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SPRING Working Group                                           C. Bowers
Internet-Draft                                                 P. Sarkar
Intended status: Standards Track                              H. Gredler
Expires: April 7, 2016                                  Juniper Networks
                                                             U. Chunduri
                                                            Ericsson Inc
                                                         October 5, 2015


        Advertising Per-Topology and Per-Algorithm Label Blocks
         draft-bowers-spring-adv-per-algorithm-label-blocks-02

Abstract

   When segment routing is used in a network that is controlled by a
   link state IGP (such as ISIS or OSPF), each node in the network can
   be assigned one or more index numbers, known as "node-SIDs".  The
   node-SIDs are unique within the network, and are known to all the
   nodes in the network.  If an ingress node has a data packet to be
   sent to an egress node, the ingress node may select a node-SID
   corresponding to the egress node, and "translate" that node-SID to an
   MPLS label.  The MPLS label represents a particular path to the
   egress node; the path is determined by applying a routing algorithm
   to a particular view of the network topology and a particular set of
   metric assignments to the links of that topology.  The packet can
   then be forwarded by pushing the label on the packet's label stack
   and transmitting the packet to the next hop on the corresponding path
   to the egress node.  This document compares two different procedures
   for translating a node-SID to the MPLS label that represents a path
   chosen by a particular algorithm operating on a particular topology.
   It also specifies the ISIS extensions needed to support one of the
   procedures (known as the "per-topology/per-algorithm label block"
   procedure).

Status of This Memo

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



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   This Internet-Draft will expire on April 7, 2016.

Copyright Notice

   Copyright (c) 2015 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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   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Destination-based forwarding using other algorithms . . . . .   3
   3.  Multi-topology routing  . . . . . . . . . . . . . . . . . . .   5
   4.  Example: Adding Nodes when Multiple Algorithms are In Use . .   6
   5.  Proposed configured offset mapping method for assigning per-
       topology/per-algorithm node-SIDs when using Option 1  . . . .   7
   6.  Flexibility to create easy-to-interpret label values  . . . .   9
   7.  Robustness against misconfiguration . . . . . . . . . . . . .  10
   8.  ISIS extensions to encode per-topology/per-algorithm label
       blocks  . . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   9.  OSPF extensions to encode per-topology/per-algorithm label
       blocks  . . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   10. A note on algorithms and topologies . . . . . . . . . . . . .  12
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   12. Management Considerations . . . . . . . . . . . . . . . . . .  12
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  13
   14. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   15. References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     15.1.  Normative References . . . . . . . . . . . . . . . . . .  13
     15.2.  Informative References . . . . . . . . . . . . . . . . .  13
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   [I-D.ietf-spring-segment-routing] describes the segment routing
   architecture.  When segment routing is used in a network that is
   controlled by a link state IGP (such as ISIS or OSPF), each node in
   the network can be assigned one or more index numbers, known as
   "node-SIDs".  The node-SIDs are unique within the network, and are



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   known to all the nodes in the network.  If an ingress node has a data
   packet to be sent to an egress node, the ingress node may select a
   node-SID corresponding to the egress node, and "translate" that node-
   SID to an MPLS label.  The MPLS label represents a particular path to
   the egress node; the path is determined by applying a routing
   algorithm to a particular view of the network topology and a
   particular set of metric assignments to the links of that topology.
   The packet can then be forwarded by pushing the label on the packet's
   label stack and transmitting the packet to the next hop on the
   corresponding path to the egress node.

   When a particular network is using a single routing algorithm and a
   single topology, the procedure for translating a node-SID to an MPLS
   label is straightforward.  Figure 1 shows the formula used to
   translate a node-SID into an MPLS label when the paths are selected
   by using the default routing algorithm (Dijkstra's shortest path
   first algorithm) and the default topology.

              SPF_Label(X,D) = Label_Block(X) + Node_Index(D)

              D is the destination node
              X is the next-hop along the path to D


         Figure 1: Translating Node-SID to Label: The Default Case

   As a simple example, when the computing node (Y) needs to forward a
   packet ultimately destined for node D, Y first determines the
   shortest path next-hop node to reach D, which in this example is X.
   Y then adds the Node_Index value advertised by D to the Label_Block
   value advertised by X to determine the label value to apply to the
   packet before sending it to X.

