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Versions: (draft-djsmith-bgp-flowspec-oid) 00 01 02 03 04 05 06 07 08 09 10

Network Working Group                                          J. Uttaro
Internet-Draft                                                      AT&T
Updates: 5575bis (if approved)                                J. Alcaide
Intended status: Standards Track                             C. Filsfils
Expires: November 10, 2019                                      D. Smith
                                                                   Cisco
                                                            P. Mohapatra
                                                        Sproute Networks
                                                             May 9, 2019


        Revised Validation Procedure for BGP Flow Specifications
                   draft-ietf-idr-bgp-flowspec-oid-08

Abstract

   This document describes a modification to the validation procedure
   defined in RFC 5575bis for the dissemination of BGP flow
   specifications.  RFC 5575bis requires that the originator of the flow
   specification matches the originator of the best-match unicast route
   for the destination prefix embedded in the flow specification.  This
   allows only BGP speakers within the data forwarding path (such as
   autonomous system border routers) to originate BGP flow
   specifications.  Though it is possible to disseminate such flow
   specifications directly from border routers, it may be operationally
   cumbersome in an autonomous system with a large number of border
   routers having complex BGP policies.  The modification proposed
   herein enables flow specifications to be originated from a
   centralized BGP route controller.

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 November 10, 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.  Requirements Language . . . . . . . . . . . . . . . . . . . .   2
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
   4.  Revised Validation Procedure  . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   7
   8.  Normative References  . . . . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   8

1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Motivation

   Step (a) of the validation procedure in [RFC5575bis], section 6 is
   defined with the underlying assumption that the flow specification
   NLRI traverses the same path, in the inter-domain and intra-domain
   route distribution graph, as that of the longest-match unicast route
   for the destination prefix embedded in the flow specification.

   In the case of inter-domain traffic filtering, for example, the flow
   specification originator at the egress border routers of ASN1 (RTR-D
   and RTR-E in figure 1) matches the EBGP neighbor that advertised the
   longest match destination prefix (RTR-F and RTR-G respectively).
   Similarly, at the ingress border routers of ASN1 (RTR-A and RTR-B in
   figure 1), the flow specification originator matches the egress IBGP
   border routers that had advertised the unicast route for the best-



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   match destination prefix (RTR-D and RTR-E respectively).  This is
   true even when ingress border routers select paths from different
   egress border routers as best path based upon IGP distance (as an
   example, RTR-A chooses RTR-D's path as best; RTR-B chooses RTR-E as
   the best path).

                     / - - - - - - - - - - - - -  -
                     |           ASN1              |
                       +-------+        +-------+
                     | |       |        |       |  |
                       | RTR-A |        | RTR-B |
                     | |       |        |       |  |
                       +-------+        +-------+
                     |       \           /         |
                        IBGP  \         / IBGP
                     |         \       /           |
                               +-------+
                     |         |       |           |
                               | RTR-C |
                     |         |  RC   |           |
                               +-------+
                     |           /   \             |
                                /     \
                     |   IBGP  /       \ IBGP      |
                       +-------+        +-------+
                     | | RTR-D |        | RTR-E |  |
                       |       |        |       |
                     | |       |        |       |  |
                       +-------+        +-------+
                     |     |                 |     |
                      - - -|- - - - - - - - -|- - -/
                           | EBGP       EBGP |
                      - - -|- - - - - - - - -|- - -/
                     |     |                 |     |
                       +-------+        +-------+
                     | |       |        |       |  |
                       | RTR-F |        | RTR-G |
                     | |       |        |       |  |
                       +-------+        +-------+
                     |           ASN2              |
                     / - - - - - - - - - - - - -  -

                                 Figure 1

   It is highly desirable that each ASN is able to protect itself
   independently from network security attacks using the BGP flow
   specification NLRI for intra-domain purposes only.  Network operators
   often deploy a dedicated Security Operations Center (SOC) within



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   their ASN to monitor and detect such security attacks.  To mitigate
   attacks in a scalable intra-domain manner, operators require the
   ability to originate intra-domain flow specification NLRIs from a
   central BGP route controller that is not within the data forwarding
   plane.  In this way, operators can direct border routers within their
   ASN with specific attack mitigation actions (drop the traffic,
   forward to a clean-pipe center, etc.).  To originate a flow
   specification NLRI, a central BGP route controller must set itself as
   the originator in the flowspec NLRI.  This is necessary given the
   route controller is originating the flow specification not reflecting
   it, and to avoid the complexity of having to determine the egress
   border router whose path was chosen as the best in each of the
   ingress border routers.  It thus becomes necessary to modify step (a)
   of the [RFC5575bis] validation procedure such that an IBGP peer that
   is not within the data forwarding plane may originate flow
   specification NLRIs.

