Open Shortest Path First IGP P. Psenak, Ed. Internet-Draft S. Previdi, Ed. Intended status: Standards Track C. Filsfils Expires: December 7, 2014 Cisco Systems, Inc. H. Gredler Juniper Networks, Inc. R. Shakir British Telecom W. Henderickx Alcatel-Lucent J. Tantsura Ericsson June 5, 2014 OSPF Extensions for Segment Routing draft-psenak-ospf-segment-routing-extensions-05 Abstract Segment Routing (SR) allows for 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 necessary OSPF extensions that need to be introduced 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 December 7, 2014 [Page 1] Internet-Draft OSPF Extensions for Segment Routing June 2014 This Internet-Draft will expire on December 7, 2014. Copyright Notice Copyright (c) 2014 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 . . . . . . . . . . . . . . . . . . . 5 4. OSPFv2 Extended Prefix Opaque LSA type . . . . . . . . . . . 7 4.1. OSPF Extended Prefix TLV . . . . . . . . . . . . . . . . 8 4.2. Prefix SID Sub-TLV . . . . . . . . . . . . . . . . . . . 9 4.3. SID/Label Binding sub-TLV . . . . . . . . . . . . . . . . 13 4.3.1. ERO Metric sub-TLV . . . . . . . . . . . . . . . . . 15 4.3.2. ERO sub-TLVs . . . . . . . . . . . . . . . . . . . . 15 5. Adjacency Segment Identifier (Adj-SID) . . . . . . . . . . . 20 5.1. OSPFv2 Extended Link Opaque LSA . . . . . . . . . . . . . 20 5.2. OSPFv2 Extended Link TLV . . . . . . . . . . . . . . . . 21 5.3. Adj-SID sub-TLV . . . . . . . . . . . . . . . . . . . . . 22 5.4. LAN Adj-SID Sub-TLV . . . . . . . . . . . . . . . . . . . 23 6. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 25 6.1. Intra-area Segment routing in OSPFv2 . . . . . . . . . . 25 6.2. Inter-area Segment routing in OSPFv2 . . . . . . . . . . 25 6.3. SID for External Prefixes . . . . . . . . . . . . . . . . 26 6.4. Advertisement of Adj-SID . . . . . . . . . . . . . . . . 27 6.4.1. Advertisement of Adj-SID on Point-to-Point Links . . 27 6.4.2. Adjacency SID on Broadcast or NBMA Interfaces . . . . 27 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 27 7.1. OSPF Extend Prefix LSA TLV Registry . . . . . . . . . . . 28 7.2. OSPF Extend Prefix LSA sub-TLV Registry . . . . . . . . . 28 7.3. OSPF Extend Link LSA TLV Registry . . . . . . . . . . . . 29 7.4. OSPF Extend Link LSA sub-TLV Registry . . . . . . . . . . 29 Psenak, et al. Expires December 7, 2014 [Page 2] Internet-Draft OSPF Extensions for Segment Routing June 2014 8. Security Considerations . . . . . . . . . . . . . . . . . . . 30 9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 30 10. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 30 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 30 11.1. Normative References . . . . . . . . . . . . . . . . . . 30 11.2. Informative References . . . . . . . . . . . . . . . . . 31 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 31 1. Introduction Segment Routing (SR) allows for 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 of the cases, is a one-hop path. SR's control-plane can be applied to both IPv6 and MPLS data-planes, and do not require any additional signaling (other than the regular IGP). For example, when used in MPLS networks, SR paths do not require any LDP or RSVP-TE signaling. Still, SR can interoperate in the presence of LSPs established with RSVP or LDP . This draft describes the necessary OSPF extensions that need to be introduced for Segment Routing. Segment Routing architecture is described in [I-D.filsfils-rtgwg-segment-routing]. Segment Routing use cases are described in [I-D.filsfils-rtgwg-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 (defined in [RFC5250]) are defined. These new LSAs are defined as generic containers that can be used in order to advertise any additional attributes associated with the prefix or link. These new Opaque LSAs are complementary to the existing LSAs and are not aimed to replace any of the existing LSAs. Psenak, et al. Expires December 7, 2014 [Page 3] Internet-Draft OSPF Extensions for Segment Routing June 2014 2.1. SID/Label sub-TLV SID/Label sub-TLV appears in multiple TLVs or sub-TLVs defined later in this document. It is used to advertise SID or label associated with the prefix or adjacency. 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 bytes 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 capabilities of the router to be advertised to other routers in the area. These SR capabilities are advertised in Router Information Opaque LSA (defined in [RFC4970]). 