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Versions: 00 01 02 03 04 05 06 07 08 rfc2745                            
INTERNET-DRAFT                                            Andreas Terzis
Expires: October 1999                                               UCLA
<draft-ietf-rsvp-diagnostic-msgs-07.txt>                      Bob Braden
                                                     Subramaniam Vincent
                                                           Cisco Systems
                                                             Lixia Zhang
                                                              April 1999
                         RSVP Diagnostic Messages


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-

   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

   The list of Internet-Draft Shadow Directories can be accessed at


   This document specifies the RSVP diagnostic facility, which allows a
   user to collect information about the RSVP state along a path.  This
   specification describes the functionality, diagnostic message
   formats, and processing rules.

draft-ietf-rsvp-diagnostic-msgs-07.txt                          [Page 1]

INTERNET-DRAFT                                                April 1999


   A summary of the changes from the previous version (06) of this
   document follows:

      -Some editorial changes were made, using input from Tim Gleeson.
        The technical content of the document has not changed from the
        previous version.

1.  Introduction

   In the basic RSVP protocol [RSVP], error messages are the only means
   for an end host to receive feedback regarding a failure in setting up
   either path state or reservation state.  An error message carries
   back only the information from the failed point, without any
   information about the state at other hops before or after the
   failure.  In the absence of failures, a host receives no feedback
   regarding the details of a reservation that has been put in place,
   such as whether, or where, or how, its own reservation request is
   being merged with that of others.  Such missing information can be
   highly desirable for debugging purposes, or for network resource
   management in general.

   This document specifies the RSVP diagnostic facility, which is
   designed to fill this information gap.  The diagnostic facility can
   be used to collect and report RSVP state information along the path
   from a receiver to a specific sender.  It uses Diagnostic messages
   that are independent of other RSVP control messages and produce no
   side-effects; that is, they do not change any RSVP state at either
   nodes or hosts.  Similarly, they provide not an error report but
   rather a collection of requested RSVP state information.

   The RSVP diagnostic facility was designed with the following goals:

      - To collect RSVP state information from every RSVP-capable hop
        along a path defined by path state, either for an existing
        reservation or before a reservation request is made.  More
        specifically, we want to be able to collect information about
        flowspecs, refresh timer values, and reservation merging at each
        hop along the path.

      - To collect the IP hop count across each non-RSVP cloud.

      - To avoid diagnostic packet implosion or explosion.

   The following is specifically identified as a non-goal:

draft-ietf-rsvp-diagnostic-msgs-07.txt                          [Page 2]

INTERNET-DRAFT                                                April 1999

      - Checking the resource availability along a path.  Such
        functionality may be useful for future reservation requests, but
        it would require modifications to existing admission control
        modules that is beyond the scope of RSVP.

2.  Overview

   The diagnostic facility introduces two new RSVP message types:
   Diagnostic Request (DREQ) and Diagnostic Reply (DREP).  A DREQ
   message can be originated by a client in a "requester" host, which
   may or may not be a participant of the RSVP session to be diagnosed.
   A client in the requester host invokes the RSVP diagnostic facility
   by generating a DREQ packet and sending it towards the LAST-HOP node,
   which should be on the RSVP path to be diagnosed. This DREQ packet
   specifies the RSVP session and a sender host for that session.
   Starting from the LAST-HOP, the DREQ packet collects information
   hop-by-hop as it is forwarded towards the sender (see Figure 1),
   until it reaches the ending node.  Specifically, each RSVP-capable
   hop adds to the DREQ message a response (DIAG_RESPONSE) object
   containing local RSVP state for the specified RSVP session.

   When the DREQ packet reaches the ending node, the message type is
   changed to Diagnostic Reply (DREP) and the completed response is sent
   to the original requester node.  Partial responses may also be
   returned before the DREQ packet reaches the ending node if an error
   condition along the path, such as "no path state", prevents further
   forwarding of the DREQ packet.  To avoid packet implosion or
   explosion, all diagnostic packets are forwarded via unicast only.

   Thus, there are generally three nodes (hosts and/or routers) involved
   in performing the diagnostic function: the requester node, the
   starting node, and the ending node, as shown in Figure 1.  It is
   possible that the client invoking the diagnosis function may reside
   directly on the starting node, in which case that the first two nodes
   are the same.  The starting node is named "LAST-HOP", meaning the
   last-hop of the path segment to be diagnosed.  The LAST-HOP node can
   be either a receiver node or an intermediate node along the path.
   The ending node is usually the specified sender host.  However, the
   client can limit the length of the path segment to be diagnosed by
   specifying a hop-count limit in the DREQ message.

draft-ietf-rsvp-diagnostic-msgs-07.txt                          [Page 3]

INTERNET-DRAFT                                                April 1999

                       LAST-HOP                  Ending
          Receiver        node                     node           Sender
              __           __         __            __              __
             |  |---------|  |------>|  |--> ...-->|  |--> ...---->|  |
             |__|         |__| DREQ  |__|   DREQ   |__|   DREQ     |__|
                           ^                         .              |
                           |                         .              |
                           | DREQ                    . DREP         | DREP
                           |                         .              |
                          _|_               DREP     V              V
             Requester   |   | <------------------------------------
             (client)    |___|

                              Figure 1

   DREP packets can be unicast from the ending node back to the
   requester either directly or hop-by-hop along the reverse of the path
   taken by the DREQ message to the LAST-HOP, and thence to the
   requester.  The direct return is faster and more efficient, but the
   hop-by-hop reverse-path route may be the only choice if the packets
   have to cross firewalls.  Hop-by-hop return is accomplished using an
   optional ROUTE object, which is built incrementally to contain a list
   of node addresses that the DREQ packet has passed through.  The ROUTE
   object is then used in reverse as a source route to forward the DREP
   hop-by-hop back to the LAST-HOP node.

