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Versions: (draft-paraschiv-mpls-lsp-query) 00 01 02 03 04 05 06 07 08 09

 Network Working Group                                  P. Ashwood-Smith
 Internet Draft                                             A. Paraschiv
 Expiration Date: January 2004                                  D. Allan
                                                         Nortel Networks
 
                                                               June 2003
 
 
         Multi Protocol Label Switching Label Distribution Protocol
                        Query Message Description
 
 
                     draft-ietf-mpls-lsp-query-09.txt
 
 Status of this Memo
 
    This document is an Internet-Draft and is in full conformance with
    all provisions of Section 10 of RFC2026.
 
    Internet-Drafts are working documents of the Internet Engineering
    Task Force (IETF), its areas, and its working groups.  Note that
    other groups may also distribute working documents as Internet-
    Drafts.
 
    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."
 
    The list of current Internet-Drafts can be accessed at
         http://www.ietf.org/ietf/1id-abstracts.txt
    The list of Internet-Draft Shadow Directories can be accessed at
         http://www.ietf.org/shadow.html.
 
 Abstract
 
    This document describes the encoding and procedures for three new
    Label Distribution Protocol (LDP) messages: Query Message, Query-
    Reply Message and Partial Query-Reply Message.  A Label Edge Router
    (LER) sends a Query message when it needs to find out information
    about an established Label Switched Path (LSP). The Query message
    can be used for LDP LSPs as well as for Constraint-Based Label
    Switched Paths (CR-LSPs).  The queried data is encoded into the
    Query-Reply messages.
 
 
 
 
 
 
 
 
 
 
 
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Internet Draft      draft-ietf-mpls-lsp-query-09.txt          June 2003
 
 
 
 
 
 Contents
 
 1.    Introduction..................................................3
 2.    Specification.................................................3
 3.    Overview......................................................3
    3.1 LDP Overview.................................................3
    3.2 CR-LDP Overview..............................................4
 4.    LDP Message Structure Overview................................4
 5.    LSRs with constraints in handling the query messages..........5
    5.1 LSR does not support the query messages......................6
    5.2 LSR cannot share any information.............................6
    5.3 LSR cannot share some of the queried information.............6
    5.4 LSR can share the queried information........................6
 6.    Query Message.................................................7
    6.1 Query Message encoding.......................................7
    6.2 Query Message Procedures.....................................9
 7.    Reply Messages...............................................10
    7.1 Query-Reply Message encoding................................11
    7.2 Query-Reply Message Procedures..............................12
    7.3 Partial Query-Reply Message encoding........................13
    7.4 Partial Query-Reply Message Procedures......................13
 8.    Query TLVs...................................................13
    8.1 Query Label TLV.............................................14
    8.2 Query Merge Flags TLV.......................................15
    8.3 Query Payload TLV...........................................16
    8.4 Status code summary.........................................16
 9.    Security Considerations......................................17
 10.   IANA Considerations..........................................17
    10.1  Message Type Space Extension..............................17
    10.2  TLV Type Name Space Extension.............................17
    10.3  Status Code Space Extension...............................18
 11.   Acknowledgments..............................................18
 12.   Normative References.........................................18
 13.   Author's Addresses...........................................18
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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Internet Draft      draft-ietf-mpls-lsp-query-09.txt          June 2003
 
 
 
    Changes from previous version:
 
         o  Additions to support ECMP
         o  Editorial changes
         o  Elaboration on security considerations
         o  Clarification to message fragmenting issues.
 
    [Editor's note: This section has to be removed prior to publication]
 
 1. Introduction
 
    The original Multiprotocol Label Switching (MPLS) architecture
    [MPLS-ARCH] was been defined to support the forwarding of data based
    on a label. The MPLS architecture does not assume a single label
    distribution protocol. A number of different label distribution
    protocols are being standardized. This memo describes the query
    mechanism for a Label Switched Path (LSP) or Constraint Based LSP
    (CR-LSP). It specifies procedures and encodings for the new messages
    added for the query mechanism.
 
