Open Shortest Path First IGP                                    S. Hegde
Internet-Draft                                              H. Raghuveer
Intended status: Standards Track                              H. Gredler
Expires: December 28, 2014                        Juniper Networks, Inc.
                                                               R. Shakir
                                                         British Telecom
                                                              A. Smirnov
                                                     Cisco Systems, Inc.
                                                                   Z. Li
                                                     Huawei Technologies
                                                           June 26, 2014

            Advertising per-node administrative tags in OSPF


   This document describes an extension to OSPF protocol [RFC2328] to
   add an optional operational capability, that allows tagging and
   grouping of the nodes in an OSPF domain.  This allows
   simplification,ease of management and control over route and path
   selection based on configured policies.

   This document describes the protocol extensions to disseminate per-
   node admin-tags to the OSPFv2 and OSPFv3 protocol.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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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."

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   This Internet-Draft will expire on December 28, 2014.

Copyright Notice

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   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
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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Applicability . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Administrative Tag TLV  . . . . . . . . . . . . . . . . . . .   3
   4.  OSPF per-node administrative tag TLV  . . . . . . . . . . . .   3
     4.1.  TLV format  . . . . . . . . . . . . . . . . . . . . . . .   3
     4.2.  Elements of procedure . . . . . . . . . . . . . . . . . .   4
   5.  Applications  . . . . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   9
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     9.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10

1.  Introduction

   This document provides mechanisms to advertise per-node
   administrative tags in the OSPF Router Information LSA [RFC4970].  In
   certain path-selection applications like for example in traffic-
   engineering or LFA backup selection there is a need to tag the nodes
   based on their roles in the network and have policies to prefer or
   prune a certain group of nodes.

2.  Applicability

   For the purpose of advertising per-node administrative tags within
   OSPF a new TLV is proposed.  Because path selection is a functional

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   set which applies both to TE and non-TE applications, this new TLV is
   carried in the Router Information LSA (RI LSA) [RFC4970]

3.  Administrative Tag TLV

   An administrative Tag is a 32-bit integer value that can be used to
   identify a group of nodes in the OSPF domain.

   The new TLV defined will be carried within an RI LSA for OSPFV2 and
   OSPFV3.  Router information LSA [RFC4970] can have link,area or AS
   level flooding scope.  Choosing the flooding scope to flood the group
   tags are defined by the policies and is a local matter.

   The TLV specifies one or more administrative tag values.  An OSPF
   node advertises the set of groups it is part of in the OSPF domain.
   (for example, all PE-nodes are configured with certain tag value, all
   P-nodes are configured with a different tag value in a domain).  The
   total number of admin tags that a given router can advertise at one
   time is restricted to 64.  If more tags are needed in future, multi-
   instancing of the RI LSA [RFC4970] may be required.

4.  OSPF per-node administrative tag TLV

4.1.  TLV format

   The format of the TLVs within the body of an RI LSA is the same as
   the format used by the Traffic Engineering Extensions to OSPF

   The LSA payload consists of one or more nested Type/Length/Value
   (TLV) triplets.  The format of each TLV is:

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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
   |              Type             |             Length            |
   |                     Administrative Tag #1                     |
   |                     Administrative Tag #2                     |
   //                                                             //
   |                     Administrative Tag #N                     |

              Figure 1: OSPF per-node Administrative Tag TLV

   Type : TBA

   Length: A 16-bit field that indicates the length of the value portion
   in octets and will be a multiple of 4 octets dependent on the number
   of tags advertised.

   Value: A sequence of multiple 4 octets defining the administrative
   tags.  The number of tags carried in this TLV is restricted to 64.

4.2.  Elements of procedure

   Meaning of the Node administrative tags is generally opaque to OSPF.
   Router advertising the Node administrative tag (or tags) may be
   configured to do so without knowing (or even explicitly supporting)
   functionality implied by the tag.

   Interpretation of the tag values is implementation-specific.  The
   meaning of a Node administrative tag is defined by the network local
   policy and is controlled via the configuration.  There are no tag
   values defined by this specification.

