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Versions: (draft-malis-pwe3-fragmentation) 00 01 02 03 04 05 06 07 08 09 10 RFC 4623

 Internet Draft                                         Andrew G. Malis
 Document: draft-ietf-pwe3-fragmentation-03.txt                 Tellabs
 Expires:  April 2004                                  W. Mark Townsley
                                                          Cisco Systems
                                                           October 2003
 
                     PWE3 Fragmentation and Reassembly
 
 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 defines a generalized method of performing
    fragmentation for use by PWE3 protocols and services.
 
 Table of Contents
 
    1. Overview......................................................2
    2. Alternatives to PWE3 Fragmentation/Reassembly.................3
    3. Fragmentation/Reassembly Specification........................3
    4. PWE3 Fragmentation With MPLS..................................5
       4.1 Fragment Bit Locations For MPLS...........................6
       4.2 Other Considerations......................................6
    5. PWE3 Fragmentation With L2TP..................................7
       5.1 PW-specific Fragmentation vs. IP fragmentation............7
       5.2 Advertising Reassembly Support in L2TP....................8
       5.3 L2TP Maximum Receive Unit (MRU) AVP.......................8
       5.4 L2TP Maximum Reassembled Receive Unit (MRRU) AVP..........8
       5.5 Fragment Bit Locations For L2TPv3 Encapsulation...........9
       5.6 Fragment Bit Locations for L2TPv2 Encapsulation...........9
    6. Security Considerations......................................10
 
 
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    7. IANA Considerations..........................................10
    8. Acknowledgements.............................................11
    9. References...................................................11
    10. Authors' Addresses..........................................12
 
 1. Overview
 
    The PWE3 Framework Document [Framework] defines a network reference
    model for PWE3:
 
                       |<------- Pseudo Wire ------>|
                       |    |<-- PSN Tunnel -->|    |
                PW     V    V                  V    V     PW
           End Service +----+                  +----+ End Service
      +-----+    |     | PE1|==================| PE2|     |    +-----+
      |     |----------|............PW1.............|----------|     |
      | CE1 |    |     |    |                  |    |     |    | CE2 |
      |     |----------|............PW2.............|----------|     |
      +-----+    |     |    |==================|    |     |    +-----+
     Customer          +----+                  +----+          Customer
     Edge 1 |      Provider Edge 1         Provider Edge 2     | Edge 2
            |<-------------- Emulated Service ---------------->|
 
                  Figure 1: PWE3 Network Reference Model
 
 
    A Pseudo Wire (PW) payload is normally relayed across the PW as a
    single PSN (IP or MPLS) PDU. However, there are cases where the
    combined size of the payload and its associated PWE3 and PSN
    headers may exceed the PSN path Maximum Transmission Unit (MTU).
    When a packet exceeds the MTU of a given network, fragmentation and
    reassembly will allow the packet to traverse the network and reach
    its intended destination.
 
    The purpose of this document is to define a generalized method of
    performing fragmentation for use with all PWE3 protocols and
    services. This method should be utilized only in cases where MTU-
    management methods fail. Due to the increased processing overhead,
    fragmentation and reassembly in core network devices should always
    be considered something to avoid whenever possible.
 
    The PWE3 fragmentation and reassembly domain is shown in Figure 2:
 
 
 
 
 
 
 
 
 
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                       Fragmentation/Reassembly Domain
                       |                            |
                       ||<------ Pseudo Wire ----->||
                       ||   |<-- PSN Tunnel -->|   ||
                PW     VV   V                  V   VV     PW
          End Service  +----+                  +----+  End Service
      +-----+    |     | PE1|==================| PE2|     |    +-----+
      |     |----------|............PW1.............|----------|     |
      | CE1 |    |     |    |                  |    |     |    | CE2 |
      |     |----------|............PW2.............|----------|     |
      +-----+    |     |    |==================|    |     |    +-----+
     Customer          +----+                  +----+     |    Customer
     Edge 1 |      Provider Edge 1         Provider Edge 2     | Edge 2
            |<-------------- Emulated Service ---------------->|
 
              Figure 2: PWE3 Fragmentation/Reassembly Domain
 
 
    Fragmentation takes place in the PE prior to PW insertion, and
    reassembly takes place in the PE after PW extraction.
 
