Network Working Group                                          A. Azimov
Internet-Draft                                      Qrator Labs & Yandex
Intended status: Standards Track                            E. Bogomazov
Expires: July 20, 2021 February 11, 2022                                   Qrator Labs
                                                                 R. Bush
                                Internet Initiative Japan & Arrcus, Inc.
                                                                K. Patel
                                                                  Arrcus
                                                               K. Sriram
                                                                USA NIST
                                                        January 16,
                                                         August 10, 2021

   Route Leak Prevention and Detection using Roles in Update UPDATE and Open messages
                   draft-ietf-idr-bgp-open-policy-15 OPEN
                                Messages
                   draft-ietf-idr-bgp-open-policy-16

Abstract

   Route leaks are the propagation of BGP prefixes which that violate
   assumptions of BGP topology relationships; e.g. relationships, e.g., passing a route
   learned from one lateral peer to another lateral peer or a transit
   provider,
   provider and passing a route learned from one transit provider to
   another transit provider or a lateral peer.  Existing approaches to
   leak prevention rely on marking routes by operator configuration,
   with no check that the configuration corresponds to that of the eBGP
   neighbor, or enforcement that the two eBGP speakers agree on the
   relationship.  This document enhances the BGP OPEN message to
   establish an agreement of the (peer, customer, provider, Route Server, Route Server client) relationship of two neighboring on each eBGP speakers session
   between autonomous systems in order to enforce appropriate
   configuration on both sides.  Propagated routes are then marked with
   an Only to Customer (OTC) attribute
   according to the agreed relationship, allowing both prevention and
   detection of route leaks.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on July 20, 2021. February 11, 2022.

Copyright Notice

   Copyright (c) 2021 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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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Peering Relationships . .
     1.1.  Terminology . . . . . . . . . . . . . . . . . .   3
   3.  BGP Role  . . . . . .   3
   2.  Peering Relationships . . . . . . . . . . . . . . . . . . . .   4
   4.
   3.  BGP Role Capability  . . . . . . . . . . . . . . . . . . . . .   5
   5.  Role correctness  . . . . . .   4
     3.1.  BGP Role Capability . . . . . . . . . . . . . . . .   5
     5.1.  Strict mode . . .   5
     3.2.  Role Correctness  . . . . . . . . . . . . . . . . . . . .   6
   6.   5
   4.  BGP Only to Customer (OTC) Attribute  . . . . . . . . . . . .   6
   7.  Enforcement . . . . . . . . . . . . . . . . . . . . . . . . .   7
   8.
   5.  Additional Considerations . . . . . . . . . . . . . . . . . .   7
   9.   8
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   10.
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   11.   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   9
     11.1.  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   9
     11.2.  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9  11
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  10  11
   Contributors  . . . . . . . . . . . . . . . . . . . . . . . . . .  10  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  10  12

1.  Introduction

   A BGP route leak occurs when a route is learned from a transit
   provider or lateral peer and then announced to another provider or
   lateral peer.  See peer [RFC7908].  These are usually the result of
   misconfigured or absent BGP route filtering or lack of coordination
   between autonomous systems (ASes).

   Existing approaches to leak prevention rely on marking routes by
   operator configuration, with no check that the configuration
   corresponds to that of the eBGP neighbor, or enforcement that the two
   eBGP speakers.

   The mechanism proposed in
   [I-D.ietf-grow-route-leak-detection-mitigation] uses large-
   communities speakers agree on the relationship.  This document enhances the
   BGP OPEN message to perform detection and mitigation establish an agreement of route leaks.
   While signaling using communities is easy the relationship on
   each eBGP session between autonomous systems in order to implement and deploy
   quickly, it normally relies enforce
   appropriate configuration on operator-maintained policy
   configuration, which is vulnerable both sides.  Propagated routes are then
   marked according to misconfiguration [Streibelt].
   The community signal can also be stripped at the ISP boundaries. agreed relationship, allowing both prevention
   and detection of route leaks.

   This document provides configuration automation using 'BGP roles', BGP Roles,
   which are negotiated using a new BGP Role Capability Code in the OPEN message
   (see Section 4 in [RFC5492]).  Either or both BGP speakers MAY be
   configured to
   [RFC5492].  An eBGP speaker may require that the use of this capability be agreed
   and confirmation of BGP Role with a neighbor for the BGP OPEN to
   succeed.