3.1. SR-Algorithm TLV SR-Algorithm TLV is a TLV of Router Information Opaque LSA (defined in [RFC4970]). The SR-Algorithm Sub-TLV is optional, it MAY only appear once inside the Router Informational Opaque LSA. If the SID/Label Range TLV, as defined in Section 3.2, is advertised, then SR-Algorithm TLV MUST also be advertised. Router may use various algorithms when calculating reachability to other nodes in area or to prefixes attached to these nodes. Examples of these algorithms are metric based Shortest Path First (SPF), Psenak, et al. Expires December 7, 2014 [Page 4] Internet-Draft OSPF Extensions for Segment Routing June 2014 various sorts of Constrained SPF, etc. SR-Algorithm TLV allows a router to advertise algorithms that router is currently using to other routers in an area. SR-Algorithm TLV has following structure: 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: one octet identifying the algorithm. The following value has been defined: 0: IGP metric based SPT. RI LSA can be advertised at any of the defined flooding scopes (link, area, or autonomous system (AS)). For the purpose of the SR- Algorithm TLV propagation area scope flooding is required. 3.2. SID/Label Range TLV The SID/Label Range TLV is a TLV of Router Information Opaque LSA (defined in [RFC4970]). SID/Label Sub-TLV MAY appear multiple times and has following format: Psenak, et al. Expires December 7, 2014 [Page 5] Internet-Draft OSPF Extensions for Segment Routing June 2014 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 octet of the SID/label range Currently the only supported Sub-TLV is the SID/Label TLV as defined in Section 2.1. SID/Label advertised in SID/Label TLV represents the first SID/Label from the advertised range. Multiple occurrence 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 in which order the set of SID/Label Range TLVs are advertised inside Router Information Opaque LSA. The originating router MUST ensure the order is same after a graceful restart (using checkpointing, non-volatile storage or any other mechanism) in order to guarantee the same order before and after graceful restart. o Receiving router must adhere to the order in which the ranges are advertised when calculating a SID/label from the SID index. Here follows an example of advertisement of multiple ranges: Psenak, et al. Expires December 7, 2014 [Page 6] Internet-Draft OSPF Extensions for Segment Routing June 2014 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 SRGB is 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 ... RI LSA can be advertised at any of the defined flooding scopes (link, area, or autonomous system (AS)). For the purpose of the SR- Capability TLV propagation area scope flooding is required. 4. OSPFv2 Extended Prefix Opaque LSA type A new Opaque LSA (defined in [RFC5250]) is defined in OSPFv2 in order to advertise additional prefix attributes: OSPFv2 Extended Prefix Opaque LSA. Multiple OSPFv2 Extended Prefix Opaque LSAs can be advertised by a single router. Flooding scope of the OSPFv2 Extended Prefix Opaque LSA depends on the content inside the LSA and is in control of the originating router. The format of the OSPFv2 Extended Prefix Opaque LSA is as follows: Psenak, et al. Expires December 7, 2014 [Page 7] Internet-Draft OSPF Extensions for Segment Routing June 2014 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | 9, 10, or 11 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opaque type | Instance | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +- TLVs -+ | ... | Opaque type used by OSPFv2 Extended Prefix Opaque LSA is 7. The format of the TLVs within the body of the LSA is the same as the format used by the Traffic Engineering Extensions to OSPF defined in [RFC3630]. The LSA payload consists of one or more nested Type/Length/Value (TLV) triplets. The format of each TLV is: 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Length field defines the length of the value portion in octets. The TLV is padded to 4-octet alignment; padding is not included in the length field. Nested TLVs are also 32-bit aligned. Unrecognized types are ignored. 