2.  Destination-based forwarding using other algorithms

   Figure 2 shows two options for generalizing the above formula, to
   determine locally significant labels corresponding to forwarding
   next-hops computed using other algorithms.













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                Option 1a: per-algorithm node index
                Label(X,D,A) = Label_Block(X) + Node_Index(D,A)

                Option 2a: per-algorithm label block
                Label(X,D,A) = Label_Block(X,A) + Node_Index(D)

            A is the algorithm for computing destination-based
              forwarding next-hops
            D is the destination node
            X is the next hop along the path to D that is
              determined by algorithm A



    Figure 2: Translating Node-SID to Label: Algorithm-Specific Options

   Suppose router Y needs to forward a packet to node D along a path
   computed by algorithm A.  Using either option, Y determines the next-
   hop computed by algorithm A to reach D, which in this example is X.
   Y then needs to figure out the correct label to apply to the packet
   so that so that X will also understand that the packet is to be sent
   to node D along a path computed by algorithm A.  The two options
   shown in Figure 2 differ in how Y determines that label value.

   In Option 1a each node advertises a single label block, but
   advertises a different node index for each algorithm.  Y determines
   the label value of local significance to X to reach D using algorithm
   A by adding the Node_Index advertised by node D for algorithm A to
   the Label_Block advertised by node X.  We refer to this as the per-
   algorithm node index option.

   In Option 2a each node advertises only a single node index, but
   advertises a different label block for each algorithm.  Y determines
   the label value of local significance to X to reach D using algorithm
   A by adding the Node_Index advertised by node D to the Label_Block
   for algorithm A advertised by node X.  We refer to this as the per-
   algorithm label block option.

   The extensions currently defined in
   [I-D.ietf-isis-segment-routing-extensions] and
   [I-D.ietf-ospf-segment-routing-extensions] specify encodings for
   Option 1a, the per-algorithm node index option.  This draft proposes
   extensions that can be used to support option 2a, the per-algorithm
   label block option.  However, before discussing those extensions, we
   generalize the formula in Figure 2 further to take into account
   multiple topologies.  This will allow us to define extensions that
   address the use of both multiple topologies and multiple algorithms.




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3.  Multi-topology routing

   The IGP extensions to support multi-topology routing are defined in
   [RFC4915] for OSPF and [RFC5120] for IS-IS.  Figure 3 further
   generalizes the formulas above to take into account multiple
   topologies.  It shows two options for determining locally significant
   labels for different topologies and algorithms.


              Option 1: per-topology / per-algorithm node index
              Label(X,D,T,A) = Label_Block(X) + Node_Index(D,T,A)

              Option 2: per-topology / per-algorithm label block
              Label(X,D,T,A) = Label_Block(X,T,A) + Node_Index(D)

          T is the topology
          A is the algorithm for computing destination-based
            forwarding next-hops
          D is the destination node
          X is the next hop along the path to D that is
            determined by algorithm A for topology T



     Figure 3: Translating Node-SID to Label: Topology and Algorithm-
                             Specific Options

   In Option 1 each node advertises a single label block, but advertises
   a different node index for each combination of topology and algorithm
   used.  In order for Y to determine the label value that tells X to
   reach D via the path chosen by algorithm A for topology T, Y adds the
   Node_Index advertised by node D for topology T and algorithm A to the
   Label_Block advertised by node X.  We refer to this as the per-
   topology/per-algorithm node index option.

   In Option 2 each node advertises a single node index and a unique
   label block along for each combination of topology and algorithm
   used.  In order for Y to determine the label value that tells X to
   reach D via the path chosen by algorithm A for topology T, Y adds the
   Node_Index advertised by node D to the Label_Block advertised by node
   X for topology T and algorithm A.  We refer to this as the per-
   topology/per-algorithm label block option.