   A new

   An optional, transitive BGP Path Attribute Attribute, called Only to Customer (OTC)
   (OTC), is specified that SHOULD be automatically configured using BGP roles.
   This attribute in Section 4.  It prevents networks ASes from creating
   leaks, and detects leaks created by third parties. the ASes in the middle of an AS
   path.  The main focus/applicability is the Internet (IPv4 and IPv6
   unicast route advertisements).

1.1.  Terminology

   In the rest of this document, we use the term "peer" "Peer" is used to refer to a
   "lateral peer" for simplicity.

2.  Peering Relationships

   Despite  Also, the terms Provider and Customer
   are used to refer to a transit provider and a transit customer,
   respectively.  Further, the terms RS and RS-Client are used to refer
   to a Route Server and its client, respectively.

   The terms "local AS" and "remote AS" are used to refer to the two
   ends of an eBGP session.  The "local AS" is the AS where the protocol
   action being described is to be performed, and "remote AS" is the AS
   at the other end of the eBGP session in consideration.

   The use of terms such the term "route is ineligible" in this document has the
   same meaning as "customer", "peer", etc. in [RFC4271], i.e., "route is ineligible to be
   installed in Loc-RIB and will be excluded from the next phase of
   route selection."

2.  Peering Relationships

   The terms defined and used in this
   document, these are document (see below) do not
   necessarily represent business relationships based on payment
   agreements.  These terms are used to represent restrictions on BGP
   route propagation, sometimes known as the Gao-Rexford model [Gao].
   The following is a list of various roles in BGP Roles for eBGP peering and the
   corresponding rules for route propagation:

   Provider:  MAY send propagate any available route to a customer all available prefixes. Customer.

   Customer:  MAY send to a provider prefixes which the sender
      originates and prefixes propagate any route learned from any of their customers.  A
      customer MUST NOT send a Customer, or
      locally originated, to a provider prefixes learned from its
      peers, from Provider.  All other providers, or from Route Servers. routes MUST NOT be
      propagated.

   Route Server (RS):  MAY send propagate any available route to an a Route
      Server client (RS-client)
      all available prefixes.

   RS-client: Client (RS-Client).

   RS-Client:  MAY send to an RS prefixes which the sender originates
      and prefixes propagate any route learned from its customers.  An RS-client MUST NOT
      send a Customer, or
      locally originated, to an RS prefixes learned from its peers or providers, or
      from another RS.  All other routes MUST NOT be
      propagated.

   Peer:  MAY send to a peer prefixes which the sender originates and
      prefixes propagate any route learned from its customers.  A peer MUST NOT send a Customer, or locally
      originated, to a
      peer prefixes learned from Peer.  All other peers, from its providers, or
      from RS(s).

   Of course, any routes MUST NOT be propagated.

   A BGP speaker may apply policy to reduce what is announced, and a
   recipient may apply policy to reduce the set of routes they accept.
   Violation of the above rules may result in route
   leaks and MUST NOT be allowed. leaks.  Automatic
   enforcement of these rules should significantly reduce route leaks
   that may otherwise occur due to manual configuration mistakes.  While enforcing the above rules
   will address most BGP peering scenarios, their configuration is not
   part of BGP itself; therefore, configuration of ingress and egress
   prefix filters is still strongly advised.

3.  BGP Role

   The BGP Role is characterizes the relationship between the eBGP speakers
   forming a new configuration option that session.  BGP Role is configured on a per-
   session per-session basis.
   An eBGP speaker SHOULD configure the BGP Role locally based on the
   local AS's knowledge of its Role.  The only exception is when the
   eBGP connection is complex (see Section 5).  BGP Roles reflect are mutually
   confirmed using the agreement between two BGP
   speakers about their relationship. Role Capability (described in Section 3.1) on
   each eBGP session between autonomous systems (ASes).  One of the
   Roles described below SHOULD be configured on at the local AS for each
   eBGP session between ISPs that carry
   IPv4 and(or) IPv6 unicast prefixes. with a neighbor (remote AS) (see definitions in
   Section 1.1).

