Open Shortest Path First IGP                                    S. Hegde
Internet-Draft                                    Juniper Networks, Inc.
Intended status: Standards Track                            H. Raghuveer
Expires: March 12, 2016
                                                              H. Gredler
                                                  Juniper Networks, Inc.
                                                               R. Shakir
                                                              A. Smirnov
                                                     Cisco Systems, Inc.
                                                                   Z. Li
                                                     Huawei Technologies
                                                             B. Decraene
                                                       September 9, 2015

            Advertising per-node administrative tags in OSPF


   This document describes an extension to OSPF protocol 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 an extension to OSPF
   protocol to advertise per-node administrative tags.  This optional
   operational capability allows to express and act upon locally-defined
   network policy which considers node properties conveyed by tags.
   Node tags may be used either by OSPF itself or by other applications
   consuming information propagated via OSPF.

   This document describes the protocol extensions to disseminate per-
   node administrative-tags to the OSPFv2 and OSPFv3 protocol.  It
   provides example use cases of administrative node tags.

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.

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   This Internet-Draft will expire on March 12, 2016.

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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Administrative Tag TLV  . . . . . . . . . . . . . . . . . . .   3
   3.  OSPF per-node administrative tag TLV  . . . . . . . . . . . .   3
     3.1.  TLV format  . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Elements of procedure . . . . . . . . . . . . . . . . . .   4
   4.  Applications  . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  Service auto-discovery  . . . . . . . . . . . . . . . . .   6
     4.2.  Fast-Rerouting policy . . . . . . . . . . . . . . . . . .   6
     4.3.  Controlling Remote LFA tunnel termination . . . . . . . .   7
     4.4.  Mobile backhaul network service deployment  . . . . . . .   7
     4.5.  Explicit routing policy . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   7.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

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1.  Introduction

   It is useful to assign a per-node administrative tag to a router in
   the OSPF domain and use it as an attribute associated with the node.
   The per-node administrative tag can be used in variety of
   applications, for ex: - Traffic-engineering applications to provide
   different path-selection criteria, - Prefer or prune certain paths in
   Loop Free Alternate (LFA) backup selection via local policies.

   This document provides mechanisms to advertise per-node
   administrative tags in the OSPF.  Path selection is a functional set
   which applies both to TE and non-TE applications and hence new TLV
   for carrying per-node administrative tags is included in Router
   Information LSA [RFC4970] .

2.  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).
   Multiple TLVs MAY be added in same RI-LSA or in different instance of
   the RI LSA as defined in [I-D.acee-ospf-rfc4970bis].

3.  OSPF per-node administrative tag TLV

3.1.  TLV format

   [RFC4970], defines Router Information (RI) LSA which may be used to
   advertise properties of the originating router.  Payload of the RI
   LSA consists of one or more nested Type/Length/Value (TLV) triplets.
   Node administrative tags are advertised in the Node Administrative
   Tag TLV.  The format of Node Administrative Tag 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, Suggested value 10

   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.  At least one tag MUST be carried if this TLV is included in
   the RI-LSA.

3.2.  Elements of procedure

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

   Interpretation of tag values is specific to the administrative domain
   of a particular network operator.  The meaning of a per-node
   administrative tag is defined by the network local policy and is
   controlled via the configuration.  If a receiving node does not
   understand the tag value, it ignores the specific tag and floods the
   RI LSA without any change as defined in [RFC4970].

   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.  Tags carried by the

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   administrative tag TLV SHOULD be used to indicate independent
   characteristics of a node.  The TLV SHOULD be considered an unordered
   list.  Whilst policies may be implemented based on the presence of
   multiple tags (e.g., if tag A AND tag B are present), they MUST NOT
   be reliant upon the order of the tags (i.e., all policies should be
   considered commutative operations, such that tag A preceding or
   following tag B does not change their outcome).

   To avoid incomplete or inconsistent interpretations of the per-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 per-node administrative tags are not meant to be extended by the
   future OSPF standards.  The new OSPF extensions MUST NOT require use
   of per-node administrative tags or define well-known tag values.
   Node administrative tags are for generic use and do not require IANA
   registry.  The future OSPF extensions requiring well known values MAY
   define their own data signalling tailored to the needs of the feature
   or MAY use capability TLV as defined in [RFC4970].

   Being part of the RI LSA, the per-node administrative tag TLV must be
   reasonably small and stable.  In particular, but not limited to,
   implementations supporting the per-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.

