Network Working Group                                          A. Azimov
Internet-Draft                                              E. Bogomazov
Intended status: Standards Track                             Qrator Labs
Expires: August 19, 2019 January 9, 2020                                         R. Bush
                                      Internet Initiative Japan & Arrcus
                                                                K. Patel
                                                            Arrcus, Inc.
                                                               K. Sriram
                                                                 US NIST
                                                       February 15,
                                                            July 8, 2019

     Route Leak Prevention using Roles in Update and Open messages
                   draft-ietf-idr-bgp-open-policy-05
                   draft-ietf-idr-bgp-open-policy-06

Abstract

   Route Leaks are the propagation of BGP prefixes which violate
   assumptions of BGP topology relationships; e.g. passing a route
   learned from one peer to another peer or to a transit provider,
   passing a route learned from one transit provider to another transit
   provider or to a peer.  Today, approaches to leak prevention rely on
   marking routes according to by operator configuration options, configuration, with no check that the
   configuration corresponds to that of the BGP neighbor, or enforcement
   that the two BGP speakers agree on the relationship.  This document
   enhances BGP Open OPEN to establish agreement of the (peer, customer,
   provider, RS, RS-client, internal) Route Server, Route Server client) relationship of two
   neighboring BGP speakers to enforce appropriate configuration on both
   sides.  Propagated routes are then marked with an iOTC OTC attribute
   according to the agreed relationship 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 RFC 2119
   BCP 14 [RFC2119] [RFC8174] when, and only when when, they appear in all upper case.  They may also appear in lower or mixed
   case
   capitals, as English words, without normative meaning. 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 August 19, 2019. January 9, 2020.

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
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   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   3
   2.  Peering Relationships . . . . . . . . . . . . . . . . . . . .   3
   3.  BGP Role  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Role capability . . . . . . . . . . . . . . . . . . . . . . .   4
   5.  Role correctness  . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Strict mode . . . . . . . . . . . . . . . . . . . . . . .   6   5
   6.  BGP Internal Only To Customer attribute  . . . . . . . . . . .   6
   7.  Attribute or Community  . . . . . . . . . . . .   6
   7.  Enforcement . . . . . . .   6
   8.  Compatibility with BGPsec . . . . . . . . . . . . . . . . . .   7
   9.   6
   8.  Additional Considerations . . . . . . . . . . . . . . . . . .   7
   10.
   9.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   11.
   10. Security Considerations . . . . . . . . . . . . . . . . . . .   8
   12.
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . .   8
   13.
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     13.1.
     12.1.  Normative References . . . . . . . . . . . . . . . . . .   8
     13.2.
     12.2.  Informative References . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   This document specifies a new BGP Capability Code, [RFC5492] Sec 4,
   which two BGP speakers MAY use to ensure that they MUST agree on
   their relationship; i.e. customer and provider or peers.  Either or
   both MAY optionally be configured to require that this option be
   exchanged for the BGP Open to succeed.

   Also this document specifies a way to mark routes according to BGP
   Roles established in OPEN message and a way to create double-boundary
   filters for prevention of route leaks using the new BGP Path
   Attribute.

   For the purpose of this document,

   BGP route leaks are when a BGP
   route was route(s) which were learned from transit
   provider or peer and is then announced to another provider or peer.  See[RFC7908].  See
   [RFC7908].  These are usually the result of misconfigured or absent
   BGP route filtering or lack of coordination between two BGP speakers.

   [I-D.ietf-idr-route-leak-detection-mitigation]

   The mechanism proposed in that draft provides the opportunity
   [I-D.ietf-idr-route-leak-detection-mitigation] uses large-communities
   to detect attempt detection of route leaks made by
   third parties but provides no mechanism leaks.  While signaling using
   communities is easy to strongly prevent route
   leak creation.

   Also, route tagging which implement, ut relies on operator maintained
   policy configuration which is too easily, and too often,
   misconfigured.  Another problem may occur if the community signal is
   stripped, accidentally or maliciously.

