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Versions: (draft-hegde-ospf-link-overload) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 RFC 8379

Open Shortest Path First IGP                                    S. Hegde
Internet-Draft                                    Juniper Networks, Inc.
Intended status: Standards Track                               P. Sarkar
Expires: August 22, 2017                                      H. Gredler
                                                              Individual
                                                              M. Nanduri
                                                   Microsoft Corporation
                                                                L. Jalil
                                                                 Verizon
                                                       February 18, 2017


                           OSPF Link Overload
                    draft-ietf-ospf-link-overload-04

Abstract

   When a link is being prepared to be taken out of service, the traffic
   needs to be diverted from both ends of the link.  Increasing the
   metric to the highest metric on one side of the link is not
   sufficient to divert the traffic flowing in the other direction.

   It is useful for routers in an OSPFv2 or OSPFv3 routing domain to be
   able to advertise a link being in an overload state to indicate
   impending maintenance activity on the link.  This information can be
   used by the network devices to re-route the traffic effectively.

   This document describes the protocol extensions to disseminate link-
   overload information in OSPFv2 and OSPFv3.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in 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 http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any



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   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 August 22, 2017.

Copyright Notice

   Copyright (c) 2017 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
   (http://trustee.ietf.org/license-info) 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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Flooding Scope  . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Area scope flooding . . . . . . . . . . . . . . . . . . .   4
     3.2.  Link scope flooding . . . . . . . . . . . . . . . . . . .   4
   4.  Link-Overload sub-TLV . . . . . . . . . . . . . . . . . . . .   4
     4.1.  OSPFv2 Link-overload sub-TLV  . . . . . . . . . . . . . .   4
     4.2.  OSPFv3 Link-Overload sub-TLV  . . . . . . . . . . . . . .   5
   5.  Elements of procedure . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Point-to-point links  . . . . . . . . . . . . . . . . . .   6
     5.2.  Broadcast/NBMA links  . . . . . . . . . . . . . . . . . .   6
     5.3.  Point-to-multipoint links . . . . . . . . . . . . . . . .   7
     5.4.  Unnumbered interfaces . . . . . . . . . . . . . . . . . .   7
     5.5.  Hybrid Broadcast and P2MP interfaces  . . . . . . . . . .   7
   6.  Backward compatibility  . . . . . . . . . . . . . . . . . . .   7
   7.  Applications  . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Pseudowire Services . . . . . . . . . . . . . . . . . . .   8
     7.2.  Controller based Traffic Engineering Deployments  . . . .   8
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     11.2.  Informative References . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11




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1.  Introduction

   When a node is being prepared for a planned maintenance or upgrade,
   [RFC6987] provides mechanisms to advertise the node being in an
   overload state by setting all outgoing link costs to MAX-METRIC
   (0xffff).  These procedures are specific to the maintenance activity
   on a node and cannot be used when a single link attached to the node
   requires maintenance.

   In traffic-engineering deployments, LSPs need to be diverted from the
   link without disrupting the services.  It is useful to be able to
   advertise the impending maintenance activity on the link and to have
   LSP re-routing policies at the ingress to route the LSPs away from
   the link.

   Many OSPFv2 or OSPFv3 deployments run on overlay networks provisioned
   by means of pseudo-wires or L2-circuits.  Prior to devices in the
   underlying network going offline for maintenance, it is useful to
   divert the traffic away from the node before the maintenance is
   actually scheduled.  Since the nodes in the underlying network are
   not visible to OSPF, the existing stub router mechanism described in
   [RFC6987] cannot be used.  An application specific to this use case
   is described in Section 7.1

   This document provides mechanisms to advertise link-overload state in
   the flexible encodings provided by OSPFv2 Prefix/Link Attribute
   Advertisement([RFC7684]) and RI LSA ([RFC7770]).  Throughout this
   document, OSPF is used when the text applies to both OSPFv2 and
   OSPFv3.  OSPFv2 or OSPFv3 is used when the text is specific to one
   version of the OSPF protocol.

2.  Motivation

   The motivation of this document is to reduce manual intervention
   during maintenance activities.  The following objectives help to
   accomplish this in a range of deployment scenarios.

   1.  Advertise impending maintenance activity so that traffic from
       both directions can be diverted away from the link.

   2.  Allow the solution to be backward compatible so that nodes that
       do not understand the new advertisement do not cause routing
       loops.

   3.  Advertise the maintenance activity to other nodes in the network
       so that LSP ingress routers/controllers can learn of the
       impending maintenance activity and apply specific policies to re-
       route the LSPs for traffic-engineering based deployments.



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   4.  Allow the link to be used as last resort link to prevent traffic
       disruption when alternate paths are not available.