   Note that the formulas in Figure 3 can of course be applied even if
   there is only one algorithm and/or only one topology.  For example,
   if the use case uses multiple topologies but only uses the default
   shortest path algorithm (algorithm=0), then option 2 can be written
   as: Label(X,D,T,0) = Label_Block(X,T,0) + Node_Index(D), which is



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   independent of algorithm.  Similarly, if the use case only uses the
   default topology (topology=0) but uses different algorithms, then
   option 2 can be written as Label(X,D,0,A) = Label_Block(X,0,A) +
   Node_Index(D).

4.  Example: Adding Nodes when Multiple Algorithms are In Use

   The following example illustrates the practical difficulties
   associated with using the per-topology/per-algorithm node index
   option alone (option 1 in Figure 3 ).  This example is intentionally
   simplified to illustrate the need for some kind of convention to
   manage the assignment of the unique node index values required by
   option 1, even in a simple scenario.  The sections below discuss a
   more complex example, as well as a specific proposal to manage the
   assignment of unique node index values.  This simplified example
   assumes that the operator does not use multi-topology routing, i.e.
   that the default topology is used.

   Suppose an operator has a network with 100 nodes, which we will refer
   to as R0-R99.  The operator assigns the unique node index values 0-99
   to those nodes for algorithm=0, in order to accomplish shortest path
   routing based on IGP metrics with SR labels.  Each node will need to
   advertise a label block of size=100.

   Assume that at some future point in time, the IETF defines
   algorithm=2 to mean shortest path routing based on latency, and
   vendors implement this.  (See section Section 10 for more discussion
   of this example.)  Suppose that the operator wants to use latency-
   based SPF routes for some traffic and metric-based SPF routes for
   other traffic.  The operator will need to define a new set of unique
   node index values for algorithm=2.  A reasonable choice would be to
   assign node index values of 100-199 to R0-R99 for algorithm=2.  Each
   node will now need to advertise a label block of size=200.  So far
   the need for per-algorithm node index values is an annoyance, but not
   too difficult to deal with.

   Now assume that the operator needs to add 10 new nodes to the SR
   domain, specifically nodes R100-R109.  Each node will now need to
   advertise a label block of size=220.  The main issue is deciding how
   to assign per-algorithm node index for the 10 new nodes.  One option
   is to redo the node index numbering scheme so that R0-R109 have node
   index values 0-109 for algorithm=0 and node index values 110-229 for
   algorithm=2.  However, this requires renumbering existing nodes.  The
   other option is to avoid renumbering of nodes by assigning nodes
   R100-R109 node index values 200-209 for algorithm=0 and node index
   values 210-219 for algorithm=1.  Each of these approaches has
   drawbacks.  The first requires renumbering existing nodes, while the




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   second is difficult to maintain since there is no obvious
   relationship between the node index values for different algorithms.

   In order to reduce the complexity associated with option 1 in this
   simple example, a certain amount of pre-planning together with some
   convention for assigning node index values to algorithms or
   topologies would be useful.  Specific proposals for managing unique
   node index values when using option 1 are discussed below.  First
   however, we illustrate the advantages of option 2 for this simple
   example.

   The use of per-algorithm label blocks avoids the problems associated
   with assigning and maintaining unique node index values for each
   forwarding algorithm.

   When the SR domain is initially deployed, R0-R99 can be assigned node
   index values 0-99, as one would expect.  When support for algorithm=1
   gets added, the operator does not need to assign and configure any
   new node index values.  Instead, the routers automate the process by
   advertising different label blocks for each forwarding algorithm.

   When another 10 nodes are added to the SR domain, R100-R109 get
   assigned node index values 100-109 as one would expect.  And the
   router advertises a label block of size=110 for each algorithm, as
   one would expect.  Adding new nodes in the presence of multiple
   forwarding algorithms is simplified significantly with the use of
   per-algorithm label blocks.

5.  Proposed configured offset mapping method for assigning per-
    topology/per-algorithm node-SIDs when using Option 1

   If a network operator uses option 1, which requires the assignment of
   unique per-topology/per-algorithm node-SIDs, then it is clear that a
   common convention or methodology would be useful to help assign and
   maintain those unique node-SIDs.  The methodology described in this
   section represents the authors' understanding of a proposal to manage
   assignment of node-SIDs when using option 1, as discussed on the
   SPRING mailing list.

