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Versions: 00 01 02 03 04 05 06 07 draft-ietf-lsr-isis-spine-leaf-ext

Networking Working Group                                         N. Shen
Internet-Draft                                          S. Thyamagundalu
Intended status: Standards Track                           Cisco Systems
Expires: October 27, 2016                                 April 25, 2016


                 IS-IS Routing for Spine-Leaf Topology
                   draft-shen-isis-spine-leaf-ext-01

Abstract

   This document describes a mechanism for routers and switches in
   Spine-Leaf type topology to have non-reciprocal Intermediate System
   to Intermediate System (IS-IS) routing relationships between the
   leafs and spines.  The leaf nodes do not need to have the topology
   information of other nodes and exact prefixes in the network.  This
   extension also has application in the Internet of Things (IoT).

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."

   This Internet-Draft will expire on October 27, 2016.

Copyright Notice

   Copyright (c) 2016 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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   publication of this document.  Please review these documents
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   include Simplified BSD License text as described in Section 4.e of




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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Motivations . . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  Spine-Leaf (SL) Extension . . . . . . . . . . . . . . . . . .   4
     3.1.  Topology Example  . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Applicability Statement . . . . . . . . . . . . . . . . .   4
     3.3.  Extension Encoding  . . . . . . . . . . . . . . . . . . .   5
     3.4.  Mechanism . . . . . . . . . . . . . . . . . . . . . . . .   6
     3.5.  Implementation and Operation  . . . . . . . . . . . . . .   7
       3.5.1.  CSNP PDU  . . . . . . . . . . . . . . . . . . . . . .   7
       3.5.2.  Leaf to Leaf connection . . . . . . . . . . . . . . .   8
       3.5.3.  Overload Bit  . . . . . . . . . . . . . . . . . . . .   8
       3.5.4.  Spine Node Hostname . . . . . . . . . . . . . . . . .   8
       3.5.5.  Default Route Metric  . . . . . . . . . . . . . . . .   8
       3.5.6.  Other End-to-End Services . . . . . . . . . . . . . .   9
       3.5.7.  Address Family and Topology . . . . . . . . . . . . .   9
       3.5.8.  Migration . . . . . . . . . . . . . . . . . . . . . .   9
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   6.  Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .  10
   7.  Document Change Log . . . . . . . . . . . . . . . . . . . . .  10
     7.1.  Changes to draft-shen-isis-spine-leaf-ext-01.txt  . . . .  10
     7.2.  Changes to draft-shen-isis-spine-leaf-ext-00.txt  . . . .  10
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The IS-IS routing protocol defined by [ISO10589] has been widely
   deployed in provider networks, data centers and enterprise campus
   environments.  In the data center and enterprise switching networks,
   Spine-Leaf topology is commonly used.  This document describes the
   mechanism where IS-IS routing can be optimized to take the advantage
   of the unique Spine-Leaf topology.

   When the network is in Spine-Leaf topology, normally a leaf node
   connects to a number of spine nodes.  Data traffic going from one
   leaf node to another leaf node needs to pass through one of the spine
   nodes.  Also, the decision to choose one of the spine nodes is
   usually part of the equal cost multi-path (ECMP) load sharing.  The
   spine nodes can be considered as gateway devices to reach the



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   destination leaf nodes.  In this type of topologies, the spine nodes
   have to know the topology and routing information of the entire
   network, but the leaf nodes only need to know how to reach the
   gateway devices which are the spine nodes they are uplinked to.

   This document describes the IS-IS Spine-Leaf extension that allows
   the spine nodes to have all the topology and routing information,
   while keeping the leaf nodes free of topology information other than
   the default gateway routing information.  The leaf nodes do not even
   need to run their Shortest Path First (SPF) since there is no network
   topology to run for.

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Motivations

   o  The leaf nodes in Spine-Leaf topology do not benefit much to have
      the complete topology and routing information of the entire domain
      while the forwarding actions are only to use ECMP with spine nodes
      as nexthops.

   o  The spine nodes in Spine-Leaf topology are richly connected to
      leaf nodes, and they need to flood every Link State PDUs (LSPs) to
      all the leaf nodes.  It saves the spine nodes' CPU and link
      bandwidth resources if the flooding is blocked to those leaf
      nodes.

   o  During the time a spine node has a network problem, every leaf
      node connected to it will generate its LSP update to report the
      problem to all the other spine nodes, and those spine nodes will
      further flood them to all the leaf nodes, causing a O(n^2)
      flooding storm unnecessarily since every leaf node already knows
      that spine node having problem.

   o  Small devices and appliances of Internet of Things (IoT) can be
      considered as leafs in the routing topology sense.  They have CPU
      and memory constrains in design, and those IoT devices do not have
      to know the exact network topology and prefixes as long as there
      are ways to reach the cloud servers or other devices and they want
      to be part of the dynamic routing.







