Internet DRAFT - draft-chen-isis-black-hole-avoid

draft-chen-isis-black-hole-avoid







Network Working Group                                            Z. Chen
Internet-Draft                                                    Huawei
Intended status: Standards Track                                   X. Xu
Expires: March 9, 2019                                           Alibaba
                                                                D. Cheng
                                                                  Huawei
                                                       September 5, 2018


      Avoiding Traffic Black-Holes for Route Aggregation in IS-IS
                  draft-chen-isis-black-hole-avoid-03

Abstract

   When the Intermediate System to Intermediate System (IS-IS) routing
   protocol is adopted by a highly symmetric network such as the Leaf-
   Spine or Fat-Tree network, the Leaf nodes (e.g., Top of Rack switches
   in datacenters) are recommended to be prevented from receiving other
   nodes' explicit routes in order to achieve scalability.  However,
   such a setup would cause traffic black-holes or suboptimal routing if
   link failure happens in the network.  This document introduces
   INFINITE cost to IS-IS LSPs to solve this problem.

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].

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on March 9, 2019.






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Copyright Notice

   Copyright (c) 2018 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
   (https://trustee.ietf.org/license-info) 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.  Problem Description . . . . . . . . . . . . . . . . . . . . .   3
   3.  Solution  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   When running the Intermediate System to Intermediate System (IS-IS)
   routing protocol in a highly symmetric network such as the Leaf-Spine
   or Fat-Tree network, the Leaf nodes (e.g., Top of Rack switches in
   datacenters) are recommended to be prevented from receiving other
   nodes' explicit routes in order to achieve scalability, as proposed
   in [IS-IS-SL-Extension], [IS-IS-Overhead-Reduction], [RIFT], and
   [OpenFabric].  In particular, each Leaf node SHOULD simply maintain a
   default (or aggregated) route (e.g., 0.0.0.0/0) in its routing table,
   of which the next hop SHOULD be an Equal Cost Multi Path (ECMP) group
   including all Spines nodes that the Leaf node connects to.  However,
   such a setup would cause traffic black-holes or suboptimal routing if
   link failure happens in the network, since the Leaf nodes are not
   aware of any topology information.

   To solve this problem, this document introduces INFINITE cost to IS-
   IS LSPs.  When link failure happens between a Spine node and a Leaf
   node, the Spine node SHOULD advertise all prefixes attached to the
   Leaf node, whose costs SHOULD be set to be INFINITE, to every other
   Leaf node it connects to.  On receiving the prefixes (with INFINITE




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   cost), each Leaf node SHOULD add the prefixes to its routing table,
   thus avoiding traffic black-holes and suboptimal routing.

2.  Problem Description

   This section illustrates why link failure would cause traffic black-
   hole or suboptimal routing when Leaf nodes only maintain default (or
   aggregated) routes.

           +--------+          +--------+          +--------+
           | Spine1 |          | Spine2 |          | Spine3 |
           +-+-+-+-++          +-+-+-+-++          +-+-+-+-++
      +------+ | | |             | | | |             | | | |
      | +------|-|-|-------------+ | | |             | | | X
      | | +----|-|-|---------------|-|-|-------------+ | | X
      | | |    | | |        +------+ | |               | | X
      | | |    | | |        | +------|-|---------------+ | |
      | | |    | | |        | |      | |                 | |
      | | |    | | |        | |      | |                 | |
      | | |    | | |        | |      | |         +-------+ +-----+
      | | |    | | |        | |      | +---------|-------------+ |
      | | |    | | |        | |      +---------+ |             | |
      | | |    | | +--------|-|----------------|-|-----------+ | |
      | | |    | +----------|-|--------------+ | |           | | |
      | | |    +----------+ | |              | | |           | | |
    +-+-+-+-+           +-+-+-+-+          +-+-+-+-+       +-+-+-+-+
    | Leaf1 |           | Leaf2 |          | Leaf3 |       | Leaf4 |
    +-------+           +-------+          +-------+       +-------+
                                                            |     |
                                                           ---   ---
                                                       prefixA   prefixB

                      Figure 1: Topology Example


   Figure 1 shows a Spine-Leaf topology example where Leaf1 to Leaf4 are
   connected to Spine1 to Spine3, and prefixA and prefixB are attached
   to Leaf4.  To achieve scalability, as proposed in [IS-IS-SL-
   Extension], [IS-IS-Overhead-Reduction], [RIFT], and [OpenFabric],
   Leaf1 to Leaf4 SHOULD NOT receive explict routes from each other nor
   the Spine nodes.  Instead, each of them maintains a default (or
   aggregated) route (e.g., 0.0.0.0/0) in the routing table, of which
   the next hop is an ECMP group including Spine1, Spine2, and Spine3.
   Flows from one Leaf node to another are shared among Spine1, Spine2,
   and Spine3 based on the well known 5-tuple hashing.

   However, such a setup would cause traffic black-hole or suboptimal
   routing when link failure happens in the network.  For example, if



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   the link between Spine3 and Leaf4 is broken, Leaf1, Leaf2, and Leaf3
   could not get aware of the failure.  As a result, these Leaf nodes
   will still send a portion of traffic destined for prefixA or prefixB
   toward Spine3, which makes the traffic be discarded at Spine3,
   causing traffic black-hole.  On the other hand, if there are a set of
   links or a higher tier of switches interconnecting Spine1, Spine2,
   and Spine3, the traffic will be steered to other spine nodes or the
   higher-tier switches by Spine3, causing suboptimal routing.