 2. Alternatives to PWE3 Fragmentation/Reassembly
 
    Fragmentation and reassembly in network equipment generally
    requires significantly greater resources than sending a packet as a
    single unit. As such, fragmentation and reassembly should be
    avoided whenever possible. Ideal solutions for avoiding
    fragmentation include proper configuration and management of MTU
    sizes between the CE, PE and across the PSN, as well as adaptive
    measures which operate with the originating host [e.g. [PATHMTU],
    [PATHMTUv6]] to reduce the packet sizes at the source.
 
    A PE MAY choose to fragment a packet before allowing it to enter a
    PW. For example, if an IP packet arrives from a CE with an MTU
    which will yield a PW packet which is greater than the PW MTU, the
    PE may perform IP fragmentation on the packet. This effectively
    creates two (or more) packets, each carrying an IP fragment, for
    transport individually across the PW. The receiving PE is unaware
    that the originating host did not perform the IP fragmentation, and
    as such does not treat the PW packets in any special way. This
    ultimately has the affect of placing the burden of fragmentation on
    the PE, and reassembly on the IP destination host.
 
 3. Fragmentation/Reassembly Specification
 
    The fragmentation of large packets into smaller units for
    transmission is not new.  One fragmentation and reassembly method
    was defined in RFC 1990, Multi-Link PPP [MLPPP].  This method was
    also adopted for both Frame Relay [FRF.12] and ATM [FAST] network
 
 
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    technology.  This document adopts the RFC 1990 fragmentation and
    reassembly procedures as well, with some distinct modifications
    described in this section.  Familiarity with RFC 1990 is assumed
    for the remainder of this document.
 
    RFC 1990 was designed for use in environments where packet
    fragments may arrive out of order due to their transmission on
    multiple parallel links, specifying that buffering be used to place
    the fragments in correct order.  For PWE3, the ability to reorder
    fragments prior to reassembly is OPTIONAL; receivers MAY choose to
    drop frames when a lost fragment is detected. Thus, when the
    sequence number on received fragments shows that a fragment has
    been skipped, the partially reassembled packet MAY be dropped, or
    the receiver MAY wish to wait for the fragment to arrive out of
    order.  In the latter case, a reassembly timer MUST be used to
    avoid locking up buffer resources for too long a period.
 
    Dropping out-of-order fragments on a given PW can provide a
    considerable scalability advantage for network equipment performing
    reassembly. If out-of-order fragments are a relatively rare event
    on a given PW, throughput should not be adversely affected by this.
    Note, however, if there are cases where fragments of a given frame
    are received out-or-order in a consistent manner (e.g. a short
    fragment is always switched ahead of a larger fragment) then
    dropping out-of-order fragments will cause the fragmented frame to
    never be received. This condition may result in an effective denial
    of service to a higher-lever application. As such, implementations
    fragmenting a PW frame MUST at the very least ensure that all
    fragments are sent in order from their own egress point.
 
    An implementation may also choose to allow reassembly of a limited
    number of fragmented frames on a given PW, or across a set of PWs
    with reassembly enabled. This allows for a more even distribution
    of reassembly resources, reducing the chance of a single or small
    set of PWs exhausting all reassembly resources for a node. As with
    dropping out-of-order fragments, there are perceivable cases where
    this may also provide an effective denial of service. For example,
    if fragments of multiple frames are consistently received before
    each frame can be reconstructed in a set of limited PW reassembly
    buffers, then a set of these fragmented frames will never be
    delivered.
 