    The new LDP messages are: Query Message, Query-Reply Message and
    Partial Query-Reply Message. The Partial Query Reply is almost
    Identical to the Query Reply message; therefore all references to
    the Query Reply message imply the Partial Query Reply Message as
    well unless explicitly noted.
 
    The following new TLVs are added to accommodate the encodings for
    the new query messages:
       - Query TLV
       - Query Label TLV
       - Query Merge Flags TLV
       - Query Payload TLV
 
    LDP uses the TCP transport for session, advertisement and
    notification messages; i.e., for everything but the UDP-based
    discovery mechanism. The messages which are added to support the
    query mechanism are sent over TCP as well.
 
 
 2. Specification
 
    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].
 
 
 3. Overview
 
 3.1 LDP Overview
 
 
 
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    Label Distribution Protocol (LDP) defined in [4] contains a set of
    procedures and messages by which Label Switched Routers (LSR)
    establish Label Switch Paths (LSP) through a network by mapping
    network layer routing information directly to data-link layer
    switched paths.  LDP associates a Forwarding Equivalence Class (FEC)
    with each LSP it creates.  The FEC associated with an LSP specifies
    which packets are mapped to that LSP.
 
 
 3.2 CR-LDP Overview
 
    As described in CR-LDP [1], Constraint Base Routing offers the
    opportunity to extend the information used to setup paths beyond
    what is available from the routing protocol. For instance, an LSP
    can be setup based on explicit route constraints, QoS constraints,
    and other constraints.
 
 
 4. LDP Message Structure Overview
 
    The LDP message format is specified in the LDP Specification [4].
    All LDP messages have the following format:
 
        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |U|   Message Type              |      Message Length           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Message ID                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                     Mandatory Parameters                      |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                     Optional Parameters                       |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
    U bit
         Unknown message bit.  Upon receipt of an unknown message, if U
         is clear (=0), a notification is returned to the message
         originator; if U is set (=1), the unknown message is silently
         ignored.
 
    Message Type
         Identifies the type of message
 
 
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    Message Length
         Specifies the cumulative length in octets of the Message ID,
         Mandatory Parameters, and Optional Parameters.
 
    Message ID
         32-bit value used to identify this message.  It is used by the
         sending LSR to facilitate identifying notification messages
         that may apply to this message.  An LSR sending a notification
         message in response to this message should include this
         MessageId in the Status TLV carried by the notification
         message.
 
    Mandatory Parameters
         Variable length set of required message parameters. Some
         messages have no required parameters.
 
    For messages that have required parameters, the required parameters
    must appear in the order specified by the individual message
    specifications in the sections that follow.
 
    Optional Parameters
       Variable length set of optional message parameters. Many messages
       have no optional parameters.
 
    For messages that have optional parameters, the optional parameters
    may appear in any order.
 
 
 5. LSRs with constraints in handling the query messages
 
    Upon receiving a Query message, an LSR has to behave according to
    its configuration constraints in handling the query messages and
    returning the queried information. The following cases were
    identified:
           - The LSR does not support the code to handle the messages
             for the query mechanism
           - The LSR supports the code to handle the messages for the
             query mechanism, but it is configured not to return any
             data
           - The LSR supports the code to handle the messages for the
             query mechanism, but it is configured not to return part of
             the queried data
           - The LSR supports the code to handle the messages for the
             query mechanism, and it is configured to return all the
             data which is queried.
 
    This memo provides flexibility to handle each of the above cases.
 
 
 
 
 
 
 
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 5.1 LSR does not support the query messages
 
    In this case, the LSR has to behave as if it received an unknown
    message type. It therefore honors the U bit. Where this is in
    response to query with Query flag Q8 clear, the originating LSR may
    then repeat the request with Q8 set (partial repliers requested) to
    obtain LSP information up to the non-implementing LSR along the LSP
    path.
 
