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Versions: (draft-ali-6man-spring-srv6-oam) 00 01 02 03

6man                                                              Z. Ali
Internet-Draft                                               C. Filsfils
Intended status: Standards Track                           Cisco Systems
Expires: June 20, 2020                                     S. Matsushima
                                                                Softbank
                                                                D. Voyer
                                                             Bell Canada
                                                                 M. Chen
                                                                  Huawei
                                                       December 18, 2019


  Operations, Administration, and Maintenance (OAM) in Segment Routing
                  Networks with IPv6 Data plane (SRv6)
                   draft-ietf-6man-spring-srv6-oam-03

Abstract

   This document defines building blocks for Operations, Administration,
   and Maintenance (OAM) in Segment Routing Networks with IPv6 Dataplane
   (SRv6).  The document also describes some SRv6 OAM mechanisms.

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 [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 https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 20, 2020.







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Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   3
     2.1.  Abbreviations . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Terminology and Reference Topology  . . . . . . . . . . .   3
   3.  OAM Building Blocks . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  O-flag in Segment Routing Header  . . . . . . . . . . . .   5
       3.1.1.  O-flag Processing . . . . . . . . . . . . . . . . . .   6
     3.2.  OAM Segments  . . . . . . . . . . . . . . . . . . . . . .   6
     3.3.  End.OP: OAM Endpoint with Punt  . . . . . . . . . . . . .   7
     3.4.  End.OTP: OAM Endpoint with Timestamp and Punt . . . . . .   7
   4.  OAM Mechanisms  . . . . . . . . . . . . . . . . . . . . . . .   7
     4.1.  Ping  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
       4.1.1.  Classic Ping  . . . . . . . . . . . . . . . . . . . .   8
       4.1.2.  Pinging a SID . . . . . . . . . . . . . . . . . . . .   9
     4.2.  Traceroute  . . . . . . . . . . . . . . . . . . . . . . .  11
       4.2.1.  Classic Traceroute  . . . . . . . . . . . . . . . . .  11
       4.2.2.  Traceroute to a SID . . . . . . . . . . . . . . . . .  12
     4.3.  Monitoring of SRv6 Paths  . . . . . . . . . . . . . . . .  15
   5.  Implementation Status . . . . . . . . . . . . . . . . . . . .  16
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     7.1.  ICMPv6 type Numbers RegistrySEC . . . . . . . . . . . . .  16
     7.2.  SRv6 OAM Endpoint Types . . . . . . . . . . . . . . . . .  16
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  17
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  17
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  18
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  18
     10.2.  Informative References . . . . . . . . . . . . . . . . .  19
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  19





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1.  Introduction

   This document defines building blocks for Operations, Administration,
   and Maintenance (OAM) in Segment Routing Networks with IPv6 Dataplane
   (SRv6).  The document also describes some SRv6 OAM mechanisms.

2.  Conventions Used in This Document

2.1.  Abbreviations

   The following abbreviations are used in this document:

      SID: Segment ID.

      SL: Segment Left.

      SR: Segment Routing.

      SRH: Segment Routing Header.

      SRv6: Segment Routing with IPv6 Data plane.

      TC: Traffic Class.

      ICMPv6: ICMPv6 Specification [RFC4443].

2.2.  Terminology and Reference Topology

   This document uses the terminology defined in [I-D.ietf- spring-srv6-
   network-programming].  The readers are expected to be familiar with
   the same.

   Throughout the document, the following simple topology is used for
   illustration.

















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            +--------------------------| N100 |------------------------+
            |                                                          |
               ====== link1====== link3------ link5====== link9------
               ||N1||======||N2||======| N3 |======||N4||======| N5 |
               ||  ||------||  ||------|    |------||  ||------|    |
               ====== link2====== link4------ link6======link10------
                              |                      |
                              |       ------         |
                              +-------| N6 |---------+
                                link7 |    | link8
                                      ------

                            Figure 1 Reference Topology


   In the reference topology:

      Nodes N1, N2, and N4 are SRv6 capable nodes.

      Nodes N3, N5 and N6 are classic IPv6 nodes.

      Node N100 is a controller.

      Node k has a classic IPv6 loopback address A:k::/128.

      A SID at node k with locator block B and function F is represented
      by B:k:F::.