   This document provides configuration automation using 'BGP roles',
   which are negotiated using a new BGP Capability Code in OPEN message,
   [RFC5492] Sec 4.  Either or both BGP speakers MAY be configured to
   require that this capability be agreed for the BGP OPEN to succeed.

   A new BGP Path Attribute is specified that SHOULD be automatically
   configured using BGP roles.  This attribute prevents networks from
   creating leaks, and detects leaks created by third-parties.

2.  Peering Relationships

   Despite uses of words such as "Customer," "Peer." etc. described
   above etc.; these are not
   business relationships, who pays whom, etc.  These are common terms
   to represent restrictions on BGP route propagation, sometimes known
   as the Gao-Rexford model. model [cite].

   A Provider:  MAY send to a customer all available prefixes.

   A Customer:  MAY send to a provider their own prefixes and prefixes
      learned from any of their customers.  A customer MUST NOT send to
      a provider prefixes learned from its peers, from other providers,
      or RS. from Route Servers.

   A Route Server (RS)  MAY send to a RS client Client all available prefixes.

   A Route Server Client (RS-client)  MAY send to an RS its own prefixes
      and prefixes learned from its customers.  A RS-client MUST NOT
      send to an RS prefixes learned from peers, from its providers, or
      from other RS. RS(s).

   A Peer:  MAY send to a peer its own prefixes and prefixes learned
      from its customers.  A peer MUST NOT send to a peer prefixes
      learned from other peers, from its providers, or RS.

   An Internal:  MAY send all available prefixes through internal link. from RS(s).

   Of course, any BGP speaker may apply policy to reduce what is
   announced, and a recipient may apply policy to reduce the set of
   routes they accept.  But violation  Violation of the above rules marked MUST NOT may result in route leaks.
   leaks so MUST not be allowed.  Automatic enforment of these rules
   should significantly reduce configuration mistakes.  While these
   enforcing the above rules will address most BGP peering relations cover 99% of
   possible scenarios,
   their configuration isn't part of the BGP itself,
   thus itself; therefore requiring
   configuration of communities ingress and corresponding egress prefix filters.  The automation of this process may significantly
   decrease number of configuration mistakes. filters is still strongly
   advised.

3.  BGP Role

   BGP Role is new configuration option that SHOULD be configured on
   each BGP session.  It reflects the real-world agreement between two
   BGP speakers about their peering relationship.

   Allowed Role values for eBGP sessions are:

   o  Provider - sender is a transit provider to neighbor;

   o  Customer - sender is transit customer of neighbor;

   o  RS - sender is route server a Route Server, usually at internet exchange point
      (IX)

   o  RS-client  RS-Client - sender is client of RS at internet exchange point (IX)

   o  Peer - sender and neighbor are peers;

   o  Internal - sender and neighbor are part of the same organization.

   For iBGP sessions, only the Internal role MAY be configured.

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

4.  Role capability

   The TLV (type, length, value) of the BGP Role capability are:

   o  Type - <TBD1>;

   o  Length - 1 (octet);

   o  Value - integer corresponding to speaker' BGP Role.

                      +-------+---------------------+
                      | Value | Role name           |
                      +-------+---------------------+
                      |   0   | Sender is Internal  |
                      |   1   | Sender is Provider  |
                      |   2   1   | Sender is RS        |
                      |   3   2   | Sender is RS-Client |
                      |   4   3   | Sender is Customer  |
                      |   5   4   | Sender is Peer      |
                      +-------+---------------------+

                    Table 1: Predefined BGP Role Values

5.  Role correctness

   Section 3 described how BGP Role is a reflection of encodes the relationship between two
   BGP speakers.  But the mere presence of BGP Role doesn't
   automatically guarantee role agreement between two BGP peers.

   To enforce correctness, the BGP Role check is used with a set of
   constrains on how speakers' BGP Roles MUST correspond.  Of course,
   each speaker MUST announce and accept the BGP Role capability in the
   BGP OPEN message exchange.

