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     6MAN                                                             Z. Ali
     Internet Draft                                              C. Filsfils
     Intended status: Informational                                 N. Kumar
     Expires: January 2, 2018                                       F. Iqbal
                                                         Cisco Systems, Inc.
                                                                   R. Raszuk
                                                                Bloomberg LP
                                                                  B. Peirens
                                                                    Proximus
                                                                     G. Naik
                                                           Drexel University
                                                                 July 2, 2017
     
     
     
        Operations, Administration, and Maintenance (OAM) in Segment Routing
                         Networks with IPv6 Dataplane (SRv6)
                           draft-ali-6man-srv6-oam-00.txt
     
     
     Status of this Memo
     
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        provisions of BCP 78 and BCP 79.
     
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        This Internet-Draft will expire on January 2, 2018.
     
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     Abstract
     
        This document outlines various use-cases for Operations,
        Administration, and Maintenance (OAM) in Segment Routing with the
        IPv6 data plane (SRv6) network. It also describes how the existing
        OAM mechanisms can be used to address SRv6 OAM requirements.
     
     Table of Contents
     
        1. Introduction...................................................2
           1.1. Terminology and Reference Topology........................3
        2. Use-cases......................................................4
           2.1. Connectivity Verification.................................4
           2.2. Monitoring A Specific Flow................................5
           2.3. Monitoring all ECMP/ UCMP Paths...........................5
           2.4. Proof of Transit..........................................5
           2.5. Detecting Path Divergence.................................6
           2.6. Fault Isolation...........................................6
           2.7. Centralized OAM...........................................6
        3. OAM Mechanisms.................................................6
           3.1. ICMPv6 Applicability......................................6
              3.1.1. Ping.................................................7
              3.1.2. Error Reporting......................................8
              3.1.3. Traceroute...........................................8
           3.2. In-situ OAM..............................................10
           3.3. Seamless BFD Applicability...............................10
           3.4. Controller based OAM.....................................11
        4. Security Considerations.......................................12
        5. IANA Considerations...........................................12
        6. References....................................................12
           6.1. Normative References.....................................12
           6.2. Informative References...................................12
        7. Acknowledgments...............................................12
     
     1. Introduction
     
        This document outlines various SRv6 OAM use-cases. It also describes
        how the existing OAM mechanisms can be used to address SRv6 OAM
        requirements.
     
        Additional OAM use-cases and mechanisms will be added in a future
        revision of the document.
     
     
     
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     1.1. Terminology and Reference Topology
     
        This document uses the terminology defined in [I-D.filsfils-
        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.
     
                    |--------------------| N100 |------------------|
                    |                                              |
                 ====== link1====== link3------ link5====== link9------
                 ||N1||======||N2||======| N3 |======||N4||======| N5 |
                 ||  ||------||  ||------|    |------||  ||------|    |
                 ====== link2====== link4------ link6======link10------
                                |                      |
                                |       ------         |
                                +-------| N6 |---------+
                                  link7 |    | link8
                                        ------
     
     
                                      Reference Topology
     
        In the reference topology:
        All nodes are internal nodes within a single SRv6 domain of trust
        Nodes N1, N2, and N4 are SRv6 capable nodes.
     
        Nodes N3, N5 and N6 are classic IPv6 nodes.
     
        Node 100 is an SRv6 capable node that acts as controller.
     
        Node Nk has a classic IPv6 loopback address Bk::/128
     
        Node Nk has Ak::/48 for its local SID space from which Local SIDs
        are explicitly allocated.
     
        The IPv6 address of the nth Link between node X and Y at the X side
        is represented as 99:X:Y::Xn. e.g.,the IPv6 address of link6 (the
        2nd link) between N3 and N4 at N3 in Figure 1 is 99:3:4:32.
        Similarly, the IPv6 address of link5 (the 1st link between N3 and
        N4) at node 3 is 99:3:4:31.
     
        Ak::0 is explicitly allocated as the END function at Node k.
     
        Ak::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.
     
     
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        e.g., A2::C31 represents END.X at N2 towards N3 via link3 (the 1st
        link between N2 and N3). Similarly, A4::C52 represents the END.X at
        N4 towards N5 via link10.
     