   Allowed Role values Roles for eBGP sessions between ISPs are:

   o  Provider - sender the local AS is a transit provider to neighbor; Provider of the remote AS;
   o  Customer - sender the local AS is a transit customer Customer of neighbor; the remote AS;

   o  RS - sender the local AS is a Route Server, usually Server (usually at an Internet
      exchange
      point (IX); point) and the remote AS is its RS-Client;

   o  RS-client  RS-Client - sender the local AS is a client of an RS; RS and the RS is the
      remote AS;

   o  Peer - sender the local and neighbor remote ASes are peers.

   Since BGP Role reflects the relationship between two BGP speakers, it
   could also be used for other purposes besides route leak mitigation.

4. Peers (i.e., have a lateral
      peering relationship).

3.1.  BGP Role Capability

   The TLV (type, length, value) of the BGP Role capability are: Capability is defined as follows:

   o  Type  Code - <TBD1>; 9

   o  Length - 1 (byte); (octet)

   o  Value - integer corresponding to speaker's BGP Role (see Table 1).

                      +-------+---------------------+

                 +-------+------------------------------+
                 | Value | Role name (for the local AS) |
                      +-------+---------------------+
                 +-------+------------------------------+
                 |   0   | Sender is Provider                     |
                 |   1   | Sender is RS                           |
                 |   2   | Sender is RS-client RS-Client                    |
                 |   3   | Sender is Customer                     |
                 |   4   | Sender is Peer (Lateral Peer)          |
                 |
                      +-------+---------------------+ 5-255 | Unassigned                   |
                 +-------+------------------------------+

                    Table 1: Predefined BGP Role Values

5.

   If BGP Role correctness is locally configured, the eBGP speaker MUST advertise
   BGP Role Capability in the BGP OPEN message.  An eBGP speaker MUST
   NOT advertise multiple versions of the BGP Role Capability.

3.2.  Role Correctness

   Section 3 3.1 described how BGP Role encodes the relationship between two on each
   eBGP speakers.  But the session between autonomous systems (ASes).

   The mere presence receipt of BGP Role doesn't Capability does not automatically
   guarantee role the Role agreement between two BGP peers.

   To enforce correctness, eBGP neighbors.  If the BGP
   Role check Capability is applied with a set of
   constraints on how speakers' BGP Roles MUST correspond.  Of course,
   each speaker MUST announce advertised, and accept one is also received from the BGP Role capability
   peer, the roles MUST correspond to the relationships in Table 2.  If
   the roles do not correspond, the BGP OPEN message exchange.

   If a speaker receives a BGP Role capability, it MUST check the value
   of reject the received capability (i.e.,
   connection using the sender's role) with its own BGP
   Role.  The allowed pairings are as follows:

                    +---------------+-----------------+ Role Mismatch Notification (code 2, subcode 8).

                    +---------------+----------------+
                    | Sender's Local AS Role | Receiver's Remote AS Role |
                    +---------------+-----------------+
                    +---------------+----------------+
                    | Provider      | Customer       |
                    | Customer      | Provider       |
                    | RS            | RS-client RS-Client      |
                    | RS-client RS-Client     | RS             |
                    | Peer          | Peer           |
                    +---------------+-----------------+
                    +---------------+----------------+

                Table 2: Allowed Pairs of Role Capabilities

   If the role of the receiving speaker for the eBGP session in
   consideration is included in Table 1 and the observed BGP Role pair Capability is sent, but one is not in the above table, received, then the receiving speaker MUST reject
   connection MAY be rejected using the
   eBGP connection, send a Role Mismatch Notification (code
   2, subcode
   <TBD2>), 8); this mode of operation is called the "strict mode".
   For backward compatibility, if the BGP speaker does not receive the
   capability from its peer, it SHOULD ignore the absence of BGP Role
   Capability and also send a Connection Rejected Notification [RFC4486]
   (Notification proceed with error code 6, subcode 5).

5.1.  Strict session establishment; this SHOULD be the
   default non-strict mode

   A new of operation.  In this case, the locally
   configured BGP configuration option "strict mode" Role is defined with values
   of true or false. used for the procedures described in
   Section 4.