4.1. OSPF Extended Prefix TLV The OSPF Extended Prefix TLV is used in order to advertise additional attributes associated with the prefix. Multiple OSPF Extended Prefix TLVs MAY be carried in each OSPFv2 Extended Prefix Opaque LSA, however all prefixes included in the single OSPFv2 Extended Prefix Opaque LSA MUST have the same flooding scope. The structure of the OSPF Extended Prefix TLV is as follows: Psenak, et al. Expires December 7, 2014 [Page 8] Internet-Draft OSPF Extensions for Segment Routing June 2014 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Route Type | Prefix Length | AF | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Address Prefix (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs (variable) | +- -+ | | where: Type: TBD, suggested value 1. Length: variable Route type: type of the OSPF route. Supported types are: 0 - unspecified 1 - intra-area 3 - inter-area 5 - external 7 - NSSA external If the route type is 0 (unspecified) the information inside the OSPF External Prefix TLV applies to the prefix regardless of what route-type it is. This is useful when some prefix specific attributes are advertised by some external entity, which is not aware of the route-type associated with the prefix. Prefix length: length of the prefix AF: 0 - IPv4 unicast Address Prefix: the prefix itself encoded as an even multiple of 32-bit words, padded with zeroed bits as necessary. This encoding consumes ((PrefixLength + 31) / 32) 32-bit words. The default route is represented by a prefix of length 0. 4.2. Prefix SID Sub-TLV The Prefix SID Sub-TLV is a Sub-TLV of the OSPF Extended Prefix TLV. It MAY appear more than once and has following format: Psenak, et al. Expires December 7, 2014 [Page 9] Internet-Draft OSPF Extensions for Segment Routing June 2014 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Range Size | Reserved + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Index/Label (variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ where: Type: TBD, suggested value 2. Length: variable Flags: 1 octet field. The following flags are defined: 0 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |N|P|M|E|V|L| | +-+-+-+-+-+-+-+-+ where: N-Flag: Node-SID flag. If set, then the Prefix-SID refers to the router identified by the prefix. Typically, the N-Flag is set on Prefix-SIDs attached to a router loopback address. The N-Flag is set when the Prefix-SID is a Node- SID as described in [I-D.filsfils-rtgwg-segment-routing]. P-Flag: no-PHP flag. If set, then the penultimate hop MUST NOT pop the Prefix-SID before delivering the packet to the node that advertised the Prefix-SID. M-Flag: Mapping Server Flag. If set, the SID is advertised from the Segment Routing Mapping Server functionality as described in [I-D.filsfils-rtgwg-segment-routing-use-cases]. E-Flag: Explicit-Null Flag. If set, any upstream neighbor of the Prefix-SID originator MUST replace the Prefix-SID with a Prefix-SID having an Explicit-NULL value (0 for IPv4) before forwarding the packet. Psenak, et al. Expires December 7, 2014 [Page 10] Internet-Draft OSPF Extensions for Segment Routing June 2014 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 PrefixSID has local significance. If not set, then the value/index carried by this subTLV has global significance. Other bits: MUST be zero when sent and ignored when received. MT-ID: Multi-Topology ID (as defined in [RFC4915]). Algorithm: one octet identifying the algorithm the Prefix-SID is associated with as defined in Section 3.1. Range size: this field provides the ability to specify a range of addresses and their associated Prefix SIDs. It represents a compression scheme to distribute a continuous Prefix and their continuous, corresponding SID/Label Block. If a single SID is advertised then the Range Size field MUST be set to one. For range advertisements > 1, Range Size represents the number of addresses that need to be mapped into a Prefix-SID. 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 ones. When calculating the outgoing label for the prefix, the router MUST take into account E and P flags advertised by the next-hop router, if next-hop router advertised the SID for the prefix. This MUST be done regardless of next-hop router contributing to the best path to the prefix or not. P-Flag (no-PHP) MUST be set on the Prefix-SIDs allocated to inter- area prefixes that are originated by the ABR based on intra-area or inter-area reachability between areas. In case the inter-area prefix is generated based on the prefix which is directly attached to the ABR, P-Flag SHOULD NOT be set Psenak, et al. Expires December 7, 2014 [Page 11] Internet-Draft OSPF Extensions for Segment Routing June 2014 P-Flag (no-PHP) MUST NOT be set on the Prefix-SIDs allocated to redistributed prefixes, unless the redistributed prefix is directly attached to ASBR, in which case the P-Flag SHOULD NOT be set. If the P-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 to the ultimate hop (the Prefix-SID being removed). If the P-flag is unset the received E-flag is ignored. If the P-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 inter-area border router (prefix propagation from one area to another) or at an inter- domain border 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 PrefixSID with a Prefix-SID having an Explicit-NULL value. 