3.  Flooding Scope

   The link-overload information can be flooded in area scoped extended
   link LSA [RFC7684] or a link scoped RI LSA [RFC7770] or both based on
   the needs of the application.  Section 7 describes applications
   requiring area scope as well as link scope link-overload information.

3.1.  Area scope flooding

   For OSPFv2, Link-Overload sub-TLV is carried in the extended Link TLV
   as defined in [RFC7684].

3.2.  Link scope flooding

   The link local scope RI LSA MAY carry the Link-Overload sub-TLV as
   defined in Section 4.  The link local scope RI-LSA corresponds to the
   link on which the LSA arrives and there is no need to explicitly
   specify the remote IPv4 address.  The remote IPv4 address field MAY
   be zero when the Link-Overload sub-TLV is carried in the link local
   RI LSA.  The Link-Overload sub-TLV MAY appear in any instance of the
   link local RI-LSA.  The Link-Overload sub-TLV is carried in the RI-
   LSA for both OSPFv2 and OSPFv3.

4.  Link-Overload sub-TLV

4.1.  OSPFv2 Link-overload sub-TLV

   The Link-Overload sub-TLV identifies the link being in overload
   state.  It is carried in extended Link TLV as defined in [RFC7684] or
   link local scope RI LSA as defined in [RFC7770].



        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Type             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Remote IP address                         |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                Figure 1: Link-Overload sub-TLV for OSPFv2

   Type : TBA (suggested value 4)



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   Length: 4

   Value: Remote IPv4 address.  The remote IP4 address is used to
   identify the particular link that is in the overload state when there
   are multiple parallel links between two nodes.


4.2.  OSPFv3 Link-Overload sub-TLV

   The OSPFv3 Link-Overload sub-TLV is carried in the link local scope
   OSPFV3 RI LSA as defined in [RFC7770].  The area scope advertisement
   of Link-Overload sub-TLV will be carried in the Router-Link TLV as
   defined in the [I-D.ietf-ospf-ospfv3-lsa-extend]and will be described
   in a separate document.  The Router-Link TLV contains the neighbour
   interface-id and can uniquely identify the link on the remote node.



        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              Type             |             Length            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 2: Link-Overload sub-TLV for OSPFv3

   Type : TBA (Suggested value 4)

   Length: 0

5.  Elements of procedure

   The Link-Overload sub-TLV indicates that the link identified by the
   sub-TLV is overloaded.  The node that has the link to be taken out of
   service SHOULD originate the Link-Overload sub-TLV in the Extended
   Link TLV in the Extended Link Opaque LSA as defined in [RFC7684] for
   OSPFv2.  The Link-Overload information is carried as a property of
   the link and is flooded across the area.  This information can be
   used by ingress routers or controllers to take special actions.  An
   application specific to this use case is described in Section 7.2.

   The precise action taken by the remote node at the other end of the
   link identified as overloaded depends on the link type.








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5.1.  Point-to-point links

   The node that has the link to be taken out of service SHOULD set
   metric of the link to MAX-METRIC (0xffff) and re- originate the
   Router-LSA.  The TE metric SHOULD be set to MAX-TE-METRIC-1
   (0xfffffffe) and the node SHOULD re-originate the TE Link Opaque
   LSAs.  When a Link-Overload sub-TLV is received for a point-to-point
   link, the remote node SHOULD identify the local link which
   corresponds to the overloaded link and set the metric to MAX-METRIC
   (0xffff).  The remote node MUST re-originate the router-LSA with the
   changed metric.  The TE metric SHOULD be set to MAX-TE-METRIC-1
   (0xfffffffe) and the TE opaque LSA for the link MUST be re-originated
   with new value.

   In multi-topology deployments [RFC4915], the Link-Overload sub-TLV
   carried in an Extended Link opaque LSA corresponds to all the
   topologies the link belongs to.  The receiver node SHOULD change the
   metric in the reverse direction corresponding to all the topologies
   to which the reverse link belongs.

   When the originator of the Link-Overload sub-TLV purges the Extended
   Link Opaque LSA/E-Router-LSA or re-originates it without the Link-
   Overload sub-TLV, the remote node must re-originate the appropriate
   LSAs with the metric and TE metric values set to their original
   values.

5.2.  Broadcast/NBMA links

   Broadcast or NBMA networks in OSPF are represented by a star topology
   where the Designated Router (DR) is the central point to which all
   other routers on the broadcast or NBMA network connect logically.  As
   a result, routers on the broadcast or NBMA network advertise only
   their adjacency to the DR.  Routers that do not act as DR do not form
   or advertise adjacencies with each other.  For the Broadcast links,
   the MAX-METRIC on the remote link cannot be changed since all the
   neighbours are on same link.  Setting the link cost to MAX-METRIC
   would impact paths going via all neighbours.

