised in the translated Type-7 LSA and finds the advertising router associated with that path. If the advertising router has advertised a Prefix-SID for the prefix, then the NSSA ABR uses it when advertising the Prefix-SID for the Type-5 prefix. Otherwise, the Prefix-SID advertised by any other router will be used. 8.4. Advertisement of Adj-SID The Adjacency Segment Routing Identifier (Adj-SID) is advertised using the Adj-SID Sub-TLV as described in Section 7. 8.4.1. Advertisement of Adj-SID on Point-to-Point Links An Adj-SID MAY be advertised for any adjacency on a P2P link that is in neighbor state 2-Way or higher. If the adjacency on a P2P link transitions from the FULL state, then the Adj-SID for that adjacency MAY be removed from the area. If the adjacency transitions to a state lower then 2-Way, then the Adj-SID advertisement MUST be removed from the area. 8.4.2. Adjacency SID on Broadcast or NBMA Interfaces Broadcast, NBMA or or hybrid [RFC6845] networks in OSPF are represented by a star topology where the Designated Router (DR) is the central point to which all other routers on the broadcast, NBMA, or hybrid network connect. As a result, routers on the broadcast, NBMA, or hybrid network advertise only their adjacency to the DR. Routers that do not act as DR do not form or advertise adjacencies with each other. They do, however, maintain 2-Way adjacency state with each other and are directly reachable. When Segment Routing is used, each router on the broadcast or NBMA network MAY advertise the Adj-SID for its adjacency to the DR using the Adj-SID Sub-TLV as described in Section 7.1. Psenak, et al. Expires January 7, 2017 [Page 25] Internet-Draft OSPF Extensions for Segment Routing July 2016 SR capable routers MAY also advertise an LAN-Adj-SID for other neighbors (e.g., BDR, DR-OTHER) on the broadcast, NBMA or hybrid network using the LAN-ADJ-SID Sub-TLV as described in Section 7.2. 9. IANA Considerations This specification updates several existing OSPF registries. 9.1. OSPF OSPF Router Information (RI) TLVs Registry o 8 (IANA Preallocated) - SR-Algorithm TLV o 9 (IANA Preallocated) - SID/Label Range TLV 9.2. OSPF Extended Prefix LSA TLV Registry Following values are allocated: o 2 - OSPF Extended Prefix Range TLV 9.3. OSPF Extended Prefix LSA Sub-TLV Registry Following values are allocated: o 1 - SID/Label Sub-TLV o 2 - Prefix SID Sub-TLV o 3 - SID/Label Binding Sub-TLV o 4 - IPv4 ERO Sub-TLV o 5 - Unnumbered Interface ID ERO Sub-TLV o 6 - IPv4 Backup ERO Sub-TLV o 7 - Unnumbered Interface ID Backup ERO Sub-TLV o 8 - ERO Metric Sub-TLV 9.4. OSPF Extended Link LSA Sub-TLV Registry Following initial values are allocated: o 1 - SID/Label Sub-TLV o 2 - Adj-SID Sub-TLV Psenak, et al. Expires January 7, 2017 [Page 26] Internet-Draft OSPF Extensions for Segment Routing July 2016 o 3 - LAN Adj-SID/Label Sub-TLV 10. Implementation Status An implementation survey with seven questions related to the implementer's support of OSPFv2 Segment Routing was sent to the OSPF WG list and several known implementers. This section contains responses from two implementers who completed the survey. No external means were used to verify the accuracy of the information submitted by the respondents. The respondents are considered experts on the products they reported on. Additionally, responses were omitted from implementers who indicated that they have not implemented the function yet. Responses from Nokia (former Alcatel-Lucent): Link to a web page describing the implementation: https://infoproducts.alcatel-lucent.com/cgi-bin/dbaccessfilename.cgi/ 3HE10799AAAATQZZA01_V1_7450%20ESS%207750%20SR%20and%207950%20XRS%20Un icast%20Routing%20Protocols%20Guide%20R14.0.R1.pdf The implementation's level of maturity: Production. Coverage: We have implemented all sections and have support for the latest draft. Licensing: Part of the software package that needs to be purchased. Implementation experience: Great spec. We also performed inter- operability testing with Cisco's OSPF Segment Routing implementation. Contact information: wim.henderickx@nokia.com Responses from Cisco Systems: Link to a web page describing the implementation: www.segment-routing.net/home/tutorial The implementation's level of maturity: Production. Coverage: All sections, except the section 6 (SID/Label Binding Sub- TLV) have been implemented according to the latest draft. Licensing: Part of a commercial software package. Implementation experience: Many aspects of the draft are result of the actual implementation experience, as the draft evolved from its Psenak, et al. Expires January 7, 2017 [Page 27] Internet-Draft OSPF Extensions for Segment Routing July 2016 initial version to the current one. Interoperability testing with Alcatel-Lucent was performed, which confirmed the draft's ability to serve as a reference for the implementors. Contact information: ppsenak@cisco.com Responses from Juniper: The implementation's name and/or a link to a web page describing the implementation: Feature name is OSPF SPRING The implementation's level of maturity: To be released in 16.2 (second half of 2016) Coverage: All sections implemented except Sections 4, and 6. Licensing: JUNOS Licensing needed. Implementation experience: NA Contact information: shraddha@juniper.net 11. Security Considerations Implementations must assure that malformed TLV and Sub-TLV permutations do not result in errors which cause hard OSPF failures. 