   The semantics of the tag order has no meaning.  That is, there is no
   implied meaning to the ordering of the tags that indicates a certain
   operation or set of operations that need to be performed based on the

   Each tag SHOULD be treated as an independent identifier that MAY be
   used in policy to perform a policy action.  Whether or not tag A
   precedes or succeeds tag B SHOULD not change the meaning of the tag

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   To avoid incomplete or inconsistent interpretations of the Node
   administrative tags the same tag value MUST NOT be advertised by a
   router in RI LSAs of different scopes.  The same tag MAY be
   advertised in multiple RI LSAs of the same scope, for example, OSPF
   Area Border Router (ABR) may advertise the same tag in area-scope RI
   LSAs in multiple areas connected to the ABR.

   The Node administrative tags are not meant to be extended by the
   future OSPF standards.  The new OSPF extensions MUST NOT require use
   of Node administrative tags or define well-known tag values.
   Instead, the future OSPF extensions must define their own data
   signaling tailored to the needs of the feature.

   Being part of the RI LSA, the Node administrative tag TLV must be
   reasonably small and stable.  In particular, but not limited to,
   implementations supporting the Node administrative tags MUST NOT tie
   advertised tags to changes in the network topology (both within and
   outside the OSPF domain) or reachability of routes.

5.  Applications

   This section lists several examples of how implementations might use
   the Node administrative tags.  These examples are given only to
   demonstrate generic usefulness of the router tagging mechanism.
   Implementation supporting this specification is not required to
   implement any of the use cases.  It is also worth noting that in some
   described use cases routers configured to advertise tags help other
   routers in their calculations but do not themselves implement the
   same functionality.

   1.  Service auto-discovery

       Router tagging may be used to automatically discover group of
       routers sharing a particular service.

       For example, service provider might desire to establish full mesh
       of MPLS TE tunnels between all PE routers in the area of MPLS VPN
       network.  Marking all PE routers with a tag and configuring
       devices with a policy to create MPLS TE tunnels to all other
       devices advertising this tag will automate maintenance of the
       full mesh.  When new PE router is added to the area, all other PE
       devices will open TE tunnels to it without the need of
       reconfiguring them.

   2.  Fast-Rerouting policy

       Increased deployment of Loop Free Alternates (LFA) as defined in
       [RFC5286] poses operation and management challenges.

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       [I-D.litkowski-rtgwg-lfa-manageability] proposes policies which,
       when implemented, will ease LFA operation concerns.

       One of the proposed refinements is to be able to group the nodes
       in IGP domain with administrative tags and engineer the LFA based
       on configured policies.

       (a)  Administrative limitation of LFA scope

           Service provider access infrastructure is frequently designed
           in layered approach with each layer of devices serving
           different purposes and thus having different hardware
           capabilities and configured software features.  When LFA
           repair paths are being computed, it may be desirable to
           exclude devices from being considered as LFA candidates based
           on their layer.

           For example, if the access infrastructure is divided into the
           Access, Distribution and Core layers it may be desirable for
           a Distribution device to compute LFA only via Distribution or
           Core devices but not via Access devices.  This may be due to
           features enabled on Access routers; due to capacity
           limitations or due to the security requirements.  Managing
           such a policy via configuration of the router computing LFA
           is cumbersome and error prone.

           With the Node administrative tags it is possible to assign a
           tag to each layer and implement LFA policy of computing LFA
           repair paths only via neighbors which advertise the Core or
           Distribution tag.  This requires minimal per-node
           configuration and network automatically adapts when new links
           or routers are added.

       (b)  LFA calculation optimization

           Calculation of LFA paths may require significant resources of
           the router.  One execution of Dijkstra algorithm is required
           for each neighbor eligible to become next hop of repair
           paths.  Thus a router with a few hundreds of neighbors may
           need to execute the algorithm hundreds of times before the
           best (or even valid) repair path is found.  Manually
           excluding from the calculation neighbors which are known to
           provide no valid LFA (such as single-connected routers) may
           significantly reduce number of Dijkstra algorithm runs.

           LFA calculation policy may be configured so that routers
           advertising certain tag value are excluded from LFA
           calculation even if they are otherwise suitable.

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   3.  Controlling Remote LFA tunnel termination

       [I-D.ietf-rtgwg-remote-lfa] proposed method of tunneling traffic
       after connected link failure to extend the basic LFA coverage and
       algorithm to find tunnel tail-end routers fitting LFA
       requirement.  In most cases proposed algorithm finds more than
       one candidate tail-end router.  In real life network it may be
       desirable to exclude some nodes from the list of candidates based
       on the local policy.  This may be either due to known limitations
       of the node (the router does accept targeted LDP sessions
       required to implement Remote LFA tunneling) or due to
       administrative requirements (for example, it may be desirable to
       choose tail-end router among co-located devices).