   The node that has the link to be taken out of service SHOULD set
   metric of the link to MAX-METRIC(0xffff) and re-originate the Router-
   LSA.  The TE metric SHOULD be set to MAX-TE-METRIC-1(0xfffffffe) and
   the node SHOULD re-originate the TE Link Opaque LSAs.  For a
   broadcast link, the two part metric as described in [RFC8042] is
   used.  The node originating the Link-Overload sub-TLV MUST set the
   metric in the Network-to-Router Metric sub-TLV to MAX-METRIC 0xffff
   for OSPFv2 and OSPFv3 and re-originate the LSAs the TLV is carried-
   in.  The nodes that receive the two part metric should follow the
   procedures described in [RFC8042].  The backward compatibility



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   procedures described in [RFC8042] should be followed to ensure loop
   free routing.

5.3.  Point-to-multipoint links

   Operation for the point-to-multipoint links is similar to the point-
   to-point links.  When a Link-Overload sub-TLV is received for a
   point-to-multipoint link the remote node SHOULD identify the
   neighbour which corresponds to the overloaded link and set the metric
   to MAX-METRIC (0xffff).  The remote node MUST re-originate the
   Router-LSA with the changed metric and flood into the OSPF area.

5.4.  Unnumbered interfaces

   Unnumbered interface do not have a unique IP addresses and borrow
   address from other interfaces.  [RFC2328] describes procedures to
   handle unnumbered interfaces.  The link-data field in the Extended
   Link TLV carries the interface-id instead of the IP address.  The
   Link-Overload sub-TLV carries the remote interface-id in the Remote-
   ip-address field if the interface is unnumbered.  Procedures to
   obtain interface-id of the remote side are defined in [RFC4203].

5.5.  Hybrid Broadcast and P2MP interfaces

   Hybrid Broadcast and P2MP interfaces represent a broadcast network
   modeled as P2MP interfaces.  [RFC6845] describes procedures to handle
   these interfaces.  Operation for the Hybrid interfaces is similar to
   the P2MP interfaces.  When a Link-Overload sub-TLV is received for a
   hybrid link the remote node SHOULD identify the neighbour which
   corresponds to the overloaded link and set the metric to MAX-METRIC
   (0xffff).  All the remote nodes connected to originator MUST re-
   originate the Router-LSA with the changed metric and flood into the
   OSPF area.

6.  Backward compatibility

   The mechanism described in the document is fully backward compatible.
   It is required that the originator of the Link-Overload sub-TLV as
   well as the node at the remote end of the link identified as
   overloaded understand the extensions defined in this document.  In
   the case of broadcast links, the backward compatibility procedures as
   described in [RFC8042] are applicable.

7.  Applications







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7.1.  Pseudowire Services


           ---------PE3----------------PE4----------
          |                                         |
          |                                         |
        CE1---------PE1----------------PE2---------CE2
          |                                         |
          |                                         |
           -----------------------------------------
                    Private VLAN


                       Figure 3: Pseudowire Services

   Many service providers offer pseudo-wire services to customers using
   L2 circuits.  The IGP protocol that runs in the customer network
   would also run over the pseudo-wire to create seamless private
   network for the customer.  Service providers want to offer overload
   kind of functionality when the PE device is taken-out for
   maintenance.  The provider should guarantee that the PE is taken out
   for maintenance only after the service is successfully diverted on an
   alternate path.  There can be large number of customers attached to a
   PE node and the remote end-points for these pseudo-wires are spread
   across the service provider's network.  It is a tedious and error-
   prone process to change the metric for all pseudo-wires in both
   directions.  The link-overload feature simplifies the process by
   increasing the metric on the link in the reverse direction as well so
   that traffic in both directions is diverted away from the PE
   undergoing maintenance.  The Link-Overload feature allows the link to
   be used as a last resort link so that traffic is not disrupted when
   alternative paths are not available.

   When the PE1 node is going for maintenance, service provider sets the
   PE1 to overload state.  The PE1 going in overload state triggers all
   the CEs connected to the PE to set their pseudowire links passing via
   PE1 to link-overload state.  The mechanisms used to communicate
   between PE1 and CE1 is outside the scope of this document.  CE1 sets
   the link-overload state on its link and modifies the metric to
   MAX_METRIC and floods the information, the remote end of the link
   also sets the metric on the link to MAX-METRIC and the traffic from
   both directions gets diverted away from the link.