   A DREQ message always consists of a single unfragmented IP datagram.
   On the other hand, one DREQ message can generate multiple DREP
   packets, each containing a fragment of the total DREQ message.  When
   the path consists of many hops, the total length of a DREP message
   will exceed the MTU size before reaching the ending node; thus, the
   message has to be fragmented.  Relying on IP fragmentation and
   reassembly, however, can be problematic, especially when DREP
   messages are returned to the requester hop-by-hop, in which case
   fragmentation/reassembly would have to be performed at every hop.  To
   avoid such excessive overhead, we let the requester define a default
   path MTU size that is carried in every DREQ packet.  If an
   intermediate node finds that the default MTU size is bigger than the
   MTU of the incoming interface, it reduces the default MTU size to the
   MTU size of the incoming interface. If an intermediate node detects
   that a DREQ packet size is larger than the default MTU size, it
   returns to the requester (in either manner described above) a DREP
   fragment containing accumulated responses.  It then removes these
   responses from the DREQ and continues to forward it.  The requester

draft-ietf-rsvp-diagnostic-msgs-07.txt                          [Page 4]

INTERNET-DRAFT                                                April 1999

   node can reassemble the resulting DREP fragments into a complete DREP

   When discussing diagnostic packet handling, this document uses
   direction terminology that is consistent with the RSVP functional
   specification [RSVP], relative to the direction of data packet flow.
   Thus, a DREQ packet enters a node through an "outgoing interface" and
   is forwarded towards the sender through an "incoming interface",
   because DREQ packets travel in the reverse direction to the data

   Notice that DREQ packets can be forwarded only after the RSVP path
   state has been set up.  If no path state exists, one may resort to
   the traceroute or mtrace facility to examine whether the
   unicast/multicast routing is working correctly.

3.  Diagnostic Packet Format

   Like other RSVP messages, DREQ and DREP messages consist of an RSVP
   Common Header followed by a variable set of typed RSVP data objects.
   The following sequence must be used:

              |        RSVP Common Header         |
              |         Session object            |
              |      Next-Hop RSVP_HOP object     |
              |       DIAGNOSTIC object           |
              |    (optional) DIAG_SELECT object  |
              |    (optional) ROUTE object        |
              | zero or more DIAG_RESPONSE objects|

   The session object identifies the RSVP session for which the state
   information is being collected.  We describe each of the other parts.

draft-ietf-rsvp-diagnostic-msgs-07.txt                          [Page 5]

INTERNET-DRAFT                                                April 1999

3.1.  RSVP Message Common Header

   The RSVP message common header is defined in [RSVP].  The following
   specific exceptions and extensions are needed for DREP and DREQ.

   Type field: define:

         Type = 8: DREQ     Diagnostic Request

         Type = 9: DREP     Diagnostic Reply

   RSVP length:

      If this is a DREP message and the MF flag in the DIAGNOSTIC object
      (see below) is set, this field indicates the length of this single
      DREP fragment rather than the total length of the complete DREP
      reply message (which cannot generally be known in advance).

3.2.  Next-Hop RSVP_HOP Object

   This RSVP_HOP object carries the LIH of the interface through which
   the DREQ should be received at the upstream node. This object is
   updated hop-by hop. It is used for the same reasons that a RESV
   message contains an RSVP_HOP object: to distinguish logical
   interfaces and avoid problems caused by routing asymmetries and non-
   RSVP clouds.

   While the IP address is not really used during DREQ processing , for
   consistency with the use of the RSVP_HOP object in other RSVP
   messages, the IP address in the RSVP_HOP object to contain the
   address of the interface through which the DREQ was sent.

3.3.  DIAGNOSTIC Object

   A DIAGNOSTIC object contains the common diagnostic control
   information in both DREQ and DREP messages.

   o IPv4 DIAGNOSTIC object: Class = 30, C-Type = 1

draft-ietf-rsvp-diagnostic-msgs-07.txt                          [Page 6]

INTERNET-DRAFT                                                April 1999

    | Max-RSVP-hops | RSVP-hop-count|         Reserved            |MF|
    |                          Request ID                           |
    |           Path MTU            |     Fragment Offset           |
    |                         LAST-HOP Address                      |
    |                                                               |
    |                     SENDER_TEMPLATE object                    |
    |                                                               |
    |                                                               |
    |                 Requester FILTER_SPEC object                  |
    |                                                               |

   Here all IP addresses use the 4 byte IPv4 format, both explicitly in
   the LAST-HOP Address and by using the IPv4 forms of the embedded
   FILTER_SPEC and RSVP_HOP objects.

   o IPv6 DIAGNOSTIC object: Class = 30, C-Type = 2

   The format is the same, except all explicit and embedded IP addresses
   are 16 byte IPv6 addresses.