    RFC 1990 headers use two bits which indicate the first and last
    fragments in a frame, and a sequence number.  The sequence number
    may be either 12 or 24 bits in length (from [MLPPP]):
 
 
 
 
 
 
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                     0             7 8            15
                    +-+-+-+-+-------+---------------+
                    |B|E|0|0|    sequence number    |
                    +-+-+-+-+-------+---------------+
 
                    +-+-+-+-+-+-+-+-+---------------+
                    |B|E|0|0|0|0|0|0|sequence number|
                    +-+-+-+-+-+-+-+-+---------------+
                    |      sequence number (L)      |
                    +---------------+---------------+
 
                    Figure 3: RFC 1990 Header Formats
 
 
    PWE3 fragmentation takes advantage of existing PW sequence numbers
    and control bit fields wherever possible, rather than defining a
    separate header exclusively for the use of fragmentation.  Thus, it
    uses neither of the RFC 1990 sequence number formats described
    above, relying instead on the sequence number that already exists
    in the PWE3 header.
 
    RFC 1990 defines a two one-bit fields, a (B)eginning fragment bit
    and an (E)nding fragment bit. The B bit is set to 1 on the first
    fragment derived from a PPP packet and set to 0 for all other
    fragments from the same PPP packet. The E bit is set to 1 on the
    last fragment and set to 0 for all other fragments.  A complete
    unfragmented frame has both the B and E bits set to 1.
 
    PWE3 fragmentation inverts the value of the B and E bits, while
    retaining the operational concept of marking the beginning and
    ending of a fragmented frame. Thus, for PW the B bit is set to 0 on
    the first fragment derived from a PW frame and set to 1 for all
    other fragments derived from the same frame. The E bit is set to 0
    on the last fragment and set to 1 for all other fragments.  A
    complete unfragmented frame has both the B and E bits set to 0. The
    motivation behind this value inversion for the B and E bits is to
    allow complete frames (and particularly, implementations that only
    support complete frames) to simply leave the B and E bits in the
    header set 0.
 
    In order to support fragmentation, the B and E bits MUST be defined
    or identified for all PWE3 tunneling protocols. Sections 4 and 5
    define these locations for PWE3 MPLS [MPLS-TRANS], L2TPv2 [L2TPv2],
    and L2TPv3 [L2TPv3] tunneling protocols.
 
 
 
 
 
 
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 4. PWE3 Fragmentation With MPLS
 
    When using the signaling procedures in [MPLS-TRANS], there is a
    Virtual Circuit FEC element parameter ID used to signal the use of
    fragmentation when advertising a VC label:
 
       Parameter   ID Length    Description
            0x09           2    Fragmentation indicator
 
    The presence of this parameter ID in the VC FEC element indicates
    that the receiver is able to reassemble fragments when the control
    word is in use for the VC label being advertised.  It does not
    obligate the sender to use fragmentation; it is simply an
    indication that the sender MAY use fragmentation.  The sender MUST
    NOT use fragmentation if this parameter ID is not present in the VC
    FEC element.
 
    If [MPLS-TRANS] signaling is not in use, then whether or not to use
    fragmentation MUST be provisioned in the sender.
 
 4.1 Fragment Bit Locations For MPLS
 
    MPLS-based PWE3 [MPLS-ATM], [MPLS-Ethernet], [MPLS-FR] uses the
    following control word format, with the B and E fragmentation bits
    identified in position 8 and 9:
 
      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Rsvd  | Flags |B|E|   Length  |     Sequence Number           |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
                    Figure 4: MPLS PWE3 Control Word
 
 
    The Sequence Number is used as already specified in the above
    protocol specifications.  Specifically, since the value 0 indicates
    that the sequence number is not in use, its use for fragmentation
    must follow this same rule – as the sequence number is incremented,
    it skips zero and wraps from 65535 to 1.  Since a sequence number
    is necessary for the RFC 1990 procedures, using the Sequence Number
    field on fragmented packets is REQUIRED.
 