   The proposed method for managing the assignment of unique node index
   values for each topology/algorithm pair involves configuring a
   mapping from each topology/algorithm pair to an offset value.  This
   offset mapping would need to be configured identically on every
   router in the network.  Figure 4 shows the formula for a router Y to
   compute its own unique node index value for each topology/algorithm
   pair.  Y would then treat those computed node index values as if they
   were directly configured via CLI or via Netconf/Yang, advertising




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   them into the IGP and installing the appropriate label operations in
   the FIB.


       Node_Index(Y,T,A) = Configured_Offset(T,A) + Base_Node_Index(Y)

     Y is the computing router
     T is the topology
     A is the algorithm


       Figure 4: Proposed configured offset mapping method to manage
     assignment of unique per-topology/per-algorithm node index values
                            when using Option 1

   We illustrate the operation of the configured offset mapping method
   with a specific example.  In this example, the operator has a network
   with 500 nodes, and wants to support four different topologies using
   different algorithms.  The default topology (topology=0) needs to
   support algorithms 0, 4, and 5.  Topology 2 and topology 6 need to
   support algorithm 0, while topology 7 needs to support algorithm 2.
   There are a total of six topology/algorithm pairs.  In order to avoid
   renumbering the network in the event of unanticipated increases in
   the number of nodes or the number of topology/algorithm pairs, the
   operator sizes the label offsets and overall label block size to
   accomodate 1000 nodes and 12 topology/algorithm pairs.

   Figure 5 shows the configuration data required on each of the 500
   routers using option 1 together with the configured offset mapping
   method to manage node index assignment.

                    base_node_index=123
                    label_block_size=12000
                    topology=0 algorithm=0 offset=0
                    topology=0 algorithm=4 offset=1000
                    topology=0 algorithm=5 offset=2000
                    topology=2 algorithm=0 offset=3000
                    topology=6 algorithm=0 offset=4000
                    topology=7 algorithm=2 offset=5000

           Figure 5: Required configuration data using option 1

   The base_node_index value is the unique node index for a given node,
   and will thus be different for each node.  The other values define
   the overall size of the label block and associate topology algorithm
   pairs with an offset value.  This set of values must be configured
   identically across all routers in the network in order avoid
   advertising duplicate node index values.  Advertisement of duplicate



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   node index values would disrupt forwarding.  The configuration above
   would result in R123 computing node index values of 123, 1123, 2123,
   3123, 4123, and 5123 for the corresponding topology/algorithm pairs.

   For comparison, Figure 6 shows the configuration data required on
   each of the 500 routers using option 2.  Since the per-topology/per-
   algorithm label blocks are advertised independently by each node,
   option 2 requires no additional configuration beyond what is required
   for default topology shortest path forwarding (topology=0,
   algorithm=0).

                           node_index=123
                           label_block_size=1000

           Figure 6: Required configuration data using option 2

6.  Flexibility to create easy-to-interpret label values

   For some applications, it may be desirable to arrange things so that
   the meaning of label values used for forwarding can be readily
   understood by people trouble-shooting the network.  When using the
   configured offset mapping method with option 1, if one configures a
   meaningful base value for the single label block, then the configured
   offset values can also be chosen to provide understandable label
   values.  In the example above with 500 nodes and 6 topology/algorithm
   pairs, if the single logically advertised label block consists of a
   single numerically contiguous label block from 20000 through 31999
   across all routers in the network, then the label values
   corresponding to forwarding to R123 using different topology/
   algorithm pairs will be meaningful to a people.  They will be 20123,
   21123, 22123, 23123, 24123, and 25123 for the corresponding topology/
   algorithm pairs, so an operator who remembers the mapping between
   topology/algorithm pair and offset can tell that 25123 is the label
   corresponding to topology=7, algorithm=2, node=123.