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 M-Flag is set, P-flag MUST be set and E-bit MUST NOT be set. 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 Extended Prefix TLV would be set to 192.0.2.1, Prefix Length would be set to 32, Range Size in Prefix SID sub-TLV would be 4 and Index value would be set to 1. Example 2: If the following prefixes need to be mapped into the corresponding Prefix-SID indexes: Psenak, et al. Expires December 7, 2014 [Page 12] Internet-Draft OSPF Extensions for Segment Routing June 2014 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 Extended Prefix TLV would be set to 10.1.1.0, Prefix Length would be set to 24, Range Size in Prefix SID sub-TLV would be 7 and Index value would be set to 51. 4.3. SID/Label Binding sub-TLV SID/Label Binding sub-TLV is used to advertise SID/Label mapping for a path to the prefix. The SID/Label Binding 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 into 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 to anchor SID/ label bindings to both link and node IP addresses any label switched path, can be described. Furthermore also SID/Label Bindings from external protocols can get easily re-advertised. The SID/Label Binding TLV may be used for advertising SID/Label Bindings and their associated Primary and Backup paths. In one single TLV either a primary ERO Path, a backup ERO Path or both are 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 with respect with a given FEC Prefix has accumulating and not canceling semantics. SID/Label Binding sub-TLV is as sub-TLV of the OSPF Extended Prefix TLV. Multiple SID/Label Binding TLVs can be present in OSPF Extended Prefix TLV. SID/Label Binding sub-TLV has following format: Psenak, et al. Expires December 7, 2014 [Page 13] Internet-Draft OSPF Extensions for Segment Routing June 2014 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Range Size | Reserved + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs (variable) | +- -+ | | where: Type: TBD, suggested value 3 Length: variable Flags: 1 octet field of following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |M| | +-+-+-+-+-+-+-+-+ where: M-bit - When the bit is set the binding represents the 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.filsfils-rtgwg-segment-routing]. Range Size: usage is the same as described in Section 4.2. SID/Label Binding TLV currently supports 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 MUST only appear once. ERO Metric sub-TLV as defined in Section 4.3.1. ERO sub-TLVs as defined in Section 4.3.2. Psenak, et al. Expires December 7, 2014 [Page 14] Internet-Draft OSPF Extensions for Segment Routing June 2014 4.3.1. ERO Metric sub-TLV ERO Metric sub-TLV is a Sub-TLV of the SID/Label Binding TLV. The ERO Metric sub-TLV carries 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. 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 distract traffic from and to the advertised segment it MAY be manually overridden. 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: 4 bytes Metric: 4 bytes 4.3.2. ERO sub-TLVs All 'ERO' information represents an ordered set which describes the segments of a path. The last ERO sub-TLV describes the segment closest to the egress point, contrary the first ERO sub-TLV describes the first segment of a path. If a router extends or stitches a path it MUST prepend the new segments path information to the ERO list. The above similarly applies to backup EROs. All ERO Sub-TLVs must immediately follow the (SID)/Label Sub-TLV. All Backup sub-ERO TLVs must immediately follow last ERO Sub-TLV. Psenak, et al. Expires December 7, 2014 [Page 15] Internet-Draft OSPF Extensions for Segment Routing June 2014 4.3.2.1. IPv4 ERO subTLV 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 of encoding. Its semantics have been borrowed from [RFC3209]. 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 bytes Flags: 1 octet field of following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |L| | +-+-+-+-+-+-+-+-+ where: L-bit - If the L bit is set, then the value of the attribute is 'loose.' Otherwise, the value of the attribute is 'strict.' IPv4 Address - the address of the explicit route hop. 4.3.2.2. Unnumbered Interface ID ERO sub-TLV 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]. Psenak, et al. Expires December 7, 2014 [Page 16] Internet-Draft OSPF Extensions for Segment Routing June 2014 The Unnumbered Interface-ID ERO sub-TLV describes a path segment that spans over an unnumbered interface. Unnumbered interfaces are referenced using the interface index. Interface indices are assigned local to the router and therefore 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. 