--- /dev/null
+Network Working Group S. Previdi, Ed.
+Internet-Draft C. Filsfils
+Intended status: Standards Track Cisco Systems, Inc.
+Expires: June 12, 2015 B. Field
+ Comcast
+ I. Leung
+ Rogers Communications
+ December 9, 2014
+
+
+ IPv6 Segment Routing Header (SRH)
+ draft-previdi-6man-segment-routing-header-05
+
+Abstract
+
+ Segment Routing (SR) allows a node to steer a packet through a
+ controlled set of instructions, called segments, by prepending a SR
+ header to the packet. A segment can represent any instruction,
+ topological or service-based. SR allows to enforce a flow through
+ any path (topological, or application/service based) while
+ maintaining per-flow state only at the ingress node to the SR domain.
+
+ Segment Routing can be applied to the IPv6 data plane with the
+ addition of a new type of Routing Extension Header. This draft
+ describes the Segment Routing Extension Header Type and how it is
+ used by SR capable nodes.
+
+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."
+
+
+
+
+Previdi, et al. Expires June 12, 2015 [Page 1]
+
+Internet-Draft IPv6 Segment Routing Header (SRH) December 2014
+
+
+ This Internet-Draft will expire on June 12, 2015.
+
+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. Structure of this document . . . . . . . . . . . . . . . . . 3
+ 2. Segment Routing Documents . . . . . . . . . . . . . . . . . . 3
+ 3. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
+ 3.1. Data Planes supporting Segment Routing . . . . . . . . . 4
+ 3.2. Illustration . . . . . . . . . . . . . . . . . . . . . . 4
+ 4. Abstract Routing Model . . . . . . . . . . . . . . . . . . . 7
+ 4.1. Segment Routing Global Block (SRGB) . . . . . . . . . . . 8
+ 4.2. Traffic Engineering with SR . . . . . . . . . . . . . . . 9
+ 4.3. Segment Routing Database . . . . . . . . . . . . . . . . 10
+ 5. IPv6 Instantiation of Segment Routing . . . . . . . . . . . . 10
+ 5.1. Segment Identifiers (SIDs) and SRGB . . . . . . . . . . . 10
+ 5.1.1. Node-SID . . . . . . . . . . . . . . . . . . . . . . 11
+ 5.1.2. Adjacency-SID . . . . . . . . . . . . . . . . . . . . 11
+ 5.2. Segment Routing Extension Header (SRH) . . . . . . . . . 11
+ 5.2.1. SRH and RFC2460 behavior . . . . . . . . . . . . . . 15
+ 6. SRH Procedures . . . . . . . . . . . . . . . . . . . . . . . 15
+ 6.1. Segment Routing Operations . . . . . . . . . . . . . . . 15
+ 6.2. Segment Routing Node Functions . . . . . . . . . . . . . 16
+ 6.2.1. Ingress SR Node . . . . . . . . . . . . . . . . . . . 16
+ 6.2.2. Transit Non-SR Capable Node . . . . . . . . . . . . . 18
+ 6.2.3. SR Intra Segment Transit Node . . . . . . . . . . . . 18
+ 6.2.4. SR Segment Endpoint Node . . . . . . . . . . . . . . 18
+ 6.3. FRR Flag Settings . . . . . . . . . . . . . . . . . . . . 18
+ 7. SR and Tunneling . . . . . . . . . . . . . . . . . . . . . . 18
+ 8. Example Use Case . . . . . . . . . . . . . . . . . . . . . . 19
+ 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 21
+ 10. Manageability Considerations . . . . . . . . . . . . . . . . 21
+ 11. Security Considerations . . . . . . . . . . . . . . . . . . . 21
+ 12. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 21
+
+
+
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+
+ 13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 21
+ 14. References . . . . . . . . . . . . . . . . . . . . . . . . . 21
+ 14.1. Normative References . . . . . . . . . . . . . . . . . . 21
+ 14.2. Informative References . . . . . . . . . . . . . . . . . 21
+ Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 22
+
+1. Structure of this document
+
+ Section 3 gives an introduction on SR for IPv6 networks.
+
+ Section 4 describes the Segment Routing abstract model.
+
+ Section 5 defines the Segment Routing Header (SRH) allowing
+ instantiation of SR over IPv6 dataplane.
+
+ Section 6 details the procedures of the Segment Routing Header.
+
+2. Segment Routing Documents
+
+ Segment Routing terminology is defined in
+ [I-D.filsfils-spring-segment-routing].
+
+ Segment Routing use cases are described in
+ [I-D.filsfils-spring-segment-routing-use-cases].
+
+ Segment Routing IPv6 use cases are described in
+ [I-D.ietf-spring-ipv6-use-cases].
+
+ Segment Routing protocol extensions are defined in
+ [I-D.ietf-isis-segment-routing-extensions], and
+ [I-D.psenak-ospf-segment-routing-ospfv3-extension].