   When using option 2 (per-topology/per-algorithm label blocks) and
   requiring that the topology, algorithm, and node associated with a
   label value be easy to interpret, each topology/algorithm pair needs
   to have an associated label_block_base configured on every router.
   Figure 7 show an example configuration of a mapping from topology/
   algorithm pairs to label_block_base values.










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              node_index=123
              label_block_size=1000
              topology=0 algorithm=0 label_block_base=100000
              topology=0 algorithm=4 label_block_base=104000
              topology=0 algorithm=5 label_block_base=105000
              topology=2 algorithm=0 label_block_base=120000
              topology=6 algorithm=0 label_block_base=160000
              topology=7 algorithm=2 label_block_base=172000

     Figure 7: Configuration data for 500 node example with option 2,

   Note in this example that we have taken advantage of the additional
   flexibility of option 2 to create label values that are more readable
   than from option 1.  In this example, a first digit of "1" indicates
   that this is a SPRING node label.  The second and third digits are
   readable as the topology and algorithm, while the last three digits
   encode the node number.  So 172123 would indicate the node label for
   topology=7, algorithm=2, node=123.

   In the above example, we have illustrated the flexibility of option 2
   to create more readable labels in a hypothetical network with no
   constraints on label space.  However, it is likely that in a multi-
   vendor network with multiple generations of hardware supporting
   different MPLS applications there will exist constraints regarding
   the location and size of contiguous label blocks for use by SPRING.
   This would impose constraints on one's ability to construct readable
   label values using option 1 with the configured offset mapping.
   Option 2 provides more flexibility to construct easy-to-interpret
   label values in such a network.

7.  Robustness against misconfiguration

   Option 2 is much more robust against misconfiguration than is option
   1.  This is true both in scenarios that require easy-to-interpret
   label values and in scenarios that do not.

   In the simple case where the application does not require easy-to-
   interpret label values, option 2 has clear advantages over option 1
   in terms of robustness again misconfiguration.  Option 1 requires
   identical offset mapping configurations on all routers for proper
   forwarding.  Option 2 requires no configuration, so there is nothing
   to misconfigure.

   In scenarios requiring easy-to-interpret label values, where option 2
   requires a label_block_base mapping configuration, option 2 is still
   more robust against misconfiguration than option 1.  Misconfiguration
   of the label_block_base mapping in option 2 does not affect
   forwarding.  The explicit advertisement of the per-topology/per-



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   algorithm label blocks ensures that forwarding will continue to work
   properly.

8.  ISIS extensions to encode per-topology/per-algorithm label blocks

   Below is a concrete proposal for encoding per-topology/per-algorithm
   label blocks in ISIS compatible with the encodings in
   [I-D.ietf-isis-segment-routing-extensions].

   The newly-defined Topology-Algorithm-Label-Block sub-TLV is shown in
   Figure 8.  It is carried in the IS-IS Router Capability TLV-242.  It
   contains a 12-bit MT-ID field as well as an 8-bit Algorithm field
   which associates the SRGB Descriptor entries carried in the sub-TLV
   with a particular topology and algorithm.  Otherwise, the structure
   and interpretation of the Topology-Algorithm-Label-Block sub-TLV is
   identical to that of the SR-Capabilities sub-TLV defined in section
   3.1 of [I-D.ietf-isis-segment-routing-extensions].


       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    |R|R|R|R|         MT-ID         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Algorithm   |     Flags     |                One or more    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |      SRGB Descriptor entries (variable)                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


             Figure 8: Topology-Algorithm-Label-Block sub-TLV

   A single network must use either option 1 or option 2 for all
   routers.  Mixed mode operation is not supported.  When the Topology-
   Algorithm-Label-Block sub-TLV is present with a given pair of
   topology and algorithm values, routers MUST determine the label
   values associated with that topology/algorithm pair using the per-
   topology/per-algorithm label block method and the concatenated label
   block carried by the Topology-Algorithm-Label-Block sub-TLV.  The
   node indices used in this calculation are those carried in Node-SID
   advertisements with algorithm value=0 in TLV-135(IPv4) or TLV-
   236(IPv6).

