Network Working Group                                            M. Chen
Internet-Draft                                                     X. Xu
Intended status: Standards Track                                   Z. Li
Expires: January 4, 2015                                          Huawei
                                                                 L. Fang
                                                               G. Mirsky
                                                            July 3, 2014

           MultiProtocol Label Switching (MPLS) Source Label


   A MultiProtocol Label Switching (MPLS) label was originally defined
   to identify a Forwarding Equivalence Class (FEC), a packet is
   assigned to a specific FEC based on its network layer destination
   address.  It's difficult or even impossible to derive the source
   identity information from the label.  For some applications, source
   identification is a critical requirement.  For example, performance
   monitoring, where the monitoring node needs to identify where a
   packet was sent from.

   This document introduces the concept of Source Label (SL) that is
   carried in the label stack and used to identify the ingress Label
   Switching Router (LSR) of an Label Switched Path (LSP).

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

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

   This Internet-Draft will expire on January 4, 2015.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

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

Table of Contents

   1.  Problem Statement and Introduction  . . . . . . . . . . . . .   3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Source Label  . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Performance Measurement . . . . . . . . . . . . . . . . .   5
   5.  Data Plane Processing . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Ingress LSR . . . . . . . . . . . . . . . . . . . . . . .   6
     5.2.  Transit LSR . . . . . . . . . . . . . . . . . . . . . . .   6
     5.3.  Egress LSR  . . . . . . . . . . . . . . . . . . . . . . .   6
     5.4.  Penultimate Hop LSR . . . . . . . . . . . . . . . . . . .   6
   6.  Source Label Signaling  . . . . . . . . . . . . . . . . . . .   7
     6.1.  Source Label Capability Signaling . . . . . . . . . . . .   7
       6.1.1.  LDP Extensions  . . . . . . . . . . . . . . . . . . .   7
       6.1.2.  BGP Extensions  . . . . . . . . . . . . . . . . . . .   8
       6.1.3.  IGP Extensions  . . . . . . . . . . . . . . . . . . .   9
     6.2.  Source Label Distribution . . . . . . . . . . . . . . . .   9
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Source Label Indication . . . . . . . . . . . . . . . . .  10
     7.2.  LDP Source Label Capability TLV . . . . . . . . . . . . .  10
     7.3.  BGP Source Label Capability Attribute . . . . . . . . . .  10
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10  11
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     10.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Problem Statement and Introduction

   A MultiProtocol Label Switching (MPLS) label [RFC3031] was originally
   defined for packet forwarding and assumes the forwarding/destination
   address semantics.  As no source identity information is carried in
   the label stack, there is no way to directly derive the source
   identity information from the label or label stack.

   MPLS LSPs can be categorized into four different types:

      Point-to-Point (P2P)

      Point-to-Multipoint (P2MP)

      Multipoint-to-Point (MP2P)

      Multipoint-to-Multipoint (MP2MP)

   For P2P and P2MP LSPs (e.g., the Resource Reservation Protocol
   Traffic Engineering (RSVP-TE) [RFC3209] based and statically
   configured P2P and P2MP LSPs), the source identity may be implicitly
   derived by the egress LSR from the label when Penultimate Hop Popping
   (PHP) is disabled and the correlation between ingress LSR and the LSP
   is explicitly signaled through the control plane.  Such LSP may be
   characterized as MPLS-TP LSP [RFC5960].

   However, for MP2P and MP2MP LSPs (e.g., the Distribution Protocol
   (LDP) based LSPs [RFC5036] [RFC6388], and Layer 3 Private Network
   (L3VPN) [RFC4364] LSPs), ingress LSRs of those LSPs cannot be
   identified by egress LSRs.

   Comparing to the pure IP forwarding where both source and destination
   addresses are encoded in the IP packet header, the essential issue of
   the MPLS encoding is that the label stack does not explicitly include
   any source identity information.  For some applications, source
   identification is a critical requirement.  For example, performance
   monitoring, the monitoring nodes need to identify where packets were
   sent from and then can count the packets according to some

   This document introduces the concept of Source Label (SL).  An SL
   uniquely identifies a node within an administrative domain, it is
   carried in the label stack and used to identify the ingress LSR that
   originated the MPLS frame.