+
+ The security mechanisms of the Segment Routing Header (SRH) are
+ described in [I-D.vyncke-6man-segment-routing-security].
+
+3. Introduction
+
+ Segment Routing (SR), defined in
+ [I-D.filsfils-spring-segment-routing], allows a node to steer a
+ packet through a controlled set of instructions, called segments, by
+ prepending a SR header to the packet. A segment can represent any
+ instruction, topological or service-based. SR allows to enforce a
+ flow through any path (topological or service/application based)
+ while maintaining per-flow state only at the ingress node to the SR
+ domain. Segments can be derived from different components: IGP, BGP,
+ Services, Contexts, Locators, etc. The list of segment forming the
+ path is called the Segment List and is encoded in the packet header.
+
+
+
+
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+
+
+ SR allows the use of strict and loose source based routing paradigms
+ without requiring any additional signaling protocols in the
+ infrastructure hence delivering an excellent scalability property.
+
+ The source based routing model described in
+ [I-D.filsfils-spring-segment-routing] is inherited from the ones
+ proposed by [RFC1940] and [RFC2460]. The source based routing model
+ offers the support for explicit routing capability.
+
+3.1. Data Planes supporting Segment Routing
+
+ Segment Routing (SR), can be instantiated over MPLS
+ ([I-D.filsfils-spring-segment-routing-mpls]) and IPv6. This document
+ defines its instantiation over the IPv6 data-plane based on the use-
+ cases defined in [I-D.ietf-spring-ipv6-use-cases].
+
+ Segment Routing for IPv6 (SR-IPv6) is required in networks where MPLS
+ data-plane is not used or, when combined with SR-MPLS, in networks
+ where MPLS is used in the core and IPv6 is used at the edge (home
+ networks, datacenters).
+
+ This document defines a new type of Routing Header (originally
+ defined in [RFC2460]) called the Segment Routing Header (SRH) in
+ order to convey the Segment List in the packet header as defined in
+ [I-D.filsfils-spring-segment-routing]. Mechanisms through which
+ segment are known and advertised are outside the scope of this
+ document.
+
+3.2. Illustration
+
+ In the context of Figure 1 where all the links have the same IGP
+ cost, let us assume that a packet P enters the SR domain at an
+ ingress edge router I and that the operator requests the following
+ requirements for packet P:
+
+ The local service S offered by node B must be applied to packet P.
+
+ The links AB and CE cannot be used to transport the packet P.
+
+ Any node N along the journey of the packet should be able to
+ determine where the packet P entered the SR domain and where it
+ will exit. The intermediate node should be able to determine the
+ paths from the ingress edge router to itself, and from itself to
+ the egress edge router.
+
+ Per-flow State for packet P should only be created at the ingress
+ edge router.
+
+
+
+
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+
+ The operator can forbid, for security reasons, anyone outside the
+ operator domain to exploit its intra-domain SR capabilities.
+
+ I---A---B---C---E
+ \ | / \ /
+ \ | / F
+ \|/
+ D
+
+ Figure 1: An illustration of SR properties
+
+ All these properties may be realized by instructing the ingress SR
+ edge router I to push the following abstract SR header on the packet
+ P.
+
+ +---------------------------------------------------------------+
+ | | |
+ | Abstract SR Header | |
+ | | |
+ | {SD, SB, SS, SF, SE}, Ptr, SI, SE | Transported |
+ | ^ | | Packet |
+ | | | | P |
+ | +---------------------+ | |
+ | | |
+ +---------------------------------------------------------------+
+
+ Figure 2: Packet P at node I
+
+ The abstract SR header contains a source route encoded as a list of
+ segments {SD, SB, SS, SF, SE}, a pointer (Ptr) and the identification
+ of the ingress and egress SR edge routers (segments SI and SE).
+
+ A segment identifies a topological instruction or a service
+ instruction. A segment can either be global or local. The
+ instruction associated with a global segment is recognized and
+ executed by any SR-capable node in the domain. The instruction
+ associated with a local segment is only supported by the specific
+ node that originates it.
+
+ Let us assume some IGP (i.e.: ISIS and OSPF) extensions to define a
+ "Node Segment" as a global instruction within the IGP domain to
+ forward a packet along the shortest path to the specified node. Let
+ us further assume that within the SR domain illustrated in Figure 1,
+ segments SI, SD, SB, SE and SF respectively identify IGP node
+ segments to I, D, B, E and F.
+
+ Let us assume that node B identifies its local service S with local
+ segment SS.
+
+
+
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+
+ With all of this in mind, let us describe the journey of the packet
+ P.
+
+ The packet P reaches the ingress SR edge router. I pushes the SR
+ header illustrated in Figure 2 and sets the pointer to the first
+ segment of the list (SD).
+
+ SD is an instruction recognized by all the nodes in the SR domain
+ which causes the packet to be forwarded along the shortest path to D.