   If set to true, an eBGP speaker receives multiple but identical BGP Role
   Capabilities with the same value in each, then the speaker MUST refuse
   consider it to
   establish be a single BGP session with a neighbor which does not announce the Role Capability and proceed [RFC5492].
   If multiple BGP Role capability in Capabilities are received and not all of them
   have the OPEN message.  If a same value, then the BGP speaker rejects a
   connection, it MUST send a send a reject the connection
   using the Role Mismatch Notification (code 2, subcode <TBD2>), and also send a Connection Rejected Notification
   [RFC4486] (Notification with error code 6, subcode 5).  By default,
   strict mode SHOULD be set to false for backward compatibility with 8).

   The BGP speakers that do not yet support this mechanism.

6. Role value for the local AS is used in the route leak
   prevention and detection procedures described in Section 4.

4.  BGP Only to Customer (OTC) Attribute

   Newly defined here, the

   The Only to Customer (OTC) Attribute is an optional, 4
   bytes long, optional transitive BGP Path path
   attribute with the Attribute Type Code <TBD3>. 35 and a length of 4 octets.  The
   purpose of this attribute is to guarantee that once a route is sent
   to customer, peer, a Customer, Peer, or RS-client, RS-Client, it will subsequently go only to
   customers.
   Customers.  The attribute value of OTC is an AS number determined by policy as
   described below.  The semantics and usage of the OTC attribute are
   made clear by the ingress and egress policies
   policy described below.

   The following ingress policy applies to the processing of the OTC attribute:
   Attribute:

   1.  If a route with the OTC attribute Attribute is received from a Customer or RS-
       client,
       RS-Client, then it is a route leak and MUST be rejected. considered
       ineligible (see Section 1.1).

   2.  If a route with the OTC attribute Attribute is received from a Peer and its at
       least one of the OTC Attributes has a value that is not equal to
       the sending neighbor's Autonomous System
       (AS) remote (i.e., Peer's) AS number, then it is a route leak and
       MUST be rejected. considered ineligible.

   3.  If a route is received from a Provider, Peer, or RS RS, and the OTC
       attribute
       Attribute is not present, then it MUST be added with a value
       equal to the sending neighbor's AS number. number of the remote AS.

   The following egress policy MUST be:

   1.  A route with applies to the processing of the OTC attribute set MUST NOT be sent to Providers,
       Peers, or RS(s).

   2.
   Attribute:

   1.  If a route is sent to be advertised to a Customer or Customer, Peer, or an RS-client RS-Client
       (when the sender is an RS) RS), and the OTC attribute Attribute is not present,
       then it an OTC Attribute MUST be added with a value equal to the AS
       number of the sender.

   Once local AS.

   2.  If a route already contains the OTC attribute has been set, Attribute, it MUST NOT be preserved unchanged.

7.  Enforcement

   Having
       propagated to Providers, Peers, or RS(s).

   The described policies provide both leak prevention for the relationship unequivocally agreed between local AS
   and leak detection and mitigation multiple hops away.  In the two peers in
   BGP OPEN is critical; BGP implementations MUST enforce case of
   prevention at the
   relationship/role establishment rules (see Section 5) in order to
   ameliorate operator policy configuration errors (if any).

   Similarly, local AS, the application presence of that relationship on prefix propagation
   using an OTC MUST be enforced by Attribute
   indicates to the BGP implementations, egress router that the route was learned from a
   Peer, Provider, or RS, and not
   exposed it can be advertised only to user misconfiguration.

   As opposed the
   customers.  The same OTC Attribute which is set locally also provides
   a way to communities, BGP attributes detect route leaks by an AS multiple hops away if a route is
   received from a Customer, Peer, or RS-Client.

   The OTC Attribute may not be generally
   modified or stripped set by the operator; BGP router implementations
   enforce such treatment.  This is egress policy of remote AS or by
   the desired property for ingress policy of local AS.  In both scenarios, the OTC
   marking.  Hence, this document specifies OTC as value
   will be the same.  This makes the scheme more robust and benefits
   early adopters.

   If an attribute.

