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Versions: (draft-chen-bfd-unsolicited) 00 01

Network Working Group                                            E. Chen
Internet-Draft                                                   N. Shen
Intended status: Standards Track                           Cisco Systems
Expires: December 30, 2019                                     R. Raszuk
                                                            Bloomberg LP
                                                               R. Rahman
                                                           Cisco Systems
                                                           June 28, 2019


              Unsolicited BFD for Sessionless Applications
                     draft-ietf-bfd-unsolicited-01

Abstract

   For operational simplification of "sessionless" applications using
   BFD, in this document we present procedures for "unsolicited BFD"
   that allow a BFD session to be initiated by only one side, and be
   established without explicit per-session configuration or
   registration by the other side (subject to certain per-interface or
   per-router policies).

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

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 https://datatracker.ietf.org/drafts/current/.

   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 December 30, 2019.





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Copyright Notice

   Copyright (c) 2019 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.  Procedures for Unsolicited BFD  . . . . . . . . . . . . . . .   3
   3.  YANG Data Model . . . . . . . . . . . . . . . . . . . . . . .   4
     3.1.  Unsolicited BFD Hierarchy . . . . . . . . . . . . . . . .   4
     3.2.  Unsolicited BFD Module  . . . . . . . . . . . . . . . . .   5
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
     5.1.  BFD Protocol Security Considerations  . . . . . . . . . .   9
     5.2.  YANG Module Security Considerations . . . . . . . . . . .   9
   6.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     6.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     6.2.  Informative References  . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  12

1.  Introduction

   The current implementation and deployment practice for BFD ([RFC5880]
   and [RFC5881]) usually requires BFD sessions be explicitly configured
   or registered on both sides.  This requirement is not an issue when
   an application like BGP [RFC4271] has the concept of a "session" that
   involves both sides for its establishment.  However, this requirement
   can be operationally challenging when the prerequisite "session" does
   not naturally exist between two endpoints in an application.
   Simultaneous configuration and coordination may be required on both
   sides for BFD to take effect.  For example:

   o  When BFD is used to keep track of the "liveness" of the nexthop of
      static routes.  Although only one side may need the BFD
      functionality, currently both sides need to be involved in
      specific configuration and coordination and in some cases static
      routes are created unnecessarily just for BFD.



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   o  When BFD is used to keep track of the "liveness" of the third-pary
      nexthop of BGP routes received from the Route Server [RFC7947] at
      an Internet Exchange Point (IXP).  As the third-party nexthop is
      different from the peering address of the Route Server, for BFD to
      work, currently two routers peering with the Route Server need to
      have routes and nexthops from each other (although indirectly via
      the Router Server), and the nexthop of each router must be present
      at the same time.  These issues are also discussed in
      [I-D.ietf-idr-rs-bfd].

   Clearly it is beneficial and desirable to reduce or eliminate
   unnecessary configurations and coordination in these "sessionless"
   applications using BFD.

   In this document we present procedures for "unsolicited BFD" that
   allow a BFD session to be initiated by only one side, and be
   established without explicit per-session configuration or
   registration by the other side (subject to certain per-interface or
   per-router policies).

   With "unsolicited BFD" there is potential risk for excessive resource
   usage by BFD from "unexpected" remote systems.  To mitigate such
   risks, several mechanisms are recommended in the Security
   Considerations section.

   Compared to the "Seamless BFD" [RFC7880], this proposal involves only
   minor procedural enhancements to the widely deployed BFD itself.
   Thus we believe that this proposal is inherently simpler in the
   protocol itself and deployment.  As an example, it does not require
   the exchange of BFD discriminators over an out-of-band channel before
   the BFD session bring-up.

   When BGP Add-Path [RFC7911] is deployed at an IXP using the Route
   Server, multiple BGP paths (when exist) can be made available to the
   clients of the Router Server as described in [RFC7947].  The
   "unsolicited BFD" can be used in BGP route selection by these clients
   to eliminate paths with "inaccessible nexthops".

2.  Procedures for Unsolicited BFD

   With "unsolicited BFD", one side takes the "Active role" and the
   other side takes only the "Passive role" as described in [RFC5880].