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3.  Spine-Leaf (SL) Extension

3.1.  Topology Example

             +--------+    +--------+             +--------+
             |        |    |        |             |        |
             | Spine1 +----+ Spine2 +- ......... -+ SpineN |
             |        |    |        |             |        |
             +-+-+-+-++    ++-+-+-+-+             +-+-+-+-++
        +------+ | | |      | | | |                 | | | |
        |  +-----|-|-|------+ | | |                 | | | |
        |  |  +--|-|-|--------+-|-|-----------------+ | | |
        |  |  |  | | |    +---+ | |                   | | |
        |  |  |  | | |    |  +--|-|-------------------+ | |
        |  |  |  | | |    |  |  | |              +------+ +----+
        |  |  |  | | |    |  |  | +--------------|----------+  |
        |  |  |  | | |    |  |  +-------------+  |          |  |
        |  |  |  | | +----|--|----------------|--|--------+ |  |
        |  |  |  | +------|--|--------------+ |  |        | |  |
        |  |  |  +------+ |  |              | |  |        | |  |
       ++--+--++      +-+-+--++            ++-+--+-+     ++-+--+-+
       | Leaf1 +~~~~~~+ Leaf2 |  ........  | LeafX |     | LeafY |
       +-------+      +-------+            +-------+     +-------+

                      Figure 1: A Spine-Leaf Topology

3.2.  Applicability Statement

   This extension assumes the network is a basic Spine-Leaf topology,
   and it will not work in an arbitrary network setup.  The spine nodes
   can be viewed as the aggregation layer of the network, and the leaf
   nodes as the access layer of the network.  The leaf nodes use load
   sharing algorithm with spine nodes as nexthops in routing and
   forwarding.

   This extension assumes the spine nodes are inter-connected.  Spine
   nodes exchanges normal IS-IS topology and routing information among
   themselves.  This extension does not apply in the case where spine
   nodes only have links to leaf nodes but not to themselves.

   Although the example diagram in Figure 1 shows a fully meshed Spine-
   Leaf topology, but this extension also works in the case where they
   are partially meshed.  For instance, the leaf1 through leaf10 are
   fully meshed with spine1 through spine5; and leaf11 through leaf20
   are fully meshed with spine4 through spine8, and all the spines are
   inter-connected in a redundant fashion.





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   This extension also works with the topology with more than the
   typical two layers of spine and leaf.  For instance, in example
   diagram Figure 1, there can be another Core layer of routers/switches
   on top of the aggregation layer.  From an IS-IS routing point of
   view, the Core nodes are not affected by this extension and will have
   the complete topology and routing information just like the spine
   nodes.  To make the network even more scalable, the Core layer can be
   run at the level-2 IS-IS domain while the Spine layer and the Leaf
   layer staying at the level-1 IS-IS domain.

   This extension also supports the leaf nodes having local connections
   to other leaf nodes, in the example diagram Figure 1 there is a
   connection between 'Leaf1' node and 'Leaf2' node, and an external
   host can be dual homed into both of the leaf nodes.

   This extension assumes the link between the spine and leaf nodes are
   point-to-point, or point-to-point over LAN [RFC5309].  The links
   connecting the spine nodes, or the links between the leaf nodes can
   be any type.

3.3.  Extension Encoding

   This extension introduces one TLV for IS-IS Hello (IIH) PDU and it is
   used by both spine and leaf nodes in the Spine-Leaf mechanism.

       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    |            SL Flag            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      Default Route Metric                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         .. Optional Sub-TLVs
       +-+-+-+-+-+-+-+-+-....

   The fields of this TLV are defined as follows:



      Type:    TBD. 8 bits value, suggested value 150.

      Length:  Variable. 8 bits value.  The mandatory part is 6 octets.