+
+ Once at D, the pointer is incremented and the next segment is
+ executed (SB).
+
+ SB is an instruction recognized by all the nodes in the SR domain
+ which causes the packet to be forwarded along the shortest path to B.
+
+ Once at B, the pointer is incremented and the next segment is
+ executed (SS).
+
+ SS is an instruction only recognized by node B which causes the
+ packet to receive service S.
+
+ Once the service applied, the next segment is executed (SF) which
+ causes the packet to be forwarded along the shortest path to F.
+
+ Once at F, the pointer is incremented and the next segment is
+ executed (SE).
+
+ SE is an instruction recognized by all the nodes in the SR domain
+ which causes the packet to be forwarded along the shortest path to E.
+
+ E then removes the SR header and the packet continues its journey
+ outside the SR domain.
+
+ All of the requirements are met.
+
+ First, the packet P has not used links AB and CE: the shortest-path
+ from I to D is I-A-D, the shortest-path from D to B is D-B, the
+ shortest-path from B to F is B-C-F and the shortest-path from F to E
+ is F-E, hence the packet path through the SR domain is I-A-D-B-C-F-E
+ and the links AB and CE have been avoided.
+
+ Second, the service S supported by B has been applied on packet P.
+
+ Third, any node along the packet path is able to identify the service
+ and topological journey of the packet within the SR domain. For
+ example, node C receives the packet illustrated in Figure 3 and hence
+ is able to infer where the packet entered the SR domain (SI), how it
+
+
+
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+
+ got up to itself {SD, SB, SS, SE}, where it will exit the SR domain
+ (SE) and how it will do so {SF, SE}.
+
+ +---------------------------------------------------------------+
+ | | |
+ | SR Header | |
+ | | |
+ | {SD, SB, SS, SF, SE}, Ptr, SI, SE | Transported |
+ | ^ | | Packet |
+ | | | | P |
+ | +--------+ | |
+ | | |
+ +---------------------------------------------------------------+
+
+ Figure 3: Packet P at node C
+
+ Fourth, only node I maintains per-flow state for packet P. The
+ entire program of topological and service instructions to be executed
+ by the SR domain on packet P is encoded by the ingress edge router I
+ in the SR header in the form of a list of segments where each segment
+ identifies a specific instruction. No further per-flow state is
+ required along the packet path. The per-flow state is in the SR
+ header and travels with the packet. Intermediate nodes only hold
+ states related to the IGP global node segments and the local IGP
+ adjacency segments. These segments are not per-flow specific and
+ hence scale very well. Typically, an intermediate node would
+ maintain in the order of 100's to 1000's global node segments and in
+ the order of 10's to 100 of local adjacency segments. Typically the
+ SR IGP forwarding table is expected to be much less than 10000
+ entries.
+
+ Fifth, the SR header is inserted at the entrance to the domain and
+ removed at the exit of the operator domain. For security reasons,
+ the operator can forbid anyone outside its domain to use its intra-
+ domain SR capability.
+
+4. Abstract Routing Model
+
+ At the entrance of the SR domain, the ingress SR edge router pushes
+ the SR header on top of the packet. At the exit of the SR domain,
+ the egress SR edge router removes the SR header.
+
+ The abstract SR header contains an ordered list of segments, a
+ pointer identifying the next segment to process and the
+ identifications of the ingress and egress SR edge routers on the path
+ of this packet. The pointer identifies the segment that MUST be used
+ by the receiving router to process the packet. This segment is
+ called the active segment.
+
+
+
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+
+ A property of SR is that the entire source route of the packet,
+ including the identity of the ingress and egress edge routers is
+ always available with the packet. This allows for interesting
+ accounting and service applications.
+
+ We define three SR-header operations:
+
+ "PUSH": an SR header is pushed on an IP packet, or additional
+ segments are added at the head of the segment list. The pointer
+ is moved to the first entry of the added segments.
+
+ "NEXT": the active segment is completed, the pointer is moved to
+ the next segment in the list.
+
+ "CONTINUE": the active segment is not completed, the pointer is
+ left unchanged.
+
+ In the future, other SR-header management operations may be defined.
+
+ As the packet travels through the SR domain, the pointer is
+ incremented through the ordered list of segments and the source route
+ encoded by the SR ingress edge node is executed.
+
+ A node processes an incoming packet according to the instruction
+ associated with the active segment.
+
+ Any instruction might be associated with a segment: for example, an
+ intra-domain topological strict or loose forwarding instruction, a
+ service instruction, etc.
+
+ At minimum, a segment instruction must define two elements: the
+ identity of the next-hop to forward the packet to (this could be the
+ same node or a context within the node) and which SR-header
+ management operation to execute.
+
+ Each segment is known in the network through a Segment Identifier
+ (SID). The terms "segment" and "SID" are interchangeable.