      The IPv6 address of the nth Link between node X and Y at the X
      side is represented as 2001:DB8:X:Y:Xn::, e.g., the IPv6 address
      of link6 (the 2nd link) between N3 and N4 at N3 in Figure 1 is
      2001:DB8:3:4:32::.  Similarly, the IPv6 address of link5 (the 1st
      link between N3 and N4) at node 3 is 2001:DB8:3:4:31::.

      B:k:Cij:: is explicitly allocated as the END.X function at node k
      towards neighbor node i via jth Link between node i and node j.
      e.g., B:2:C31:: represents END.X at N2 towards N3 via link3 (the
      1st link between N2 and N3).  Similarly, B:4:C52:: represents the
      END.X at N4 towards N5 via link10.

      A SID list is represented as <S1, S2, S3> where S1 is the first
      SID to visit, S2 is the second SID to visit and S3 is the last SID
      to visit along the SR path.

      (SA,DA) (S3, S2, S1; SL)(payload) represents an IPv6 packet with:

      *  IPv6 header with source address SA, destination addresses DA
         and SRH as next-header



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      *  SRH with SID list <S1, S2, S3> with SegmentsLeft = SL

      *  Note the difference between the < > and () symbols: <S1, S2,
         S3> represents a SID list where S1 is the first SID and S3 is
         the last SID to traverse.  (S3, S2, S1; SL) represents the same
         SID list but encoded in the SRH format where the rightmost SID
         in the SRH is the first SID and the leftmost SID in the SRH is
         the last SID.  When referring to an SR policy in a high-level
         use-case, it is simpler to use the <S1, S2, S3> notation.  When
         referring to an illustration of the detailed packet behavior,
         the (S3, S2, S1; SL) notation is more convenient.

      *  (payload) represents the the payload of the packet.

      SRH[SL] represents the SID pointed by the SL field in the first
      SRH.  In our example, SRH[2] represents S1, SRH[1] represents S2
      and SRH[0] represents S3.

3.  OAM Building Blocks

   This section defines the various building blocks for implementing OAM
   mechanisms in SRv6 networks.

3.1.  O-flag in Segment Routing Header

   [I-D.ietf-6man-segment-routing-header] describes the Segment Routing
   Header (SRH) and how SR capable nodes use it.  The SRH contains an
   8-bit "Flags" field [I-D.draft-ietf-6man-segment- routing-header].
   This document defines the following bit in the SRH.Flags to carry the
   O-flag:

                  0 1 2 3 4 5 6 7
                 +-+-+-+-+-+-+-+-+
                 |   |O|         |
                 +-+-+-+-+-+-+-+-+


   Where:

      O-flag: OAM flag.  When set, it indicates that this packet is an
      operations and management (OAM) packet.  This document defines the
      usage of the O-flag in the SRH.Flags.

   The document does not define any other flag in the SRH.Flags and
   meaning and processing of any other bit in SRH.Flags is outside of
   the scope of this document.





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3.1.1.  O-flag Processing

   The SRH.Flags.O-flag implements the "punt a timestamped copy of the
   packet" behavior.  This enables an SRv6 Endpoint node to send a
   timestamped copy of the packets marked with o-flag to a local OAM
   process.  To prevent multiple evaluations of the datagram, the OAM
   process MUST NOT respond to any upper-layer header (like ICMP, UDP,
   etc.) payload.  However, the OAM process MAY export the time-stamped
   copy of the packet to a controller using e.g., IPFIX [RFC7011].  To
   avoid hitting any performance impact, the processing node SHOULD
   rate-limit the number of packets punted to the OAM process.
   Specification of the OAM process or the external controller
   operations are beyond the scope of this document.

   Implementation of the O-flag is OPTIONAL.  If a node does not support
   the O-flag, then upon reception it simply ignores it.

   If a node supports the O-flag, it can optionally advertise its
   potential via node capability advertisement in IGP [I-D.ietf-isis-
   srv6- extensions] and BGP-LS [I-D.ietf-idr-bgpls-srv6-ext].

   When N receives a packet whose IPv6 DA is S and S is a local SID, the
   line S01 of the the pseudo-code associated with the SID S, as defined
   in section 4.3.1.1 of [I-D.ietf-6man-segment-routing-header], is
   modified as follows for the O-flag processing.