12. Contributors The following people gave a substantial contribution to the content of this document: Acee Lindem, Ahmed Bashandy, Martin Horneffer, Bruno Decraene, Stephane Litkowski, Igor Milojevic, Rob Shakir and Saku Ytti. 13. Acknowledgements We would like to thank Anton Smirnov for his contribution. Many thanks to Yakov Rekhter, John Drake and Shraddha Hedge for their contribution on earlier incarnations of the "Binding / MPLS Label TLV" in [I-D.gredler-ospf-label-advertisement]. Thanks to Acee Lindem for the detail review of the draft, corrections, as well as discussion about details of the encoding. Psenak, et al. Expires January 7, 2017 [Page 28] Internet-Draft OSPF Extensions for Segment Routing July 2016 14. References 14.1. 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, . [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998, . [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001, . [RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)", RFC 3477, DOI 10.17487/RFC3477, January 2003, . [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering (TE) Extensions to OSPF Version 2", RFC 3630, DOI 10.17487/RFC3630, September 2003, . [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, DOI 10.17487/RFC4915, June 2007, . [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The OSPF Opaque LSA Option", RFC 5250, DOI 10.17487/RFC5250, July 2008, . [RFC6845] Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast and Point-to-Multipoint Interface Type", RFC 6845, DOI 10.17487/RFC6845, January 2013, . [RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W., Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute Advertisement", RFC 7684, DOI 10.17487/RFC7684, November 2015, . Psenak, et al. Expires January 7, 2017 [Page 29] Internet-Draft OSPF Extensions for Segment Routing July 2016 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, February 2016, . 14.2. Informative References [I-D.filsfils-spring-segment-routing-ldp-interop] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe, "Segment Routing interoperability with LDP", draft- filsfils-spring-segment-routing-ldp-interop-02 (work in progress), September 2014. [I-D.filsfils-spring-segment-routing-use-cases] Filsfils, C., Francois, P., Previdi, S., Decraene, B., Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R., Ytti, S., Henderickx, W., Tantsura, J., Kini, S., and E. Crabbe, "Segment Routing Use Cases", draft-filsfils- spring-segment-routing-use-cases-01 (work in progress), October 2014. [I-D.gredler-ospf-label-advertisement] Gredler, H., Amante, S., Scholl, T., and L. Jalil, "Advertising MPLS labels in OSPF", draft-gredler-ospf- label-advertisement-03 (work in progress), May 2013. [I-D.ietf-spring-segment-routing] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B., Litkowski, S., Horneffer, M., Shakir, R., Tantsura, J., and E. Crabbe, "Segment Routing Architecture", draft-ietf- spring-segment-routing-00 (work in progress), December 2014. [I-D.minto-rsvp-lsp-egress-fast-protection] Jeganathan, J., Gredler, H., and Y. Shen, "RSVP-TE LSP egress fast-protection", draft-minto-rsvp-lsp-egress-fast- protection-03 (work in progress), November 2013. Authors' Addresses Psenak, et al. Expires January 7, 2017 [Page 30] Internet-Draft OSPF Extensions for Segment Routing July 2016 Peter Psenak (editor) Cisco Systems, Inc. Apollo Business Center Mlynske nivy 43 Bratislava 821 09 Slovakia Email: ppsenak@cisco.com Stefano Previdi (editor) Cisco Systems, Inc. Via Del Serafico, 200 Rome 00142 Italy Email: sprevidi@cisco.com Clarence Filsfils Cisco Systems, Inc. Brussels Belgium Email: cfilsfil@cisco.com Hannes Gredler Individual Austria Email: hannes@gredler.at Rob Shakir Jive Communications, Inc. 1275 West 1600 North, Suite 100 Orem, UT 84057 US Email: rrjs@rob.sh Psenak, et al. Expires January 7, 2017 [Page 31] Internet-Draft OSPF Extensions for Segment Routing July 2016 Wim Henderickx Nokia Copernicuslaan 50 Antwerp 2018 BE Email: wim.henderickx@nokia.com Jeff Tantsura Individual US Email: jefftant.ietf@gmail.com Psenak, et al. Expires January 7, 2017 [Page 32]