3.  Introduction

   [RFC5575bis] defined a new BGP capability that can be used to
   distribute traffic flow specifications amongst BGP speakers in
   support of traffic filtering.  The primary intention of [RFC5575bis]
   is to enable downstream autonomous systems to signal traffic
   filtering policies to upstream autonomous systems.  In this way,
   traffic is filtered closer to the source and the upstream autonomous
   system(s) avoid carrying the traffic to the downstream autonomous
   system only to be discarded.  [RFC5575bis] also enables more granular
   traffic filtering based upon upper layer protocol information (e.g.,
   protocol port numbers) as opposed to coarse IP destination prefix-
   based filtering.  Flow specification NLRIs received from a BGP peer
   are subject to validity checks before being considered feasible and
   subsequently installed within the respective Adj-RIB-In.  The
   validation procedure defined within [RFC5575bis] requires that the
   originator of the flow specification NLRI matches the originator of
   the best-match unicast route for the destination prefix embedded in
   the flow specification.  This allows only BGP speakers [RFC4271]
   within the data forwarding path (such as autonomous system border
   routers) to originate BGP flow specification NLRIs.  Though it is
   possible to disseminate such flow specification NLRIs directly from
   border routers, it may be operationally cumbersome in an autonomous
   system with a large number of border routers having complex BGP
   policies.  This document describes a modification to the [RFC5575bis]
   validation procedure allowing flow specification NLRIs to be
   originated from a centralized BGP route controller within the local
   autonomous system that is not in the data forwarding path.  While the
   proposed modification cannot be used for inter-domain coordination of
   traffic filtering, it greatly simplifies distribution of intra-domain
   traffic filtering policies in an autonomous system with a large



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   number of border routers having complex BGP policies.  By relaxing
   the validation procedure for IBGP, the proposed modification allows
   flow specifications to be distributed in a standard and scalable
   manner throughout an autonomous system.

4.  Revised Validation Procedure

   Step (a) of the validation procedure specified in [RFC5575bis],
   section 6 is redefined as follows:

   a.  One of the following conditions MUST hold true.

       *  The originator of the flow specification matches the
          originator of the best-match unicast route for the destination
          prefix embedded in the flow specification.

       *  The AS_PATH attribute of the flow specification does not
          contain AS_SET and/or AS_SEQUENCE segments.

   An AS_PATH without AS_SET and/or AS_SEQUENCE segments indicates that
   the flow specification was originated inside the local AS [RFC4271]
   or inside the local confederation (in the case that the local AS
   belongs to a confederation of ASes) [RFC5065].  With this
   modification to the [RFC5575bis] validation procedure, it is now
   possible for an IBGP peer that is not within the data forwarding path
   to originate flow specification NLRIs.  This applies whether the AS
   belongs or not to a confederation of ASes.  Checking the (newly
   introduced) second condition above MAY be disabled by configuration
   on a BGP speaker.  However, it SHOULD be enabled by default.
   Disabling the condition may be a good practice when the administrator
   knows with certainty that there are not flow specification NLRI
   originated inside the local AS (or local confederation).  The default
   behavior is thus to validate an empty AS_PATH.  In this context, an
   empty AS_PATH means that it does not have AS_SET and/or AS_SEQUENCE
   segments.  Optionally, an implementation MAY also validate a specific
   non-empty AS_PATH.  For instance, it could validate a flowspec NLRI
   whose AS_PATH contains only an AS_SEQUENCE of ASes known (via
   configuration) to belong to the same administrative domain.

   Further, [RFC5575bis] states that "BGP (flow specification)
   implementations MUST also enforce that AS_PATH attribute of a route
   received via the External Border Gateway Protocol (EBGP) contains the
   neighboring AS in the left-most position of the AS_PATH attribute".
   This rule is not valid for all topologies.  For example, it prevents
   the exchange of BGP flow specification NLRIs at Internet exchanges
   with BGP route servers.  Therefore, this document also redefines the
   [RFC5575bis] AS_PATH validation procedure referenced above as
   follows:



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   BGP flow specification implementations MUST enforce that the last AS
   added within the AS_PATH attribute of a EBGP learned flow
   specification NLRI MUST match the last AS added within the AS_PATH
   attribute of the best-match unicast route for the destination prefix
   embedded in the flow specification.  This proposed modification
   enables the exchange of BGP flow specification NLRIs at Internet
   exchanges with BGP route servers while at the same time, for security
   reasons, prevents an EBGP peer from advertising an inter-domain flow
   specification for a destination prefix that it does not provide
   reachability information for.  Note, comparing only the last ASes
   added is sufficient for EBGP learned flow specification NLRIs.
   Requiring a full AS_PATH match would limit origination of inter-
   domain flow specifications to the origin (or first) AS of the best-
   match unicast route for the destination prefix embedded in the flow
   specification only.  As such, a full AS_PATH validity check may
   prevent transit ASes from originating inter-domain flow
   specifications, which is not desirable.