   If a speaker receives a BGP Role capability, it MUST check the value
   of the received capability with its own BGP Role (if it is set).  The
   allowed pairings are (first a sender's Role, second the receiver's
   Role):

                      +-------------+---------------+
                      | Sender Role | Receiver Role |
                      +-------------+---------------+
                      | Internal    | Internal      |
                      | Provider    | Customer      |
                      | Customer    | Provider      |
                      | RS          | RS-Client     |
                      | RS-Client   | RS            |
                      | Peer        | Peer          |
                      +-------------+---------------+

                    Table 2: Allowed Role Capabilities

   In case of any other pairs of roles,

   If the Role pair is not in the above table, a speaker MUST send a
   Role Mismatch Notification (code 2, sub-code <TBD2>).

5.1.  Strict mode

   A new BGP configuration option "strict mode" is defined with values
   of true or false.  If set to true, then the speaker MUST refuse to
   establish a BGP session with a neighbor which does not announce the
   BGP Role capability in their the OPEN message.  If a speaker rejects a
   connection, it MUST 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 BGP speakers
   that do not yet support this mechanism.

6.  BGP Internal Only To Customer attribute

   The Internal Only To Customer (iOTC) attribute (OTC) BGP Attribute is a new optional,
   non-transitive
   transitive BGP Path attribute with the Type Code <TBD3>.

   This
   attribute has zero length as it is used only as a flag.

   There are four rules of iOTC byte attribute usage: MUST apply the following policy:

   1.  The iOTC  If a route with OTC attribute is received from Customer or RS-
       client - it's a route leak and MUST be added rejected.

   2.  If a route with OTC attribute is received from Peer and its value
       isn't equal to all incoming routes if the
       receiver's Role neighbor's ASN - it's a route leak and MUST be
       rejected.

   3.  If a route is Customer, Peer, received from a Provider, Peer or RS-client;

   2.  Routes with RS and the iOTC OTC
       attribute has not been set it MUST NOT be announced by a
       sender whose Role is Customer, Peer, or RS-client;

   3. added with value equal to
       AS number of the neighbor (sender).

   The egress policy MUST be:

   1.  A sender route with the OTC attribute set MUST NOT include iOTC in UPDATE messages advertised be sent to
       eBGP neighbor if its Role isn't Internal.

   4. providers,
       peers, or RS(s).

   2.  If iOTC route is contained in an UPDATE message from eBGP speaker sent to customer or peer and
       receiver's Role isn't Internal then this the OTC attribute is not
       set it MUST be
       removed.

   These rules provide mechanism added with value equal to strongly prevent route leak creation
   by an AS. AS number of the sender.

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

7.  Attribute or Community  Enforcement

   Having the relationship hard set by agreement unequivocally agreed between the two peers in
   BGP OPEN is critical; the routers BGP implementations enforce the
   relationship irrespective of operator policy configuration errors.

   Similarly, it is critical that the application of that relationship on prefix propagation
   using iOTC is OTC MUST BE enforced by the router(s), BGP implementations, and
   minimally not
   exposed to user mis-configuration.  There is a question
   whether the iOTC marking should be an attribute or a well-known
   community.

   There is a long and sordid history of mis-configurations inserting
   incorrect communities, deleting communities, ignoring well-known
   community markings etc.  In this mechanism's case, an operator could,
   for example, accidentally strip the well-known community on receipt.

   As opposed to communities, BGP attributes may not be generally
   modified or filtered by the operator.  The router(s) enforce them.
   This is the desired property for the iOTC OTC marking.  Hence, this
   document specifies iOTC OTC as an attribute.

8.  Compatibility with BGPsec

   As the iOTC attribute is non-transitive, it is not seen by or signed
   by BGPsec [RFC8205].