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 bytes Flags: 1 octet field of following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |L| | +-+-+-+-+-+-+-+-+ where: L-bit - If the L bit is set, then the value of the attribute is 'loose.' Otherwise, the value of the attribute is 'strict.' Router-ID: Router-ID of the next-hop. Interface ID: is the identifier assigned to the link by the router specified by the Router-ID. Psenak, et al. Expires December 7, 2014 [Page 17] Internet-Draft OSPF Extensions for Segment Routing June 2014 4.3.2.3. 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]. 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 bytes Flags: 1 octet field of following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |L| | +-+-+-+-+-+-+-+-+ where: L-bit - If the L bit is set, then the value of the attribute is 'loose.' Otherwise, the value of the attribute is 'strict.' IPv4 Address - the address of the explicit route hop. 4.3.2.4. Unnumbered Interface ID Backup ERO sub-TLV Unnumbered Interface ID Backup -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]. Psenak, et al. Expires December 7, 2014 [Page 18] Internet-Draft OSPF Extensions for Segment Routing June 2014 The Unnumbered Interface-ID ERO sub-TLV describes a path segment that spans over an unnumbered interface. Unnumbered interfaces are referenced using the interface index. Interface indices are assigned local to the router and therefore 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. 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 bytes Flags: 1 octet field of following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |L| | +-+-+-+-+-+-+-+-+ where: L-bit - If the L bit is set, then the value of the attribute is 'loose.' Otherwise, the value of the attribute is 'strict.' Router-ID: Router-ID of the next-hop. Interface ID: is the identifier assigned to the link by the router specified by the Router-ID. Psenak, et al. Expires December 7, 2014 [Page 19] Internet-Draft OSPF Extensions for Segment Routing June 2014 5. Adjacency Segment Identifier (Adj-SID) An Adjacency Segment Identifier (Adj-SID) represents a router adjacency in Segment Routing. At the current stage of Segment Routing architecture it is assumed that the Adj-SID value has local significance (to the router). 5.1. OSPFv2 Extended Link Opaque LSA A new Opaque LSA (defined in [RFC5250] is defined in OSPFv2 in order to advertise additional link attributes: the OSPFv2 Extended Link Opaque LSA. The OSPFv2 Extended Link Opaque LSA has an area flooding scope. Multiple OSPFv2 Extended Link Opaque LSAs can be advertised by a single router in an area. The format of the OSPFv2 Extended Link Opaque LSA is as follows: 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS age | Options | 10 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Opaque type | Instance | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Advertising Router | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS sequence number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | LS checksum | length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | +- TLVs -+ | ... | Opaque type used by OSPFv2 Extended Link Opaque LSA is 8. The format of the TLVs within the body of LSA is the same as the format used by the Traffic Engineering Extensions to OSPF defined in [RFC3630]. The LSA payload consists of one or more nested Type/Length/Value (TLV) triplets. The format of each TLV is: Psenak, et al. Expires December 7, 2014 [Page 20] Internet-Draft OSPF Extensions for Segment Routing June 2014 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Value... | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ The Length field defines the length of the value portion in octets. The TLV is padded to 4-octet alignment; padding is not included in the length field. Nested TLVs are also 32-bit aligned. Unrecognized types are ignored. 5.2. OSPFv2 Extended Link TLV OSPFv2 Extended Link TLV is used in order to advertise various attributes of the link. It describes a single link and is constructed of a set of Sub-TLVs. There are no ordering requirements for the Sub-TLVs. Only one Extended Link TLV SHALL be carried in each Extended Link Opaque LSA, allowing for fine granularity changes in the topology. The Extended Link 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link-Type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Link Data | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs (variable) | +- -+ | | where: Type is 1. Length is variable. Link-Type: as defined in section A.4.2 of [RFC2328]. Link-ID: as defined in section A.4.2 of [RFC2328]. Psenak, et al. Expires December 7, 2014 [Page 21] Internet-Draft OSPF Extensions for Segment Routing June 2014 Link Data: as defined in section A.4.2 of [RFC2328]. 