     S01.1. IF SRH.Flags.O-flag is set and local configuration permits
            O-flag processing THEN
            a. Make a copy of the packet.
            b. Send the copied packet, along with a timestamp
               to the OAM process.      ;; Ref1
     Ref1: An implementation SHOULD copy and record the timestamp as soon as
     possible during packet processing. Timestamp is not carried in the packet
     forwarded to the next hop.


   Please note that the O-flag processing happens before execution of
   regular processing of the local SID S.

3.2.  OAM Segments

   The presence of an OAM SID in the Destination address of the IPv6
   header instructs the segment endpoint implementing the OAM SID that
   the content of the packet is of interest to the node and to process
   the upper-layer payload, accordingly.






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3.3.  End.OP: OAM Endpoint with Punt

   When N receives a packet destined to S and S is a local End.OP SID, N
   does:

        S01.   Send the packet to the OAM process


   The local OAM process further processes the packet, this MAY involve
   processing protocol layers above IPv6.  For example, ping and
   traceroute will require ICMP or UDP protocol processing.  Once the
   packet leaves the IPv6 layer the processing is considered host
   processing and the upper layer protocols MUST be processed as such.

3.4.  End.OTP: OAM Endpoint with Timestamp and Punt

   When N receives a packet destined to S and S is a local End.OTP SID,
   N does:

      S01.1. Timestamp the packet ;; Ref1
      S01.2. Send the packet, along with a timestamp, to the
      OAM process
      Ref1: Timestamping SHOULD be done in hardware, as soon as possible
      during the packet processing.


   The local OAM process further processes the packet, this MAY involve
   processing protocol layers above IPv6.  For example, ping and
   traceroute will require ICMP or UDP protocol processing.  Once the
   packet leaves the IPv6 layer the processing is considered host
   processing and the upper layer protocols MUST be processed as such.

4.  OAM Mechanisms

   This section describes how OAM mechanisms can be implemented using
   the OAM building blocks described in the previous section.

   [RFC4443] describes Internet Control Message Protocol for IPv6
   (ICMPv6) that is used by IPv6 devices for network diagnostic and
   error reporting purposes.  As Segment Routing with IPv6 data plane
   (SRv6) simply adds a new type of Routing Extension Header, existing
   ICMPv6 ping mechanisms can be used in an SRv6 network.  This section
   describes the applicability of ICMPv6 in the SRv6 network and how the
   existing ICMPv6 mechanisms can be used for providing OAM
   functionality.

   The document does not propose any changes to the standard ICMPv6
   [RFC4443], [RFC4884] or standard ICMPv4 [RFC792].



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4.1.  Ping

   The following subsections outline some use cases of the ICMP ping in
   the SRv6 networks.

4.1.1.  Classic Ping

   The existing mechanism to ping a remote IP prefix, along the shortest
   path, continues to work without any modification.  The initiator may
   be an SRv6 node or a classic IPv6 node.  Similarly, the egress or
   transit may be an SRv6 capable node or a classic IPv6 node.

   If an SRv6 capable ingress node wants to ping an IPv6 prefix via an
   arbitrary segment list <S1, S2, S3>, it needs to initiate ICMPv6 ping
   with an SR header containing the SID list <S1, S2, S3>.  This is
   illustrated using the topology in Figure 1.  Assume all the links
   have IGP metric 10 except both links between node2 and node3, which
   have IGP metric set to 100.  User issues a ping from node N1 to a
   loopback of node 5, via segment list <B:2:C31, B:4:C52>.

   Figure 2 contains sample output for a ping request initiated at node
   N1 to the loopback address of node N5 via a segment list <B:2:C31,
   B:4:C52>.


       > ping A:5:: via segment-list B:2:C31, B:4:C52

       Sending 5, 100-byte ICMP Echos to B5::, timeout is 2 seconds:
       !!!!!
       Success rate is 100 percent (5/5), round-trip min/avg/max = 0.625
       /0.749/0.931 ms

               Figure 2 A sample ping output at an SRv6 capable node


   All transit nodes process the echo request message like any other
   data packet carrying SR header and hence do not require any change.
   Similarly, the egress node (IPv6 classic or SRv6 capable) does not
   require any change to process the ICMPv6 echo request.  For example,
   in the ping example of Figure 2:

   o  Node N1 initiates an ICMPv6 ping packet with SRH as follows
      (A:1::, B:2:C31)(A:5::, B:4:C52, B:2:C31, SL=2, NH =
      ICMPv6)(ICMPv6 Echo Request).

   o  Node N2, which is an SRv6 capable node, performs the standard SRH
      processing.  Specifically, it executes the END.X function
      (B:2:C31) and forwards the packet on link3 to N3.