 
 5.2 LSR cannot share any information
 
    In this case, the LSR is able to decode and process the query
    messages. However, it is configured to hide all the data. It should
    propagate the message after it encodes a zero-length TLV for its hop
    in the hop list in the Query message. When Query-Reply message is
    received from downstream, the LSR is requested to propagate the
    reply message upstream after it encodes the zero-length TLVs for the
    queried data. When the ingress receives back the reply, it can
    identify which TLVs are empty; it can therefore ignore the zero-
    length TLVs and process the rest of the data.
 
    Note: zero-length TLV encoding can be used for all types of queried
    information except the merge information.  The LSR is requested to
    signal the fact that the merging information is private by encoding
    a special value in the corresponding merge bits (for more
    information on the merge flags values please refer to Section 7.2 of
    this memo - Query Merge Flags TLV).
 
 
 5.3 LSR cannot share some of the queried information
 
    In this case, the LSR is able to decode and process the query
    messages. It has to propagate the query messages. It has to encode
    values for the data types that it is willing to return and zero-
    length TLVs for values for the data that is hidden.
 
    Note: zero-length TLV encoding can be used for all types of queried
    information except the merge information.  The LSR is requested to
    signal the fact that the merging information is private by encoding
    a special value in the corresponding merge bits (for more
    information on the merge flags values please refer to Section 7.2 of
    this memo - Query Merge Flags TLV).
 
 
 5.4 LSR can share the queried information
 
    In this case, the LSR's behavior has to follow the query and replies
    procedures described in the following sections of this memo.
 
    In order to have consistency among data encoded in the query and
    reply messages, each LSR which can propagate the messages has to
    encode its information in the query and in the reply messages.
 
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    The decision that an LSR can share the queried information has to be
    controlled through configuration flags. This way each node along the
    path can protect its data if they consider it private.
 
    Note: It would be more efficient to control/restrict the private
    data per MPLS cloud (inter MPLS domain) and not per LSR node (inter
    and intra MPLS domain).  When there are different MPLS clouds which
    have nodes belonging to different vendors, the control of the
    private information could be restricted to the boundary nodes.
    Within an MPLS domain, there should be no restrictions on the
    queried information. It would be useful to have some knowledge on
    which are the nodes on the boundaries and have only those hiding the
    queried data. Because there is no mechanism to identify which are
    the boundary nodes, this is subject for future study.
 
 
 6. Query Message
 
    This section describes the Query message and its encodings and
    procedures.  This message is meant to be used to gather information
    about an LSP.  It can be sent at any time for an established LSP.
    This memo currently describes the procedures for the cases when the
    Query Message is initiated by the ingress LER. Additional procedures
    may be added in the future for the query message when issued from an
    LSR or from egress.
 
    The Query Message can be used to gather information about:
            - LSRs which form the LSP
            - Labels along the LSP
            - Information on what LSRs are merging points along the path
            - Unused bandwidth (as described in "Improving Topology Data
              Base Accuracy with LSP Feedback" [2])
            - What path any specific payload may follow in the presence
              of load spreading mechanisms such as ECMP
            - Anything that is needed in the future and can be computed
              and encoded in a TLV.
 
    It should be noted that useful information can still be extracted
    from partial responses due constraints on handling messages placed
    on some LSRs along the LSP. In the fault diagnosis scenario
    (particularly in the presence of ECMP), those LSRs that at a minimum
    return their own LSR ID facilitate diagnosis when combined with data
    plane tracing tools as those LSRs can act as segmentation boundaries
    for fault isolation.
 
    The queried information is encoded in the Query-Reply message which
    is sent back upstream, as a response to the Query message.
 