2.  Terminology

   SL - Source Label

   SLC - Source Label Capability

   SLI - Source Label Indicator

   SLAD - Source Label Administrative Domain

3.  Source Label

   A Source Label is defined to uniquely identify a node that is (one
   of) the ingress LSR(s) to a specific LSP.  In its function as a
   Source Label, it MUST be unique within a domain.  In cases where a
   Source Label is used across domains it MUST be unique within the
   scope it is used.  In this document, the domain or domains that the
   Source Label is required to be unique is referred as a "Source Label
   Administrative Domain" (SLAD).

   To prevent the Source Label from leaking to unintended domains, two
   aspects need to be considered:

      In control plane, it SHOULD make sure that the Source Label will
      not be distributed outside the SLAD where it is used.  And since
      the ingress LSR is based on the Source Label Capability signaled
      by the egress LSR to determine whether to insert the Source Label,
      the SLC signaling SHOULD make sure that the SLC will not be
      signaled to the LSRs that reside in other SLADs.

      In data plane, the domain boundary nodes (e.g., the ASBR) SHOULD
      have the capability to filter out the packets that carry the SL/
      SLI and are received from other SLADs.  For example, some policies
      (e.g., by ACL) could be deployed at the ASBR to filter out the
      packets that carry SLI and are from other SLADs.

   The Source Labels are allocated from a dedicated label space that is
   completely different from the space of the normal forwarding labels.
   Configuration system (e.g., static configuration or NMS) is one way
   to make sure the uniqueness of each SL assigned to specific LSR.
   There may be some other potential dynamic solutions that can be used
   for SL allocation and distribution.  This is left for future study.

   For most of the cases, one Source Label per LSR is enough.  But for
   some cases, there may need more than one Source Labels.  For example,
   in the L3VPN scenario, it may require to allocate dedicated Source
   Label to identify each VPN instance.  This requires that the Source
   Label distribution protocol MUST have the capability to process this
   "one or more Source Labels per LSR" situation.

   In order to indicate whether a label is a Source Label, a Source
   Label Indicator (SLI) is introduced.  The SLI is a special purpose
   label [RFC7274] that is placed immediately before the source label in
   the label stack, which is used to indicate that the next label in the
   label stack is the Source Label.  Throughout the document mention to
   a Source Label refers to the combination of SLI and SL.  The value of
   SLI is TBD1.

4.  Use Cases

   This section outlines the use cases which benefit from application of
   Source Label.

4.1.  Performance Measurement

   There are two general types of performance measurement: one is active
   performance measurement, and the other is passive performance

   In active performance measurement the receiver measures the injected
   packets to evaluate the performance of a path.  The active
   measurement measures the performance of the extra injected packets.
   The IP Performance Metrics (IPPM) working group has defined
   specifications [RFC4656][RFC5357] for the active performance

   In passive performance measurement, no additional traffic is injected
   into the flow and measurements are taken to record the performance
   metrics of the data traffic.  The MPLS performance measurement
   protocol [RFC6374] for packet loss is an example of passive
   performance measurement, but it can only apply to MPLS-TE LSPs.  For
   a specific receiver, in order to count the received packets of a
   flow, it has to know whether a received packet belongs to which
   target flow under test and the source identification is a critical

   As discussed in the previous section, the existing MPLS label or
   label stack do not carry the source information.  So, for an LSP, the
   ingress LSR can put its Source Label in the label stack, and then the
   egress LSR can use the Source Label for packets identification of
   frame's source and accounting.

5.  Data Plane Processing

5.1.  Ingress LSR

   For an LSP, the ingress LSR MUST make sure that the egress LSR is
   able to process the Source Label before inserting the SLI/SL
   combination into the label stack.  Therefore, an egress LSR SHOULD
   signal (see Section 6.1) to the ingress LSR whether it is able to
   process the Source Label.  Once the ingress LSR knows that the egress
   LSR can process Source Label, it can choose whether or not to insert
   the SL and SLI into the label stack.