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   o  Node N3, which is a classic IPv6 node, performs the standard IPv6
      processing.  Specifically, it forwards the echo request based on
      DA B:4:C52 in the IPv6 header.

   o  Node N4, which is an SRv6 capable node, performs the standard SRH
      processing.  Specifically, it observes the END.X function
      (B:4:C52) with PSP (Penultimate Segment POP) on the echo request
      packet and removes the SRH and forwards the packet across link10
      to N5.

   o  The echo request packet at N5 arrives as an IPv6 packet without an
      SRH.  Node N5, which is a classic IPv6 node, performs the standard
      IPv6/ ICMPv6 processing on the echo request and responds,
      accordingly.

4.1.2.  Pinging a SID

   The classic ping described in the previous section cannot be used to
   ping a remote SID function, as explained using an example in the
   following.

   Consider the case where the user wants to ping the remote SID
   function B:4:C52 from node N1.  Node N1 constructs the ping packet
   (A:1::, B:4:C52)(ICMPv6 Echo Request).  The ping fails because the
   node N4 receives the ICMPv6 echo request with DA set to B:4:C52 but
   the next header is ICMPv6, instead of SRH.

   To perform ICMPv6 ping to a target SID an echo request message is
   generated by the initiator with the END.OP or END.OTP SID in the
   segment-list of the SRH immediately preceding the target SID.  There
   MAY or MAY NOT be additional segments preceding the END.OP/ END.OTP
   SID.

   When the node instantiating a SID S of type END.OP or END.OTP
   receives a packet with S in the destination address of the IPv6
   header it sends it to the OAM process.  The OAM process verifies the
   segment following S is a locally instantiated SID.  It then processes
   the Upper layer header of the packet, as a host, responding to the
   echo request message in the ICMPv6 payload.

   When the segment following S is not verified by the OAM process an
   ICMPv6 error message type 4 (parameter problem) code 0 (erroneous
   header field encountered) with pointer set to the segment following S
   (the target SID) is generated for the packet and the packet is
   discarded.

   An implementation of the OAM process SID verification SHOULD do the
   following:



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   o  Verify that the SID is locally instantiated.

   o  Verify that the SID is instantiated in the data plane (this may
      include verification of the SID in NPUs or forwarding hardware, as
      applicable).

4.1.2.1.  Ping using END.OP/ END.OTP

   This section uses END.OTP SID for the ping illustration but the
   procedures are equally applicable to the END.OP SID.

   Consider the example where the user wants to ping a remote SID
   function B:4:C52, via B:2:C31, from node N1.  To force a punt of the
   ICMPv6 echo request at the node N4, node N1 inserts the END.OTP SID
   just before the target SID B:4:C52 in the SRH.  The ICMPv6 echo
   request is processed at the individual nodes along the path as
   follows:

   o  Node N1 initiates an ICMPv6 ping packet with SRH as follows
      (A:1::, B:2:C31)(B:4:C52, B:4:OTP, B:2:C31; SL=2;
      NH=ICMPv6)(ICMPv6 Echo Request).

   o  Node N2, which is an SRv6 capable node, performs the standard SRH
      processing.  Specifically, it executes the END.X function
      (B:2:C31) on the echo request packet.

   o  Node N3 receives the packet as follows (A:1::, B:4:OTP)(B:4:C52,
      B:4:OTP, B:2:C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request).  Node
      N3, which is a classic IPv6 node, performs the standard IPv6
      processing.  Specifically, it forwards the echo request based on
      DA B:4:OTP in the IPv6 header.

   o  When node N4 receives the packet (A:1::, B:4:OTP)(B:4:C52,
      B:4:OTP, B:2:C31 ; SL=1; NH=ICMPv6)(ICMPv6 Echo Request), it
      processes the END.OTP SID, as described in the pseudocode in
      Section 3.  The packet gets time-stamped and punted to the OAM
      process for processing.  The OAM process checks if the next SID in
      SRH (the target SID B:4:C52) is locally programmed.

   o  If the next SID is not locally programmed, the OAM process returns
      an ICMPv6 error message type 4 (parameter problem) code 0
      (erroneous header field encountered) with pointer set to the
      target SID B:4:C52 and the packet is discarded.

   o  If the next SID is locally programmed, the node processes the
      upper layer header.  As part of the upper layer header (ICMPv6)
      processing node N4 sends the ICMPv6 Echo Reply message [RFC4443].