 
 
 6.1 Query Message encoding
 
 
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      The encoding for the Query message is:
 
        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |0|         Query type TBD IANA |      Message Length           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Message ID                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Query Label TLV                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      Query TLV                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      Hop Count TLV                            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Optional Parameters                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
    Message ID
       32-bit value used to identify this message.
 
    Query Label TLV
       The label associated to the LSP which is queried. This TLV is a
       list of Generalized Label TLVs [3].  The Generalized Label TLV
       provides a more generic encoding for different types of labels.
       Most of the time the list has one element; this is the case when
       the LSP is not tunneled.  For tunneled LSPs, the Label TLV has
       more that one element; it has to behave like a label stack (it
       contains the previous label and the tunnel's label). See Section
       8.1 of this memo - Query Label TLV - for more information on
       Label TLV encoding.
 
    Query TLV
       What to query. See Section 8 of this memo - Query TLV - for
       encoding.
 
    Hop Count TLV
       Specifies the number of LSR hops that can still be traversed
       before the message is dropped due to loop detection. It is
       initialized to the max default value of 255 (or the configured
       value, if any). Every LSR that receives the Query Message has to
       subtract 1 from the Hop Count value.  The Query message should
       be dropped if the hop count value becomes zero; a Notification
       signaling Loop Detection should be sent in reply to the sender
       of the message. See [4] for Hop Count TLV encoding.
 
 
    Optional Parameters
       This variable length field contains 0 or more parameters, each
       encoded as a TLV.
 
                Optional Parameter       Length          Value
 
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                ER TLV                   var             See [1]
                LSPID TLV                var             See [1]
                FEC TLV                  var             See [4]
                Query Payload TLV        var             See below
 
    The ER TLV is a list of hops. It is used when the Query flag Q3 is
    set. Every LSR should add its IP address. The address to be added
    should be the outgoing interface address. Addresses are organized as
    a last-in-first-out stack (the first address in TLV is considered
    the top). By carrying this TLV in the Query Message and preserving
    this order for the hops, we allow the possibility to interwork the
    Query Message with the RSVP Path message.
 
    FEC TLV is used when penultimate hop popping (PHP) is in use, for
    LDP.
 
    LSPID TLV is used when PHP is in use, for CR-LDP.
 
    Query Payload TLV is used where ECMP is deployed in order to qualify
    the specific LSP hops chosen by intermediate LSRs.
 
 
    For more details on the FEC, LSPID, or Query Payload TLVs usage,
    please refer to the Query Message Procedures below.
 
 
 6.2 Query Message Procedures
 
    The LER ingress initiates the Query message. It populates the Query
    TLV Parameters according to what kind of information it wants to
    gather. The query for an LSP is done by its label. The only data
    that the Query Message could carry is the list of hops. This way,
    each node along the path can have a complete route from source to
    destination.  This is useful for network management. Please note
    that this parameter is optional. If the Query message does not
    contain the ER TLV, it should be propagated by LSRs along the path
    without the ER TLV.
 
    Upon receiving a Query Message, an LSR decodes the label to identify
    which LSP is queried. If it cannot find the LSP which is using the
    label, it sends back a Notification message with "No LSP to query"
    status. Otherwise, it checks which is the out label which is bound
    to the queried in-label and which is the downstream LSR peer. It
    replaces the in-label from Query Label TLV with the out-label used
    by the LSP. It then passes the Query message to the downstream peer.
 
    Where there is more than one valid downstream peer, AND the Payload
    Query TLV is present, the LSR may use the Payload Query TLV to
    select the appropriate downstream LSP peer using the same algorithms
    that it would use if the payload was carried in the LSP data plane.
    If the Payload Query TLV is not present but the ECMP implementation
    requires the payload information for downstream path selection, it
 
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    sends back a Notification message with "Payload Query TLV Required"
    status.
 
    When the Query message gets to a tunnel, it has to be able to handle
    both the previous label and the tunnel's label. The Query Label TLV
    behaves like a label stack. The previous label is pushed and the
    tunnel label is used. At the end of the tunnel, we need to pop the
    stack and start substituting the lower level labels.
 