        SRH is the abbreviation for the Segment Routing Header.
     
        SL is the abbreviation for the Segment Left.
     
        SID is the abbreviation for the Segment ID.
     
        <S1, S2, S3> represents a SID list where S1 is the first SID and S3
        is the last SID. (S3, S2, S1; SL) represents the same SID list but
        encoded in the SRH format where the rightmost SID (S1) in the SRH is
        the first SID and the leftmost SID (S3) in the SRH is the last SID.
     
        ECMP is the abbreviation for the Equal Cost Multi-Path.
     
        UCMP is the abbreviation for the Unequal Cost Multi-Path.
     
     2. Use-cases
     
        This section outlines some for the basic OAM use-cases in an SRv6
        network. Additional use-cases will be added in a future revision of
        the document.
     
     2.1. Connectivity Verification
     
        One of the basic OAM use-cases for any network is the capability to
        perform path monitoring between different end points over any
        possible shortest path without any path preference. Such essential
        path monitoring helps to monitor the path availability and the
        liveliness of the remote end point.
     
        The shortest path monitoring can be done continuously or can be
        triggered on demand basis using an external event like a script or a
        CLI trigger. It may be required to perform the connectivity
        verification in the order of milliseconds, or at a slower pace.
     
        In the reference topology in Figure 1, N1 can send OAM probe packet
        destined to loopback address of N5 (B5::) to monitor the path
        liveliness between N1 and N5. N1 optionally may include any relevant
        segment list in SRH. N1 is not concerned about which route is taken
        by the probe between N1 and N5 as long as N1 receives the response
        back from N5. All transit nodes treat the probe packet as like other
        data packet and forward it based on the Destination Address (DA). N5
        looks into the payload of probe packet and respond back to the
        source address of the probe packet (N1).
     
     
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     2.2. Monitoring A Specific Flow
     
        The network OAM needs to have the ability to monitor a particular
        path from the available ECMP paths. For example, in the reference
        topology in figure 1, there are many ECMP paths between N1 and N5.
        However, the service provider may like to monitor a flow that
        follows [N1]<link1>[N2]<link7>[N6]<link8>[N4]<link9>[N5].
     
        The flow monitoring can be done continuously or can be triggered on
        demand basis. It may be required to perform the connectivity
        verification in the order of milliseconds, or at a slower pace.
     
     2.3. Monitoring all ECMP/ UCMP Paths
     
        In any network, it is common to see multiple ECMP paths between end
        points that are used for load balancing or redundancy. While
        monitoring, the shortest path helps to monitor the path and
        liveliness of remote node, it may not be sufficient to detect any
        failure in one of the ECMP paths. In our reference topology in
        figure 1, N6 has 2 ECMP paths to reach N5 as below:
     
        N6--<link8>--N4--<link9>--N5
     
        N6--<link8>--N4--<link10>--N5
     
        If the probe packet from N6 to N5 uses link10, it may not detect any
        failure on link9. It is critical and beneficial to discover and
        monitor all ECMP/ UCMP paths. Monitoring of all ECMP/ UCMP paths can
        be done by probing the candidate paths from end-to-end or by each
        node by monitoring its data plane.
     
     2.4. Proof of Transit
     
        Various scenarios require the packet to be steered over a particular
        links or nodes. For example:
     
        -    Voice traffic in a SLA constrained network needs to traverse a
        low latency path between endpoints which may not be the shortest
        path, i.e. the voice traffic needs to be traffic engineered and
        steered over the specified segment list that satisfies the SLA
        constraint.
     
        -    In a service chaining environment, the traffic may need to
        traverse over an ordered list of service functions.
     
        In these scenarios, the SRH contains the list of SID functions that
        the packet should execute before reaching the destination. It is
     
     
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        possible, due to an error, that the packet may reach the destination
        without visiting all the segments in the segment list. It is,
        therefore, important to have the ability to verify that all the
        function SIDs have been executed correctly before the packet is
        delivered to the destination. It is also important to ensure that
        the order of execution of the SID function has been consistent with
        the SRH contents.
     