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4.2.  Traceroute

   There is no hardware or software change required for traceroute
   operation at the classic IPv6 nodes in an SRv6 network.  That
   includes the classic IPv6 node with ingress, egress or transit roles.
   Furthermore, no protocol changes are required to the standard
   traceroute operations.  In other words, existing traceroute
   mechanisms work seamlessly in the SRv6 networks.

   The following subsections outline some use cases of the traceroute in
   the SRv6 networks.

4.2.1.  Classic Traceroute

   The existing mechanism to traceroute a remote IP prefix, along the
   shortest path, continues to work without any modification.  The
   initiator may be an SRv6 node or a classic IPv6 node.  Similarly, the
   egress or transit may be an SRv6 node or a classic IPv6 node.

   If an SRv6 capable ingress node wants to traceroute to IPv6 prefix
   via an arbitrary segment list <S1, S2, S3>, it needs to initiate
   traceroute probe with an SR header containing the SID list <S1, S2,
   S3>.  That is illustrated using the topology in Figure 1.  Assume all
   the links have IGP metric 10 except both links between node2 and
   node3, which have IGP metric set to 100.  User issues a traceroute
   from node N1 to a loopback of node 5, via segment list <B:2:C31,
   B:4:C52>.  Figure 3 contains sample output for the traceroute
   request.


        > traceroute A:5:: via segment-list B:2:C31, B:4:C52

        Tracing the route to A:5::
         1  2001:DB8:1:2:21:: 0.512 msec 0.425 msec 0.374 msec
            SRH: (A:5::, B:4:C52, B:2:C31, SL=2)
         2  2001:DB8:2:3:31:: 0.721 msec 0.810 msec 0.795 msec
            SRH: (A:5::, B:4:C52, B:2:C31, SL=1)
         3  2001:DB8:3:4::41:: 0.921 msec 0.816 msec 0.759 msec
            SRH: (A:5::, B:4:C52, B:2:C31, SL=1)
         4  2001:DB8:4:5::52:: 0.879 msec 0.916 msec 1.024 msec

         Figure 3 A sample traceroute output at an SRv6 capable node


   Please note that information for hop2 is returned by N3, which is a
   classic IPv6 node.  Nonetheless, the ingress node is able to display
   SR header contents as the packet travels through the IPv6 classic
   node.  This is because the "Time Exceeded Message" ICMPv6 message can



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   contain as much of the invoking packet as possible without the ICMPv6
   packet exceeding the minimum IPv6 MTU [RFC4443].  The SR header is
   also included in these ICMPv6 messages initiated by the classic IPv6
   transit nodes that are not running SRv6 software.  Specifically, a
   node generating ICMPv6 message containing a copy of the invoking
   packet does not need to understand the extension header(s) in the
   invoking packet.

   The segment list information returned for hop1 is returned by N2,
   which is an SRv6 capable node.  Just like for hop2, the ingress node
   is able to display SR header contents for hop1.

   There is no difference in processing of the traceroute probe at an
   IPv6 classic node and an SRv6 capable node.  Similarly, both IPv6
   classic and SRv6 capable nodes may use the address of the interface
   on which probe was received as the source address in the ICMPv6
   response.  ICMP extensions defined in [RFC5837] can be used to also
   display information about the IP interface through which the datagram
   would have been forwarded had it been forwardable, and the IP next
   hop to which the datagram would have been forwarded, the IP interface
   upon which a datagram arrived, the sub-IP component of an IP
   interface upon which a datagram arrived.

