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Advertising Per-node Admin Tags in IS-IS

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This is an older version of an Internet-Draft that was ultimately published as RFC 7917.
Authors Hannes Gredler , Shraddha Hegde , Stephane Litkowski , Bruno Decraene , Zhenbin Li , Ebben Aries , Rafael Rodriguez , Harish Raghuveer
Last updated 2014-12-22
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IS-IS for IP Internets                                    P. Sarkar, Ed.
Internet-Draft                                                H. Gredler
Intended status: Standards Track                                S. Hegde
Expires: June 25, 2015                            Juniper Networks, Inc.
                                                            S. Litkowski
                                                             B. Decraene
                                                                   Z. Li
                                                     Huawei Technologies
                                                                E. Aries
                                                            R. Rodriguez
                                                            H. Raghuveer

                                                       December 22, 2014

                Advertising Per-node Admin Tags in IS-IS


   This document describes an extension to IS-IS protocol [ISO10589],
   [RFC1195] to add an optional operational capability, that allows
   tagging and grouping ofthe nodes in an IS-IS domain.  This allows
   simple management and easy control over route and path selection,
   based on local configured policies.

   This document describes the protocol extensions to disseminate per-
   node administrative tags in IS-IS protocols.

Requirements Language

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

Status of This Memo

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

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

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

   This Internet-Draft will expire on June 25, 2015.

Copyright Notice

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

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

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Administrative Tag  . . . . . . . . . . . . . . . . . . . . .   3
   3.  TLV format  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Per-node Admin Tag sub-TLV  . . . . . . . . . . . . . . .   4
   4.  Elements of Procedure . . . . . . . . . . . . . . . . . . . .   5
   5.  Applications  . . . . . . . . . . . . . . . . . . . . . . . .   6
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   8.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  13

1.  Introduction

   This document provides mechanisms to advertise per-node
   administrative tags in the IS-IS Link State PDU [RFC1195].  In
   certain path-selection applications like for example in traffic-
   engineering or LFA [RFC5286] 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.

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2.  Administrative Tag

   For the purpose of advertising per-node administrative tags within
   IS-IS, a new sub-TLV to the IS-IS Router Capability TLV-242 that is
   defined in [RFC4971] is proposed.  Because path selection is a
   functional set which applies both to TE and non-TE applications the
   same has not been added as a new sub-TLV in the Traffic Engineering
   TLVs [RFC5305].

   An administrative Tag is a 32-bit integer value that can be used to
   identify a group of nodes in the IS-IS domain.  The new sub-TLV
   specifies one or more administrative tag values.  An IS-IS router
   advertises the set of groups it is part of in the specific IS-IS
   level.  As an example, all PE-nodes may be configured with certain
   tag value, whereas all P-nodes are configured with a different tag
   value in.

   The new sub-TLV defined will be carried inside the IS-IS Router
   Capability TLV-242 (defined in [RFC4971]) in the Link State PDUs
   originated by the router.  Link State PDUs [ISO10589] that has either
   level-wise (i.e.  L1 or L2) or domain-wide flooding scope.  Choosing
   the flooding scope to flood the group tags are defined by the needs
   of the operator's usage and is a matter of local policy or

   Operator may choose to advertise a set of per-node administrative
   tags across levels and another set of per-node administrative tags
   within the specific level.  But evidently the same set of per-node
   administrative tags cannot be advertised both across levels and
   within a specific level.  A receiving IS-IS router will not be able
   to distinguish between the significance of a per-node administrative
   tag advertised globally from that of a administrative tag advertised
   locally if they have the same value associated but different
   significance across different scopes.

   Implementations SHOULD allow configuring one or more 'global' as well
   as 'level-wide' administrative tags.  A operator may only need to
   advertise and flood a specific per-node administrative tag, either
   across all levels, or only within a specific level.  Hence
   implementations MUST NOT allow configuring the same per-node
   administrative tag values in both 'global' and 'level-wide' scopes.
   However the same administrative tag value MAY be allowed to be
   configured and advertised for multiple levels with 'level-wide'
   flooding scope.

   The 'global' per-node administrative tags shall have significance
   across the entire administrative domain and hence MUST be advertised
   in a Router-Capability TLV with 'global' scope (i.e.  S-bit set to

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   1), and inserted in the LSP PDUs generated for all levels applicable.
   The 'level-wide' administrative tags should be copied in to a Router-
   Capability with 'level-wide' scope only (i.e S-bit reset to 0) and
   copied into the LSP PDU for the specific level.

   In deployments using multi-topology routing [RFC5120], since multiple
   topologies within same IS-IS level share the same flooding scope
   configuring the same per-node administrative tag across different
   topologies, SHOULD NOT be allowed.  Advertising the same tag value
   across multiple topologies will lead to same inconsistencies as with
   the case of advertising same tag value across 'global' and 'level-
   wide' flooding scope.  If there is need to distinguish between the
   per-node administrative tags used for one topology to another,
   operators are advised to use disjoint sets of per-node administrative
   tags across such topologies.

3.  TLV format

3.1.  Per-node Admin Tag sub-TLV

   The new Per-node Administrative Tag sub-TLV, like other ISIS
   Capability sub-TLVs, is formatted as Type/Length/Value (TLV)triplets.
   Figure 1 below shows the format of the new sub-TLV.