   On the passive side, the "unsolicited BFD" SHOULD be configured
   explicitly on an interface.  The BFD parameters can be either per-
   interface or per-router based.  It MAY also choose to use the
   parameters that the active side uses in its BFD Control packets.  The




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   "Discriminator", however, MUST be chosen to allow multiple
   unsolicited BFD sessions.

   The active side initiates the BFD Control packets as specified in
   [RFC5880].  The passive side does not initiates the BFD Control
   packets.

   When the passive side receives a BFD Control packet from the active
   side with 0 as the "remote-discriminator", and it does not find an
   existing session with the same source address as in the packet and
   "unsolicited BFD" is allowed on the interface by local policy, it
   SHOULD then create a matching BFD session toward the active side
   (based on the source address and destination address in the BFD
   Control packet) as if the session were locally registered.  It would
   then start sending the BFD Control packets and perform necessary
   procedure for bringing up, maintaining and tearing down the BFD
   session.  If the BFD session fails to get established within certain
   specified time, or if an established BFD session goes down, the
   passive side would stop sending BFD Control packets and delete the
   BFD session created until the BFD Control packets is initiated by the
   active side again.

   The "Passive role" may change to the "Active role" when a local
   client registers for the same BFD session, and from the "Active role
   " to the "Passive role " when there is no longer any locally
   registered client for the BFD session.

3.  YANG Data Model

   This section extends the YANG data model for BFD [I-D.ietf-bfd-yang]
   to cover the unsolicited BFD.

3.1.  Unsolicited BFD Hierarchy


















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   module: ietf-bfd-unsolicited
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh:
       +--rw unsolicited {bfd-unsol:unsolicited-params-global}?
          +--rw enable?                           boolean
          +--rw local-multiplier?                 multiplier
          +--rw (interval-config-type)?
             +--:(tx-rx-intervals)
             |  +--rw desired-min-tx-interval?    uint32
             |  +--rw required-min-rx-interval?   uint32
             +--:(single-interval) {single-minimum-interval}?
                +--rw min-interval?               uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh
               /bfd-ip-sh:interfaces:
       +--rw unsolicited {bfd-unsol:unsolicited-params-per-interface}?
          +--rw enable?                           boolean
          +--rw local-multiplier?                 multiplier
          +--rw (interval-config-type)?
             +--:(tx-rx-intervals)
             |  +--rw desired-min-tx-interval?    uint32
             |  +--rw required-min-rx-interval?   uint32
             +--:(single-interval) {single-minimum-interval}?
                +--rw min-interval?               uint32
     augment /rt:routing/rt:control-plane-protocols
               /rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh
               /bfd-ip-sh:sessions/bfd-ip-sh:session:
       +--ro unsolicited
          +--ro role?   bfd-unsol:unsolicited-role


3.2.  Unsolicited BFD Module

 <CODE BEGINS> file "ietf-bfd-unsolicited@2019-06-26.yang"

 module ietf-bfd-unsolicited {

   yang-version 1.1;

   namespace "urn:ietf:params:xml:ns:yang:ietf-bfd-unsolicited";

   prefix "bfd-unsol";

   // RFC Ed.: replace occurences of XXXX/YYYY with actual RFC numbers
   // and remove this note

   import ietf-bfd-types {
     prefix "bfd-types";



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     reference "RFC XXXX: YANG Data Model for BFD";
   }

   import ietf-bfd {
     prefix "bfd";
     reference "RFC XXXX: YANG Data Model for BFD";
   }

   import ietf-bfd-ip-sh {
     prefix "bfd-ip-sh";
     reference "RFC XXXX: YANG Data Model for BFD";
   }

   import ietf-routing {
     prefix "rt";
     reference
       "RFC 8349: A YANG Data Model for Routing Management
        (NMDA version)";
   }

   organization "IETF BFD Working Group";

   contact
     "WG Web:   <http://tools.ietf.org/wg/bfd>
      WG List:  <rtg-bfd@ietf.org>

      Editors:  Enke Chen (enkechen@cisco.com),
                Naiming Shen (naiming@cisco.com),
                Robert Raszuk (robert@raszuk.net),
                Reshad Rahman (rrahman@cisco.com)";

   description
     "This module contains the YANG definition for BFD unsolicited
      as per RFC YYYY.