   When an SL to be included in a label stack, the steps are as follows:

   1.  Push the SL, the TTL of the SL MUST be set to 1, the BoS bit for
       the SL depends on whether the SL is the bottom label.  Setting
       and interpretation of TC field of the SL is for further study;

   2.  Push the SLI, the TTL and TC fields for the SLI MUST be set to
       the same values as for the LSP Label (L);

   3.  Push the LSP Label (L).

   Then the label stack looks like: <...L, SLI, SL [,...]>.  There MAY
   be multiple pairs of SLI and SL inserted into the label stack, each
   pair is related to an LSP.  For the given LSP, only one pair of SLI
   and SL MUST be inserted.

5.2.  Transit LSR

   There is no change in forwarding behavior for transit LSRs.  If a
   transit LSR can recognize the SLI, it can use the SL to collect
   traffic throughput and/or measure the performance of the LSP.

5.3.  Egress LSR

   When an egress LSR receives a packet with a SLI/SL combination, if
   the egress LSR is able to process the SL; it pops the LSP label (if
   any), SLI and SL; then processes remaining packet header as normal.
   If the egress LSR is not able to process the SLI, the packet SHOULD
   be dropped as specified for the handling of any unknown label
   according to [RFC3031].

5.4.  Penultimate Hop LSR

   There is no change in forwarding behavior for the penultimate hop

6.  Source Label Signaling

   Source label signaling includes two aspects: one is source label
   capability signaling, the other is source label distribution.

6.1.  Source Label Capability Signaling

   Before inserting a Source Label in the label stack, an ingress LSR
   SHOULD know whether the egress LSR is able to process the Source
   Label.  Therefore, an egress LSR SHOULD signal to the ingress LSRs
   its ability to process the Source Label.  This is called Source Label
   Capability (SLC), it is very similar to the "Entropy Label Capability

6.1.1.  LDP Extensions

   A new LDP TLV [RFC5036], SLC TLV, is defined to signal an egress's
   ability to process Source Label.  The SLC TLV MAY appear as an
   Optional Parameter of the Label Mapping Message.  The presence of the
   SLC TLV in a Label Mapping Message indicates to ingress LSRs that the
   egress LSR can process Source Labels for the associated LSP.

   The structure of the SLC TLV is shown 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
      |U|F|        Type (TBD2)        |           Length (0)          |

                     Figure 1: Source Label Capability TLV

   This U bit MUST be set to 1.  If the SLC TLV is not understood by the
   receiver, then it MUST be ignored.

   This F bit MUST be set to 1.  Since the SLC TLV is going to be
   propagated hop-by-hop, it should be forwarded even by nodes that may
   not understand it.

   Type: TBD2.

   Length field: This field specifies the total length in octets of the
   SLC TLV and is defined to be 0.

   An LSR that receives a Label Mapping with the SLC TLV but does not
   understand it MUST propagate it intact to its neighbors and MUST NOT
   send a notification to the sender (following the meaning of the U-
   and F-bits).  If the LSR has no other neighbors and does not
   understand the SLC TLV, means it is the ingress LSR, it could just
   ignore it.  An LSR X may receive multiple Label Mappings for a given
   FEC F from its neighbors.  In its turn, X may advertise a Label
   Mapping for F to its neighbors.  If X understands the SLC TLV, and if
   any of the advertisements it received for FEC F does not include the
   SLC TLV, X MUST NOT include the SLC TLV in its own advertisements of
   F.  If all the advertised Mappings for F include the SLC TLV, then X
   MUST advertise its Mapping for F with the SLC TLV.  If any of X's
   neighbors resends its Mapping, sends a new Mapping or sends a Label
   Withdraw for a previously advertised Mapping for F, X MUST re-
   evaluate the status of SLC for FEC F, and, if there is a change, X
   MUST re-advertise its Mapping for F with the updated status of SLC.

   LDP is normally running within an AS, technically, it can be deployed
   across ASes.  An implementation supports the SLC MUST support a per-
   session/per-interface configuration item to enable/disable the SLC.
   For the session/interface that connects to other SLADs, the SLC MUST
   be disabled.