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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                       |

    Type :  TBA

    Length: A 8-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.

            Figure 1: IS-IS Per-node Administrative Tag sub-TLV

   The 'Per-node Admin Tag' sub-TLV may be generated more than once by
   an originating router.  This MAY happen if a node carries more than
   63 per-node administrative groups and a single sub-TLV does not
   provide sufficient space.  As such occurence of the 'Per-node Admin
   Tag' sub-TLV does not cancel previous announcements, but rather is

4.  Elements of Procedure

   Meaning of the Per-node administrative tags is generally opaque to
   IS-IS.  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
   Router Capability TLV without any change as defined in [RFC4971].

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   The semantics of the tag order has no meaning.  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
   administrative tag TLV SHOULD be used to indicate independent
   characteristics of a node.  The TLV SHOULD be considered as 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).

   As mentioned earlier, to avoid incomplete or inconsistent
   interpretations of the per-node administrative tags the same tag
   value MUST NOT be advertised by a router in Router Capabilities of
   different scopes.  Implementations MUST NOT allow configuring the
   same tag value across domain-wide and 'level-wide' scopes.  The same
   tag value MAY be allowed to be configured and advertised under
   'level-wide' scope for all levels.  A IS-IS Area Border Routers (ABR)
   participating in both levels 1 and 2 MAY advertise the same tag value
   in the level-specific Router Capability TLVs with 'level-wide' scope
   (S-bit reset to 0) generated by it.  But the same tag value MUST not
   be advertised in any of level 1 or level 2 Router-Capability TLV with
   'global' scope (S-bit set to 1).

   The per-node administrative tags are not meant to be extended by the
   future IS-IS standards.  The new IS-IS extensions MUST NOT require
   use of per-node administrative tags or define well-known tag values.
   Per-node administrative tags are for generic use and do not require
   IANA registry.  The future IS-IS extensions requiring well known
   values MAY use new Capability sub-TLVs tailored to the needs of the
   feature, as defined in [RFC4971].

   Being part of the Router Capability TLV, the per-node administrative
   tag sub-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 IS-IS domain) or
   reachability of routes.

5.  Applications

   This section lists several examples of how implementations might use
   the Per-node administrative tags.  These examples are given only to
   demonstrate generic usefulness of the router tagging mechanism.

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   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.  Auto-discovery of Services

       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.  Policy-based Fast-Reroute

       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

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           such a policy via configuration of the router computing LFA
           is cumbersome and error prone.

           With the Per-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)  Optimizing LFA calculations

           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.

   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 per-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 Per-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

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       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.

                   /                \
                  /                  \
                 /                    \
    +------+   +----+    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

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       requirements using cost, link color or explicit path
       configurations.  The per-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 per-node administrative

   5.  Policy-based Explicit Routing

       Partially meshed network provides multiple paths between any two
       nodes in the network.  In a data center 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, fiber 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

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                                  |                    |
                                  |    +----------+    |
                                  |    |          |    |
                                  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: - 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 nodes with per-node
       administrative tag, tag A can be configured on all A nodes,
       (similarly I, R, T), and then configure this single CSPF policy
       on all A nodes to avoid I nodes for path calculation.

6.  Security Considerations

   This document does not introduce any further security issues other
   than those discussed in [ISO10589] and [RFC1195].

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7.  IANA Considerations

   IANA maintains the registry for the Router Capability sub-TLVs.  IS-
   IS Administrative Tags will require new type code for the following
   new sub-TLV defined in this document.

   i) Per-Node-Admin-Tag Sub-TLV, Type: TBD

8.  Acknowledgments

   Many thanks to Les Ginsberg, Dhruv Dhody, Uma Chunduri for useful
   inputs.  Thanks to Chris Bowers for providing useful inputs to remove
   ambiguity related to tag-ordering.

9.  References

9.1.  Normative References

              "Intermediate system to Intermediate system intra-domain
              routeing information exchange protocol for use in
              conjunction with the protocol for providing the
              connectionless-mode Network Service (ISO 8473), ISO/IEC
              10589:2002, Second Edition.", Nov 2002.

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

9.2.  Informative References

              Litkowski, S., Decraene, B., Filsfils, C., Raza, K.,
              Horneffer, M., and p., "Operational
              management of Loop Free Alternates", draft-ietf-rtgwg-lfa-
              manageability-04 (work in progress), August 2014.

              Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
              So, "Remote LFA FRR", draft-ietf-rtgwg-remote-lfa-09 (work
              in progress), December 2014.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
              dual environments", RFC 1195, December 1990.

   [RFC4971]  Vasseur, JP., Shen, N., and R. Aggarwal, "Intermediate
              System to Intermediate System (IS-IS) Extensions for
              Advertising Router Information", RFC 4971, July 2007.

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   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120, February 2008.

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

   [RFC5305]  Li, T. and H. Smit, "IS-IS Extensions for Traffic
              Engineering", RFC 5305, October 2008.

Authors' Addresses

   Pushpasis Sarkar (editor)
   Juniper Networks, Inc.
   Electra, Exora Business Park
   Bangalore, KA  560103


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


   Shraddha Hegde
   Juniper Networks, Inc.
   Electra, Exora Business Park
   Bangalore, KA  560103


   Stephane Litkowski


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   Bruno Decraene


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


   Ebben Aries


   Rafael Rodriguez


   Harish Raghuveer


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