5.3. Adj-SID sub-TLV Adj-SID is an optional Sub-TLV of the Extended Link TLV. It MAY appear multiple times in Extended Link TLV. Examples where more than one Adj-SID may be used per neighbor are described in [I-D.filsfils-rtgwg-segment-routing-use-cases]. The structure of the Adj-SID Sub-TLV is as follows: 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. 1 octet field of following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |B|V|L|S| | +-+-+-+-+-+-+-+-+ where: B-Flag: Backup-flag: set if the Adj-SID refer to an adjacency being protected (e.g.: using IPFRR or MPLS-FRR) as described in [I-D.filsfils-rtgwg-segment-routing-use-cases]. 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 PrefixSID has local significance. If not set, then the value/index carried by this subTLV has global significance. Psenak, et al. Expires December 7, 2014 [Page 22] Internet-Draft OSPF Extensions for Segment Routing June 2014 The S-Flag. Set Flag. When set, the S-Flag indicates that the Adj-SID refers to a set of adjacencies (and therefore MAY be assigned to other adjacencies as well). Other bits: MUST be zero when originated and 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.filsfils-rtgwg-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. A SR capable router MAY allocate an Adj-SID for each of its adjacencies and set the B-Flag when the adjacency is protected by a FRR mechanism (IP or MPLS) as described in [I-D.filsfils-rtgwg-segment-routing-use-cases]. 5.4. LAN Adj-SID Sub-TLV LAN Adj-SID is an optional Sub-TLV of the Extended Link TLV. It MAY appear multiple times in Extended Link TLV. It is used to advertise SID/Label for adjacency to non-DR node on broadcast or NBMA 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 December 7, 2014 [Page 23] Internet-Draft OSPF Extensions for Segment Routing June 2014 Length: variable. Flags. 1 octet field of following flags: 0 1 2 3 4 5 6 7 +-+-+-+-+-+-+-+-+ |B|V|L|S| | +-+-+-+-+-+-+-+-+ where: B-Flag: Backup-flag: set if the LAN-Adj-SID refer to an adjacency being protected (e.g.: using IPFRR or MPLS-FRR) as described in [I-D.filsfils-rtgwg-segment-routing-use-cases]. 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 PrefixSID has local significance. If not set, then the value/index carried by this subTLV has global significance. The S-Flag. Set Flag. When set, the S-Flag indicates that the Adj-SID refers to a set of adjacencies (and therefore MAY be assigned to other adjacencies as well). Other bits: MUST be zero when originated and 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.filsfils-rtgwg-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. Psenak, et al. Expires December 7, 2014 [Page 24] Internet-Draft OSPF Extensions for Segment Routing June 2014 6. Elements of Procedure 6.1. Intra-area Segment routing in OSPFv2 The OSPFv2 node that supports segment routing MAY advertise Prefix- SIDs for any prefix that it is advertising reachability for (e.g. loopback IP address) as described in Section 4.2. If multiple routers advertise Prefix-SID for the same prefix, then the Prefix-SID MUST be the same. This is required in order to allow traffic load-balancing if multiple equal cost paths to the destination exist in the network. Prefix-SID can also be advertised by the SR Mapping Servers (as described in [I-D.filsfils-rtgwg-segment-routing-use-cases]). The Mapping Server advertise Prefix-SID for remote prefixes that exist in the network. Multiple Mapping Servers can advertise Prefix-SID for the same prefix, in which case the same Prefix-SID MUST be advertised by all of them. Flooding scope of the OSPF Extended Prefix Opaque LSA that is generated by the SR Mapping Server could be either area scope or autonomous system scope and is decided based on the configuration of the SR Mapping Server. 6.2. 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 in order to propagate Prefix SIDs between areas. 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 Section 4. 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 value will be set as follows: The ABR will look at its best path to the prefix in the source area and find out the advertising router associated with its best path to that prefix. 