   The information about the IP address of the incoming interface on
   which the traceroute probe was received by the reporting node is very
   useful.  This information can also be used to verify if SID functions
   B:2:C31 and B:4:C52 are executed correctly by N2 and N4,
   respectively.  Specifically, the information displayed for hop2
   contains the incoming interface address 2001:DB8:2:3:31:: at N3.
   This matches with the expected interface bound to END.X function
   B:2:C31 (link3).  Similarly, the information displayed for hop5
   contains the incoming interface address 2001:DB8:4:5::52:: at N5.
   This matches with the expected interface bound to the END.X function
   B:4:C52 (link10).

4.2.2.  Traceroute to a SID

   The classic traceroute described in the previous section cannot be
   used to traceroute a remote SID function, as explained using an
   example in the following.

   Consider the case where the user wants to traceroute the remote SID
   function B:4:C52 from node N1.  The trace route fails at N4.  This is
   because the node N4 receives a trace route probe where next header is
   UDP or ICMPv6, instead of SRH (even though the hop limit is set to
   1).





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   To traceroute a target SID a probe message is generated by the
   initiator with the END.OP or END.OTP SID in the segment-list of the
   SRH immediately preceding the target SID.  There MAY or MAY NOT be
   additional segments preceding the END.OP/ END.OTP SID.

   The node instantiating a SID S of type END.OP or END.OTP receives a
   packet with S in the destination address of the IPv6 header and sends
   it to the OAM process (before processing the TTL).  The OAM process
   verifies the segment following S is a locally instantiated SID.  It
   then processes the Upper layer header of the packet, as a host,
   responding to the probe message.

   When the segment following S is not verified by the OAM process an
   ICMPv6 error message type 4 (parameter problem) code 0 (erroneous
   header field encountered) with pointer set to the segment following S
   (the target SID) is generated for the packet and the packet is
   discarded.

   An implementation of the OAM process SID verification SHOULD do the
   following:

   o  Verify that the SID is locally instantiated.

   o  Verify that the SID is instantiated in the data plane (this may
      include verification of the SID in NPUs or forwarding hardware, as
      applicable).

4.2.2.1.  Traceroute using END.OP/ END.OTP

   In this section, hop-by-hop traceroute to a SID function is
   exemplified using UDP probes.  However, the procedure is equally
   applicable to other implementation of traceroute mechanism.
   Furthermore, the illustration uses the END.OTP SID but the procedures
   are equally applicable to the END.OP SID.

   Consider the same example where the user wants to traceroute to a
   remote SID function B:4:C52, via B:2:C31, from node N1.  To force a
   punt of the traceroute probe only at the node N4, node N1 inserts the
   END.OTP SID just before the target SID B:4:C52 in the SRH.  The
   traceroute probe is processed at the individual nodes along the path
   as follows:

   o  Node N1 initiates a traceroute probe packet with a monotonically
      increasing value of hop count and SRH as follows (A:1::,
      B:2:C31)(B:4:C52, B:4:OTP, B:2:C31; SL=2; NH=UDP)(Traceroute
      probe).





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   o  When node N2 receives the packet with hop-count = 1, it processes
      the hop count expiry.  Specifically, the node N2 responses with
      the ICMPv6 message (Type: "Time Exceeded", Code: "Time to Live
      exceeded in Transit").

   o  When Node N2 receives the packet with hop-count > 1, it performs
      the standard SRH processing.  Specifically, it executes the END.X
      function (B:2:C31) on the traceroute probe.

   o  When node N3, which is a classic IPv6 node, receives the packet
      (A:1::, B:4:OTP)(B:4:C52, B:4:OTP, B:2:C31 ; HC=1, SL=1;
      NH=UDP)(Traceroute probe) with hop-count = 1, it processes the hop
      count expiry.  Specifically, the node N3 responses with the ICMPv6
      message (Type: "Time Exceeded", Code: "Time to Live exceeded in
      Transit").

   o  When node N3, which is a classic IPv6 node, receives the packet
      with hop-count > 1, it performs the standard IPv6 processing.
      Specifically, it forwards the traceroute probe based on DA B:4:OTP
      in the IPv6 header.

   o  When node N4 receives the packet (A:1::, B:4:OTP)(B:4:C52,
      B:4:OTP, B:2:C31 ; SL=1; HC=1, NH=UDP)(Traceroute probe), it
      processes the END.OTP SID, as described in the pseudocode in
      Section 3.  Before hop-limit processing, the packet gets
      timestamped and punted to the OAM process for processing.  The OAM
      process checks if the next SID in SRH (the target SID B:4:C52) is
      locally programmed.

   o  If the next SID is not locally programmed, the OAM process returns
      an ICMPv6 error message type 4 (parameter problem) code 0
      (erroneous header field encountered) with pointer set to the
      target SID B:4:C52 and the packet is discarded.

   o  If the next SID is locally programmed, the node processes the
      upper layer header.  As part of the upper layer header processing
      node N4 responses with the ICMPv6 message (Type: Destination
      unreachable, Code: Port Unreachable).