+
+4.1. Segment Routing Global Block (SRGB)
+
+ In the SR abstract model, a segment is identified by a Segment
+ Routing Identifier (SID). The SR abstract model doesn't mandate a
+ specific format for the SID (IPv6 address or other formats).
+
+ In Segment Routing IPv6 the SID is an IPv6 address. Therefore, the
+ SRGB is materialized by the global IPv6 address space which
+ represents the set of IPv6 routable addresses in the SR domain. The
+ following rules apply:
+
+
+
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+
+ o Each node of the SR domain MUST be configured with the Segment
+ Routing Global Block (SRGB).
+
+ o All global segments must be allocated from the SRGB. Any SR
+ capable node MUST be able to process any global segment advertised
+ by any other node within the SR domain.
+
+ o Any segment outside the SRGB has a local significance and is
+ called a "local segment". An SR-capable node MUST be able to
+ process the local segments it originates. An SR-capable node MUST
+ NOT support the instruction associated with a local segment
+ originated by a remote node.
+
+4.2. Traffic Engineering with SR
+
+ An SR Traffic Engineering policy is composed of two elements: a flow
+ classification and a segment-list to prepend on the packets of the
+ flow.
+
+ In SR, this per-flow state only exists at the ingress edge node where
+ the policy is defined and the SR header is pushed.
+
+ It is outside the scope of the document to define the process that
+ leads to the instantiation at a node N of an SR Traffic Engineering
+ policy.
+
+ [I-D.filsfils-spring-segment-routing-use-cases] illustrates various
+ alternatives:
+
+ N is deriving this policy automatically (e.g. FRR).
+
+ N is provisioned explicitly by the operator.
+
+ N is provisioned by a controller or server (e.g.: SDN Controller).
+
+ N is provisioned by the operator with a high-level policy which is
+ mapped into a path thanks to a local CSPF-based computation (e.g.
+ affinity/SRLG exclusion).
+
+ N could also be provisioned by other means.
+
+ [I-D.filsfils-spring-segment-routing-use-cases] explains why the
+ majority of use-cases require very short segment-lists, hence
+ minimizing the performance impact, if any, of inserting and
+ transporting the segment list.
+
+
+
+
+
+
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+
+ A SDN controller, which desires to instantiate at node N an SR
+ Traffic Engineering policy, collects the SR capability of node N such
+ as to ensure that the policy meets its capability.
+
+4.3. Segment Routing Database
+
+ The Segment routing Database (SRDB) is a set of entries where each
+ entry is identified by a SID. The instruction associated with each
+ entry at least defines the identity of the next-hop to which the
+ packet should be forwarded and what operation should be performed on
+ the SR header (PUSH, CONTINUE, NEXT).
+
+ +---------+-----------+---------------------------------+
+ | Segment | Next-Hop | SR Header operation |
+ +---------+-----------+---------------------------------+
+ | Sk | M | CONTINUE |
+ | Sj | N | NEXT |
+ | Sl | NAT Srvc | NEXT |
+ | Sm | FW srvc | NEXT |
+ | Sn | Q | NEXT |
+ | etc. | etc. | etc. |
+ +---------+-----------+---------------------------------+
+
+ Figure 4: SR Database
+
+ Each SR-capable node maintains its local SRDB. SRDB entries can
+ either derive from local policy or from protocol segment
+ advertisement.
+
+5. IPv6 Instantiation of Segment Routing
+
+5.1. Segment Identifiers (SIDs) and SRGB
+
+ Segment Routing, as described in
+ [I-D.filsfils-spring-segment-routing], defines Node-SID and
+ Adjacency-SID. When SR is used over IPv6 data-plane the following
+ applies.
+
+ The SRGB is the global IPv6 address space which represents the set of
+ IPv6 routable addresses in the SR domain.
+
+ Node SIDs are IPv6 addresses part of the SRGB (i.e.: routable
+ addresses). Adjacency-SIDs are IPv6 addresses which may not be part
+ of the global IPv6 address space.
+
+
+
+
+
+
+
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+
+5.1.1. Node-SID
+
+ The Node-SID identifies a node. With SR-IPv6 the Node-SID is an IPv6
+ prefix that the operator configured on the node and that is used as
+ the node identifier. Typically, in case of a router, this is the
+ IPv6 address of the node loopback interface. Therefore, SR-IPv6 does
+ not require any additional SID advertisement for the Node Segment.
+ The Node-SID is in fact the IPv6 address of the node.
+
+5.1.2. Adjacency-SID
+
+ In the SR architecture defined in
+ [I-D.filsfils-spring-segment-routing] the Adjacency-SID (or Adj-SID)
+ identifies a given interface and may be local or global (depending on
+ how it is advertised). A node may advertise one (or more) Adj-SIDs
+ allocated to a given interface so to force the forwarding of the
+ packet (when received with that particular Adj-SID) into the
+ interface regardless the routing entry for the packet destination.
+ The semantic of the Adj-SID is:
+
+ Send out the packet to the interface this prefix is allocated to.