 4.2 Other Considerations
 
    Path MTU [PATHMTU] [PATHMTUv6] may be used to dynamically determine
    the maximum size for fragments. The application of path MTU to MPLS
    is discussed in [LABELSTACK]. The maximum size of the fragments may
    also be provisioned. The signaled Interface MTU parameter in [MPLS-
    TRANS] SHOULD be used to set the maximum size of the reassembly
 
 
 
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                   PWE3 Fragmentation and Reassembly      October 2003
 
 
    buffer for received packets to make optimal use of reassembly
    buffer resources.
 
 5. PWE3 Fragmentation With L2TP
 
    This section defines the location of the B and E bits for L2TPv3
    [L2TPv3] and L2TPv2 [L2TPv2] headers, as well as the signaling
    mechanism for advertising MRU (Maximum Receive Unit) values and
    support for fragmentation on a given PW. As IP is the most common
    PSN used with L2TP, IP fragmentation and reassembly is discussed as
    well.
 
 5.1 PW-specific Fragmentation vs. IP fragmentation
 
    L2TPv3 recognizes that when it is used over IP networks, it may be
    subject to IP fragmentation.  The following is quoted from
    [L2TPv3]:
 
       IP fragmentation may occur as the L2TP packet travels over the
       IP substrate.  L2TP makes no special efforts defined in this
       document to optimize this.
 
    When proper MTU management across a network fails, IP fragmentation
    and reassembly may be used to accommodate MTU mismatches between
    tunnel endpoints. If the overall traffic requiring fragmentation
    and reassembly is very light, or there are sufficient optimized
    mechanisms for IP fragmentation and reassembly available, IP
    fragmentation and reassembly may be sufficient and is allowed,
    particularly if PW-specific fragmentation is unavailable.
 
    When facing a large number of PW packets requiring fragmentation
    and reassembly, a PW-specific method has properties that allow for
    more resource-friendly implementations. Specifically, the ability
    to assign buffer usage on a per-PW basis and per-PW sequencing may
    be utilized to significant advantage over a general mechanism
    applying to all IP packets equally. Further, PW fragmentation may
    be easily enabled in a selective manner for some or all PWs, rather
    than enabling reassembly for all IP traffic arriving at a given
    node.
 
    Deployments MUST avoid a situation which relies upon a combination
    of IP and PW fragmentation and reassembly on the same node. Such
    operation clearly defeats the purpose behind the mechanism defined
    in this document. Care must be taken to ensure that the MTU/MRU
    values are set and advertised properly at each tunnel endpoint to
    avoid this. When fragmentation is enabled within a given PW, the DF
    bit MUST be set on all L2TP over IP packets for that PW. L2TPv3
    nodes SHOULD participate in Path MTU [PATHMTU], [PATHMTUv6] for
    automatic adjustment of the PW MTU.
 
 
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 5.2 Advertising Reassembly Support in L2TP
 
    The constructs defined in this section for advertising
    fragmentation support in L2TP are applicable to L2TPv3 and L2TPv2.
 
    This document defines two new AVPs to advertise maximum receive
    unit values and reassembly support. These AVPs MAY be present in
    the ICRQ, ICRP, ICCN, OCRQ, OCRP, OCCN, or SLI messages. The most
    recent value received always takes precedence over a previous
    value, and MUST be dynamic over the life of the session if received
    via the SLI message. One of the two new AVPs (MRRU) is used to
    advertise that PWE3 reassembly is supported by the sender of the
    AVP. Reassembly support MAY be unidirectional.
 
 5.3 L2TP Maximum Receive Unit (MRU) AVP
 
        0                   1
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              MRU              |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
    MRU (Maximum Receive Unit), attribute number TBD1, is the maximum
    size in octets of a fragmented or complete PW frame, including L2TP
    encapsulation, receivable by the side of the PW advertising this
    value. The advertised MRU does NOT include the PSN header (i.e. the
    IP and/or UDP header). This AVP does not imply that PWE3
    fragmentation or reassembly is supported. If reassembly is not
    enabled or unavailable, this AVP may be used alone to advertise the
    MRU for a complete frame.
 
