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LSR Working Group                                                A. Wang
Internet-Draft                                             China Telecom
Intended status: Standards Track                                   Z. Hu
Expires: April 1, 2021                               Huawei Technologies
                                                               G. Mishra
                                                            Verizon Inc.
                                                      September 28, 2020


                      Passive Interface Attribute
             draft-wang-lsr-passive-interface-attribute-04

Abstract

   This document describes the mechanism that can be used to
   differentiate the passive interfaces from the normal interfaces
   within ISIS or OSPF domain.

Status of This Memo

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

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   This Internet-Draft will expire on April 1, 2021.

Copyright Notice

   Copyright (c) 2020 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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   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
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
   3.  Scenario Description  . . . . . . . . . . . . . . . . . . . .   3
   4.  Passive Interface Attribute . . . . . . . . . . . . . . . . .   4
     4.1.  ISIS Passive Interface Attribute  . . . . . . . . . . . .   4
     4.2.  OSPF Passive Interface Attribute  . . . . . . . . . . . .   5
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   5
   7.  Acknowledgement . . . . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   Passive interfaces are used commonly within an operators enterprise
   or service provider networks.  One of the most common use cases for
   passive interface is in a data center Layer 2 and Layer 3 TOR(Top of
   Rack) switch where the inter connected links between the TOR switches
   and uplinks to the Core switch are only a few links and a majority of
   the links are Layer 3 VLAN Switched Virtual Interface Default
   Gateways trunked between the TOR switches serving Layer 2 broadcast
   domains.  In this scenario all the VLANs are made passive as it is
   recommended to limit the number of network LSAs between routers and
   switches to avoid unnecessary hello processing overhead.

   Another common use case is an inter-as routing scenario where the
   same routing protocol but different IGP instance is running between
   the adjacent BGP domains.  Using passive interface on the inter-as
   tiepoint connections can ensure that prefixes contained within a
   domain are only reachable within the domain itself and not allow the
   link state database to be merged between domain which could result in
   undesirable consequences.

   For operator which runs different IGP domains that interconnect with
   each other, there is desire to obtain the inter-as topology
   information as described in
   [I-D.ietf-idr-bgpls-inter-as-topology-ext].  If the router that runs
   BGP-LS is within one IGP domain and can distinguish passive
   interfaces from other interfaces with transit neighbor, it is then
   easy for the router to report these passive links using BGP-LS to
   centralized PCE controller.



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   But OSPF and ISIS have no position to flag such passive interface
   now.

   This document defines the protocol extension for OSPF and ISIS to
   indicate the prefix that comes from passive interface.

2.  Conventions used in this document

   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 [RFC2119] .

3.  Scenario Description

   Figure 1 illustrates the topology scenario when ISIS/OSPF is running
   in different domain.  B1, B3 are border routers within IGP domain A,
   B2, B4 are border routers within domain B.  S1-S4 are the internal
   routers within domain A, T1-T4 are the internal routers within domain
   B.  The two domain are interconnected via the links between B1/B2 and
   B3/B4.

   Passive interfaces are enabled in the links between B1/B2 and B3/B4
   respectively.  For domain A and B, the S2/T1 router that runs ISIS/
   OSPF can't extract the passives links from the normal links and
   report it to PCE controller via the BGP-LS protocol.  They can only
   judge the passive interfaces from other characteristics, such as no
   IGP neighbor on this link.  Such judgement can extract these passive
   links but it is not accurate, because it covers also the situation
   when there are some issues to establish the ISIS adjacency/OSPF
   neighbor but not the passive interface.

   For passive interfaces that are used in the edge router or switches
   which connects the server, for example in the router S1/S4 and T2/T4
   in Figure 1, knowing these interfaces are correctly configured will
   also benefit the management of them.

   The method to flag these passive interfaces explicitly is necessary
   then.













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                             +-----------------+
                        +----+ PCE Controller  +----+
                        |    +-----------------+    |
                        |                           |
                        |BGP-LS                     |BGP-LS
                        |                           |
        +---------------+-----+               +-----+--------------+
        | +--+        +-++   ++-+           +-++   +|-+        +--+|
        | |S1+--------+S2+---+B1+-----------+B2+---+T1+--------+T2||
        | +-++   N1   +-++   ++-+           +-++   ++++   N2   +-++|
        |   |           |     |               |     ||           | |
        |   |           |     |               |     ||           | |
        | +-++        +-++   ++-+           +-++   ++++        +-++|
        | |S4+--------+S3+---+B3+-----------+B4+---+T3+--------+T4||
        | +--+        +--+   ++-+           +-++   ++-+        +--+|
        |                     |               |                    |
        |                     |               |                    |
        |  Domain A(ISIS)     |               |  Domain B(OSPF)    |
        +---------------------+               +--------------------+