9.  Additional Considerations

   As the BGP Role reflects the peering relationship between neighbors,
   it can also might have other uses.  As an  For example, BGP Role might affect route
   priority, or be used to distinguish borders of a network if 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.

   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]

   This document doesn't provide any security

   There are peering relationships which are 'complex'; e.g. when both
   parties are intentionally sending prefixes received from each other
   to their peers and/or upstreams.  If multiple BGP peerings can
   segregate the 'complex' parts of the relationship, the complex
   peering roles can be segregated into different BGP sessions, and
   normal BGP Roles MUST be used on the non-complex sessions.  No Roles
   SHOULD be configured on 'complex' BGP sessions, and OTC MUST be set
   by configuration on a per-prefix basis.  There can be no measures to
   check correctness of iOTC usage OTC use if role isn't Role is not configured.

10.

9.  IANA Considerations

   This document defines a new Capability Codes option [to be removed
   upon publication: http://www.iana.org/assignments/capability-codes/
   capability-codes.xhtml] [RFC5492], named "BGP Role", 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 this registry is to be populated with the data in Table 1.
   Future assignments may be made by a standard action
   procedure[RFC5226].

   This document defines new subcode, "Role Mismatch", assigned value
   <TBD2> in the OPEN Message Error subcodes registry [to be removed
   upon publication: http://www.iana.org/assignments/bgp-parameters/bgp-
   parameters.xhtml#bgp-parameters-6] [RFC4271].

   This document defines a new optional, non-transitive transitive BGP Path Attributes
   option, named "Internal Only "Only To Customer", assigned value <TBD3> [To be
   removed upon publication:
   http://www.iana.org/assignments/bgp-parameters/bgp-
   parameters.xhtml#bgp-parameters-2] http://www.iana.org/assignments/bgp-
   parameters/bgp-parameters.xhtml#bgp-parameters-2] [RFC4271].  The
   length of this attribute is 0.

11.

10.  Security Considerations

   This document proposes a mechanism for prevention of route leaks that
   are the result of BGP policy mis-configuration.

   Deliberate sending of a known conflicting BGP Role could be used to
   sabotage a BGP connection.  This is easily detectable.

   BGP Role

   A misconfiguration in OTC setup may affect prefix propagation.  But
   the automation that is disclosed only to an immediate provided by BGP neighbor, so it will
   not itself reveal any sensitive information to third parties.

12. roles should make such
   misconfiguration unlikely.

11.  Acknowledgments

   The authors wish to thank Douglas Montgomery, Brian Dickson, Andrei
   Robachevsky
   Robachevsky, and Daniel Ginsburg for their contributions to a variant
   of this work.

13.

12.  References

13.1.

12.1.  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", RFC 4486, DOI 10.17487/RFC4486,
              April 2006, <https://www.rfc-editor.org/info/rfc4486>.

   [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>.

13.2.

   [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>.

12.2.  Informative References

   [I-D.ietf-idr-route-leak-detection-mitigation]
              Sriram, K. and A. Azimov, "Methods for Detection and
              Mitigation of BGP Route Leaks", draft-ietf-idr-route-leak-
              detection-mitigation-10 (work in progress), October 2018.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <https://www.rfc-editor.org/info/rfc5226>.

   [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>.

   [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>.

   [RFC8212]  Mauch, J., Snijders, J., and G. Hankins, "Default External
              BGP (EBGP) Route Propagation Behavior without Policies",
              RFC 8212, DOI 10.17487/RFC8212, July 2017,
              <https://www.rfc-editor.org/info/rfc8212>.

Authors' Addresses

   Alexander Azimov
   Qrator Labs

   Email: a.e.azimov@gmail.com

   Eugene Bogomazov
   Qrator Labs

   Email: eb@qrator.net

   Randy Bush
   Internet Initiative Japan & Arrcus

   Email: randy@psg.com

   Keyur Patel
   Arrcus, Inc.

   Email: keyur@arrcus.com
   Kotikalapudi Sriram
   US NIST

   Email: ksriram@nist.gov