    All L2TP AVPs have an M (Mandatory) bit, H (Hidden) bit, Length,
    and Vendor ID. This AVP may be hidden (the H bit may be 0 or 1).
    The M bit for this AVP SHOULD be set to 0.  The Length (before
    hiding) is 8. The Vendor ID is the IETF Vendor ID of 0.
 
 5.4 L2TP Maximum Reassembled Receive Unit (MRRU) AVP
 
        0                   1
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              MRRU             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
    MRRU (Maximum Reassembled Receive Unit AVP), attribute number TBD2,
    is the maximum size in octets of a reassembled frame, including any
    PW framing, but not including the L2TP encapsulation or L2-specific
    sublayer. Presence of this AVP signifies the ability to receive PW
 
 
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    fragments and reassemble them. Packet fragments MUST NOT be sent to
    an implementation which has not received this value from its peer
    in a control message. If the MRRU is present in a message, the MRU
    AVP MUST be present as well.
 
    All L2TP AVPs have an M (Mandatory) bit, H (Hidden) bit, Length,
    and Vendor ID. This AVP may be hidden (the H bit may be 0 or 1).
    The M bit for this AVP SHOULD be set to 0.  The Length (before
    hiding) is 8. The Vendor ID is the IETF Vendor ID of 0.
 
 5.5 Fragment Bit Locations For L2TPv3 Encapsulation
 
    The B and E bits are defined as bits 2 and 3 in the L2TPv3 default
    L2-specific sublayer as depicted below:
 
     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |P|S|B|E|x|x|x|x|              Sequence Number                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
                      Figure 5: L2TPv3 over IP Header
 
 
    Location of the B and E bits for PW-Types which use a variant L2-
    specific sublayer are outside the scope of this document.
 
    Inclusion of the MRRU AVP in a control message suggests the need
    for a control sublayer which includes sequence numbers and the B
    and E bit fields. Thus, if reassembly support has been advertised,
    and packet fragments are to be sent, then presence of this sublayer
    and associated sequencing for all packet fragments MUST be enabled
    as defined for the given PW-type.
 
 5.6 Fragment Bit Locations for L2TPv2 Encapsulation
 
    The B and E bits are defined as bits 8 and 9 for the L2TPv2 header
    as depicted below (subject to IANA action):
 
 
 
 
 
 
 
 
 
 
 
 
 
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    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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |T|L|x|x|S|x|O|P|B|E|x|x|  Ver  |          Length (opt)         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Tunnel ID           |           Session ID          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             Ns (opt)          |             Nr (opt)          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Offset Size (opt)        |    Offset pad... (opt)
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 
                      Figure 6: L2TPv2 over UDP Header
 
 
 6. Security Considerations
 
    As with any additional protocol construct, each level of complexity
    adds the potential to exploit protocol and implementation errors.
    Implementers should be especially careful of not tying up an
    abundance of resources, even for the most pathological combination
    of packet fragments that could be received. Beyond these issues of
    general implementation quality, there are no known notable security
    issues with using the mechanism defined in this document.  It
    should be pointed out that RFC 1990 and its derivatives have been
    widely implemented and extensively used in the Internet and
    elsewhere.
 
    [IPFRAG-SEC] and [TINYFRAG] describe potential network attacks
    associated with IP fragmentation and reassembly. The issues
    described in these documents attempt to bypass IP access controls
    by sending various carefully formed "tiny fragments", or by
    exploiting the IP offset field to cause fragments to overlap and
    rewrite interesting portions of an IP packet after access checks
    have been performed. The latter is not an issue with the PW-
    specific fragmentation method described in this document as there
    is no offset field; However, implementations MUST be sure to not
    allow more than one whole fragment to overwrite another in a
    reconstructed frame. The former may be a concern if packet
    filtering and access controls are being placed on tunneled frames
    within the PW encapsulation. To circumvent any possible attacks in
    either case, all filtering and access controls should be applied to
    the resulting reconstructed frame rather than any PW fragments.
 
