Open Shortest Path First IGP                                    S. Hegde
Internet-Draft                                    Juniper Networks, Inc.
Intended status: Standards Track                               P. Sarkar
Expires: January 18, February 15, 2018                                    H. Gredler
                                                              Individual
                                                              M. Nanduri
                                                        ebay Corporation
                                                                L. Jalil
                                                                 Verizon
                                                           July 17,
                                                         August 14, 2017

                           OSPF Link Overload
                    draft-ietf-ospf-link-overload-08
                    draft-ietf-ospf-link-overload-09

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
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 18, February 15, 2018.

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
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Flooding Scope  . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Link-Overload sub-TLV . . . . . . . . . . . . . . . . . . . .   4
     4.1.  OSPFv2 Link-overload sub-TLV  . . . . . . . . . . . . . .   4
     4.2.  Remote IPv4 address sub-TLV . . . . . . . . . . . . . . .   4
     4.3.  Local/Remote Interface ID . . . . sub-TLV . . . . . . . . . . . .   5
     4.4.  OSPFv3 Link-Overload sub-TLV  . . . . . . . . . . . . . .   6
   5.  Elements of procedure . . . . . . . . . . . . . . . . . . . .   6
     5.1.  Point-to-point links  . . . . . . . . . . . . . . . . . .   6
     5.2.  Broadcast/NBMA links  . . . . . . . . . . . . . . . . . .   7
     5.3.  Point-to-multipoint links . . . . . . . . . . . . . . . .   7
     5.4.  Unnumbered interfaces . . . . . . . . . . . . . . . . . .   8
     5.5.  Hybrid Broadcast and P2MP interfaces  . . . . . . . . . .   8
   6.  Backward compatibility  . . . . . . . . . . . . . . . . . . .   8
   7.  Applications  . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Pseudowire Services . . . . . . . . . . . . . . . . . . .   8
     7.2.  Controller based Traffic Engineering Deployments  . . . .   9  10
     7.3.  L3VPN Services and sham-links . . . . . . . . . . . . . .  10
     7.4.  Hub and spoke deployment  . . . . . . . . . . . . . . . .  11
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11  12
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  12
     11.2.  Informative References . . . . . . . . . . . . . . . . .  12

   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

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 on the node requires
   maintenance.

   In traffic-engineering deployments, LSPs need to be diverted from the
   link without disrupting the services.  [RFC5817] describes
   requirements and procedures for graceful shutdown of MPLS links.  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 7.1.

   This document provides mechanisms to advertise link-overload state in
   the flexible encodings provided by OSPFv2 Prefix/Link Attribute
   Advertisement([RFC7684]).  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.

   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 is flooded in area scoped Extended Link
   Opaque LSA [RFC7684].  The Link-Overload sub-TLV MAY be processed by
   the head-end nodes or the controller as described in the Section 7.
   The procedures for processing the Link-Overload sub-TLV is are described
   in Section 5.

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
   state.It is carried in extended Link TLV in the Extended Link Opaque
   LSA as defined in [RFC7684].

        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 1: Link-Overload sub-TLV for OSPFv2

   Type : TBA (suggested value 5)

   Length: 0

4.2.  Remote IPv4 address sub-TLV

   This sub-TLV specifies the IPv4 address of the link on remote side. endpoint on the
   link.  It is carried advertised in extended Link TLV as defined in
   [RFC7684].This sub-
   TLV sub-TLV is optional and MAY be advertised in area
   scoped Extended Link Opaque LSA to identify the link when there are
   multiple parallel
   interfaces links between two nodes.

        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 IPv4 address                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: Remote IPv4 address sub-TLV

   Type : TBA (suggested value 4)

   Length: 4

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

4.3.  Local/Remote Interface ID sub-TLV

   This sub-TLV specifies local and remote interface identifiers.  It is
   carried
   advertised in extended Link TLV as defined in [RFC7684].This sub-TLV
   is optional and MAY be advertised in area scoped Extended Link Opaque
   LSA to identify the link when there are multiple parallel unnumbered
   interfaces
   links between two nodes.  The local interface-id is generally readily
   available.  One of the mechanisms to obtain remote interface-
   id interface-id is
   described in [RFC4203].