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, then the ABR will use the Prefix-SID advertised by any other router (e.g.: a Prefix-SID coming from an SR Mapping Server as defined in [I-D.filsfils-rtgwg-segment-routing-use-cases]) when propagating Prefix-SID for the prefix to other areas. Psenak, et al. Expires December 7, 2014 [Page 25] Internet-Draft OSPF Extensions for Segment Routing June 2014 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 Section 4. 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 source area and find out the advertising router associated with its best path to that prefix. The ABR will then look 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 ABR that contributes to the best path to the prefix, the originating ABR will use the Prefix-SID advertised by any other router (e.g.: a Prefix-SID coming from an SR Mapping Server as defined in [I-D.filsfils-rtgwg-segment-routing-use-cases]) when propagating Prefix-SID for the prefix to other areas. 6.3. 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 Section 4. The flooding scope of the Extended Prefix Opaque LSA type is set to AS-scope. The route-type in OSPF Extended Prefix TLV is set to external. 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 a NSSA ASBR 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 such path. If such advertising router has advertised a Prefix-SID for the prefix, then the NSSA ASBR uses it when advertising the Prefix-SID for the Type-5 prefix. Otherwise the Prefix-SID advertised by any other router will be used (e.g.: a Prefix-SID coming from an SR Mapping Server as defined in [I-D.filsfils-rtgwg-segment-routing-use-cases]). Psenak, et al. Expires December 7, 2014 [Page 26] Internet-Draft OSPF Extensions for Segment Routing June 2014 6.4. Advertisement of Adj-SID The Adjacency Segment Routing Identifier (Adj-SID) is advertised using the Adj-SID Sub-TLV as described in Section 5. 6.4.1. Advertisement of Adj-SID on Point-to-Point Links Adj-SID MAY be advertised for any adjacency on p2p link that is in a 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 MUST be removed from the area. 6.4.2. Adjacency SID on Broadcast or NBMA Interfaces Broadcast or NBMA networks in OSPF are represented by a star topology where the Designated Router (DR) is the central point all other routers on the broadcast or NBMA network connect to. As a result, routers on the broadcast or NBMA network advertise only their adjacency to DR and BDR. Routers that are neither DR nor BDR do not form and do not advertise adjacencies between them. They, however, maintain a 2-Way adjacency state between them. When Segment Routing is used, each router on the broadcast or NBMA network MAY advertise the Adj-SID for its adjacency to DR using Adj- SID Sub-TLV as described in Section 5.3. SR capable router MAY also advertise Adj-SID for other neighbors (e.g. BDR, DR-OTHER) on broadcast or NBMA network using the LAN ADJ- SID Sub-TLV as described in section 5.1.1.2. Section 5.4. 7. IANA Considerations This specification updates two existing OSPF registries. Opaque Link-State Advertisements (LSA) Option Types: o suggested value 7 - OSPFv2 Extended Prefix Opaque LSA o suggested value 8 - OSPFv2 Extended Link Opaque LSA OSPF Router Information (RI) TLVs: o suggested value 8 - SR-Algorithm TLV o suggested value 9 - SID/Label Range TLV This specification also creates four new registries: Psenak, et al. Expires December 7, 2014 [Page 27] Internet-Draft OSPF Extensions for Segment Routing June 2014 - OSPF Extended Prefix LSA TLVs and sub-TLVs - OSPF Extended Link LSA TLVs and sub-TLVs 7.1. OSPF Extend Prefix LSA TLV Registry The OSPF Extend Prefix LSA TLV registry will define top-level TLVs for Extended Prefix LSAs and should be placed in the existing OSPF IANA registry. New values can be allocated via IETF Consensus or IESG Approval. Following initial values are allocated: o 0 - Reserved o 1 - OSPF Extended Prefix TLV Types in the range 32768-32023 are for experimental use; these will not be registered with IANA, and MUST NOT be mentioned by RFCs. Types in the range 32023-65535 are not to be assigned at this time. Before any assignments can be made in this range, there MUST be a Standards Track RFC that specifies IANA Considerations that covers the range being assigned. 