      SL Flag: 16 bits value field of following flags:







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      0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |        Reserved         |B|R|L|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



         L bit (0x01):  Only leaf node sets this bit.  If the L bit is
                  set in the SL flag, the node indicates it is in 'Leaf-
                  Mode'.

         R bit (0x02):  Only Spine node sets this bit.  If the R bit is
                  set, the node indicates to the leaf neighbor that it
                  can be used as the default route gateway.

         B bit (0x04):  Only leaf node sets this bit on Leaf-Leaf link,
                  in additional to the 'L' bit setting.  If the B bit is
                  set, the node indicates to its leaf neighbor that it
                  can be used as the backup default route gateway.  It
                  will also sets high 'Default Route Metric' value.

      Default Route Metric:  Normal only spine nodes set this default
               route metric.  This default route metric is for all the
               address families and IS-IS topologies.  A leaf node
               SHOULD add this metric on top of the outbound interface
               IS-IS metric towards the spine node when installing the
               default route.  In the case where the leaf node sets the
               'B' bit in SL-flag on the Leaf-Leaf link, this 'Default
               Route Metric' SHOULD be set to very high for the neighbor
               leaf node to use it as the backup gateway.

      Optional Sub-TLV:  Not defined in this document, for future
               extension on SL.

3.4.  Mechanism

   Each leaf node is provisioned by network operators as in IS-IS 'Leaf-
   Mode'.  A spine node does not need explicit configuration.  A leaf
   node inserts the Spine-Leaf TLV and sets the 'L' bit in the SL flag
   field when sending out its IIH PDU over all its links.

   The spine node when receiving the IIH with the SL TLV and 'L' bit
   set, it labels the point-to-point interface and adjacency to be a
   'Leaf-Peer'.  When the spine node sending out IIH PDU to the 'Leaf-
   Peer', it will also insert the Spine-Leaf TLV and set the 'R' bit in
   the SL flag field.  This 'R' bit indicates to the 'Leaf-Peer'
   neighbor that the spine node can be used as a default routing
   nexthop.



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   There is no change to the IS-IS adjacency bring-up mechanism for the
   point-to-point interface.

   For the spine node with 'Leaf-Peer' adjacencies, the IS-IS LSP
   flooding is blocked to the 'Leaf-Peer' interface, except for the LSP
   PDUs in which the IS-IS System-ID matches the System-ID of the 'Leaf-
   Peer' adjacency.  This exception is needed since when the leaf node
   reboots, the spine node needs to forward to the leaf node its
   previous generation of LSP.  No other LSP PDU needs to be flooded
   over this 'Leaf-Peer' interface.

   The leaf node will perform IS-IS LSP flooding as normal over all of
   its IS-IS adjacencies, this means the leaf node will flood its own
   LSPs over to spine nodes since those are all the LSPs in its LSP
   database.

   The spine node will receive all the LSP PDUs in the network,
   including all the spine nodes and leaf nodes.  It will perform
   Shortest Path First (SPF) as normal IS-IS node does.  There is no
   change to the route calculation and forwarding on the spine nodes.

   But the leaf node does not have any LSP in the network except for its
   own, and there is no need to perform SPF algorithm on the system.  It
   only needs to download the default route with the nexthops of those
   'Spine-Peer' which has the 'R' bit set in the Spine-Leaf TLV in IIH
   PDUs.  IS-IS can perform equal cost or unequal cost load sharing
   while using the spine nodes as nexthops.  The aggregated metric of
   the outbound interface and the 'Default Route Metric' in the Spine-
   Leaf TLV can be used for this purpose.

   In summary, this extension requires leaf node to insert Spine-Leaf
   TLV in IIH, and set the 'L' bit in the SL flag, and download IS-IS
   default route using the spine nodes as nexthops where the 'Spine-
   Peer' set the 'R' bit in its IIH PDU; It requires spine node to
   respond from 'Leaf-Peer' by inserting Spine-Leaf TLV in its IIH,
   setting the 'R' bit in the SL flag, and blocking the LSP flooding
   with the exception that it will set SRMflag on the LSPs that belong
   to the 'Leaf-Peer' over that interface.