   The Topology-Algorithm-Label-Block sub-TLV MUST NOT be advertised
   with both MT-ID=0 and Algorithm value=0.  In this way, the
   concatenated label block used to compute the label values for the
   default topology and algorithm=0 can only be carried by the SR
   Capabilities sub-TLV.



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   When using the Topology-Algorithm-Label-Block sub-TLV in a network,
   nodes SHOULD only advertise a node index value corresponding to
   algorithm=0 in Node-SID advertisements in TLV-135(IPv4) and/or TLV-
   236(IPv6).  Node index values (with algorithm=0 or any other value)
   SHOULD NOT be advertised in TLV-235(MT-IPv4) and TLV-237(MT-IPv6).
   If a node originates the Topology-Algorithm-Label-Block sub-TLV
   (meaning that it supports option 2), then it MUST ignore the receipt
   of node indices for non-zero algorithms in TLV-135 and TLV-236 and
   any node index values in TLV-235 and TLV-237.

9.  OSPF extensions to encode per-topology/per-algorithm label blocks

   OSPF extensions to encode per-topology/per-algorithm label blocks
   will be provided in a future version of this draft.

10.  A note on algorithms and topologies

   The example given in Section 4 supposes that at some point in the
   future the IETF defines algorithm=2 to mean shortest path routing
   based on latency.  This simple example was chosen since it is easy to
   understand.  However, the same result could also have been achieved
   by defining a second topology which uses latency as the metric for
   that topology, and running the default SPF algorithm on that second
   topology.

   In general, when using other algorithms for computing next-hops for
   destination-based forwarding, it is not possible to achieve the same
   results by simply defining a new topology with modified metrics and
   running the default SPF algorithm.  An example of such an algorithm
   is that used to compute Maximally Redundant Trees (MRTs), as defined
   in [I-D.ietf-rtgwg-mrt-frr-algorithm].

11.  IANA Considerations

   This document requests the following registration in the "sub-TLVs
   for TLV 242" registry.

      Value: TBA (suggested value 20)

      Description: Topology-Algorithm-Label-Block

      Reference: This document (Section 8)

12.  Management Considerations

   This document proposes the use of per-topology/per-algorithm label
   blocks (option 2) to support destination-based forwarding along next-
   hops computed using different algorithms for different topologies.



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   The automated advertisement of per-topology/per-algorithm label
   blocks significantly simplifies network management compared to
   configuration and maintenance of unique per-topology/per-algorithm
   node indices.

13.  Security Considerations

   TBD

14.  Acknowledgements

   The authors thank John Scudder and Eric Rosen for their helpful
   review of this document and suggestions.

15.  References

15.1.  Normative References

   [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>.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <http://www.rfc-editor.org/info/rfc5120>.

15.2.  Informative References

   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
              Litkowski, S., Decraene, B., and J. Tantsura, "IS-IS
              Extensions for Segment Routing", draft-ietf-isis-segment-
              routing-extensions-05 (work in progress), June 2015.

   [I-D.ietf-ospf-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions-05 (work in progress), June 2015.

   [I-D.ietf-rtgwg-mrt-frr-algorithm]
              Envedi, G., Csaszar, A., Atlas, A., Bowers, C., and A.
              Gopalan, "Algorithms for computing Maximally Redundant
              Trees for IP/LDP Fast- Reroute", draft-ietf-rtgwg-mrt-frr-
              algorithm-05 (work in progress), July 2015.



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   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
              and r. rjs@rob.sh, "Segment Routing Architecture", draft-
              ietf-spring-segment-routing-04 (work in progress), July
              2015.

Authors' Addresses

   Chris Bowers
   Juniper Networks
   1194 N. Mathilda Ave.
   Sunnyvale, CA  94089
   US

   Email: cbowers@juniper.net


   Pushpasis Sarkar
   Juniper Networks
   Embassy Business Park
   Bangalore, KA  560093
   India

   Email: psarkar@juniper.net


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

   Email: hannes@juniper.net


   Uma Chunduri
   Ericsson Inc
   300 Holger Way
   San Jose, CA  95134
   US

   Email: uma.chunduri@ericsson.com@









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