   This document also clarifies proper handling when the BGP flow
   specification does not embed a destination prefix component.  The
   default behavior SHOULD be not to perform any validation procedure.
   Further, support for two-octet AS number space is out of the scope of
   this document.

   In this context, AS_PATH attribute is defined as the reconstructed AS
   Path information (by combining AS_PATH and AS4_PATH attributes, if
   the BGP speaker is a NEW speaker and receives the route from an OLD
   speaker), according to section 4.2.3 of [RFC6793].

   [RFC5575bis] references "the best-match unicast route for the
   destination prefix embedded in the flow specification".  For clarity,
   this route is defined hereby as the best path of the unicast network
   that covers destination prefix embedded in the flow specification
   with the longer prefix-length.  In other words, we consider only the
   best-match network and we do not consider unicast non-best paths
   (even if it is received from the same peer than the flowspec route).

   Note that, per [RFC5575bis], originator may refer to the BGP
   ORIGINATOR_ID attribute or the transport address of the peer from
   which we received the update.  If the later, a network must be
   designed so it has a congruent topology.  Otherwise, using two
   peering sessions between the same pair of BGP speakers, one for
   unicast and one for flowspec, will cause the flowspec validation
   procedure to fail.  Consider, for example, the case where a BGP route
   reflector receives the NLRIs from a route reflector client, thus not
   receiving the ORIGINATOR_ID attribute.  If the speaker belongs to a
   confederation [RFC5065] and we are receiving a flowspec route from
   different peers than its best match unicast route, the flowspec



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   validation procedure will fail as well.  Consider also a
   misconfiguration where flowspec address-family is not configured for
   a particular peering between different member-AS (but it is
   configured for unicast).  Even if we receive the flowspec route via a
   redundant peer, we may receive the unicast route and the flowspec
   from different peers, and thus flowspec validation will fail.  Thus,
   with the (newly introduced) second condition above applied,
   incongruent topologies are supported.

   Note that if the flowspec NLRI is learned from another AS (and thus
   the AS_PATH is not empty), the original validation procedures defined
   in [RFC5575bis] still apply and incongruent topologies may cause
   validation rules to fail.

5.  IANA Considerations

   This memo includes no request to IANA.

6.  Security Considerations

   No new security issues are introduced by relaxing the validation
   procedure for IBGP learned flow specifications.  With this proposal,
   the security characteristics of BGP flow specifications remain
   equivalent to the existing security properties of BGP unicast
   routing.  Traffic flow specifications learned from IBGP peers are
   trusted, hence, it is not required to validate that the originator of
   an intra-domain traffic flow specification matches the originator of
   the best-match unicast route for the flow destination prefix.
   Conversely, this proposal continues to enforce the validation
   procedure for EBGP learned traffic flow specifications.  In this way,
   the security properties of [RFC5575bis] are maintained such that an
   EBGP peer cannot cause a denial-of-service attack by advertising an
   inter-domain flow specification for a destination prefix that it does
   not provide reachability information for.

7.  Acknowledgements

   The authors would like to thank Han Nguyen for his direction on this
   work as well as Waqas Alam, Keyur Patel, Robert Raszuk, Eric Rosen
   and Shyam Sethuram for their review comments.

8.  Normative References

   [I-D.ietf-idr-rfc5575bis]
              Hares, S., Loibl, C., Raszuk, R., McPherson, D., and M.
              Bacher, "Dissemination of Flow Specification Rules",
              draft-ietf-idr-rfc5575bis-14 (work in progress), April
              2019.



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   [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>.

   [RFC4456]  Bates, T., Chen, E., and R. Chandra, "BGP Route
              Reflection: An Alternative to Full Mesh Internal BGP
              (IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
              <https://www.rfc-editor.org/info/rfc4456>.

   [RFC5065]  Traina, P., McPherson, D., and J. Scudder, "Autonomous
              System Confederations for BGP", RFC 5065,
              DOI 10.17487/RFC5065, August 2007,
              <https://www.rfc-editor.org/info/rfc5065>.

   [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
              Autonomous System (AS) Number Space", RFC 6793,
              DOI 10.17487/RFC6793, December 2012,
              <https://www.rfc-editor.org/info/rfc6793>.

Authors' Addresses

   James Uttaro
   AT&T
   200 S. Laurel Ave
   Middletown, NJ  07748
   USA

   Email: ju1738@att.com


   Juan Alcaide
   Cisco
   7100 Kit Creek Road
   Research Triangle Park, NC  27709
   USA

   Email: jalcaide@cisco.com








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   Clarence Filsfils
   Cisco

   Email: cf@cisco.com


   David Smith
   Cisco
   111 Wood Ave South
   Iselin, NJ  08830
   USA

   Email: djsmith@cisco.com


   Pradosh Mohapatra
   Sproute Networks

   Email: mpradosh@yahoo.com
































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