      Copyright (c) 2018 IETF Trust and the persons
      identified as authors of the code.  All rights reserved.

      Redistribution and use in source and binary forms, with or
      without modification, is permitted pursuant to, and subject
      to the license terms contained in, the Simplified BSD License
      set forth in Section 4.c of the IETF Trust's Legal Provisions
      Relating to IETF Documents
      (http://trustee.ietf.org/license-info).

      This version of this YANG module is part of RFC XXXX; see
      the RFC itself for full legal notices.";




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   reference "RFC YYYY";

   revision 2019-06-26 {
     description "Initial revision.";
     reference "RFC YYYY: A YANG data model for BFD unsolicited";
   }

   /*
    * Feature definitions
    */
    feature unsolicited-params-global {
      description
        "This feature indicates that the server supports global
         parameters for unsolicited sessions.";
    }

   feature unsolicited-params-per-interface {
     description
       "This feature indicates that the server supports per-interface
        parameters for unsolicited sessions.";
   }

   /*
    * Type Definitions
    */
   typedef unsolicited-role {
     type enumeration {
       enum unsolicited-active {
         description "Active role";
       }
       enum unsolicited-passive {
         description "Passive role";
       }
     }
     description "Unsolicited role";
   }

   /*
    * Augments
    */
    augment "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh" {
      description
        "Augmentation for BFD unsolicited parameters";
      container unsolicited {
        if-feature bfd-unsol:unsolicited-params-global;
        description
          "BFD unsolicited top level container";



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        leaf enable {
          type boolean;
          default false;
          description
            "Enable BFD unsolicited globally for IP single-hop.";
        }
        uses bfd-types:base-cfg-parms;
      }
    }

    augment "/rt:routing/rt:control-plane-protocols/"
          + "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/"
          + "bfd-ip-sh:interfaces" {
      description
        "Augmentation for BFD unsolicited on IP single-hop interface";
      container unsolicited {
        if-feature bfd-unsol:unsolicited-params-per-interface;
        description
          "BFD IP single-hop interface unsolicited top level container";
        leaf enable {
          type boolean;
          default false;
          description "Enable BFD unsolicited on this interface.";
        }
        uses bfd-types:base-cfg-parms;
      }
    }

   augment "/rt:routing/rt:control-plane-protocols/"
         + "rt:control-plane-protocol/bfd:bfd/bfd-ip-sh:ip-sh/"
         + "bfd-ip-sh:sessions/bfd-ip-sh:session" {
     description
       "Augmentation for BFD unsolicited on IP single-hop session";
     container unsolicited {
       config false;
       description
         "BFD IP single-hop session unsolicited top level container";
       leaf role {
         type bfd-unsol:unsolicited-role;
         description "Role.";
       }
     }
   }
 }

 <CODE ENDS>





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4.  IANA Considerations

   This documents makes no IANA requests.

5.  Security Considerations

5.1.  BFD Protocol Security Considerations

   The same security considerations as those described in [RFC5880] and
   [RFC5881] apply to this document.  With "unsolicited BFD" there is
   potential risk for excessive resource usage by BFD from "unexpected"
   remote systems.  To mitigate such risks, the following measures are
   RECOMMENDED:

   o  Limit the feature to specific interfaces, and to a single-hop BFD
      with "TTL=255" [RFC5082].  In addition make sure the source
      address of an incoming BFD packet belongs to the subnet of the
      interface from which the BFD packet is received.
   o  Apply "access control" to allow BFD packets only from certain
      subnets or hosts.
   o  Deploy the feature only in certain "trustworthy" environment,
      e.g., at an IXP, or between a provider and its customers.
   o  Adjust BFD parameters as needed for the particular deployment and
      scale.
   o  Use BFD authentication.

5.2.  YANG Module Security Considerations

   The YANG module specified in this document defines a schema for data
   that is designed to be accessed via network management protocols such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC5246].

   The NETCONF access control model [RFC6536] provides the means to
   restrict access for particular NETCONF or RESTCONF users to a
   preconfigured subset of all available NETCONF or RESTCONF protocol
   operations and content.