   The fields are as follows:


      An octet specifying the maximum number of RSVP hops over which
      information will be collected.  If an error condition in the
      middle of the path prevents the DREQ packet from reaching the
      specified ending node, the Max-RSVP-hops field may be used to
      perform an expanding-length search to reach the point just before
      the problem.  If this value is 1, the starting node and the ending
      node of the query will be the same.  If it is zero, there is no
      hop limit.


      Records the number of RSVP hops that have been traversed so far.
      If the starting and ending nodes are the same, this value will be
      1 in the resulting DREP message.

draft-ietf-rsvp-diagnostic-msgs-07.txt                          [Page 7]

INTERNET-DRAFT                                                April 1999

   Fragment Offset

      Indicates where this DREP fragment belongs in the complete DREP
      message, measured in octets.  The first fragment has offset zero.
      Fragment Offset is used to determine if a DREQ message containing
      zero DIAG_RESPONSE objects should be processed at an RSVP capable

   MF flag

      Flag means "more fragments".  It must be set to zero (0) in all
      DREQ messages.  It must be set to one (1) in all DREP packets that
      carry partial results and are returned by intermediate nodes due
      to the MTU limit.  When the DREQ message is converted to a DREP
      message in the ending node, the MF flag must remain zero.

   Request ID

      Identifies an individual DREQ message and the corresponding DREP
      message (or all the fragments of the reply message).

      One possible way to define the Request ID would use 16 bits to
      specify the ID of the process making the query and 16 bits to
      distinguish different queries from this process.

   Path MTU

      Specifies a default MTU size in octets for DREP and DREQ messages.
      This value should not be smaller than the size of the "base" DREQ
      packet. A "base" DREQ packet is one that contains a Common Header,
      a Session object , a Next-Hop RSVP_HOP object, a DIAGNOSTIC
      object, an empty ROUTE object and a single default DIAG_RESPONSE
      (see below). The assumption made here is that a diagnostic packet
      of this size can always be forwarded without being fragmented.

   LAST-HOP Address

      The IP address of the LAST-HOP node.  The DREQ message starts
      collecting information at this node and proceeds toward the


      This IPv4/IPv6 SENDER_TEMPLATE object contains the IP address and
      the port of a sender for the session being diagnosed.  The DREQ
      packet is forwarded hop-by-hop towards this address.

draft-ietf-rsvp-diagnostic-msgs-07.txt                          [Page 8]

INTERNET-DRAFT                                                April 1999

   Requester FILTER_SPEC Object

      This IPv4/IPv6 FILTER_SPEC object contains the IP address and the
      port from which the request originated and to which the DREP
      message(s) should be sent.

3.4.  DIAG_SELECT Object

   o DIAG_SELECT Class = 33, C-Type = 0.

   A Diagnostic message may optionally contain a DIAG_SELECT object to
   specify which specific RSVP objects should be reported in a
   DIAG_RESPONSE object.  In the absence of a DIAG_SELECT object, the
   DIAG_RESPONSE object added by the node will contain a default set of
   object types (see DIAG_RESPONSE object below).

   The DIAG_SELECT object contains a list of [Class, C-type] pairs, in
   the following format:

    |    class      |     C-Type    |    class      |     C-Type    |
    //                                                             //
    |    class      |     C-Type    |    class      |     C-Type    |

   When a DIAG_SELECT object is included in a DREQ message, each RSVP
   node along the path will add a DIAG_RESPONSE object containing
   response objects (see below) whose classes and C-Types match entries
   in the DIAG_SELECT list (and are from matching path and reservation
   state). A C-type octet of zero is a 'wildcard', matching any C-Type
   associated with the associated class.

   Depending on the type of objects requested, a node can find the
   associated information in the path or reservation state stored for
   the session described in the SESSION object. Specifically,
   and FILTER_SPEC objects can be extracted from the node's path state,
   while information for the FLOWSPEC, CONFIRM, STYLE and SCOPE objects
   can be found in the node's reservation state (if existent).

   If the number of [Class, C-Type] pairs is odd, the last two octets of
   the DIAG_SELECT object must be  zero. A maximum DIAG_SELECT object is

draft-ietf-rsvp-diagnostic-msgs-07.txt                          [Page 9]

INTERNET-DRAFT                                                April 1999

   one that contains the [Class, C-type] pairs for all the RSVP objects
   that can be requested in a Diagnostic query.

3.5.  ROUTE Object

   A diagnostic message may contain a ROUTE object, which is used to
   record the route of the DREQ message and as a source route for
   returning the DREP message(s) hop-by-hop.

   o IPv4 ROUTE object: Class = 31, C-Type = 1.

    |             reserved                          |    R-pointer  |
    |                                                               |
    +                     RSVP Node List                            |
    |                                                               |

   This message signifies how the reply should be returned.  If it does
   not exist in the DREQ packet then DREP packets should be sent to the
   requester directly. If it does exist, DREP packets must be returned
   hop-by-hop along the reverse path to the LAST-HOP node and thence to
   the requester node.