     2.5. Detecting Path Divergence
     
        Path divergence occurs when network traffic diverges from the
        expected path that packet was supposed to take. Path divergence may
        result in congestion, delay, or breakage of strict SLAs promised to
        customers. It is, therefore, important to exercise mechanisms that
        can detect path divergence in the SRv6 network.
     
     2.6. Fault Isolation
     
        In the cases where a monitoring technique discovers an issue, it is
        required to have the ability to pinpoint the failure location. The
        fault isolation mechanisms are required to help service providers
        troubleshoot failure in an SRv6 network.
     
     2.7. Centralized OAM
     
        In the recent past, network operators are interested in performing
        network operations, administration, and maintenance configuration in
        a centralized manner. In this use-case, one of the requirements is
        to implement centralized OAM functionality without any control plane
        intervention at the monitored nodes.
     
        Additional OAM use-cases will be included in a future revision of
        the document.
     
     3. OAM Mechanisms
     
        This section describes how existing OAM mechanisms can be used in an
        SRv6 network. Additional OAM mechanisms will be added in a future
        revision of the document.
     
     3.1. ICMPv6 Applicability
     
        [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 mechanisms can be used in an SRv6 network. This section
     
     
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        describes the applicability of ICMPv6 in the SRv6 network and how
        the existing ICMPv6 mechanisms can be used for basic OAM
        functionality to address many use-cases outlined in Section 2.
     
        Throughout this document, unless otherwise specified, the acronym
        ICMPv6 refers to multi-part ICMPv6 messages [RFC4884]. The document
        does not propose any changes to the standard ICMPv6 [RFC4443],
        [RFC4884] or standard ICMPv4 [RFC792].
     
     3.1.1. Ping
     
        There is no change required for ping operation at the classic IPv6.
        Similarly, the existing ping mechanism works along the IGP shortest
        paths at an SRv6 capable node. However, 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>. The originator can
        appropriately set the flow-label field in the IPv6 header of the
        echo request to influence Equal-Cost Multi-Path (ECMP).
     
        Figure 2 contains sample output for a ping request initiated at node
        N1 to the loopback address of node N5 via a segment list <A2::C31,
        A4::C52>.
     
        > ping B5:: via segment-list A2::C31, A4::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
                         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:
     
        - Node N2, which is an SRv6 capable node, performs the standard SRH
          processing. Specifically, it executes the END.X function (A2::C31)
          on the echo request packet.
        - Node N3, which is a classic IPv6 node, performs the standard IPv6
          processing. Specifically, it forwards the echo request based on DA
          A4::C52 in the IPv6 header.
        - Node N4, which is an SRv6 capable node, performs the standard SRH
          processing. Specifically, it observes the END.X function
          (A4::C52)with PSP (Penultimate Segment POP) on the echo request
     
     
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          packet and removes the SRH and forwards the packet across link10
          to N5.
        - The echo request packet at N5 arrives as an IPv6 packet without a
          SRH. If the SRH arrives at classic N5, with SL=0, it should ignore
          the routing header and process normally. Node N5, which is a
          classic IPv6 node, performs the standard IPv6/ ICMPv6 processing
          on the echo request.
     
     3.1.2. Error Reporting
     
        Any IPv6 node can use ICMPv6 control messages to report packet
        processing errors to the host that originated the datagram packet.
        To name a few such scenarios:
     
        - If the router receives an undeliverable IP datagram, or
        - If the router receives a packet with a Hop Limit of zero, or
        - If the router receives a packet such that if the router decrements
          the packet's Hop Limit it becomes zero, or
        - If the router receives a packet with problem with a field in the
          IPv6 header or the extension headers such that it cannot complete
          processing the packet, or
        - If the router cannot forward a packet because the packet is larger
          than the MTU of the outgoing link.
     
        In the scenarios listed above, the ICMPv6 response also contains the
        IP header, IP extension headers and leading payload octets of the
        "original datagram" to which the ICMPv6 message is a response.
        Specifically, the Destination Unreachable Message, Time Exceeded
        Message, Packet Too Big Message and Parameter Problem Message
        ICMPV6 messages can contain as much of the invoking packet as
        possible without the ICMPv6 packet exceeding the minimum IPv6 MTU
        [RFC4443], [RFC4884]. In an SRv6 network, the copy of the invoking
        packet contains the SR header. The packet originator can use this
        information for diagnostic purposes. For example, traceroute can use
        this information as detailed in the following.
     