7.2.  Controller based Traffic Engineering Deployments







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                         _____________
                        |             |
           -------------| Controller  |--------------
          |             |____________ |             |
          |                                         |
          |--------- Primary Path ------------------|
          PE1---------P1----------------P2---------PE2
                      |                  |
                      |                  |
                      |________P3________|

                         Alternate Path


              Figure 4: Controller based Traffic Engineering

   In controller-based deployments where the controller participates in
   the IGP protocol, the controller can also receive the link-overload
   information as a warning that link maintenance is imminent.  Using
   this information, the controller can find alternate paths for traffic
   which use the affected link.  The controller can apply various
   policies and re-route the LSPs away from the link undergoing
   maintenance.  If there are no alternate paths satisfying the traffic
   engineering constraints, the controller might temporarily relax those
   constraints and put the service on a different path.

   In the above example, PE1->PE2 LSP is set-up to satisfy a constraint
   of 10 GB bandwidth on each link.  The links P1->P3 and P3->P2 have
   only 1 GB capacity and there is no alternate path satisfying the
   bandwidth constraint of 10GB.  When P1->P2 link is being prepared for
   maintenance, the controller receives the link-overload information,
   as there is no alternate path available which satisfies the
   constraints, controller chooses a path that is less optimal and
   temporarily sets up an alternate path via P1->P3->P2.  Once the
   traffic is diverted, the P1->P2 link can be taken out of service for
   maintenance/upgrade.

8.  Security Considerations

   This document does not introduce any further security issues other
   than those discussed in [RFC2328] and [RFC5340].

9.  IANA Considerations

   This specification updates one OSPF registry:

   OSPF Extended Link TLVs Registry




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   i) TBD - Link-Overload sub-TLV

   OSPFV3 Router Link TLV Registry

   i) TBD - Link-Overload sub-TLV

   OSPF RI TLV Registry

   i) TBD - Link-Overload sub-TLV

   BGP-LS Link NLRI Registry [RFC7752]

   i)TBD - Link-Overload sub-TLV

10.  Acknowledgements

   Thanks to Chris Bowers for valuable inputs and edits to the document.
   Thanks to Jeffrey Zhang and Acee Lindem for inputs.  Thanks to
   Karsten Thomann for careful review and inputs.

11.  References

11.1.  Normative References

   [RFC6845]  Sheth, N., Wang, L., and J. Zhang, "OSPF Hybrid Broadcast
              and Point-to-Multipoint Interface Type", RFC 6845,
              DOI 10.17487/RFC6845, January 2013,
              <http://www.rfc-editor.org/info/rfc6845>.

   [RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
              Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
              Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
              2015, <http://www.rfc-editor.org/info/rfc7684>.

   [RFC7752]  Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
              S. Ray, "North-Bound Distribution of Link-State and
              Traffic Engineering (TE) Information Using BGP", RFC 7752,
              DOI 10.17487/RFC7752, March 2016,
              <http://www.rfc-editor.org/info/rfc7752>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <http://www.rfc-editor.org/info/rfc7770>.

   [RFC8042]  Zhang, Z., Wang, L., and A. Lindem, "OSPF Two-Part
              Metric", RFC 8042, DOI 10.17487/RFC8042, December 2016,
              <http://www.rfc-editor.org/info/rfc8042>.



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11.2.  Informative References

   [I-D.ietf-ospf-ospfv3-lsa-extend]
              Lindem, A., Mirtorabi, S., Roy, A., and F. Baker, "OSPFv3
              LSA Extendibility", draft-ietf-ospf-ospfv3-lsa-extend-06
              (work in progress), February 2015.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,
              <http://www.rfc-editor.org/info/rfc2328>.

   [RFC4203]  Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
              Support of Generalized Multi-Protocol Label Switching
              (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
              <http://www.rfc-editor.org/info/rfc4203>.

   [RFC4915]  Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P.
              Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF",
              RFC 4915, DOI 10.17487/RFC4915, June 2007,
              <http://www.rfc-editor.org/info/rfc4915>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <http://www.rfc-editor.org/info/rfc5340>.

   [RFC6987]  Retana, A., Nguyen, L., Zinin, A., White, R., and D.
              McPherson, "OSPF Stub Router Advertisement", RFC 6987,
              DOI 10.17487/RFC6987, September 2013,
              <http://www.rfc-editor.org/info/rfc6987>.

Authors' Addresses

   Shraddha Hegde
   Juniper Networks, Inc.
   Embassy Business Park
   Bangalore, KA  560093
   India

   Email: shraddha@juniper.net







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   Pushpasis Sarkar
   Individual

   Email: pushpasis.ietf@gmail.com


   Hannes Gredler
   Individual

   Email: hannes@gredler.at


   Mohan Nanduri
   Microsoft Corporation
   One Microsoft Way
   Redmond, WA  98052
   US

   Email: mnanduri@microsoft.com


   Luay Jalil
   Verizon

   Email: luay.jalil@verizon.com


























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