   An empty ROUTE object is one that has an empty RSVP Node list and R-
   pointer is equal to zero.

   RSVP Node List

      A list of RSVP node IPv4 addresses.  The number of addresses in
      this list can be computed from the object size.


      Used in DREP messages only (see Section 4.2 for details), but it
      is incremented as each hop adds its incoming interface address in
      the ROUTE object.

   o IPv6 ROUTE object: Class = 31, C-Type = 2

   The same, except RSVP Node List contains IPv6 addresses.

   In a DREQ message, RSVP Node List specifies all RSVP hops between the

draft-ietf-rsvp-diagnostic-msgs-07.txt                         [Page 10]

INTERNET-DRAFT                                                April 1999

   LAST-HOP address specified in the DIAGNOSTIC object, and the last
   RSVP node the DREQ message has visited.  In a DREP message, RSVP Node
   List specifies all RSVP hops between the LAST-HOP and the node that
   returns this DREP message.

3.6.  DIAG_RESPONSE Object

   Each RSVP node attaches a DIAG_RESPONSE object to each DREQ message
   it receives, before forwarding the message.  The DIAG_RESPONSE object
   contains the state to be reported for this node.  It has a fixed-
   format header and then a variable list of RSVP state objects, or
   "response objects".

   o IPv4 DIAG_RESPONSE object: Class = 32, C-Type = 1.

    |                       DREQ Arrival Time                       |
    |                  Incoming Interface Address                   |
    |                  Outgoing Interface Address                   |
    |                 Previous-RSVP-Hop Router Address              |
    |   D-TTL       |M|R-err|  K    |      Timer value              |
    |                                                               |
    |                  (optional) TUNNEL object                     |
    |                                                               |
    |                                                               |
    //                       Response objects                      //
    |                                                               |

   o IPv6 DIAG_RESPONSE object: Class = 32, C-Type = 2.

   This object has the same format, except that all explicit and
   embedded IP addresses are IPv6 addresses.

   The fields are as follows:

   DREQ Arrival Time

draft-ietf-rsvp-diagnostic-msgs-07.txt                         [Page 11]

INTERNET-DRAFT                                                April 1999

      A 32-bit NTP timestamp specifying the time the DREQ message
      arrived at this node.  The 32-bit form of an NTP timestamp
      consists of the middle 32 bits of the full 64-bit form, that is,
      the low 16 bits of the integer part and the high 16 bits of the
      fractional part.

   Incoming Interface Address

      Specifies the IP address of the interface on which messages from
      the sender are expected to arrive, or 0 if unknown.

   Outgoing Interface Address

      Specifies the IP address of the interface through which the DREQ
      message arrived and to which messages from the given sender and
      for the specified session address flow, or 0 if unknown.

   Previous-RSVP-Hop Router Address

      Specifies the IP address from which this node receives RSVP PATH
      messages for this source, or 0 if unknown.  This is also the
      interface to which the DREQ will be forwarded.


      The number of IP hops this DREQ message traveled from the down-
      stream RSVP node to the current node.

   M flag

      A single-bit flag which indicates whether the reservation
      described by the response objects is merged with reservations from
      other downstream interfaces when being forwarded upstream.


      A 3-bit field that indicates error conditions at a node. Currently
      defined values are:

           0x00: no error
           0x01: No PATH state
           0x02: packet too big
           0x04: ROUTE object too big


      The refresh timer multiple (defined in [RSVP]).

draft-ietf-rsvp-diagnostic-msgs-07.txt                         [Page 12]

INTERNET-DRAFT                                                April 1999

   Timer value

      The local refresh timer value in seconds.

   The set of response objects to be included at the end of the
   DIAG_RESPONSE object is determined by a DIAG_SELECT object, if one is
   present.  If no DIAG_SELECT object is present, the response objects
   belong to the default list of classes:

           SENDER_TSPEC object         FILTER_SPEC object
           FLOWSPEC object         STYLE object

   Any C-Type present in the local RSVP state will be used.  These
   response objects may be in any order but they must all be at the end
   of the DIAG_RESPONSE object.

   A default DIAG_RESPONSE object is one containing the default list of
   classes described above.

3.7.  TUNNEL Object

   The optional TUNNEL object should be inserted when a DREQ message
   arrives at an RSVP node that acts as a tunnel exit point.

   The TUNNEL object provides the mapping between the end-to-end RSVP
   session that is being diagnosed and the RSVP session over the tunnel.
   This mapping information allows the diagnosis client to conduct
   diagnosis over the involved tunnel session, by invoking a separate
   Diagnostic query for the corresponding Tunnel Session and Tunnel
   Sender.  Keep in mind, however, that multiple end-to-end sessions may
   all map to one pre-configured tunnel session that may have totally
   different parameter settings.