     3.1.3. Traceroute
     
        There is no change required for traceroute operation at the classic
        IPv6. Similarly, the existing ping mechanism works along the IGP
        shortest paths at an SRv6 capable node. However, 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>. The
        originator can appropriately set the flow-label field in the IPv6
        header of the traceroute probe to influence Equal-Cost Multi-Path
        (ECMP).
     
     
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        Figure 3 contains sample output for a traceroute request initiated
        at node N1 to the loopback address of node N5 via a segment list <
        A2::C31, A4::C52>.
     
        > traceroute B5:: via segment-list A2::C31, A4::C52
     
        Tracing the route to B5::
     
         1  99:1:2::21 0.512 msec 0.425 msec 0.374 msec
            SRH: (B5::, A4::C52, A2::C31, SL=2)
     
         2  99:2:3::31 0.721 msec 0.810 msec 0.795 msec
            SRH: (B5::, A4::C52, A2::C31, SL=1)
     
         3  99:3:4::41 0.921 msec 0.816 msec 0.759 msec
            SRH: (B5::, A4::C52, A2::C31, SL=1)
     
         5  99:4:5::52 0.879 msec 0.916 msec 1.024 msec
     
                      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
        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 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.
     
     
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        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 A2::C31 and A4::C52 are executed correctly by N2 and N4,
        respectively. Specifically, the information displayed for hop2
        contains the incoming interface address 99:2:3::31 at N3. This
        matches with the expected interface bound to END.X function A2::C31
        (link3). Similarly, the information displayed for hop5 contains the
        incoming interface address 99:4:5::52 at N5. This matches with the
        expected interface bound to the END.X function A4::C52 (link10).
     
     3.2. In-situ OAM
     
        [I-D.brockners-inband-oam-requirements] describes motivation
        and requirements for In-situ OAM (iOAM). iOAM records operational
        and telemetry information in the data packet while the packet
        traverses the network of telemetry domain. iOAM complements out-of-
        band probe based OAM mechanisms such ICMP ping and traceroute by
        directly encoding tracing and the other kind of telemetry
        information to the regular data traffic.
     
        [I-D.brockners-inband-oam-transport] describes transport mechanisms
        for iOAM data including IPv6 and Segment Routing traffic.
        furthermore, [I-D.brockners-inband-oam-data] defines information
        encoding for iOAM data.
     
        One of the applications of iOAM is to provide the Proof of Transit
        (POT). Among other features of iOAM, SRv6 networks can use the POT
        feature of iOAM to verify that all the function SIDs in SRH have
        been executed before the packet is delivered to the destination. It
        can also ensure that the order of execution of the SID function has
        been consistent with the SRH contents.
     
        More details on various applications of iOAM in SRv6 networks will
        be included in future versions of this document.
     
     3.3. Seamless BFD Applicability
     
        [RFC7880] defines Seamless BFD (S-BFD) architecture that simplifies
        BFD mechanism and enables it to perform path monitoring in a
        controlled and scalable manner. [RFC7881] describes the procedure to
        perform continuity check using S-BFD in different environments
        including IPv6 networks. Section 5.1 of [RFC7881] explains the
        SBFDInitiator specification and procedure to initiate S-BFD control
        packet in IP and MPLS network. The specification described for IP-
        routed S-BFD control packet is also directly applicable to the SRv6
        network.
     
     
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        S-BFD has a fast bootstrapping capability. Furthermore, in S-BFD,
        only the ingress is required to keep BFD states; the egress and
        transit node does not have any knowledge of the BFD session. These
        attributes of S-BFD makes it an excellent candidate for rapid
        failure detection in the SRv6 network. More details on various S-BFD
        usage on the SRv6 network will be included in a future version.
     
     3.4. Controller based OAM
     
        In the recent past, network operators are interested in performing
        network operations, administration, and maintenance configuration 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. [I.D-draft-ietf-spring-oam-usecase]
        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.
     