   Multiple node administrative tag TLVs MAY appear in an RI LSA or
   multiple node administrative tag TLVs MAY be contained in different
   instances of the RI LSA.  The node administrative tags associated
   with a node for the purpose of any computation or processing SHOULD
   be a superset of node administrative tags from all the TLVs in all
   instances of the RI LSA originated by that node.

   When there is a change in the node administrative tag TLV or removal/
   addition of a TLV in any instance of the RI-LSA, implementations MUST
   take appropriate measures to update its state according to the
   changed set of tags.  Exact actions depend on features working with
   administrative tags and is outside of scope of this specification.

4.  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

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   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.

4.1.  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.

4.2.  Fast-Rerouting policy

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

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       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.

4.3.  Controlling Remote LFA tunnel termination

   [RFC7490] 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 not accept targeted
   LDP sessions required to implement Remote LFA tunnelling) 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.

4.4.  Mobile backhaul network service deployment

   The topology of mobile back-haul network usually adopts ring topology
   to save fibre 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)

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   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.

                    /                \
                   /                  \
                  /                    \
     +------+   +----+    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 back-haul network with access rings and aggregate
   links is shown in figure above.  The mobile back-haul 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 back-haul 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 back-haul 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 tags.

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4.5.  Explicit routing policy

   Partially meshed network provides multiple paths between any two
   nodes in the network.  In a data centre environment, the topology is
   usually highly symmetric with many/all paths having equal cost.  In a
   long distance network, this is usually less the case for a variety of
   reasons (e.g. historic, fibre availability constraints, different
   distances between transit nodes, different roles ...).  Hence between
   a given source and destination, a path is typically preferred over
   the others, while between the same source and another destination, a
   different path may be preferred.

                               |                    |
                               |    +----------+    |
                               |    |          |    |
                               T-10-T          |    |
                              /|   /|          |    |
                             / |  / |          |    |
                          --+  | |  |          |    |
                         /  +--+-+ 100         |    |
                        /  /   |    |          |    |
                       /  /    R-18-R          |    |
                      /  /    /\   /\          |    |
                     /  |    /  \ /  \         |    |
                    /   |   /    x    \        |    |
                   A-25-A  10  10 \    \       |    |
                          /    /   10   10     |    |
                         /    /     \    \     |    |
                        A-25-A       A-25-A    |    |
                         \    \     /    /     |    |
                         201  201  201 201     |    |
                           \    \ /    /       |    |
                            \    x    /        |    |
                             \  / \  /         |    |
                              \/   \/          |    |
                              I-24-I          100  100
                              |    |           |    |
                              |    +-----------+    |
                              |                     |

                    Figure 3: Explicit Routing topology

   In the above topology, operator may want to enforce the following
   high level explicitly routed policies:

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      - Traffic from A nodes to A nodes must not go through I nodes

      - Traffic from A nodes to I nodes must not go through R and T

   With node admin tags, tag A (resp.  I, R, T) can be configured on all
   A (resp.  I, R, T) nodes to advertise their role.  Then a generic
   CSPF policy can be configured on all A nodes to enforce the above
   explicit routing objectives.  (e.g.  CSPF to destinations A exclude
   node with tags I).

5.  Security Considerations

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

6.  IANA Considerations

   This specification updates one OSPF registry: OSPF Router Information
   (RI) TLVs Registry

   i) TBD - Node Admin tag TLV

7.  Acknowledgments

   Thanks to Bharath R, Pushpasis Sarakar and Dhruv Dhody for useful
   inputs.  Thanks to Chris Bowers for providing useful inputs to remove
   ambiguity related to tag-ordering.  Thanks to Les Ginsberg and Acee
   Lindem for the inputs.

8.  References

8.1.  Normative References

              Lindem, A., Shen, N., Vasseur, J., Aggarwal, R., and S.
              Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", draft-acee-ospf-rfc4970bis-00 (work
              in progress), July 2014.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

   [RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
              DOI 10.17487/RFC2328, April 1998,

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   [RFC4970]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 4970, DOI 10.17487/RFC4970, July
              2007, <>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,

   [RFC7490]  Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
              So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
              RFC 7490, DOI 10.17487/RFC7490, April 2015,

8.2.  Informative References

              Litkowski, S., Decraene, B., Filsfils, C., Raza, K.,
              Horneffer, M., and P. Sarkar, "Operational management of
              Loop Free Alternates", draft-ietf-rtgwg-lfa-
              manageability-11 (work in progress), June 2015.

   [RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
              IP Fast Reroute: Loop-Free Alternates", RFC 5286,
              DOI 10.17487/RFC5286, September 2008,

Authors' Addresses

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


   Harish Raghuveer


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


   Rob Shakir


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


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


   Bruno Decraene


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