   The tunnel object is defined in the RSVP Tunnel Specification

4.  Diagnostic Packet Forwarding Rules

4.1.  DREQ Packet Forwarding

   DREQ messages are forwarded  hop-by-hop via unicast from the LAST-HOP
   address to the Sender address, as specified in the DIAGNOSTIC object.
   If an RSVP capable node, other than the LAST-HOP node, receives a
   DREQ message  that contains no DIAG_RESPONSE objects and has a zero
   Fragment Offset, the node should forward the DREQ packet towards the

draft-ietf-rsvp-diagnostic-msgs-07.txt                         [Page 13]

INTERNET-DRAFT                                                April 1999

   LAST-HOP without doing any of the processing mentioned below. The
   reason is that such conditions apply only for nodes downstream of the
   LAST-HOP where no information should be collected.

   Processing begins when a DREQ message, DREQ_in, arrives at a node.
   The following processing is performed before DREQ_in is forwarded:

     1. Create a new DIAG_RESPONSE object. Compute the IP hop count from
        the previous RSVP hop. This is done by subtracting the value of
        the TTL value in the IP header from Send_TTL in the RSVP common
        header. Save the result in the D-TTL field of the DIAG_RESPONSE

     2. Set the DREQ Arrival Time and the Outgoing Interface Address in
        the DIAG_RESPONSE object.  If this node is the LAST-HOP, then
        the Outgoing Interface Address field in the DIAG_RESPONSE object
        contains the following value depending on the session being

           * If the session in question is a unicast session, then the
             Outgoing Interface Address field contains the address of
             the interface LAST-HOP uses to send PATH messages and data
             to the receiver specified by the session address.

           * Otherwise, if it is a multicast session and there is at
             least one receiver for this session, LAST_HOP should use
             the address of one of local interfaces used to reach one of
             the receivers.

           * Otherwise Outgoing Interface Address should be zero.

        If no PATH state exists for the specified session, set R-error =
        0x01 (No PATH state).

     3. Increment the RSVP-hop-count field in the DIAGNOSTIC message
        object by one.

     4. If the "No PATH state" bit is set, goto Send_DREP.

     5. Set the rest of the fields in the DIAG_RESPONSE object. If
        DREQ_in contains a DIAG_SELECT object, the response object
        classes are those specified in the DIAG_SELECT; otherwise, they
        are SENDER_TSPEC, FILTER_SPEC, STYLE, and FLOWSPEC objects. If
        no reservation state exists for the specified RSVP session, the
        DIAG_RESPONSE object will contain no FILTER_SPEC or FLOWSPEC or
        STYLE object. If neither PATH nor reservation state exists for
        the specified RSVP session, then no response objects will be
        appended to the DIAG_RESPONSE object.

draft-ietf-rsvp-diagnostic-msgs-07.txt                         [Page 14]

INTERNET-DRAFT                                                April 1999

     6. If RSVP-hop-count is equal to Max-RSVP-hops or this node is the
        sender, go to Send_DREP.

     7. If the Path MTU value is larger than the MTU size of the
        incoming interface for the sender being diagnosed, change the
        Path MTU value to the MTU value of the incoming interface.

     8. If the size of DREQ_in plus the size of the new DIAG_RESPONSE
        object plus the size of an IP address ,if a ROUTE object exists,
        is larger than Path MTU set the "packet too big" (0x02) error
        bit in DIAG_RESPONSE, goto Send_DREP.

     9. If a ROUTE object exists, append the "Incoming Interface
        Address" to the end of the ROUTE object, increment R-Pointer by
        one, update the Next-Hop RSVP_HOP object, append the new
        DIAG_RESPONSE object to the list of DIAG_RESPONSE object and
        update the message length field in the RSVP common header
        accordingly. Finally, forward DREQ_in to the next hop towards
        the sender, after recomputing the checksum. Return.


     1. If the size of DREQ_in plus the size of the new DIAG_RESPONSE
        object plus the size of an IP address ,if a ROUTE object exists,
        is larger than Path MTU set the "packet too big" (0x02) error
        bit in DIAG_RESPONSE, otherwise goto step 11.

     2. Make a copy of DREQ_in and change the type field in RSVP common
        header from DREQ to DREP. Trim all DIAG_RESPONSE objects from
        DREQ_in and adjust the Fragment Offset.

     3. If a ROUTE object is present in the DREP message, decrement the
        R-pointer and set target address to the last address in the
        ROUTE object, otherwise set target address to the requester
        address. Set the MF bit, recompute the checksum and send the
        DREP message back to the target address.

     4. If the size of DREQ_in plus the size of DIAG_RESPONSE plus the
        size of an IP address ,if a ROUTE object exists, is smaller than
        Path MTU goto Step 9.

     5. Make a copy of DREQ_in and change the type field in RSVP common
        header from DREQ to DREP. If a ROUTE object exists, replace the
        ROUTE object in DREQ_in with an empty ROUTE object. Turn on the
        "ROUTE object too big" (0x04) error bit in the DIAG_RESPONSE.