        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            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Local Interface ID                        |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                     Remote Interface ID                       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                Figure 3: Local/Remote Interface ID sub-TLV

   Type : TBA (suggested value 11)

   Length: 8
   Value: 4 octets of Local Interface ID followed by 4 octets of Remote
   interface ID.

4.4.  OSPFv3 Link-Overload sub-TLV

   The definition of OSPFv3 Link-Overload sub-TLV is defined below.  The
   area scope scoped advertisement of Link-Overload sub-TLV for OSPFv3 will be
   described in a separate document.

        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 4: 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 advertise 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 advertised 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.

5.1.  Point-to-point links

   The node that has the link to be taken out of service MUST 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 MUST identify the local link which corresponds to the overloaded
   link and set the metric to MAX-METRIC (0xffff)and 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 SHOULD be re-originated with new value.

   Extended link opaque LSAs and the Extended link TLV are not scoped
   for multi-topology [RFC4915].  In multi-topology deployments
   [RFC4915], the Link-Overload sub-TLV carried advertised in an Extended Link
   opaque LSA corresponds to all the topologies which include the link belongs to. link.
   The receiver node SHOULD change the metric in the reverse direction
   corresponding to
   for all the topologies to which include the reverse remote link belongs and re-originate
   the Router LSA as defined in [RFC4915].

   When the originator of the Link-Overload sub-TLV purges the Extended
   Link Opaque 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 MUST 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 corresponding 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. corresponding LSAs.  The
   nodes that receive the two part metric should follow the procedures
   described in [RFC8042].  The backward compatibility 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 MUST 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. metric.

5.4.  Unnumbered interfaces

   Unnumbered interface do not have a unique IP addresses address and borrow their
   address from other interfaces.  [RFC2328] describes procedures to
   handle unnumbered interfaces in the context of the Router LSA.  We
   apply a similar procedure to the Extended Link TLV carrying advertising the Link-
   Overload
   Link-Overload sub-TLV in to handle unnumbered interfaces.  The link-data link-
   data field in the Extended Link TLV carries includes the Local interface-id
   instead of the IP address.  The Local/Remote Interface ID sub-TLV
   MUST be
   originated advertised when there are multiple parallel unnumbered
   interfaces between two nodes.  One of the mechanisms to obtain the
   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 MUST 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. metric.

6.  Backward compatibility

   The mechanism mechanisms described in the document is are fully backward
   compatible.  It is required that the originator of node adverting the Link-Overload
   sub-TLV as well as the node at the remote end of the link identified as overloaded understand link
   support the extensions defined in this document. described herein for the traffic to diverted
   from the overloaded link.  If the remote node doesn't support the
   capability, it will still use the overloaded link but there are no
   other adverse effects.  In the case of broadcast links, links using two-part
   metrics, the backward compatibility procedures as described in
   [RFC8042] are applicable.

7.  Applications

7.1.  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 a 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 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.

                   Private VLAN
           =======================================
          |                                       |
          |                                       |
          |     ------PE3---------------PE4------CE3
          |   /                             \
          | /                                 \
        CE1---------PE1----------PE2---------CE2
          |                       \
          |                        \
          |                         ------CE4
          |                                 |
          |                                 |
          |                                 |
           =================================
                   Private VLAN

                       Figure 5: Pseudowire Services

   In the example shown in Figure 5, when the PE1 node is going out of
   service for maintenance, service providers set the PE1 to overload
   state.  The PE1 going in to overload state triggers all the CEs (In
   this example CE1)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 private VLAN
   connecting CE3, CE2 and CE4 and modifies changes the metric to MAX_METRIC and floods the information,
   re-originates the corresponding LSA.  The remote end of the link at
   CE3, CE2, and CE4 also set the metric on the link to MAX-METRIC and
   the traffic from both directions gets diverted away from the link.
   pseudowires.