   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., config true, which is the
   default).  These data nodes may be considered sensitive or vulnerable
   in some network environments.  Write operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  These are the subtrees and data nodes
   and their sensitivity/vulnerability:



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   /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh
   /unsolicited:

   o  data node "enable" enables creation of unsolicited BFD IP single-
      hop sessions globally, i.e. on all interfaces.  See Section 5.1.
   o  data nodes local-multiplier, desired-min-tx-interval, required-
      min-rx-interval and min-interval all impact the parameters of the
      unsolicited BFD IP single-hop sessions.

   /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh
   /interfaces/interface/unsolicited:

   o  data node "enable" enables creation of unsolicited BFD IP single-
      hop sessions on a specific interface.  See Section 5.1.
   o  data nodes local-multiplier, desired-min-tx-interval, required-
      min-rx-interval and min-interval all impact the parameters of the
      unsolicited BFD IP single-hop sessions on the interface.

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or
   notification) to these data nodes.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

   /routing/control-plane-protocols/control-plane-protocol/bfd/ip-sh
   /sessions/session/unsolicited: access to this information discloses
   the role of the local system in the creation of the unsolicited BFD
   session.

6.  References

6.1.  Normative References

   [I-D.ietf-bfd-yang]
              Rahman, R., Zheng, L., Jethanandani, M., Networks, J., and
              G. Mirsky, "YANG Data Model for Bidirectional Forwarding
              Detection (BFD)", draft-ietf-bfd-yang-17 (work in
              progress), August 2018.

   [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>.

   [RFC5082]  Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
              Pignataro, "The Generalized TTL Security Mechanism
              (GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
              <https://www.rfc-editor.org/info/rfc5082>.



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   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246,
              DOI 10.17487/RFC5246, August 2008,
              <https://www.rfc-editor.org/info/rfc5246>.

   [RFC5880]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
              <https://www.rfc-editor.org/info/rfc5880>.

   [RFC5881]  Katz, D. and D. Ward, "Bidirectional Forwarding Detection
              (BFD) for IPv4 and IPv6 (Single Hop)", RFC 5881,
              DOI 10.17487/RFC5881, June 2010,
              <https://www.rfc-editor.org/info/rfc5881>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC6536]  Bierman, A. and M. Bjorklund, "Network Configuration
              Protocol (NETCONF) Access Control Model", RFC 6536,
              DOI 10.17487/RFC6536, March 2012,
              <https://www.rfc-editor.org/info/rfc6536>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

6.2.  Informative References

   [I-D.ietf-idr-rs-bfd]
              Bush, R., Haas, J., Scudder, J., Nipper, A., and C.
              Dietzel, "Making Route Servers Aware of Data Link Failures
              at IXPs", draft-ietf-idr-rs-bfd-07 (work in progress),
              March 2019.

   [RFC4271]  Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
              Border Gateway Protocol 4 (BGP-4)", RFC 4271,
              DOI 10.17487/RFC4271, January 2006,
              <https://www.rfc-editor.org/info/rfc4271>.



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   [RFC7880]  Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
              Pallagatti, "Seamless Bidirectional Forwarding Detection
              (S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
              <https://www.rfc-editor.org/info/rfc7880>.

   [RFC7911]  Walton, D., Retana, A., Chen, E., and J. Scudder,
              "Advertisement of Multiple Paths in BGP", RFC 7911,
              DOI 10.17487/RFC7911, July 2016,
              <https://www.rfc-editor.org/info/rfc7911>.

   [RFC7947]  Jasinska, E., Hilliard, N., Raszuk, R., and N. Bakker,
              "Internet Exchange BGP Route Server", RFC 7947,
              DOI 10.17487/RFC7947, September 2016,
              <https://www.rfc-editor.org/info/rfc7947>.

Authors' Addresses

   Enke Chen
   Cisco Systems
   560 McCarthy Blvd.
   Milpitas, CA  95035
   USA

   Email: enkechen@cisco.com


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

   Email: naiming@cisco.com


   Robert Raszuk
   Bloomberg LP
   731 Lexington Ave
   New York City, NY  10022
   USA

   Email: robert@raszuk.net









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   Reshad Rahman
   Cisco Systems
   2000 Innovation Drive
   Kanata, Ontario  K2K 3E8
   Canada

   Email: rrahman@cisco.com












































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