8.  Additional Considerations eBGP speaker receives an UPDATE with an OTC Attribute with a
   length different from 4 octets, then the UPDATE SHALL be considered
   malformed.  If malformed, the UPDATE message SHALL be handled using
   the approach of "treat-as-withdraw" [RFC7606].

   Once the OTC Attribute has been set, it MUST be preserved unchanged.

   Correct implementation of the procedures specified in this document
   is not expected to result in the presence of multiple OTC Attributes
   in an UPDATE.  However, if an eBGP speaker receives multiple OTC
   Attributes with a route, then the only difference in the processing
   is in Step 2 of the ingress policy.

   The described ingress and egress policies are applicable only for
   unicast IPv4 and IPv6 address families and MUST not affect other
   address families by default.  The operator MUST NOT have the ability
   to modify the policies defined in this section.

5.  Additional Considerations

   There are peering relationships that are 'complex', i.e., both
   parties are intentionally sending advertise prefixes received from each other to
   their non-transit peers Peers and/or transit providers. Providers.  If multiple BGP
   peerings eBGP sessions can
   segregate the 'complex' parts of the relationship, then the complex
   peering roles can be segregated into different normal BGP eBGP sessions,
   and BGP Roles MUST be used on each of the resulting normal
   (non-complex) BGP (non-
   complex) eBGP sessions.

   No Roles SHOULD be configured on a 'complex' BGP eBGP session (assuming
   it is not segregated) and in that case, the OTC Attribute processing
   MUST be set by done relying on configuration on a per-prefix basis.  Also,
   in this case, the per-prefix peering configuration MUST follow the
   same definitions of peering relations as described in Section 2.
   However, in this case, there are no built-in measures to check
   correctness of OTC use if BGP Role is not configured. the per-prefix peering configuration.

   The incorrect setting of BGP Roles and/or OTC attributes Attributes may affect
   prefix propagation.  Further, this document doesn't does not specify any
   special handling of incorrect/private ASNs incorrect AS numbers in the OTC attribute; such Attribute.  Such
   errors should not happen with proper configuration.

   As the

6.  IANA Considerations

   IANA has registered a new BGP Role reflects Capability described in Section 3.1 in
   the peering relationship between neighbors,
   it might have other uses beyond "Capability Codes" registry's "IETF Review" range [RFC5492].  The
   description for the route leak solution discussed so
   far.  For example, new capability is "BGP Role".  IANA has assigned
   the value 9 [to be removed upon publication:
   https://www.iana.org/assignments/capability-codes/capability-
   codes.xhtml].  This document is the reference for the new capability.

   The BGP Role might affect route priority, or be used capability includes a Value field, for which IANA is
   requested to distinguish borders create and maintain a new sub-registry called "BGP Role
   Value" in the Capability Codes registry.  Assignments consist of a network if
   Value and a network consists of multiple
   ASs.  Though such uses may be worthwhile, they are not the goal of
   this document.  Note that such uses would require local policy
   control.

   The use of BGP Roles are specified for unicast IPv4 and IPv6 address
   families.  While BGP roles can be configured on other address
   families its applicability for these cases is out of scope of this
   document.

   As BGP role configuration results in automatic creation of inbound/
   outbound filters, existence of roles should be treated as existence
   of Import and Export policy [RFC8212].

9.  IANA Considerations

   This document defines a new Capability Codes option [to be removed
   upon publication: https://www.iana.org/assignments/capability-codes/
   capability-codes.xhtml ] [RFC5492], named "BGP Role" with an assigned
   value <TBD1>.  The length of this capability is 1.

   The BGP Role capability includes a Value field, for which IANA is
   requested to create and maintain a new sub-registry called "BGP Role
   Value".  Assignments consist of Value and corresponding Role name.
   Initially  Initially, this registry is to
   be populated with the data contained in Table 1 found in Section 4. 3.1.
   Future assignments may be made by a
   Standard Action procedure [RFC8126].  The allocation policy for new
   entries up to and including value 127 is "Expert the "IETF Review" [RFC8126].
   The allocation policy for values 128 through 251 is "First Come First
   Served". as defined
   in [RFC8126].  The values from 252 through 255 are for "Experimental Use". registry is as shown in Table 3.