     6. If the "No PATH state" (0x01) error bit is set or if RSVP-hop-

draft-ietf-rsvp-diagnostic-msgs-07.txt                         [Page 15]

INTERNET-DRAFT                                                April 1999

        count is equal to Max-RSVP-hops or if this node is the sender,
        goto Step 8.

     7. If a ROUTE object exists, append the "Incoming Interface
        Address" to the end of the ROUTE object, increment R-Pointer by
        one, update the Next-Hop RSVP_HOP object, append the new
        DIAG_RESPONSE object to the list of DIAG_RESPONSE object, update
        the message length field in the RSVP common header accordingly
        and adjust the Fragment Offset. Finally, forward DREQ_in to the
        next hop towards the sender, after recomputing the checksum.

     8. Append the DIAG_RESPONSE object to the end of DREP. Set target
        address to the requester address. Turn on the MF bit. Update the
        packet length, recompute the checksum in the DREP message and
        send it towards the target address. Return

     9. If the "No PATH state" (0x01) error bit is set or if RSVP-hop-
        count is equal to Max-RSVP-hops or if this node is the sender,
        goto Step 11.

     10. If a ROUTE object exists, append the "Incoming Interface
        Address" to the end of the ROUTE object, increment R-Pointer by
        one, update the Next-Hop RSVP_HOP object, append the new
        DIAG_RESPONSE object to the list of DIAG_RESPONSE object and
        update the message length field in the RSVP common header
        accordingly. Finally, forward DREQ_in to the next hop towards
        the sender, after recomputing the checksum. Return.

     11. Append the DIAG_RESPONSE object to the end of DREQ_in. If a
        ROUTE object is present in the message, decrement the R-pointer
        and set target address to the last address in the ROUTE object,
        otherwise set target address to the requester address. Change
        the Type Field in the Common header from DREQ to DREP.Update the
        packet length, recompute the checksum in the DREP message and
        send it towards the target address. The MF bit in this case must
        be off.

4.2.  DREP Forwarding

   When a ROUTE object is present, DREP messages are forwarded hop-by-
   hop towards the requester, by reversing the route as listed in the
   ROUTE object. Otherwise, DREP messages are sent directly to the
   original requester.

   When a node receives a DREP message, it simply decreases R-pointer by

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   one (address length), recomputes the checksum and forwards the
   message to the address pointed to by R-pointer in the route list. If
   a node, other than the LAST-HOP, receives a DREP packet where R-
   pointer is equal to zero, it must send it directly to the requester.

   When the LAST-HOP node receives a DREP message, it sends the message
   to the requester.

4.3.  MTU Selection and Adjustment

   Because the DREQ message carries the allowed MTU size of previous
   hops that the DREP messages will later traverse, this unique feature
   allows easy semantic fragmentation as described above.  Whenever the
   DREQ message approaches the size of Path MTU, it can be trimmed
   before being forwarded again.

   When a requester sends a DREQ message, the Path MTU field in the
   DIAGNOSTIC object can be set to a configured default value. It is
   possible that the original Path MTU value is chosen larger than the
   actual MTU value along some portion of the path being traced.
   Therefore each intermediate RSVP node must check the MTU value when
   processing a DREQ message.  If the specified MTU value is larger than
   the MTU of the incoming interface (that the DREQ message will be
   forwarded to), the node changes the MTU value in the header to the
   smaller value.

   Whenever a DREQ message size becomes larger than the Path MTU value,
   an intermediate RSVP node makes a copy of the message, converts it to
   a DREP message to send back, and then trims off the partial results
   from the DREQ message. If in this case also the DREQ cannot be
   forwarded upstream due to a large ROUTE object, the "ROUTE object too
   big" is set and the ROUTE object is trimmed. As a result of the ROUTE
   object trimming, DREP(s) will come hop-by-hop up to this node and
   will then immediately be forwarded to the requester address.

   Even if the steps shown above are followed there are a few cases
   where fragmentation at the IP layer will happen. For example, non-
   RSVP hops with smaller MTUs may exist before LAST-HOP is reached, or
   if the response is sent directly back to requester (as opposed to hop
   by hop) the DREP may take a different route to the requester than the
   DREQ took from the requester. Another case is when there exists a
   link with MTU smaller than the minimum Path MTU value defined in
   Section 3.2.

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4.4.  Errors

   If an error condition prevents a DREP message from being forwarded
   further, the message is simply dropped.

   If an error condition, such as lack of PATH state, prevents a DREQ
   message from being forwarded further, the node must change the
   current message to DREP type and return it to the response address.

5.  Problem Diagnosis by Using RSVP Diagnostic Facility

5.1.  Across Firewalls

   Firewalls may cause problems in diagnostic message forwarding.  Let
   us look at two different cases.

   First, let us assume that the querier resides on a receiving host of
   the session to be examined.  In this case, firewalls should not
   prevent the forwarding of the diagnostic messages in a hop-by-hop
   manner, assuming that proper holes have been punched on the firewall
   to allow hop-by-hop forwarding of other RSVP messages.  The querier
   may start by not including a ROUTE object, which can give a faster
   response delivery and reduced overhead at intermediate nodes.
   However if no response is received, the querier may resend the DREQ
   message with a ROUTE object, specifying that a hop-by-hop reply
   should be sent.