                    Figure 1: Inter-AS Domain Scenarios

4.  Passive Interface Attribute

4.1.  ISIS Passive Interface Attribute

   [RFC7794] defines the "IPv4/IPv6 Extended Reachability Attribute
   Flags" sub-TLV to advertise the additional flags associated with a
   given prefix advertisement.  We propose new bit(Bit 5 is desired) to
   be assigned by the IANA for the passive interface attribute, as
   illustrated in Figure 2:

                      0 1 2 3 4 5 6 7
                     +-+-+-+-+-+-+-+-+
                     |X|R|N|E|A|U| | |
                     +-+-+-+-+-+-+-+-+
                Figure 2: Prefix Attribute Flags

        U-flag: Unactive Flag(Bit 5)
                Set for local interface that is configured as passive interface.

   When the interfaces on one router be configured as passive interface,
   the U-flag bit will be set in the "IPv4/IPv6 Extended Reachability
   Attribute Flags" sub-TLV.  This sub-TLV will be included in the TLV
   135, TLV 235, TLV 236 and TLV 237 as necessary and be flooded within
   the ISIS domain.





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4.2.  OSPF Passive Interface Attribute

   [RFC5340] defines the "Prefix Option field" in "Intra-Area-Prefix-
   LSAs" to describe the prefix capabilities.  The bits in this field
   can be defined to flag the prefix coming from the passive interface.
   We propose new bit(Bit 0 is desired) to be assigned by the IANA for
   the passive interface, as illustrated in Figure 3:

                     0  1  2  3  4  5  6  7
                    +--+--+--+--+--+-+--+--+
                    | U| E| N|DN| P|x|LA|NU|
                    +--+--+--+--+--+-+--+--+

                 Figure 3: The Prefix Options Field

        U-flag: Unactive Flag(Bit 0)
                Set for local interface that is configured as passive interface.

   When the interfaces on one router is configured as passive interface,
   the U-flag bit will be set in the "Prefix Option field" of Intra-
   Area-Prefix-LSAs.

   The router that receives such advertisement can then easily
   distinguish the passive interfaces from the normal interface, and
   reports them to the PCE controller if it runs the BGP-LS protocol.

5.  Security Considerations

   Security concerns for ISIS are addressed in [RFC5304] and[RFC5310]

   Security concern for OSPFv3 is addressed in [RFC4552]

   Advertisement of the additional information defined in this document
   introduces no new security concerns.

6.  IANA Considerations

   IANA is requested to allocate the U-bit (Bit position 5 is desired)
   from the "Bit Values for Prefix Attribute Flags Sub-TLV" registry of
   ISIS TLV codepoint.

   IANA is requested to allocate the U-bit(Bit position 0 is desired)
   from the "OSPFv3 Prefix Options" registry of OSPFv3 Parameters
   codepoint.







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7.  Acknowledgement

   Thanks Shunwan Zhang, Tony Li, Les Ginsberg and Robert Raszuk for
   their suggestions and comments on this idea.

8.  References

8.1.  Normative References

   [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>.

   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
              <https://www.rfc-editor.org/info/rfc4552>.

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

   [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, <https://www.rfc-editor.org/info/rfc5310>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC7794]  Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
              U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
              and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
              March 2016, <https://www.rfc-editor.org/info/rfc7794>.

8.2.  Informative References

   [I-D.ietf-idr-bgpls-inter-as-topology-ext]
              Wang, A., Chen, H., Talaulikar, K., and S. Zhuang, "BGP-LS
              Extension for Inter-AS Topology Retrieval", draft-ietf-
              idr-bgpls-inter-as-topology-ext-08 (work in progress),
              April 2020.








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Authors' Addresses

   Aijun Wang
   China Telecom
   Beiqijia Town, Changping District
   Beijing  102209
   China

   Email: wangaj3@chinatelecom.cn


   Zhibo Hu
   Huawei Technologies
   Huawei Bld., No.156 Beiqing Rd.
   Beijing  100095
   China

   Email: huzhibo@huawei.com


   Gyan S. Mishra
   Verizon Inc.
   13101 Columbia Pike
   Silver Spring  MD 20904
   United States of America

   Email: gyan.s.mishra@verizon.com
























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