        +-------+--------------------------------+---------------+
        | Value | Role name (for the local AS)   |   Reference   |
        +-------+--------------------------------+---------------+
        |   0   | Provider                       | This document |
        |   1   | RS                             | This document defines |
        |   2   | RS-Client                      | This document |
        |   3   | Customer                       | This document |
        |   4   | Peer (i.e., Lateral Peer)      | This document |
        | 5-255 | To be assigned by IETF Review  |
        +-------+--------------------------------+---------------+

                    Table 3: IANA Registry for BGP Role

   IANA has registered a new subcode, OPEN Message Error subcode named the "Role
   Mismatch" with an assigned
   value <TBD2> (see Section 3.2) in the OPEN Message Error subcodes registry
   registry.  IANA has assigned the value 8 [to be removed upon
   publication: http://www.iana.org/assignments/bgp-
   parameters/bgp-parameters.xhtml#bgp-parameters-6] [RFC4271]. https://www.iana.org/assignments/bgp-parameters/bgp-
   parameters.xhtml#bgp-parameters-6].  This document defines is the reference
   for the new subcode.

   IANA has also registered a new optional, transitive BGP Path Attributes
   option, path attribute named "Only to Customer
   (OTC)" with an (see Section 4) in the "BGP Path Attributes" registry.  IANA
   has assigned code value <TBD3> 35 [To be removed upon publication: http://www.iana.org/assignments/bgp-
   parameters/bgp-parameters.xhtml#bgp-parameters-2] [RFC4271].
   http://www.iana.org/assignments/bgp-parameters/bgp-
   parameters.xhtml#bgp-parameters-2].  This document is the reference
   for the new attribute.

7.  Security Considerations

   The
   length security considerations of BGP (as specified in [RFC4271] and
   [RFC4272]) apply.

   This document proposes a mechanism using BGP Role for the prevention
   and detection of route leaks that are the result of BGP policy
   misconfiguration.  A misconfiguration of the BGP Role may affect
   prefix propagation.  For example, if a downstream (i.e., towards a
   Customer) peering link were misconfigured with a Provider or Peer
   role, this will limit the number of prefixes that can be advertised
   in this direction.  On the other hand if an upstream provider were
   misconfigured (by a local AS) with the Customer role, this may result
   in propagating routes that are received from other Providers or
   Peers.  But the BGP Role negotiation and the resulting confirmation
   of Roles make such misconfigurations unlikely.

   Setting the strict mode of operation for BGP Role negotiation as the
   default may result in a situation where the eBGP session will not
   come up after a software update.  Such an implementation of this
   document is strongly discouraged.

   Removing the OTC Attribute or changing its value can limit the
   opportunity of route leak detection.  Such activity can be done on
   purpose as part of a Man in the Middle (MITM) attack.  For example,
   an AS can remove the OTC Attribute on a received route and then leak
   the route to its transit provider.  Such malicious activity cannot be
   prevented without cryptographically signing the BGP UPDATE [RFC8205]
   or out of band detection [I-D.ietf-sidrops-aspa-verification], but
   such schemes are beyond the scope of this attribute document.

   Adding an OTC Attribute when the route is four bytes.

10.  Security Considerations

   This document proposes a mechanism for prevention advertised from Customer to
   Provider will limit the propagation of the route.  Such a route leaks that
   are may
   be considered as ineligible by the result immediate Provider or its Peers or
   upper layer Providers.  This kind of BGP policy misconfiguration.

   A misconfiguration in OTC setup may affect prefix propagation.  But Attribute addition is
   unlikely to happen on the automation that Provider side because it will limit the
   traffic volume towards its Customer.  On the Customer side, adding an
   OTC Attribute for traffic engineering purposes is provided by BGP roles should make such
   misconfiguration unlikely.

11. also discouraged
   because it will limit route propagation in an unpredictable way.

8.  References

11.1.

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>.

   [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>.

   [RFC4486]  Chen, E. and V. Gillet, "Subcodes for BGP Cease
              Notification Message",

   [RFC4272]  Murphy, S., "BGP Security Vulnerabilities Analysis",
              RFC 4486, 4272, DOI 10.17487/RFC4486,
              April 10.17487/RFC4272, January 2006, <https://www.rfc-editor.org/info/rfc4486>.
              <https://www.rfc-editor.org/info/rfc4272>.