   If the requester is a third party host and is separated from the
   LAST-HOP address by a firewall (either the requester is behind a
   firewall, or the LAST-HOP is a node behind a firewall, or both), at
   this time we do not know any other solution but to change the LAST-
   HOP to a node that is on the same side of the firewall as the

5.2.  Examination of RSVP Timers

   One can easily collect information about the current timer value at
   each RSVP hop along the way.  This will be very helpful in situations
   when the reservation state goes up and down frequently, to find out
   whether the state changes are due to improper setting of timer
   values, or K values (when across lossy links), or frequent routing

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5.3.  Discovering Non-RSVP Clouds

   The D-TTL field in each DIAG_RESPONSE object shows the number of
   routing hops between adjacent RSVP nodes.  Therefore any value
   greater than one indicates a non-RSVP cloud in between.  Together
   with the arrival timestamps (assuming NTP works), this value can also
   give some vague, though not necessarily accurate, indication of how
   big that cloud might be.  One might also find out all the
   intermediate non-RSVP nodes by running either unicast or multicast
   trace route.

5.4.  Discovering Reservation Merges

   The flowspec value in a DIAG_RESPONSE object specifies the amount of
   resources being reserved for the data stream defined by the filter
   spec in the same data block.  When this value of adjacent
   DIAG_RESPONSE objects differs, that is, a downstream node Rd has a
   smaller value than its immediate upstream node Ru, it indicates a
   merge of reservation with RSVP request(s) from other down stream
   interface(s) at Rd.  Further, in case of SE style reservation, one
   can examine how the different SE scopes get merged at each hop.

   In particular, if a receiver sends a DREQ message before sending its
   own reservation, it can discover (1) how many RSVP hops there are
   along the path between the specified sender and itself, (2) how many
   of the hops already have some reservation by other receivers, and (3)
   possibly a rough prediction of how its reservation request might get
   merged with other existing ones.

5.5.  Error Diagnosis

   In addition to examining the state of a working reservation, RSVP
   diagnostic messages are more likely to be invoked when things are not
   working correctly.  For example, a receiver has reserved an adequate
   pipe for a specified incoming data stream, yet the observed delay or
   loss ratio is much higher than expected.  In this case the receiver
   can use the diagnostic facility to examine the reservation state at
   each RSVP hop along the way to find out whether the RSVP state is set
   up correctly, whether there is any blackhole along the way that
   caused RSVP message losses, or whether there are non-RSVP clouds, and
   where they are, that may have caused the performance problem.

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5.6.  Crossing "Legacy" RSVP Routers

   Since this diagnosis facility was developed and added to RSVP after a
   number of RSVP implementations were in place, it is possible, or even
   likely, that when performing RSVP diagnosis, one may encounter one or
   more RSVP-capable nodes that do not understand diagnostic messages
   and drop them.  When this happens, the invoking client will get no
   response from its requests.

   One way to by-pass such "legacy" RSVP nodes is to perform RSVP
   diagnosis repeatedly, guided by information from traceroute, or
   mtrace in case of multicast.  When an RSVP diagnostic query times out
   (see next section), one may first use traceroute to get the list of
   nodes along the path, and then gradually increase the value of Max-
   RSVP-hops field in the DREQ message, starting from a low value until
   one no longer receives a response.  One can then try RSVP diagnosis
   again by starting with the first node (which is further upstream
   towards the sender) after the unresponding one.

   There are two problem with the method mentioned above in the case of
   unicast sessions. Both problems are related to the fact that
   traceroute information provides the path from the requester to the
   sender. The first problem is that the LAST-HOP may not be on the path
   from the requester to the sender. In this case we can get information
   only from the portion of the path from the LAST-HOP to the sender
   which intersects with the path from the requester to the sender. If
   routers that are not on the intersection of the two paths don't have
   PATH state for the session being diagnosed then they will reply with
   R-error=0x01. The requester can overcome this problem by sending a
   DREQ to every router on the path (from itself to the sender) until it
   reaches the first router that belongs to the path from the sender to
   the LAST-HOP.

   The second problem is that traceroute provides the path from the
   requester to the sender which, due to routing asymmetries, may be
   different than the path traffic from the sender to the LAST-HOP uses.
   There is (at least) one case where this asymmetry will cause the
   diagnosis to fail. We present this case below.

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                                   Downstream Path                Sender
                                   __         __            __       __
      Receiver             +------|  |<------|  |<-- ...---|  |-----|  |
         __          __   /       |__|       |__|          |__|     |__|
        |  |--....--|X |_/                    ^
        |__|        |__|      Router B       |
                   Black          __         |
                   Hole    +----->|  |---->---+
                                  |__| Upstream Path

                                Router A

                              Figure 2

   Here the first hop upstream of the black hole is different on the
   upstream path and the downstream path. Traceroute will indicate
   router A as the previous hop (instead of router B which is the right
   one). Sending a DREQ to router A will result in A responding with R-
   error 0x01 (No PATH State). If the two paths converge again then the
   requester can use the solution proposed above to get any (partial)
   information from the rest of the path.