   Figure 4 displays a sample traceroute output for this example.











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     > traceroute srv6 B:4:C52 via segment-list B:2:C31

     Tracing the route to SID function B:4:C52
      1  2001:DB8:1:2:21 0.512 msec 0.425 msec 0.374 msec
         SRH: (B:4:C52, B:4:OTP, B:2:C31; SL=2)
      2  2001:DB8:2:3:31 0.721 msec 0.810 msec 0.795 msec
         SRH: (B:4:C52, B:4:OTP, B:2:C31; SL=1)
      3  2001:DB8:3:4::41 0.921 msec 0.816 msec 0.759 msec
         SRH: (B:4:C52, B:4:OTP, B:2:C31; SL=1)

        Figure 4 A sample output for hop-by-hop traceroute to a SID function



4.3.  Monitoring of SRv6 Paths

   In the recent past, network operators are interested in performing
   network OAM functions in a centralized manner.  Various data models
   like YANG are available to collect data from the network and manage
   it from a centralized entity.

   SR technology enables a centralized OAM entity to perform path
   monitoring from centralized OAM entity without control plane
   intervention on monitored nodes.  [RFC 8403] describes such a
   centralized OAM mechanism.  Specifically, the draft describes a
   procedure that can be used to perform path continuity check between
   any nodes within an SR domain from a centralized monitoring system,
   with minimal or no control plane intervene on the nodes.  However,
   the draft focuses on SR networks with MPLS data plane.  The same
   concept applies to the SRv6 networks.  This document describes how
   the concept can be used to perform path monitoring in an SRv6
   network.  This document describes how the concept can be used to
   perform path monitoring in an SRv6 network as follows.

   In the above reference topology, N100 is the centralized monitoring
   system implementing an END function B:100:1::. In order to verify a
   segment list <B:2:C31, B:4:C52>, N100 generates a probe packet with
   SRH set to (B:100:1::, B:4:C52, B:2:C31, SL=2).  The controller
   routes the probe packet towards the first segment, which is B:2:C31.
   N2 performs the standard SRH processing and forward it over link3
   with the DA of IPv6 packet set to B:4:C52.  N4 also performs the
   normal SRH processing and forward it over link10 with the DA of IPv6
   packet set to B:100:1::. This makes the probe loops back to the
   centralized monitoring system.

   In the reference topology in Figure 1, N100 uses an IGP protocol like
   OSPF or ISIS to get the topology view within the IGP domain.  N100
   can also use BGP-LS to get the complete view of an inter-domain



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   topology.  In other words, the controller leverages the visibility of
   the topology to monitor the paths between the various endpoints
   without control plane intervention required at the monitored nodes.

5.  Implementation Status

   This section is to be removed prior to publishing as an RFC.

   See [I-D.matsushima-spring-srv6-deployment-status] for updated
   deployment and interoperability reports.

6.  Security Considerations

   This document does not define any new protocol extensions and relies
   on existing procedures defined for ICMP.  This document does not
   impose any additional security challenges to be considered beyond
   security considerations described in [RFC4884], [RFC4443], [RFC792],
   RFCs that updates these RFCs, [I-D.ietf-6man-segment-routing-header]
   and [I-D.ietf-spring-srv6-network-programming].

7.  IANA Considerations

7.1.  ICMPv6 type Numbers RegistrySEC

   This document defines one ICMPv6 Message, a type that has been
   allocated from the "ICMPv6 'type' Numbers" registry of [RFC4443].
   Specifically, it requests to add the following to the "ICMPv6 Type
   Numbers" registry:

      TBA (suggested value: 162) SRv6 OAM Message.