+
+ When SR is applied to IPv6, any SID is in a global IPv6 address and
+ therefore, an Adj-SID has a global significance (i.e.: the IPv6
+ address representing the SID is a global address). In other words, a
+ node that advertises the Adj-SID in the form of a global IPv6 address
+ representing the link/adjacency the packet has to be forwarded to,
+ will apply to the Adj-SID a global significance.
+
+ Advertisement of Adj-SID may be done using multiple mechanisms among
+ which the ones described in ISIS and OSPF protocol extensions:
+ [I-D.ietf-isis-segment-routing-extensions] and
+ [I-D.psenak-ospf-segment-routing-ospfv3-extension]. The distinction
+ between local and global significance of the Adj-SID is given in the
+ encoding of the Adj-SID advertisement.
+
+5.2. Segment Routing Extension Header (SRH)
+
+ A new type of the Routing Header (originally defined in [RFC2460]) is
+ defined: the Segment Routing Header (SRH) which has a new Routing
+ Type, (suggested value 4) to be assigned by IANA.
+
+ As an example, if an explicit path is to be constructed across a core
+ network running ISIS or OSPF, the segment list will contain SIDs
+ representing the nodes across the path (loose or strict) which,
+ usually, are the IPv6 loopback interface address of each node. If
+ the path is across service or application entities, the segment list
+
+
+
+
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+
+ contains the IPv6 addresses of these services or application
+ instances.
+
+ The Segment Routing Header (SRH) is defined 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
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | Next Header | Hdr Ext Len | Routing Type | Segments Left |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | First Segment | Flags | HMAC Key ID |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ | Segment List[0] (128 bits ipv6 address) |
+ | |
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ | |
+ ...
+ | |
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ | Segment List[n] (128 bits ipv6 address) |
+ | |
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ | Policy List[0] (optional) |
+ | |
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ | Policy List[1] (optional) |
+ | |
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ | Policy List[2] (optional) |
+ | |
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ | |
+ | |
+ | |
+ | HMAC (256 bits) |
+
+
+
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+
+
+ | (optional) |
+ | |
+ | |
+ | |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ where:
+
+ o Next Header: 8-bit selector. Identifies the type of header
+ immediately following the SRH.
+
+ o Hdr Ext Len: 8-bit unsigned integer, is the length of the SRH
+ header in 8-octet units, not including the first 8 octets.
+
+ o Routing Type: TBD, to be assigned by IANA (suggested value: 4).
+
+ o Segments Left. Defined in [RFC2460], it contains the index, in
+ the Segment List, of the next segment to inspect. Segments Left
+ is decremented at each segment and it is used as an index in the
+ segment list.
+
+ o First Segment: offset in the SRH, not including the first 8 octets
+ and expressed in 16-octet units, pointing to the last element of
+ the segment list, which is in fact the first segment of the
+ segment routing path.
+
+ o Flags: 16 bits of flags. Following flags are defined:
+
+ 1
+ 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+ |C|P|R|R| Policy Flags |
+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+ C-flag: Clean-up flag. Set when the SRH has to be removed from
+ the packet when packet reaches the last segment.
+
+ P-flag: Protected flag. Set when the packet has been rerouted
+ through FRR mechanism by a SR endpoint node. See Section 6.3
+ for more details.
+
+ R-flags. Reserved and for future use.
+
+ Policy Flags. Define the type of the IPv6 addresses encoded
+ into the Policy List (see below). The following have been
+ defined:
+
+
+
+
+
+Previdi, et al. Expires June 12, 2015 [Page 13]
+
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+
+
+ Bits 4-6: determine the type of the first element after the
+ segment list.
+
+ Bits 7-9: determine the type of the second element.
+
+ Bits 10-12: determine the type of the third element.
+
+ Bits 13-15: determine the type of the fourth element.
+
+ The following values are used for the type:
+
+ 0x0: Not present. If value is set to 0x0, it means the
+ element represented by these bits is not present.
+
+ 0x1: SR Ingress.
+
+ 0x2: SR Egress.
+
+ 0x3: Original Source Address.
+
+ o HMAC Key ID and HMAC field, and their use are defined in
+ [I-D.vyncke-6man-segment-routing-security].
+
+ o Segment List[n]: 128 bit IPv6 addresses representing the nth
+ segment in the Segment List. The Segment List is encoded starting
+ from the last segment of the path. I.e., the first element of the
+ segment list (Segment List [0]) contains the last segment of the
+ path while the last segment of the Segment List (Segment List[n])
+ contains the first segment of the path. The index contained in
+ "Segments Left" identifies the current active segment.
+
+ o Policy List. Optional addresses representing specific nodes in
+ the SR path such as:
+
+ SR Ingress: a 128 bit generic identifier representing the
+ ingress in the SR domain (i.e.: it needs not to be a valid IPv6
+ address).