       The Node administrative tag delivers simple and scalable
       solution.  Remote LFA can be configured with a policy to accept
       during the tail-end router calculation as candidates only routers
       advertising certain tag.  Tagging routers allows to both exclude
       nodes not capable of serving as Remote LFA tunnel tail-ends and
       to define a region from which tail-end router must be selected.

   4.  Mobile backhaul network service deployment

       The topology of mobile backhaul network usually adopts ring
       topology to save fiber resource and it is divided into the
       aggregate network and the access network.  Cell Site
       Gateways(CSGs) connects the eNodeBs and RNC(Radio Network
       Controller) Site Gateways(RSGs)connects the RNCs.  The mobile
       traffic is transported from CSGs to RSGs.  The network takes a
       typical aggregate traffic model that more than one access rings
       will attach to one pair of aggregate site gateways(ASGs) and more
       than one aggregate rings will attach to one pair of RSGs.

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                   /                \
                  /                  \
                 /                    \
    +------+   +----+    Access     +----+
    |eNodeB|---|CSG1|    Ring 1     |ASG1|-------------
    +------+   +----+               +----+             \
                 \                    /                 \
                  \                  /                   +----+    +---+
                   \             +----+                  |RSG1|----|RNC|
                    -------------|    |    Aggregate     +----+    +---+
                                 |ASG2|      Ring          |
                    -------------|    |                  +----+    +---+
                   /             +----+                  |RSG2|----|RNC|
                  /                  \                   +----+    +---+
                 /                    \                 /
    +------+   +----+     Access     +----+            /
    |eNodeB|---|CSG2|     Ring 2     |ASG3|------------
    +------+   +----+                +----+
                \                     /
                 \                   /
                  \                 /

                     Figure 2: Mobile Backhaul Network

       A typical mobile backhaul network with access rings and aggregate
       links is shown in figure above.  The mobile backhaul networks
       deploy traffic engineering due to the strict Service Level
       Agreements(SLA).  The TE paths may have additional constraints to
       avoid passing via different access rings or to get completely
       disjoint backup TE paths.  The mobile backhaul networks towards
       the access side change frequently due to the growing mobile
       traffic and addition of new eNodeBs.  It's complex to satisfy the
       requirements using cost, link color or explicit path
       configurations.  The node administrative tag defined in this
       document can be effectively used to solve the problem for mobile
       backhaul networks.  The nodes in different rings can be assigned
       with specific tags.  TE path computation can be enhanced to
       consider additional constraints based on node administrative

6.  Security Considerations

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

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7.  IANA Considerations

   IANA maintains the registry for the TLVs.  OSPF Administrative Tags
   will require one new type code for the TLV defined in this document.

8.  Acknowledgments

   Thanks to Bharath R and Pushpasis Sarakar for useful inputs.  Thanks
   to Chris Bowers for providing useful inputs to remove ambiguity
   related to tag-ordering.

9.  References

9.1.  Normative References

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

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630, September

   [RFC4970]  Lindem, A., Shen, N., Vasseur, JP., Aggarwal, R., and S.
              Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 4970, July 2007.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, July 2008.

9.2.  Informative References

              Bryant, S., Filsfils, C., Previdi, S., Shand, M., and S.
              Ning, "Remote LFA FRR", draft-ietf-rtgwg-remote-lfa-02
              (work in progress), May 2013.

              Litkowski, S., Decraene, B., Filsfils, C., and K. Raza,
              "Operational management of Loop Free Alternates", draft-
              litkowski-rtgwg-lfa-manageability-01 (work in progress),
              February 2013.

   [RFC5286]  Atlas, A. and A. Zinin, "Basic Specification for IP Fast
              Reroute: Loop-Free Alternates", RFC 5286, September 2008.

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Authors' Addresses

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


   Harish Raghuveer
   Juniper Networks, Inc.
   Embassy Business Park
   Bangalore  560093


   Hannes Gredler
   Juniper Networks, Inc.
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089


   Rob Shakir
   British Telecom


   Anton Smirnov
   Cisco Systems, Inc.
   De Kleetlaan 6a
   Diegem  1831


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   Li Zhenbin
   Huawei Technologies
   Huawei Bld.  No.156 Beiqing Rd
   Beijing  100095


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