   The document also requests the creation of a new IANA registry to the
   "ICMPv6 'Code' Fields" against the "ICMPv6 Type Numbers TBA - SRv6
   OAM Message" with the following codes:

       Code  Name                                     Reference
       --------------------------------------------------------
        0     No Error                                This document
        1     SID is not locally implemented          This document
        2     O-flag punt at Transit                  This document


7.2.  SRv6 OAM Endpoint Types

   This I-D requests to IANA to allocate, within the "SRv6 Endpoint
   Behaviors Registry" sub-registry belonging to the top-level "Segment-
   routing with IPv6 dataplane (SRv6) Parameters" registry [I-D.ietf-
   spring- srv6-network-programming], the following allocations:



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           +------------------+-------------------+-----------+
           | Value (Suggested | Endpoint Behavior | Reference |
           | Value)           |                   |           |
           +------------------+-------------------+-----------+
           | TBA (40)         |        End.OP     | [This.ID] |
           | TBA (41)         |        End.OTP    | [This.ID] |
           +------------------+-------------------+-----------+


8.  Acknowledgements

   The authors would like to thank Gaurav Naik for his review comments.

9.  Contributors

   The following people have contributed to this document:

      Robert Raszuk
      Bloomberg LP
      Email: robert@raszuk.net


      John Leddy
      Individual
      Email: john@leddy.net


      Gaurav Dawra
      LinkedIn
      Email: gdawra.ietf@gmail.com


      Bart Peirens
      Proximus
      Email: bart.peirens@proximus.com


      Nagendra Kumar
      Cisco Systems, Inc.
      Email: naikumar@cisco.com


      Carlos Pignataro
      Cisco Systems, Inc.
      Email: cpignata@cisco.com






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      Rakesh Gandhi
      Cisco Systems, Inc.
      Canada
      Email: rgandhi@cisco.com


      Frank Brockners
      Cisco Systems, Inc.
      Germany
      Email: fbrockne@cisco.com


      Darren Dukes
      Cisco Systems, Inc.
      Email: ddukes@cisco.com


      Cheng Li
      Huawei
      Email: chengli13@huawei.com


      Faisal Iqbal
      Individual
      Email: faisal.ietf@gmail.com


10.  References

10.1.  Normative References

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-26 (work in
              progress), October 2019.

   [I-D.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
              Matsushima, S., and Z. Li, "SRv6 Network Programming",
              draft-ietf-spring-srv6-network-programming-06 (work in
              progress), December 2019.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.




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10.2.  Informative References

   [I-D.matsushima-spring-srv6-deployment-status]
              Matsushima, S., Filsfils, C., Ali, Z., and Z. Li, "SRv6
              Implementation and Deployment Status", draft-matsushima-
              spring-srv6-deployment-status-04 (work in progress),
              December 2019.

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, DOI 10.17487/RFC0792, September 1981,
              <https://www.rfc-editor.org/info/rfc792>.

   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,
              <https://www.rfc-editor.org/info/rfc4443>.

   [RFC4884]  Bonica, R., Gan, D., Tappan, D., and C. Pignataro,
              "Extended ICMP to Support Multi-Part Messages", RFC 4884,
              DOI 10.17487/RFC4884, April 2007,
              <https://www.rfc-editor.org/info/rfc4884>.

   [RFC5837]  Atlas, A., Ed., Bonica, R., Ed., Pignataro, C., Ed., Shen,
              N., and JR. Rivers, "Extending ICMP for Interface and
              Next-Hop Identification", RFC 5837, DOI 10.17487/RFC5837,
              April 2010, <https://www.rfc-editor.org/info/rfc5837>.

   [RFC8403]  Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N.
              Kumar, "A Scalable and Topology-Aware MPLS Data-Plane
              Monitoring System", RFC 8403, DOI 10.17487/RFC8403, July
              2018, <https://www.rfc-editor.org/info/rfc8403>.

Authors' Addresses

   Zafar Ali
   Cisco Systems

   Email: zali@cisco.com


   Clarence Filsfils
   Cisco Systems

   Email: cfilsfil@cisco.com






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   Satoru Matsushima
   Softbank

   Email: satoru.matsushima@g.softbank.co.jp


   Daniel Voyer
   Bell Canada

   Email: daniel.voyer@bell.ca


   Mach Chen
   Huawei

   Email: mach.chen@huawei.com



































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