6.1.2.  BGP Extensions

   When Border Gateway Protocol (BGP) [RFC4271] is used for distributing
   Network Layer Reachability Information (NLRI) as described in, for
   example, [RFC3107], [RFC4364], the BGP UPDATE message may include the
   SLC attribute as part of the Path Attributes.  This is an optional,
   non-transitive BGP attribute of value TBD3.  The inclusion of this
   attribute with an NLRI indicates that the advertising BGP router can
   process Source Labels as an egress LSR for all routes in that NLRI.

   A BGP speaker S that originates an UPDATE should include the SLC
   attribute only if both of the following are true:

   A1: S sets the BGP NEXT_HOP attribute to itself AND

   A2: S can process source labels.

   Suppose a BGP speaker T receives an UPDATE U with the SLC attribute.
   T has two choices.  T can simply re-advertise U with the SLC
   attribute if either of the following is true:

   B1: T does not change the NEXT_HOP attribute OR

   B2: T simply swaps labels without popping the entire label stack and
   processing the payload below.

   An example of the use of B1 is Route Reflectors.  However, if T
   changes the NEXT_HOP attribute for U and in the data plane pops the
   entire label stack to process the payload, T MAY include an SLC
   attribute for UPDATE U' if both of the following are true:

   C1: T sets the NEXT_HOP attribute of U' to itself AND

   C2: T can process source labels.  Otherwise, T MUST remove the SLC
   attribute.  Sending/Receiving Restriction

   An implementation that supports the SLC MUST support per-session
   configuration item, SL_SESSION, that indicates whether the SLC is
   enabled or disabled for use on that session.

      - The default value of SL_SESSION, for EBGP sessions, MUST be

      - The default value of SL_SESSION, for IBGP and confederation-EBGP
      [RFC5065]sessions, SHOULD be "enabled."

   The SLC attribute MUST NOT be sent on any BGP session for which
   SL_SESSION is disabled.

   If an SLC attribute is received on a BGP session for which SL_SESSION
   is disabled, the attribute MUST be treated exactly as if it were an
   unrecognized non-transitive attribute.  That is, "it MUST be quietly
   ignored and not passed along to other BGP peers" (see [RFC4271],
   section 5).

6.1.3.  IGP Extensions

   No dedicated SLC signaling defined in this document, as defined in
   [I-D.chen-isis-source-label-distribution] and
   [I-D.chen-ospf-source-label-distribution], the presence of a Source
   Label TLV MUST be interpreted as support of SLC by the LSR.  That
   means the SLC is implicitly indicated by receiving a SL distribution
   from an LSR.

6.2.  Source Label Distribution

   Based on the Source Label, an egress or intermediate LSR can identify
   from where an MPLS packet is sent.  To achieve this, the egress and/
   or intermediate LSRs have to know which ingress LSR is related to
   which Source Label before using the Source Label to derive the source
   information.  Therefore, there needs to be a mechanism to distribute
   the mapping information between an ingress LSR and its Source Label.

   IGP based Source Label distributions are defined in
   [I-D.chen-ospf-source-label-distribution], which apply to the intra-
   AS scenario.

   For inter-AS scenario, BGP extension is a naturally choice and can be
   used to convey SL mapping information from one AS to other ASes.  The
   BGP extension draft is work in progress.  For BGP based SL
   distribution, it requires that SLs MUST not be sent out of a SLAD.
   The similar sending and receiving restriction as defined in
   Section 6.1.3 is also needed.

7.  IANA Considerations

7.1.  Source Label Indication

   IANA is required to allocate a special purpose label (TBD1) for the
   Source Label Indicator (SLI) from the "Multiprotocol Label Switching
   Architecture (MPLS) Label Values" Registry.

7.2.  LDP Source Label Capability TLV

   IANA is requested to allocate a value of TBD2 from the IETF Consensus
   range (0x0001-0x07FF) in the "TLV Type Name Space" registry as the
   "Source Label Capability TLV".

7.3.  BGP Source Label Capability Attribute

   IANA is requested to allocate a Path Attribute Type Code TBD3 from
   the "BGP Path Attributes" registry as the "BGP Source Label
   Capability Attribute".