+
+ SR Egress: a 128 bit generic identifier representing the egress
+ in the SR domain (i.e.: it needs not to be a valid IPv6
+ address).
+
+ Original Source Address: IPv6 address originally present in the
+ SA field of the packet.
+
+ The segments in the Policy List are encoded after the segment list
+ and they are optional. If none are in the SRH, all bits of the
+ Policy List Flags MUST be set to 0x0.
+
+
+
+Previdi, et al. Expires June 12, 2015 [Page 14]
+
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+
+
+5.2.1. SRH and RFC2460 behavior
+
+ The SRH being a new type of the Routing Header, it also has the same
+ properties:
+
+ SHOULD only appear once in the packet.
+
+ Only the router whose address is in the DA field of the packet
+ header MUST inspect the SRH.
+
+ Therefore, Segment Routing in IPv6 networks implies that the segment
+ identifier (i.e.: the IPv6 address of the segment) is moved into the
+ DA of the packet.
+
+ The DA of the packet changes at each segment termination/completion
+ and therefore the original DA of the packet MUST be encoded as the
+ last segment of the path.
+
+ As illustrated in Section 3.2, nodes that are within the path of a
+ segment will forward packets based on the DA of the packet without
+ inspecting the SRH. This ensures full interoperability between SR-
+ capable and non-SR-capable nodes.
+
+6. SRH Procedures
+
+ In this section we describe the different procedures on the SRH.
+
+6.1. Segment Routing Operations
+
+ When Segment Routing is instantiated over the IPv6 data plane the
+ following applies:
+
+ o The segment list is encoded in the SRH.
+
+ o The active segment is in the destination address of the packet.
+
+ o The Segment Routing CONTINUE operation (as described in
+ [I-D.filsfils-spring-segment-routing]) is implemented as a
+ regular/plain IPv6 operation consisting of DA based forwarding.
+
+ o The NEXT operation is implemented through the update of the DA
+ with the value represented by the Next Segment field in the SRH.
+
+ o The PUSH operation is implemented through the insertion of the SRH
+ or the insertion of additional segments in the SRH segment list.
+
+
+
+
+
+
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+
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+
+
+6.2. Segment Routing Node Functions
+
+ SR packets are forwarded to segments endpoints (i.e.: nodes whose
+ address is in the DA field of the packet). The segment endpoint,
+ when receiving a SR packet destined to itself, does:
+
+ o Inspect the SRH.
+
+ o Determine the next active segment.
+
+ o Update the Segments Left field (or, if requested, remove the SRH
+ from the packet).
+
+ o Update the DA.
+
+ o Send the packet to the next segment.
+
+ The procedures applied to the SRH are related to the node function.
+ Following nodes functions are defined:
+
+ Ingress SR Node.
+
+ Transit Non-SR Node.
+
+ Transit SR Intra Segment Node.
+
+ SR Endpoint Node.
+
+6.2.1. Ingress SR Node
+
+ Ingress Node can be a router at the edge of the SR domain or a SR-
+ capable host. The ingress SR node may obtain the segment list by
+ either:
+
+ Local path computation.
+
+ Local configuration.
+
+ Interaction with an SDN controller delivering the path as a
+ complete SRH.
+
+ Any other mechanism (mechanisms through which the path is acquired
+ are outside the scope of this document).
+
+ When creating the SRH (either at ingress node or in the SDN
+ controller) the following is done:
+
+ Next Header and Hdr Ext Len fields are set according to [RFC2460].
+
+
+
+Previdi, et al. Expires June 12, 2015 [Page 16]
+
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+
+
+ Routing Type field is set as TBD (SRH).
+
+ The Segment List is built with the FIRST segment of the path
+ encoded in the LAST element of the Segment List. Subsequent
+ segments are encoded on top of the first segment. Finally, the
+ LAST segment of the path is encoded in the FIRST element of the
+ Segment List. In other words, the Segment List is encoded in the
+ reverse order of the path.
+
+ The original DA of the packet is encoded as the last segment of
+ the path (encoded in the first element of the Segment List).
+
+ the DA of the packet is set with the value of the first segment
+ (found in the last element of the segment list).
+
+ the Segments Left field is set to n-1 where n is the number of
+ elements in the Segment List.
+
+ The packet is sent out towards the first segment (i.e.:
+ represented in the packet DA).
+
+6.2.1.1. Security at Ingress
+
+ The procedures related to the Segment Routing security are detailed
+ in [I-D.vyncke-6man-segment-routing-security].
+
+ In the case where the SR domain boundaries are not under control of
+ the network operator (e.g.: when the SR domain edge is in a home
+ network), it is important to authenticate and validate the content of
+ any SRH being received by the network operator. In such case, the
+ security procedure described in
+ [I-D.vyncke-6man-segment-routing-security] is to be used.
+
+ The ingress node (e.g.: the host in the home network) requests the
+ SRH from a control system (e.g.: an SDN controller) which delivers
+ the SRH with its HMAC signature on it.