   We don't have, for the moment, any complete solutions for the
   problematic scenarios described here.

6.  Comments on Diagnostic Client Implementation.

   Following the design principle that nodes in the network should not
   hold more than necessary state,  RSVP nodes are responsible only for
   forwarding Diagnostic messages and filling DIAG_RESPONSE objects.
   Additional diagnostic functionality should be carried out by the
   diagnostic clients.  Furthermore, if the diagnostic function is
   invoked from a third-party host, we should not require that host be
   running an RSVP daemon to perform the function.  Below we sketch out
   the basic functions that a diagnostic client daemon should carry out.

     1. Take input from the user about the session to be diagnosed, the
        last-hop and the sender address, the Max-RSVP-hops, and possibly
        the DIAG_SELECT list, create a DREQ message and send to the
        LAST-HOP RSVP node using raw IP message with protocol number 46
        (RSVP). If the user specified that the response should be sent
        hop-by-hop include an empty ROUTE object to the DREQ message
        sent. Set the Path_MTU to the smaller of the user request and
        the MTU of the link through which the DREQ will be sent.

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        The port of the UDP socket on which the Diagnostic Client is
        listening for replies should be included in the Requester
        FILTER_SPEC object.

     2. Set a retransmission timer, waiting for the reply (one or more
        DREP messages).  Listen to the specified UDP port for responses
        from the LAST-HOP RSVP node.

        The LAST-HOP RSVP node, upon receiving DREP messages, sends them
        to the Diagnostic Client as UDP packets, using the port supplied
        in the Requester FILTER_SPEC object.

     3. Upon receiving a DREP message to an outstanding diagnostic
        request, the client should clear the retransmission timer, check
        to see if the reply contains the complete result of the
        requested diagnosis.  If so, it should pass the result up to the
        invoking entity immediately.

     4. Reassemble DREP fragments.  If the first reply to an outstanding
        diagnostic request contains only a fragment of the expected
        result, the client should set up a reassembly timer in a way
        similar to IP packet reassembly timer.  If the timer goes off
        before all fragments arrive, the client should pass the partial
        result to the invoking entity.

     5. Use retransmission and reassembly timers to gracefully handle
        packet losses and reply fragment scenarios.

        In the absence of response to the first diagnostic request, a
        client should retransmit the request a few times.  If all the
        retransmissions also fail, the client should invoke traceroute
        or mtrace to obtain the list of hops along the path segment to
        be diagnosed, and then perform an iteration of diagnosis with
        increasing hop count as suggested in Section 5.6 in order to
        cross RSVP-capable but diagnosis-incapable nodes.

     6. If all the above efforts fail, the client must notify the
        invoking entity.

7.  Security Considerations

   RSVP Diagnostics, as any other diagnostic tool, can be a security
   threat since it can reveal possibly sensitive RSVP state information
   to unwanted third parties.

   We feel that the threat is minimal, since as explained in the

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   Introduction Diagnostics messages produce no side-effects and
   therefore they cannot change RSVP state in the nodes. In this respect
   RSVP Diagnostics is less a security threat than other diagnostic
   tools and protocols such as SNMP.

   Furthermore, processing of Diagnostic messages can be disabled if it
   is felt that is a security threat.

8.  Acknowledgments

   The idea of developing a diagnostic facility for RSVP was first
   suggested by Mark Handley of UCL.  Many thanks to Lee Breslau of
   Xerox PARC and John Krawczyk of Baynetworks for their valuable
   comments on the first draft of this memo.  Lee Breslau, Bob Braden,
   and John Krawczyk contributed further comments after March 1996 IETF.
   Steven Berson provided valuable comments on various drafts of the
   memo. Tim Gleeson contributed an extensive list of editorial
   comments. We would also like to acknowledge Intel for providing a
   research grant as a partial support for this work. Subramaniam
   Vincent did most of this work while a graduate research assistant at
   the USC Information Sciences Institute (ISI).

9.  References

   [RSVP] Braden, R. Ed. et al, "Resource ReserVation Protocol --
   Version 1 Functional Specification", RFC 2205, September 1997.

   [RSVPTUN] A. Terzis, J. Krawczyk, J. Wroclawski, L. Zhang. "RSVP
   Operation Over IP Tunnels ", Internet Draft. draft-ietf-rsvp-tunnel-
   02.txt, February, 1999.

10.  Authors' Addresses

      Andreas Terzis
      4677 Boelter Hall
      Los Angeles, CA 90095

      Phone:    310-267-2190
      Email:    terzis@cs.ucla.edu

      Bob Braden
      USC Information Sciences Institute

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      4676 Admiralty Way
      Marina del Rey, CA 90292

      Phone:    310 822-1511
      EMail:    braden@isi.edu

      Subramaniam Vincent
      Cisco Systems
      275, E Tasman Drive, MS SJC04/2/1
      San Jose, CA 95134.
      Phone:    408 525 3474
      Email:    svincent@cisco.com

      Lixia Zhang
      4531G Boelter Hall
      Los Angeles, CA  90095

      Phone:    310-825-2695
      EMail:    lixia@cs.ucla.edu

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