8.  Security Considerations

   This document introduces the SLAD that is the scope of a SL, SLC and
   SL MUST NOT be signaled and distributed outside one SLAD.  The SLC
   and SL distribution is controlled by SL_SESSION configuration,
   improper configuration on both ends of an EBGP connection could
   result in the SLC and SL being passed from one SLAD to another.  This
   would likely result in potential SL conflicts.

   To prevent packets carrying SL/SLI from leaking from one SLAD to
   another, the SLAD boundary nodes SHOULD deploy some policies (e.g.,
   ACL) to filter out the packets.  Specifically, in the sending end,
   the SLAD boundary node SHOULD filter out the packets that carry the
   SLI and are sent to other SLADs; in the receiving end, the SLAD
   boundary node SHOULD drop the packets that carry the SLI and are from
   other SLADs.

9.  Acknowledgements

   The process of "Source Label Capability Signaling" is largely
   referred to the process of "ELC signaling"[RFC6790].

   The authors would like to thank Carlos Pignataro, Loa Andersson ,
   Curtis Villamizar, Eric Osborne, Eric Rosen, Yimin Shen, Lizhong Jin
   and Yakov Rekhter for their review, suggestion and comments to this

10.  References

10.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3031]  Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
              Label Switching Architecture", RFC 3031, January 2001.

   [RFC3107]  Rekhter, Y. and E. Rosen, "Carrying Label Information in
              BGP-4", RFC 3107, May 2001.

   [RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
              and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
              Tunnels", RFC 3209, December 2001.

   [RFC5036]  Andersson, L., Minei, I., and B. Thomas, "LDP
              Specification", RFC 5036, October 2007.

   [RFC5420]  Farrel, A., Papadimitriou, D., Vasseur, JP., and A.
              Ayyangarps, "Encoding of Attributes for MPLS LSP
              Establishment Using Resource Reservation Protocol Traffic
              Engineering (RSVP-TE)", RFC 5420, February 2009.

   [RFC6374]  Frost, D. and S. Bryant, "Packet Loss and Delay
              Measurement for MPLS Networks", RFC 6374, September 2011.

   [RFC7274]  Kompella, K., Andersson, L., and A. Farrel, "Allocating
              and Retiring Special-Purpose MPLS Labels", RFC 7274, June

10.2.  Informative References

              Chen, M. and G. Mirsky, "Extensions to ISIS for Source
              Label Distribution", draft-chen-isis-source-label-
              distribution-00 (work in progress), February 2014.

              Chen, M. and G. Mirsky, "Extensions to OSPF for Source
              Label Distribution", draft-chen-ospf-source-label-
              distribution-00 (work in progress), February 2014.

   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, May 2000.

   [RFC4271]  Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
              Protocol 4 (BGP-4)", RFC 4271, January 2006.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, February 2006.

   [RFC4656]  Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
              Zekauskas, "A One-way Active Measurement Protocol
              (OWAMP)", RFC 4656, September 2006.

   [RFC4761]  Kompella, K. and Y. Rekhter, "Virtual Private LAN Service
              (VPLS) Using BGP for Auto-Discovery and Signaling", RFC
              4761, January 2007.

   [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
              System Confederations for BGP", RFC 5065, August 2007.

   [RFC5357]  Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
              Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
              RFC 5357, October 2008.

   [RFC5960]  Frost, D., Bryant, S., and M. Bocci, "MPLS Transport
              Profile Data Plane Architecture", RFC 5960, August 2010.

   [RFC6388]  Wijnands, IJ., Minei, I., Kompella, K., and B. Thomas,
              "Label Distribution Protocol Extensions for Point-to-
              Multipoint and Multipoint-to-Multipoint Label Switched
              Paths", RFC 6388, November 2011.

   [RFC6790]  Kompella, K., Drake, J., Amante, S., Henderickx, W., and
              L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
              RFC 6790, November 2012.

Authors' Addresses

   Mach(Guoyi) Chen

   Xiaohu Xu


   Zhenbin Li


   Luyuan Fang


   Greg Mirsky