7.2. OSPF Extend Prefix LSA sub-TLV Registry The OSPF Extended Prefix sub-TLV registry will define will define sub-TLVs at any level of nesting for Extended Prefix LSAs and should be placed in the existing OSPF IANA registry. New values can be allocated via IETF Consensus or IESG Approval. Following initial values are allocated: o 0 - Reserved 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 Psenak, et al. Expires December 7, 2014 [Page 28] Internet-Draft OSPF Extensions for Segment Routing June 2014 o 7 - Unnumbered Interface ID Backup ERO sub-TLV o 8 - ERO Metric sub-TLV Types in the range 32768-32023 are for experimental use; these will not be registered with IANA, and MUST NOT be mentioned by RFCs. Types in the range 32023-65535 are not to be assigned at this time. Before any assignments can be made in this range, there MUST be a Standards Track RFC that specifies IANA Considerations that covers the range being assigned. 7.3. OSPF Extend Link LSA TLV Registry The OSPF Extend Link LSA TLV registry will define top-level TLVs for Extended Link LSAs and should be placed in the existing OSPF IANA registry. New values can be allocated via IETF Consensus or IESG Approval. Following initial values are allocated: o 0 - Reserved o 1 - OSPFv2 Extended Link TLV Types in the range 32768-32023 are for experimental use; these will not be registered with IANA, and MUST NOT be mentioned by RFCs. Types in the range 32023-65535 are not to be assigned at this time. Before any assignments can be made in this range, there MUST be a Standards Track RFC that specifies IANA Considerations that covers the range being assigned. 7.4. OSPF Extend Link LSA sub-TLV Registry The OSPF Extended Link LSA sub-TLV registry will define will define sub-TLVs at any level of nesting for Extended Link LSAs and should be placed in the existing OSPF IANA registry. New values can be allocated via IETF Consensus or IESG Approval. Following initial values are allocated: o 1 - SID/Label sub-TLV o 2 - Adj-SID sub-TLV o 3 - LAN Adj-SID/Label Sub-TLV Psenak, et al. Expires December 7, 2014 [Page 29] Internet-Draft OSPF Extensions for Segment Routing June 2014 Types in the range 32768-32023 are for experimental use; these will not be registered with IANA, and MUST NOT be mentioned by RFCs. Types in the range 32023-65535 are not to be assigned at this time. Before any assignments can be made in this range, there MUST be a Standards Track RFC that specifies IANA Considerations that covers the range being assigned. 8. Security Considerations In general, new LSAs defined in this document are subject to the same security concerns as those described in [RFC2328]. Additionally, implementations must assure that malformed TLV and Sub-TLV permutations do not result in errors which cause hard OSPF failures. 9. Contributors The following people gave a substantial contribution to the content of this document: Ahmed Bashandy, Martin Horneffer, Bruno Decraene, Stephane Litkowski, Igor Milojevic, Rob Shakir and Saku Ytti. 10. 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]. 11. References 11.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, 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, December 2001. [RFC3477] Kompella, K. and Y. Rekhter, "Signalling Unnumbered Links in Resource ReSerVation Protocol - Traffic Engineering (RSVP-TE)", RFC 3477, January 2003. Psenak, et al. Expires December 7, 2014 [Page 30] Internet-Draft OSPF Extensions for Segment Routing June 2014 [RFC3630] Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering (TE) Extensions to OSPF Version 2", RFC 3630, September 2003. [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, June 2007. [RFC4970] Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S. Shaffer, "Extensions to OSPF for Advertising Optional Router Capabilities", RFC 4970, July 2007. [RFC5250] Berger, L., Bryskin, I., Zinin, A., and R. Coltun, "The OSPF Opaque LSA Option", RFC 5250, July 2008. 11.2. Informative References [I-D.filsfils-rtgwg-segment-routing] 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 Architecture", draft-filsfils-rtgwg- segment-routing-01 (work in progress), October 2013. [I-D.filsfils-rtgwg-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-rtgwg- segment-routing-use-cases-02 (work in progress), October 2013. [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.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 December 7, 2014 [Page 31] Internet-Draft OSPF Extensions for Segment Routing June 2014 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 Juniper Networks, Inc. 1194 N. Mathilda Ave. Sunnyvale, CA 94089 US Email: hannes@juniper.net Rob Shakir British Telecom London UK Email: rob.shakir@bt.com Psenak, et al. Expires December 7, 2014 [Page 32] Internet-Draft OSPF Extensions for Segment Routing June 2014 Wim Henderickx Alcatel-Lucent Copernicuslaan 50 Antwerp 2018 BE Email: wim.henderickx@alcatel-lucent.com Jeff Tantsura Ericsson 300 Holger Way San Jose, CA 95134 US Email: Jeff.Tantsura@ericsson.com Psenak, et al. Expires December 7, 2014 [Page 33]