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <https://www.rfc-editor.org/info/rfc5492>.

   [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>.

11.2.  Informative References

   [Gao]      Gao, L.

   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and J. Rexford, "Stable Internet routing without
              global coordination",  IEEE/ACM Transactions on
              Networking, Volume 9, Issue 6, pp 689-692, DOI
              10.1109/90.974523, December 2001,
              <https://ieeexplore.ieee.org/document/974523>.

   [I-D.ietf-grow-route-leak-detection-mitigation]
              Sriram, K. and A. Azimov, "Methods
              Patel, "Revised Error Handling for Detection and
              Mitigation of BGP Route Leaks", draft-ietf-grow-route-
              leak-detection-mitigation-04 (work in progress), October
              2020. UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <https://www.rfc-editor.org/info/rfc7606>.

   [RFC7908]  Sriram, K., Montgomery, D., McPherson, D., Osterweil, E.,
              and B. Dickson, "Problem Definition and Classification of
              BGP Route Leaks", RFC 7908, DOI 10.17487/RFC7908, June
              2016, <https://www.rfc-editor.org/info/rfc7908>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [RFC8212]  Mauch, J., Snijders, J., and G. Hankins, "Default External
              BGP (EBGP) Route Propagation Behavior without Policies",

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 8212,
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8212, July 10.17487/RFC8174,
              May 2017,
              <https://www.rfc-editor.org/info/rfc8212>.

   [Streibelt]
              Streibelt, F., Lichtblau, F., Beverly, R., Feldmann, A.,
              Cristel, C., Smaragdakis, G., <https://www.rfc-editor.org/info/rfc8174>.

8.2.  Informative References

   [Gao]      Gao, L. and R. J. Rexford, "Stable Internet routing without
              global coordination",  IEEE/ACM Transactions on
              Networking, Volume 9, Issue 6, pp 689-692, DOI
              10.1109/90.974523, December 2001,
              <https://ieeexplore.ieee.org/document/974523>.

   [I-D.ietf-sidrops-aspa-verification]
              Azimov, A., Bogomazov, E., Bush, "BGP
              Communities: Even more Worms in R., Patel, K., and J.
              Snijders, "Verification of AS_PATH Using the Routing Can",
              <https://people.mpi-inf.mpg.de/~fstreibelt/preprint/
              communities-imc2018.pdf>. Resource
              Certificate Public Key Infrastructure and Autonomous
              System Provider Authorization", draft-ietf-sidrops-aspa-
              verification-07 (work in progress), February 2021.

   [RFC8205]  Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
              Specification", RFC 8205, DOI 10.17487/RFC8205, September
              2017, <https://www.rfc-editor.org/info/rfc8205>.

Acknowledgements

   The authors wish to thank Alvaro Retana, Andrei Robachevsky, Daniel
   Ginsburg, Jeff Haas, Ruediger Volk, Pavel Lunin, Gyan Mishra, Ignas
   Bagdonas, Sue Hares, and John Scudder for comments, suggestions, and
   critique.

Contributors
   Brian Dickson
   Independent
   Email: brian.peter.dickson@gmail.com

   Doug Montgomery
   USA National Institute of Standards and Technology
   Email: dougm@nist.gov

Authors' Addresses

   Alexander Azimov
   Qrator Labs & Yandex
   Ulitsa Lva Tolstogo 16
   Moscow  119021
   Russian Federation

   Email: a.e.azimov@gmail.com

   Eugene Bogomazov
   Qrator Labs
   1-y Magistralnyy tupik 5A
   Moscow  123290
   Russian Federation

   Email: eb@qrator.net

   Randy Bush
   Internet Initiative Japan & Arrcus, Inc.
   5147 Crystal Springs
   Bainbridge Island, Washington  98110
   United States of America

   Email: randy@psg.com

   Keyur Patel
   Arrcus
   2077 Gateway Place, Suite #400
   San Jose, CA  95119
   US

   Email: keyur@arrcus.com
   Kotikalapudi Sriram
   USA National Institute of Standards and Technology
   100 Bureau Drive
   Gaithersburg, MD  20899
   United States of America

   Email: ksriram@nist.gov