 7. IANA Considerations
 
    This document does not define any new values for IANA to maintain.
 
 
 
 
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                   PWE3 Fragmentation and Reassembly      October 2003
 
 
    This document requires definition of two reserved bits in the
    L2TPv2 [L2TPv2] header. Recommended locations are noted by the “B”
    and “E” bits in section 5.6.
 
    This document requires IANA to assign two new L2TP "Control Message
    Attribute Value Pairs" (TBD1 and TBD2 in this document).
 
 8. Acknowledgements
 
    Thanks to Eric Rosen for his review of this document.
 
 9. References
 
    [FAST] ATM Forum, "Frame Based ATM over SONET/SDH Transport
        (FAST)", af-fbatm-0151.000, July 2000
 
    [Framework] Pate, P. et al, "Framework for Pseudo Wire Emulation
        Edge-to-Edge (PWE3)", draft-ietf-pwe3-framework-01.txt, June
        2002, work in progress
 
    [FRF.12] Frame Relay Forum, "Frame Relay Fragmentation
        Implementation Agreement", FRF.12, December 1997
 
    [LABELSTACK] Rosen, E. et al, "MPLS Label Stack Encoding", RFC
        3032, January 2001
 
    [L2TPv2] Townsley, Valencia, Rubens, Pall, Zorn, Palter, "Layer Two
        Tunneling Protocol 'L2TP'", RFC 2661, June 1999
 
    [L2TPv3] Lau, J. et al, "Layer Two Tunneling Protocol (Version 3)
        'L2TPv3'", draft-ietf-l2tpext-l2tp-base-10.txt, August 2003,
        work in progress
 
    [MLPPP] Sklower, K. et al, "The PPP Multilink Protocol (MP)", RFC
        1990, August 1996
 
    [MPLS-ATM] Martini, L. et al, "Encapsulation Methods for Transport
        of ATM Cells/Frame Over IP and MPLS Networks", draft-ietf-pwe3-
        atm-encap-03.txt, October 2003, work in progress
 
    [MPLS-Ethernet] Martini, L. et al, "Encapsulation Methods for
        Transport of Ethernet Frames Over IP and MPLS Networks", draft-
        ietf-pwe3-ethernet-encap-04.txt, October 2003, work in progress
 
    [MPLS-FR] Martini, L. et al, "Frame Relay Encapsulation over
        Pseudo-Wires", draft-ietf-pwe3-frame-relay-01.txt, July 2003,
        work in progress
 
 
 
 
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                   PWE3 Fragmentation and Reassembly      October 2003
 
 
    [MPLS-TRANS] Martini, L. et al, "Transport of Layer 2 Frames Over
        MPLS", draft-ietf-pwe3-control-protocol-04.txt, October 2003,
        work in progress
 
    [PATHMTU] Mogul, J. C. et al, "Path MTU Discovery", RFC 1191,
        November 1990
 
    [PATHMTUv6] McCann, J. et al, "Path MTU Discovery for IP version
        6", RFC 1981, August 1996
 
    [IPFRAG-SEC] Ziemba, G., Reed, D., Traina, P., "Security
        Considerations for IP Fragment Filtering", RFC 1858, October
        1995
 
    [TINYFRAG] Miller, I., "Protection Against a Variant of the Tiny
        Fragment Attack", RFC 3128, June 2001
 
 
 10. Authors' Addresses
 
    Andrew G. Malis
    Tellabs
    2730 Orchard Parkway
    San Jose, CA 95134
    Email: Andy.Malis@tellabs.com
 
    W. Mark Townsley
    Cisco Systems
    7025 Kit Creek Road
    PO Box 14987
    Research Triangle Park, NC 27709
    Email: mark@townsley.net
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
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