+
+ Then, the home network host can send out SR packets (with an SRH on
+ it) that will be validated at the ingress of the network operator
+ infrastructure.
+
+ The ingress node of the network operator infrastructure, is
+ configured in order to validate the incoming SRH HMACs in order to
+ allow only packets having correct SRH according to their SA/DA
+ addresses.
+
+
+
+
+
+
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+
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+
+
+6.2.2. Transit Non-SR Capable Node
+
+ SR is interoperable with plain IPv6 forwarding. Any non SR-capable
+ node will forward SR packets solely based on the DA. There's no SRH
+ inspection. This ensures full interoperability between SR and non-SR
+ nodes.
+
+6.2.3. SR Intra Segment Transit Node
+
+ Only the node whose address is in DA inspects and processes the SRH
+ (according to [RFC2460]). An intra segment transit node is not in
+ the DA and its forwarding is based on DA and its SR-IPv6 FIB.
+
+6.2.4. SR Segment Endpoint Node
+
+ The SR segment endpoint node is the node whose address is in the DA.
+ The segment endpoint node inspects the SRH and does:
+
+ 1. IF DA = myself (segment endpoint)
+ 2. IF Segments Left > 0 THEN
+ decrement Segments Left
+ update DA with Segment List[Segments Left]
+ 3. ELSE IF Segments List[Segments Left] <> DA THEN
+ update DA with Segments List[Segments Left]
+ IF Clean-up bit is set THEN remove the SRH
+ 4. ELSE give the packet to next PID (application)
+ End of processing.
+ 5. Forward the packet out
+
+6.3. FRR Flag Settings
+
+ A node supporting SR and doing Fast Reroute (as described in
+ [I-D.filsfils-spring-segment-routing-use-cases], when rerouting
+ packets through FRR mechanisms, SHOULD inspect the rerouted packet
+ header and look for the SRH. If the SRH is present, the rerouting
+ node SHOULD set the Protected bit on all rerouted packets.
+
+7. SR and Tunneling
+
+ Encapsulation can be realized in two different ways with SR-IPv6:
+
+ Outer encapsulation.
+
+ SRH with SA/DA original addresses.
+
+ Outer encapsulation tunneling is the traditional method where an
+ additional IPv6 header is prepended to the packet. The original IPv6
+ header being encapsulated, everything is preserved and the packet is
+
+
+
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+
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+
+
+ switched/routed according to the outer header (that could contain a
+ SRH).
+
+ SRH allows encoding both original SA and DA, hence an operator may
+ decide to change the SA/DA at ingress and restore them at egress.
+ This can be achieved without outer encapsulation, by changing SA/DA
+ and encoding the original SA in the Policy List and in the original
+ DA in the Segment List.
+
+8. Example Use Case
+
+ A more detailed description of use cases are available in
+ [I-D.ietf-spring-ipv6-use-cases]. In this section, a simple SR-IPv6
+ example is illustrated.
+
+ In the topology described in Figure 6 it is assumed an end-to-end SR
+ deployment. Therefore SR is supported by all nodes from A to J.
+
+ Home Network | Backbone | Datacenter
+ | |
+ | +---+ +---+ +---+ | +---+ |
+ +---|---| C |---| D |---| E |---|---| I |---|
+ | | +---+ +---+ +---+ | +---+ |
+ | | | | | | | | +---+
+ +---+ +---+ | | | | | | |--| X |
+ | A |---| B | | +---+ +---+ +---+ | +---+ | +---+
+ +---+ +---+ | | F |---| G |---| H |---|---| J |---|
+ | +---+ +---+ +---+ | +---+ |
+ | |
+ | +-----------+
+ | SDN |
+ | Orch/Ctlr |
+ +-----------+
+
+ Figure 6: Sample SR topology
+
+ The following workflow applies to packets sent by host A and destined
+ to server X.
+
+
+
+
+
+
+
+
+
+
+
+
+
+Previdi, et al. Expires June 12, 2015 [Page 19]
+
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+
+
+ . Host A sends a request for a path to server X to the SDN
+ controller or orchestration system.
+
+ . The SDN controller/orchestrator builds a SRH with:
+ . Segment List: C, F, J, X
+ . HMAC
+ that satisfies the requirements expressed in the request
+ by host A and based on policies applicable to host A.
+
+ . Host A receives the SRH and insert it into the packet.
+ The packet has now:
+ . SA: A
+ . DA: C
+ . SRH with
+ . SL: X, J, F, C
+ . Segments Left: 3 (i.e.: Segment List size - 1)
+ . PL: C (ingress), J (egress)
+ Note that X is the last segment and C is the
+ first segment (i.e.: the SL is encoded in the reverse
+ path order).
+ . HMAC
+
+ . When packet arrives in C (first segment), C does:
+ . Validate the HMAC of the SRH.