    Upon receiving the Query message, the egress node has to reply with
    a Query Reply Message. The Query-Reply Message contains the Query
    TLV which was received in the Query Message. The Query TLV tells the
    LSRs along the path which information is being queried and allows
    intermediate LSRs to piggy back their own queried information on the
    Query reply message.
 
    The initiator of a Query reply might not receive a response back. In
    this case, it is the initiator's responsibility to decide if and
    when to retry.
 
    If PHP is in use, the Query Message sent from the PHP to the
    destination node needs to carry the FEC (for LDP) or LSPID (for CR-
    LDP). This information is required because the label between the PHP
    and the destination is a special label and the destination cannot
    uniquely identify the queried LSP just by using the label value. If
    the PHP does not encode the FEC or the LSPID, the destination node
    should reply with a notification message with "Ambiguous label
    value".
 
 
 7. Reply Messages
 
    These messages are propagated upstream.  There are two types of
    reply messages:
 
            - Query-Reply message (final reply)
            - Partial Query-Reply message.
 
    The Reply messages carry the queried information upstream. A Query-
    Reply message is sent in response to a Query message. The ingress
    which initiated the Query message is interested to gather the
    information from all the nodes along the queried LSP.  However,
    there are situations in which the Query message does not reach the
    end point of the queried LSP. In these scenarios it would be useful
    if the ingress LSR gathered at least some information about the LSRs
    which are along the path, up to the one that failed. The Partial
    Query-Reply message provides this mechanism. It is recommended to
    use the Partial Query-Reply messages when a Query message fails.
 
    Both reply messages are described in the following sections.
 
 
 
 
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 7.1  Query-Reply Message encoding
 
    This message is generated by the end point of the LSP. It is
    propagated upstream, by each LSR along the path.
 
    The encoding for the Query-Reply message is:
 
        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |0|  Query-Reply Type TBD IANA  |      Message Length           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Message ID                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      Query TLV                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     MessageId TLV                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Optional Parameters                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
    Message ID
       32-bit value used to identify this message.
 
    Query TLV
       What is to be queried. See Section 7 of this memo - Query TLV -
       for encoding.
 
    MessageId TLV
       The value of this parameter is the message id of the
       corresponding Query message.
 
    Optional Parameters
       This variable length field contains 0 or more parameters, each
       encoded as a TLV. The optional parameters are:
 
       Optional Parameter                 Length  Value
       ------------------                ------  -----
       ER TLV                             var     See [1]
 
       Query Label TLV                    var     See Query Label TLV
                                                  section
       IPV4/6 specified link feedback TLV var     See [2]
 
       Query Merge Flags TLV              var     See Query Merge Flags
                                                  TLV section
 
 
    The TLV types are defined in CR-LDP [1] and LDP [4]. They are:
 
            - IPV4/6 specified link feedback TLV
            - ER TLV
 
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            - Generalized Label TLV (used in the Query Label TLV
              encoding)
            - Hop Count TLV.
 
    The IPV4/6 specified link feedback TLV is used when the Q1 flag from
    the Query TLV is set. It is used to encode the bandwidth
    information. For more information on query flags, Q1, Q2, Q3 and Q4,
    refer to Query TLV section.
 
    The ER TLV is a list of hops. It is used when the Query flag Q3 is
    set. Every LSR should add its IP address. The address to be added
    should be the outgoing interface address. Addresses are organized as
    a last-in-first-out stack (the first address in TLV is considered
    the    top).
 
    The Query Label TLV is a list of labels. It is used when the Query
    flag Q2 is set. It is populated with the labels used for the path
    which is queried. For tunneled LSPs, the Query Label TLV represents
    a list of labels associated to the lowest level tunnel.
 
    If Q3 and Q2 flags are set, the labels should be encoded in the same
    order as the hops.
 