7.2.  Controller based Traffic Engineering Deployments

   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 uses 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.  Increasing the
   link metric alone does not specify the maintenance activity as the
   metric could increase in events such as LDP-IGP synchronisation.  An
   explicit indication from the router using the link-overload sub-TLV
   is needed to inform the Controller or head-end routers.

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

                         Alternate Path

              Figure 6: Controller based Traffic Engineering

   In the above example, PE1->PE2 LSP is set-up to satisfy a constraint
   of 10 Gbps bandwidth on each link.  The links P1->P3 and P3->P2 have
   only 1 Gbps 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.

7.3.  L3VPN Services and sham-links

   Many service providers offer L3VPN services to customers and CE-PE
   links run OSPF [RFC4577].  When PE goes out of service for
   maintenance, all the links on the PE can be set to link-overlaod
   state which will gurantee that the traffic from to/from dual-homed CEs also
   gets diverted.  The interaction between OSPF and BGP is outside the
   scope of this document.

   Another useful usecase is when ISPs provide sham-link services to
   customers [RFC4577].When PE goes out of service for maintenance, all
   sham-links on the PE can be set to link-overload state and traffic
   can be divered from both ends without having to touch the
   configurations on the remote end of the sham-links.

7.4.  Hub and spoke deployment

   OSPF is largely deployed in Hub and Spoke deployments with a number
   of spokes connecting to the Hub. It is a general practice to deploy
   multiple Hubs with all spokes connecting to these Hubs to achieve
   redundancy.  When a Hub node goes down for maintenance, all links on
   the Hub can be set to link-overload state and traffic gets divered
   from the spoke sites as well without having to make configuration
   changes on the spokes.

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

   i) TBD - Link-Overload sub-TLV - Suggested value 5

   ii) Remote IPv4 address sub-TLV - Suggested value 4

   iii) Local/Remote Interface ID sub-TLV - Suggested Value 11

   OSPFV3 Router Link TLV Registry

   i) TBD - Link-Overload sub-TLV

   OSPF RI TLV Registry

   i) TBD - Link-Overload sub-TLV suggested value 4

   BGP-LS Link NLRI Registry [RFC7752]

   i)TBD

   i)Link-Overload TLV - Link-Overload sub-TLV Suggested 1101

10.  Acknowledgements

   Thanks to Chris Bowers for valuable inputs and edits to the document.
   Thanks to Jeffrey Zhang,Acee Zhang, Acee Lindem and Ketan Talaulikar for inputs.
   Thanks to Karsten Thomann for careful review and inputs on the
   applications where link-overload is useful.

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>.

   [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>.

11.2.  Informative References

   [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>.

   [RFC4577]  Rosen, E., Psenak, P., and P. Pillay-Esnault, "OSPF as the
              Provider/Customer Edge Protocol for BGP/MPLS IP Virtual
              Private Networks (VPNs)", RFC 4577, DOI 10.17487/RFC4577,
              June 2006, <http://www.rfc-editor.org/info/rfc4577>.

   [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>.

   [RFC5817]  Ali, Z., Vasseur, JP., Zamfir, A., and J. Newton,
              "Graceful Shutdown in MPLS and Generalized MPLS Traffic
              Engineering Networks", RFC 5817, DOI 10.17487/RFC5817,
              April 2010, <http://www.rfc-editor.org/info/rfc5817>.

   [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

   Pushpasis Sarkar
   Individual

   Email: pushpasis.ietf@gmail.com

   Hannes Gredler
   Individual

   Email: hannes@gredler.at
   Mohan Nanduri
   ebay Corporation
   2025 Hamilton Avenue
   San Jose, CA  98052
   US

   Email: mnanduri@ebay.com

   Luay Jalil
   Verizon

   Email: luay.jalil@verizon.com