+ . Decrement Segments Left by one: 2
+ . Update the DA with the next segment found in
+ Segment List[2]. DA is set to F.
+ . Forward the packet to F.
+
+ . When packet arrives in F (second segment), F does:
+ . Decrement Segments Left by one: 1
+ . Update the DA with the next segment found in
+ Segment List[1]. DA is set to J.
+ . Forward the packet to J.
+
+ . Packet travels across G and H nodes which do plain
+ IPv6 forwarding based on DA. No inspection of SRH needs
+ to be done in these nodes. However, any SR capable node
+ is allowed to set the Protected bit in case of FRR
+ protection.
+
+ . When packet arrives in J (third segment), J does:
+ . Decrement Segments Left by one: 0
+ . Update the DA with the next segment found in
+ Segment List[0]. DA is set to X.
+ . If the cleanup bit is set, then node J will strip out
+ the SRH from the packet.
+ . Forward the packet to X.
+
+
+
+Previdi, et al. Expires June 12, 2015 [Page 20]
+
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+
+
+ The packet arrives in the server that may or may not support SR. The
+ return traffic, from server to host, may be sent using the same
+ procedures.
+
+9. IANA Considerations
+
+ TBD
+
+10. Manageability Considerations
+
+ TBD
+
+11. Security Considerations
+
+ Security mechanisms applied to Segment Routing over IPv6 networks are
+ detailed in [I-D.vyncke-6man-segment-routing-security].
+
+12. Contributors
+
+ The authors would like to thank Dave Barach, John Leddy, John
+ Brzozowski, Pierre Francois, Nagendra Kumar, Mark Townsley, Christian
+ Martin, Roberta Maglione, Eric Vyncke, James Connolly, David Lebrun
+ and Fred Baker for their contribution to this document.
+
+13. Acknowledgements
+
+ TBD
+
+14. References
+
+14.1. Normative References
+
+ [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+ [RFC2460] Deering, S. and R. Hinden, "Internet Protocol, Version 6
+ (IPv6) Specification", RFC 2460, December 1998.
+
+14.2. Informative References
+
+ [I-D.filsfils-spring-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-spring-
+ segment-routing-04 (work in progress), July 2014.
+
+
+
+
+
+Previdi, et al. Expires June 12, 2015 [Page 21]
+
+Internet-Draft IPv6 Segment Routing Header (SRH) December 2014
+
+
+ [I-D.filsfils-spring-segment-routing-mpls]
+ 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 with MPLS data plane", draft-filsfils-
+ spring-segment-routing-mpls-03 (work in progress), August
+ 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.ietf-isis-segment-routing-extensions]
+ Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
+ Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS
+ Extensions for Segment Routing", draft-ietf-isis-segment-
+ routing-extensions-03 (work in progress), October 2014.
+
+ [I-D.ietf-spring-ipv6-use-cases]
+ Brzozowski, J., Leddy, J., Leung, I., Previdi, S.,
+ Townsley, W., Martin, C., Filsfils, C., and R. Maglione,
+ "IPv6 SPRING Use Cases", draft-ietf-spring-ipv6-use-
+ cases-03 (work in progress), November 2014.
+
+ [I-D.psenak-ospf-segment-routing-ospfv3-extension]
+ Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
+ Shakir, R., Henderickx, W., and J. Tantsura, "OSPFv3
+ Extensions for Segment Routing", draft-psenak-ospf-
+ segment-routing-ospfv3-extension-02 (work in progress),
+ July 2014.
+
+ [I-D.vyncke-6man-segment-routing-security]
+ Vyncke, E. and S. Previdi, "IPv6 Segment Routing Header
+ (SRH) Security Considerations", July 2014.
+
+ [RFC1940] Estrin, D., Li, T., Rekhter, Y., Varadhan, K., and D.
+ Zappala, "Source Demand Routing: Packet Format and
+ Forwarding Specification (Version 1)", RFC 1940, May 1996.
+
+Authors' Addresses
+
+
+
+
+
+
+
+Previdi, et al. Expires June 12, 2015 [Page 22]
+
+Internet-Draft IPv6 Segment Routing Header (SRH) December 2014
+
+
+ Stefano Previdi (editor)
+ Cisco Systems, Inc.
+ Via Del Serafico, 200
+ Rome 00142
+ Italy
+
+ Email: sprevidi@cisco.com
+
+
+ Clarence Filsfils
+ Cisco Systems, Inc.
+ Brussels
+ BE
+
+ Email: cfilsfil@cisco.com
+
+
+ Brian Field
+ Comcast
+ 4100 East Dry Creek Road
+ Centennial, CO 80122
+ US
+
+ Email: Brian_Field@cable.comcast.com
+
+
+ Ida Leung
+ Rogers Communications
+ 8200 Dixie Road
+ Brampton, ON L6T 0C1
+ CA
+
+ Email: Ida.Leung@rci.rogers.com
Code Review / vpp.git / blobdiff