    Query Merge Flags TLV is a list of pairs of bits. It has variable
    length and every two bits in the mask will correspond to an LSR
    along the path. Its length is rounded up to the next byte. If Q4 is
    set, every LSP along the path will have to set its corresponding
    bits in the mask. The bits have to be set in the same order as the
    labels and hops. Usually, Q4 is set when Q2 set and/or Q3 set.
 
    For more information for the TLV encodings of the TLVs which are
    used, please see [1], [4] and [2].
 
 
 7.2 Query-Reply Message Procedures
 
    A Query-Reply message is initiated by an egress node which receives
    a Query message, if the egress is able to identify the queried LSP.
    If not, the egress replies with a Notification message with "No LSP
    to query" status.
 
    Upon receiving the Query message, the egress node has to reply with
    a Query Reply message. The egress node has to encode into the Query-
    Reply message a MessageId TLV. The mapping between a Query and a
    Query-Reply Message is done based on the message id. Besides the
    MessageId TLV, the egress has to encode the information that was
    queried (bandwidth, path, etc).
 
    After the encoding is done, the query reply message is sent back, on
    the reversed path, towards the ingress. Every LSR across the LSP has
    to encode its information according to what query flags are set.
 
 
 
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 7.3 Partial Query-Reply Message encoding
 
    The Partial Query-Reply message is initiated by LSRs along the
    queried path. The message is generated only if the following rules
    apply:
            - if the Query message asked for partial
              replies (the Query message signals this request
              through Q8 bit)
            - if the LSR is configured to provide partial replies.
 
    The encoding for the Partial Query-Reply message is identical to the
    Query-Reply, except the message type.   For more details on the
    encoding please refer to the Query-Reply encoding.
 
        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |0|Partial Query-Reply TBD IANA |      Message Length           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Message ID                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      Query TLV                                |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     MessageId TLV                             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Optional Parameters                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
 
 7.4 Partial Query-Reply Message Procedures
 
    The procedures are similar to the Query-Reply's procedures.  Upon
    receiving a Query message, an LSR will check the flag from the Query
    message (Q8) which signals if the partial replies are requested by
    the ingress node. If the flag is set, the LSR has to check next if
    it is configured to fulfill this request. If the LSR supports
    partial replies, it has to create a Partial Query-Reply and encode
    the queried data and send it upstream like any Query-Reply messages.
    It has then to process the Query message according to the Query
    message procedures. When an LSR receives a Partial Query-Reply from
    upstream, it should encode its information according to what is
    queried and propagate the message. It is recommended to use the
    Partial Query mechanism when the Query message fails (when the
    ingress LER does not receive a Query-Reply message in response to a
    Query message).
 
 
 8. Query TLVs
 
    The Query TLV is used to specify the information being queried.  The
    Query TLV travels in the Query message to the egress node, where it
    is copied into a reverse flowing Query-Reply messages and used by
 
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    the egress and intermediate LSRs to know what information is being
    queried.
 
    The format for the Query TLV is:
 
       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |0|0|  Query TLV  Type TBD IANA |      Length                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Query  Flags  |            Reserved                           |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
    Query Flags can be set according to what the Query  is  used  for.
    A query flag is set when it is 1.
 
       +--+--+--+--+--+--+--+--+
       |Q8|Reserved|Q4|Q3|Q2|Q1|
       +--+--+--+--+--+--+--+--+
 
    They can be:
 
         - Q1 : query the bandwidth; if set, the LSR that
                receives the Query message has to encode the bandwidth
                that is available on the link (unused bandwidth);
         - Q2 : query the labels which are associated to each hop in the
                path;
         - Q3 : query the LSRs which form the LSP which is queried;
                if set, the LSR that received the Query-Reply message
                has to encode the current hop in the ER-TLV
         - Q4 : query which LSPs along the path are merging points;
                if set, the LSR that receives the Query message has
                to encode if it is a merging point; the encoding is
                done in the Query Merge flags TLV.
         - Q8 : if set, the ingress requests partial query-replies;
                each LSR along the path is signaled to send a Partial
                Query Reply.
 