   Therefore, this document introduces INFINITE cost to IS-IS LSPs to
   solve this problem.

3.  Solution

   This document introduces the INFINITE cost to IS-IS LSPs, whose value
   is to be determined.  When link failure happens between a Spine node
   and a Leaf node, the Spine node SHOULD 1) encode all prefixes
   attached to the Leaf node into the IP Reachability TLV, 2) set the
   cost of the prefixes to be INFINITE, 3) append the IP Reachability
   TLV to the IS-IS LSP, and 4) send the LSP to every other Leaf node it
   connects to.

   When a Leaf node receives the prefixes (with INFINITE cost)
   advertised by a Spine node, it SHOULD install each of the prefixes
   into its routing table, of which the next hop SHOULD be set an ECMP
   group including all Spine nodes it connects to except the one who
   advertises the prefix.

   For example, if the link between Spine3 and Leaf4 in Figure 1 is
   broken, Spine3 SHOULD advertise prefixA and prefixB to Leaf1, Leaf2,
   and Leaf3, by sending them an IS-IS LSP containing the IP
   Reachability TLV.  The cost of prefixA and prefixB SHOULD be set
   INFINITE.  On receiving the LSP, Leaf1, Leaf2, and Leaf3 SHOULD
   install prefixA and prefixB into their routing tables, and the next
   hop of prefixA or prefixB SHOULD be set an ECMP group including
   Spine1 and Spine2.  For instance, the routing table of Leaf1 before
   and after the link failure is shown in Figure 2 and Figure 3,
   respectively.

   Note that the mechanism described above could achieve minimal
   signaling latency, which helps to avoid black-hole or suboptimal
   routing rapidly when link failure happens.









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   +-----------+-----+---+----+-----+-------+--------------+
   |Destination|Proto|Pre|Cost|Flags|NextHop|Interface     |
   +-----------+-----+---+----+-----+-------+--------------+
   |0.0.0.0/0  |ISIS |15 |20  |D    |Spine1 |Ethernet0/0/0 |
   |           |ISIS |15 |20  |D    |Spine2 |Ethernet0/0/1 |
   |           |ISIS |15 |20  |D    |Spine3 |Ethernet0/0/2 |
   +-----------+-----+---+----+-----+-------+--------------+

     Figure 2: Routing Table of Leaf1 before link failure


   +-----------+-----+---+----+-----+-------+--------------+
   |Destination|Proto|Pre|Cost|Flags|NextHop|Interface     |
   +-----------+-----+---+----+-----+-------+--------------+
   |0.0.0.0/0  |ISIS |15 |20  |D    |Spine1 |Ethernet0/0/0 |
   |           |ISIS |15 |20  |D    |Spine2 |Ethernet0/0/1 |
   |           |ISIS |15 |20  |D    |Spine3 |Ethernet0/0/2 |
   +-----------+-----+---+----+-----+-------+--------------+
   |prefixA    |ISIS |15 |20  |D    |Spine1 |Ethernet0/0/0 |
   |           |ISIS |15 |20  |D    |Spine2 |Ethernet0/0/1 |
   +-----------+-----+---+----+-----+-------+--------------+
   |prefixB    |ISIS |15 |20  |D    |Spine1 |Ethernet0/0/0 |
   |           |ISIS |15 |20  |D    |Spine2 |Ethernet0/0/1 |
   +-----------+-----+---+----+-----+-------+--------------+

     Figure 3: Routing Table of Leaf1 after link failure


4.  IANA Considerations

   TBD.

5.  Security Considerations

   TBD.

6.  Acknowledgements

   TBD.

7.  References

   [IS-IS-Overhead-Reduction]
              Chen, Z., Xu, X., and D. Cheng, "Overheads Reduction for
              IS-IS Enabled Spine-Leaf Networks", draft-chen-isis-sl-
              overheads-reduction-03 (work in progress) , March 2018.





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   [IS-IS-SL-Extension]
              Shen, N., Ginsberg, L., and S. Thyamagundalu, "IS-IS
              Routing for Spine-Leaf Topology", draft-shen-isis-spine-
              leaf-ext-06 (work in progress) , June 2018.

   [OpenFabric]
              White, R. and S. Zandi, "IS-IS Support for Openfabric",
              draft-white-openfabric-06 (work in progress) , June 2018.

   [RFC1195]  Callon, R., "Use of OSI IS-IS for Routing in TCP/IP and
              Dual Environments", RFC 1195 , December 1990.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

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

   [RIFT]     Przygienda, T., Sharma, A., Drake, J., and A. Atlas,
              "RIFT: Routing in Fat Trees", draft-ietf-rift-rift-02
              (work in progress) , June 2018.

Authors' Addresses

   Zhe Chen
   Huawei
   No. 156 Beiqing Rd
   Beijing  100095
   China

   Email: chenzhe17@huawei.com


   Xiaohu Xu
   Alibaba

   Email: xiaohu.xxh@alibaba-inc.com


   Dean Cheng
   Huawei

   Email: dean.cheng@huawei.com






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