        In the above reference topology, N100 is the centralized monitoring
        system implementing an END function A100::. In order to verify a
        segment list <A2::C31, A4::C52>, N100 generates a probe packet with
        SRH set to (A100::, A4::C52, A2::C31, SL=2). The controller routes
        the probe packet towards the first segment, which is A2::C31. N2
        performs the standard SRH processing and forward it over link3 with
        the DA of IPv6 packet set to A4::C52. N4 also performs the normal
        SRH processing and forward it over link10 with the DA of IPv6 packet
        set to A100::. This makes the probe loops back to the centralized
        monitoring system. Please note that there is no control plane
        intervention at the monitored nodes. The entire data plane is exercised
        at the monitored nodes.
     
        In our 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
        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.
     
     
     
     
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     4. 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]
        and RFCs that updates these RFCs.
     
     5. IANA Considerations
     
        This document does not define any new protocol or any extension to
        an existing protocol.
     
     6. References
     
     6.1. Normative References
     
        [RFC4884] Extended ICMP to Support Multi-Part Messages. R. Bonica,
                  D. Gan, D. Tappan, C. Pignataro. April 2007.
     
        [RFC4443] Internet Control Message Protocol (ICMPv6) for the
                  Internet Protocol Version 6 (IPv6) Specification. A.
                  Conta, S. Deering, M. Gupta, Ed. March 2006.
     
        [RFC792] Internet Control Message Protocol. J. Postel. September
                  1981.
     
        [RFC5837] Extending ICMP for Interface and Next-Hop Identification.
                  A. Atlas, Ed., R. Bonica, Ed., C. Pignataro, Ed., N. Shen,
                  JR. Rivers. April 2010.
     
        [RFC7880] Seamless Bidirectional Forwarding Detection (S-BFD). C.Pignataro,
                  D.Ward, N.Akiya, M.Bhatia, S.Pallagatti. July 2016.
        [RFC7881] Seamless Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6,
                  and MPLS. C.Pignataro, D.Ward, N.Akiya. July 2016.
     
        [RFC7880] Seamless Bidirectional Forwarding Detection (S-BFD). C.Pignataro,
                  D.Ward, N.Akiya, M.Bhatia, S.Pallagatti. July 2016.
        [RFC7881] Seamless Bidirectional Forwarding Detection (S-BFD) for IPv4, IPv6,
                  and MPLS. C.Pignataro, D.Ward, N.Akiya. July 2016.
     
        [I.D-draft-ietf-spring-oam-usecase] A Scalable and Topology-Aware
                  MPLS Dataplane Monitoring System. R. Geib, C. Filsfils, C.
                  Pignataro, N. Kumar.
     
        [I-D.brockners-inband-oam-data] Data Formats for In-situ OAM. F.
                  Brockners, work in progress.
        [I-D.brockners-inband-oam-transport] Encapsulations for In-situ OAM Data,
                  F.Brockners, work in progress.
     
     6.2. Informative References
     
        [I-D.filsfils-spring-srv6-network-programming] SRv6 Network
                  Programming, draft-filsfils-spring-srv6-network-
                  programming, C. Fisfils, et al.
     
        [I-D.brockners-inband-oam-requirements] Requirements for In-situ OAM,
                  F.Brockners, work in progress.
     
     
     7. Acknowledgments
     
        To be added.
     
     
     
     
     
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     Internet-Draft                 SRv6 OAM                       July 2017
     
     
     Authors' Addresses
     
        Clarence Filsfils
        <Cisco Systems, Inc.>
        Email: cfilsfil@cisco.com
     
        Zafar Ali
        Cisco Systems, Inc.
        Email: zali@cisco.com
     
        Nagendra Kumar
        Cisco Systems, Inc.
        Email: naikumar@cisco.com
     
        Faisal Iqbal
        Cisco Systems, Inc.
        Email: faiqbal@cisco.com
     
        Robert Raszuk
        Bloomberg LP
        731 Lexington Ave
        New York City, NY10022, USA
        Email: robert@raszuk.net
     
        Bart Peirens
        Proximus
        Netherlands
        Email: bart.peirens@proximus.com
     
        Gaurav Naik
        Drexel University
        United States of America
        Email: gn@drexel.edu
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
     
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