3.5.  Implementation and Operation

3.5.1.  CSNP PDU

   In Spine-Leaf extension, Complete Sequence Number PDU (CSNP) does not
   need to be transmitted over the Spine-Leaf link.  Some IS-IS
   implementation sends CSNPs after the initial adjacency bring-up over
   point-to-point interface.  There is no need for this optimization
   here since the Leaf does not need to receive any other LSPs from the



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   network, and the only LSPs transmitted across the Spine-Leaf link is
   the leaf node LSP.

   Also in the graceful restart case[RFC5306], for the same reason,
   there is no need to send the CSNPs over the Spine-Leaf interface.  It
   only needs to set the SRMflag on the LSPs belonging to the 'Leaf-
   Peer' on the spine node, and set the SRMflag on its own LSPs on the
   leaf node.

3.5.2.  Leaf to Leaf connection

   Leaf to leaf node links are useful in host redundancy cases in
   switching networks, and normally there is no special requirement of
   mechanism is needed for this case.  Each leaf node will set the 'L'
   bit in its IIH of the Spine-Leaf flag.  LSP will be exchanged over
   this link.  In the example diagram Figure 1, the Leaf1 will get
   Leaf2's LSP and Leaf2 will get Leaf1's LSP.  They will install more
   specific routes towards each other using this local Leaf-Leaf link.
   SPF will be performed in this case just like when the entire network
   only involves with those two IS-IS nodes.  This does not affect the
   normal Spine-Leaf mechanism they perform toward the spine nodes.

   Besides the local leaf-to-leaf traffic, the leaf node can serve as a
   backup gateway for its leaf neighbor.  It needs to remove the
   'Overload-Bit' setting in its LSP, and it sets both the 'L' bit and
   the 'B' bit in the SL-flag with a high 'Default Route Metric' value.

3.5.3.  Overload Bit

   The leaf node SHOULD set the 'overload' bit on its LSP PDU, since if
   the spine nodes were to forward traffic not meant for the local node,
   the leaf node does not have the topology information to prevent a
   routing/forwarding loop.

3.5.4.  Spine Node Hostname

   This extension creates a non-reciprocal relationship between the
   spine node and leaf node.  The spine node will receive leaf's LSP and
   will know the leaf's hostname, but the leaf does not have spine's
   LSP.  This extension allows the Dynamic Hostname TLV [RFC5301] to be
   optionally included in spine's IIH PDU when sending to a 'Leaf-Peer'.
   This is useful in troubleshooting cases.

3.5.5.  Default Route Metric

   This metric is part of the aggregated metric for leaf's default route
   installation with load sharing among the spine nodes.  When a spine




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   node is in 'overload' condition, it should set this metric to maximum
   to discourage the leaf using it as part of the loadsharing.

   In some cases, certain spine nodes may have less bandwidth in link
   provisioning or in real-time condition, and it can use this metric to
   signal to the leaf nodes dynamically.

   In other cases, such as when the spine node loses a link to a
   particular leaf node, although it can redirect the traffic to other
   spine nodes to reach that destination leaf node, but it MAY want to
   increase this metric value if the inter-spine connection becomes over
   utilized, or the latency becomes an issue.

   In the leaf-leaf link as a backup gateway use case, the 'Default
   Route Metric' SHOULD always be set to very high value.

3.5.6.  Other End-to-End Services

   Losing the topology information will have an impact on some of the
   end-to-end network services, for instance, MPLS TE or end-to-end
   segment routing.  Some other mechanisms such as those described in
   PCE [RFC4655] based solution may be used.  In this Spine-Leaf
   extension, the role of the leaf node is not too much different from
   the multi-level IS-IS routing while the level-1 IS-IS nodes only have
   the default route information towards the node which has the Attach
   Bit (ATT) set, and the level-2 backbone does not have any topology
   information of the level-1 areas.  The exact mechanism to enable
   certain end-to-end network services in Spine-Leaf network is outside
   the scope of this document.

3.5.7.  Address Family and Topology

   IPv6 Address families[RFC5308], Multi-Topology (MT)[RFC5120] and
   Multi-Instance (MI)[RFC6822] information is carried over the IIH PDU.
   Since the goal is to simplify the operation of IS-IS network, for the
   simplicity of this extension, the Spine-Leaf mechanism is applied the
   same way to all the address families, MTs and MIs.

3.5.8.  Migration

   For this extension to be deployed in existing networks, a simple
   migration scheme is needed.  To support any leaf node in the network,
   all the involved spine nodes have to be upgraded first.  So the first
   step is to migrate all the involved spine nodes to support this
   extension, then the leaf nodes can be enabled with 'Leaf-Mode' one by
   one.  No flag day is needed for the extension migration.