    The reserved bits need to be set to zero on transmission and must be
    ignored on receipt. They might be used in the future to signal other
    types of queried information. The Query Flags can only be defined by
    updating this memo.
 
 
 8.1 Query Label TLV
 
    The Query Label TLV is used to encode the labels used along the path
    which is queried.
 
    Note: Query Label TLV is used in both Query and Query Reply. It is a
    required parameter in the Query message and it is an optional
    parameter in Query Reply message. When being used in the Query
    message, it carries the label or stack of labels which are being
 
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    followed and queried. When being used in the Query Reply message, it
    carries the list of labels which make up the queried path.
 
    The format for the Query Label TLV is:
 
       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |0|0| Query Label TLV TBD IANA  |      Length                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                Generalized Label TLV 1                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                                                               ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                Generalized Label TLV n                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
 
    Generalized Label TLV is used to encode labels along the path.
    Please refer to [3] for more information on the Generalized Label
    TLV encoding. If the Q2 flag is set, every LSR has to encode the
    out-label corresponding to the queried LSP.  In the Query Label TLV,
    labels are organized as a last-in-first-out stack (the first label
    in    TLV is considered the top). They should be encoded in the same
    order    as the hops and the merge flags.
 
 
 8.2 Query Merge Flags TLV
 
    The Query Merge Flags TLV is used to encode the information about
    which LSRs along the path the queried LSP is being merged into.
 
    The format for the Query Merge Flags TLV is:
 
       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |0|0| Merge Flags TLV TBD IANA  |      Length                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Number of merge flags                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                  Merge flags                                  ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                                                               ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
    The Query Merge Flags TLV has 4 bytes field to store the number of
    merge flags. This number is equal to the number of LSRs which are
    traversed by the Query-Reply Message.  The Merge flags field
    contains the merge information. It is a variable length field which
    is rounded up to the next byte. Each pair of bits in the Merge flags
 
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    field carries the merge information for one LSR. The valid values
    for the merge bits for an LSR are:
 
               01 - LSR does not do merge for the queried LSP
               10 - LSR does merge for the queried LSP
               00 - LSR cannot share the merge information.
 
    Every LSR which is asked to encode the merging info has to update
    the number of merge flags and to set its corresponding bits
    accordingly.
 
 
 8.3 Query Payload TLV
 
    The Query Payload TLV is used to encode the payload that LSRs
    implementing ECMP or similar load spreading should use when
    selecting a downstream peer.
 
    The format for the Query Payload TLV is:
 
        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |0|0| Query Payload TLV TBD IANA|      Length                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |        Payload Identifier     |        Reserved (=0)          |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       |                       Example payload                         ~
       ~                                                               |
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
    The Query Payload TLV carries an example of the payload of the LSP
    that is of interest for tracing purposes. The payload example may
    be:
     - an MPLS label stack,
     - an MPLS label stack followed by an IPv4 or IPv6 packet header or
     - an IPv4 or IPv6 packet header.
 
    The contents of the Query Payload TLV are identified via use of the
    payload identifier (currently used as a bitmap)
         0x01 - label stack present
         0x02 - IP packet present
 
    When the IP packet present flag is set, the IP version is determined
    by examining the version number field of the packet header in the
    example payload.
 
 
 8.4 Status code summary
 
    Status Code           E   Status Data  Section Title
 
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    No LSP to query       1   TBD IANA     "Query Message Procedures..."
    Ambiguous label value 1   TBD IANA     "Query Message Procedures..."
    Payload Query TLV     1   TBD IANA     "Query Message Procedures..."
       Required
    Message space         1   TBD IANA     "Query Message Procedures..."
       exhausted
 
 
 9. Security Considerations
 
    The Query mechanism inherits the same security mechanism described
    in Section 5.0 of [4].  The Query mechanism provides an additional
    security measure for cases when a node cannot share the queried
    information. Such nodes have the option of hiding their information,
    if their configuration requires it. Please refer to Section 4 of
    this memo - "Behavior of LSRs with constraints in handling the query
    messages" - for more details.
 
    The Query mechanism focuses on the ability to trace the control
    plane, the outcome of which may then be compared against the output
    of data plane tracing tools to ensure system consistency. If the
    control plane maintains a chain of trust from LSP ingress to egress
    using mechanisms to secure individual adjacencies against known or
    yet to be developed attacks, then LSP Query will produce useful
    information. Where the chain of trust is incomplete, the partial-
    query reply mechanism may be used to trace the control plane up to
    the point of the boundary between trusted and untrusted network
    elements on the LSP path.
 
 
 10. IANA Considerations
 
    RFC 3036 [4] defines several name spaces including the Message Type
    Name Space, the TLV Type Name Space, and the Status Code Name Space.
    This document makes the following assignments within those spaces.
 
 
 10.1 Message Type Space Extension
 
    The message types for Query Message, Query-Reply Message and Partial
    Query-Reply Message are as follows:
 
             Message                                           Type
             --------------------------------------         ----------
             Query Message                                   TBD IANA
             Query Reply Message                             TBD IANA
             Partial Query Reply Message                     TBD IANA
 
 
 10.2 TLV Type Name Space Extension
 
    The TLV types for Query TLV, Query Label TLV and Query Merge Flags
 
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    TLV are as follows:
 
             TLV                                               Type
             --------------------------------------         ----------
             Query TLV                                       TBD IANA
             Query Label TLV                                 TBD IANA
             Query Merge Flags TLV                           TBD IANA
             Query Payload TLV                               TBD IANA
 
 
 10.3 Status Code Space Extension
 
    The Status codes are as follows:
 
             Status Code                                       Type
             --------------------------------------         ----------
             No LSP to query                                 TBD IANA
             Ambiguous label value                           TBD IANA
             Payload Query TLV Required                      TBD IANA
             Message space exhausted                         TBD IANA
 
 
 11. Acknowledgments
 
    The authors would like to acknowledge the careful review and
    comments of Jean-Pierre Coupal, Steve Hamilton, Don Fedyk, Gregory
    Wright and Adrian Farrel.
 
 
 12. Normative References
 
    [1] B. Jamoussi et al., "Constraint-Based LSP Setup using LDP", RFC
    3212, January 2002
 
    [2] Peter Ashwood-Smith et al., "Improving Topology Data Base
    Accuracy with LSP Feedback", Work in Progress, draft-ietf-mpls-te-
    feed-03.txt.
 
    [3] Ashwood-Smith P., Berger L., "Generalized MPLS - Signaling
    Functional Description", Work in Progress, draft-ietf-mpls-
    generalized-signaling-07.txt.
 
    [4] Andersson et al., "LDP Specification", RFC 3036, January 2001.
 
 
 13. Author's Addresses
 
       Peter Ashwood-Smith               Antonela Paraschiv
       Nortel Networks Corp.             Nortel Networks Corp.
       P.O. Box 3511 Station C,          600 Technology Park Drive
       Ottawa, ON K1Y 4H7                Billerica, MA 01821
       Canada                            USA
       Phone: +1 613-763-4534            phone: +1 978-288-6136
 
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Internet Draft      draft-ietf-mpls-lsp-query-09.txt          June 2003
 
       petera@nortelnetworks.com         antonela@nortelnetworks.com
 
       Dave Allan
       Nortel Networks Corp.
       P.O. Box 3511 Station C,
       Ottawa, ON K1Y 4H7
       Canada
       Phone: +1 613-763-6362
       dallan@nortelnetworks.com
 
 
 
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