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4.  IANA Considerations

   A new TLV codepoint is defined in this document and needs to be
   assigned by IANA from the "IS-IS TLV Codepoints" registry.  It is
   referred to as the Spine-Leaf TLV and the suggested value is 150.
   This TLV is only to be optionally inserted in the IIH PDU.  This
   document does not propose any sub-TLV out of this Spine-Leaf TLV.
   IANA is also requested to maintain the SL-flag bit values in this
   TLV, and 0x01, 0x02 and 0x04 bits are defined in this document.

      Value  Name                   IIH  LSP  SNP  Purge
      -----  ---------------------  ---  ---  ---  -----
      150    Spine-Leaf              y    n    n    n

   This extension also proposes to have the Dynamic Hostname TLV,
   already assigned as code 137, to be allowed in IIH PDU.

      Value  Name                   IIH  LSP  SNP  Purge
      -----  ---------------------  ---  ---  ---  -----
      137    Dynamic Name            y    y    n    y

5.  Security Considerations

   Security concerns for IS-IS are addressed in [ISO10589], [RFC5304],
   [RFC5310], and [RFC7602].  This extension does not raise additional
   security issues.

6.  Acknowledgments

   TBD.

7.  Document Change Log

7.1.  Changes to draft-shen-isis-spine-leaf-ext-01.txt

   o  Submitted April 2016.

   o  No change.  Refresh the draft version.

7.2.  Changes to draft-shen-isis-spine-leaf-ext-00.txt

   o  Initial version of the draft is published in November 2015.

8.  References







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8.1.  Normative References

   [ISO10589]
              ISO "International Organization for Standardization",
              "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,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [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>.

   [RFC5301]  McPherson, D. and N. Shen, "Dynamic Hostname Exchange
              Mechanism for IS-IS", RFC 5301, DOI 10.17487/RFC5301,
              October 2008, <http://www.rfc-editor.org/info/rfc5301>.

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, DOI 10.17487/RFC5304, October
              2008, <http://www.rfc-editor.org/info/rfc5304>.

   [RFC5306]  Shand, M. and L. Ginsberg, "Restart Signaling for IS-IS",
              RFC 5306, DOI 10.17487/RFC5306, October 2008,
              <http://www.rfc-editor.org/info/rfc5306>.

   [RFC5308]  Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
              DOI 10.17487/RFC5308, October 2008,
              <http://www.rfc-editor.org/info/rfc5308>.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, DOI 10.17487/RFC5310, February
              2009, <http://www.rfc-editor.org/info/rfc5310>.

   [RFC6822]  Previdi, S., Ed., Ginsberg, L., Shand, M., Roy, A., and D.
              Ward, "IS-IS Multi-Instance", RFC 6822,
              DOI 10.17487/RFC6822, December 2012,
              <http://www.rfc-editor.org/info/rfc6822>.





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   [RFC7602]  Chunduri, U., Lu, W., Tian, A., and N. Shen, "IS-IS
              Extended Sequence Number TLV", RFC 7602,
              DOI 10.17487/RFC7602, July 2015,
              <http://www.rfc-editor.org/info/rfc7602>.

8.2.  Informative References

   [RFC4655]  Farrel, A., Vasseur, J., and J. Ash, "A Path Computation
              Element (PCE)-Based Architecture", RFC 4655,
              DOI 10.17487/RFC4655, August 2006,
              <http://www.rfc-editor.org/info/rfc4655>.

   [RFC5309]  Shen, N., Ed. and A. Zinin, Ed., "Point-to-Point Operation
              over LAN in Link State Routing Protocols", RFC 5309,
              DOI 10.17487/RFC5309, October 2008,
              <http://www.rfc-editor.org/info/rfc5309>.

Authors' Addresses

   Naiming Shen
   Cisco Systems
   560 McCarthy Blvd.
   Milpitas, CA  95035
   US

   Email: naiming@cisco.com


   Sanjay Thyamagundalu
   Cisco Systems
   3625 Cisco Way
   San Jose, CA  95134
   US

   Email: sanjayt@cisco.com
















Shen & Thyamagundalu    Expires October 27, 2016               [Page 12]


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