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Versions: (draft-djsmith-bgp-flowspec-oid) 00 01 02 03 04

Network Working Group                                          J. Uttaro
Internet-Draft                                                      AT&T
Updates: 5575 (if approved)                                   J. Alcaide
Intended status: Standards Track                             C. Filsfils
Expires: September 14, 2017                                     D. Smith
                                                                   Cisco
                                                            P. Mohapatra
                                                        Sproute Networks
                                                          March 13, 2017


        Revised Validation Procedure for BGP Flow Specifications
                   draft-ietf-idr-bgp-flowspec-oid-04

Abstract

   This document describes a modification to the validation procedure
   defined in RFC 5575 for the dissemination of BGP flow specifications.
   RFC 5575 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 http://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 September 14, 2017.





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Copyright Notice

   Copyright (c) 2017 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
   (http://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 [RFC5575], 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 (or router reflector per [RFC4456]) 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 (or route reflector) 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 RFC 5575
   validation procedure such that an IBGP peer that is not within the
   data forwarding plane may originate flow specification NLRIs.

3.  Introduction

   RFC 5575 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 RFC 5575 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.
   RFC 5575 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 RFC 5575 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 RFC 5575 validation procedure
   allowing flow specification NLRIs to be originated from a centralized
   BGP route controller within the local autonomous system that is
   neither in the data forwarding path nor serving as a BGP route
   reflector [RFC4456].  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



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   an autonomous system with a large 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 RFC 5575, 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 AS_SEQUENCE segments.

   An AS_PATH without AS_SET and 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
   RFC 5575 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).  Optionally, an implementation
   could be configured to allow only flow specification NLRIs containing
   only a subset of ASes.  This could be useful, for example, with
   networks that consist of multiple ASes that operate under the same
   administrative domain.

   Further, RFC 5575 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
   RFC 5575 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 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 RFC 6793.

   RFC 5575 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 RFC 5575, 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.  With
   the (newly introduced) second condition above applied, uncongruent
   topologies are supported.

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 RFC 5575 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

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://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,
              <http://www.rfc-editor.org/info/rfc4271>.




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   [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,
              <http://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,
              <http://www.rfc-editor.org/info/rfc5065>.

   [RFC5575]  Marques, P., Sheth, N., Raszuk, R., Greene, B., Mauch, J.,
              and D. McPherson, "Dissemination of Flow Specification
              Rules", RFC 5575, DOI 10.17487/RFC5575, August 2009,
              <http://www.rfc-editor.org/info/rfc5575>.

   [RFC6793]  Vohra, Q. and E. Chen, "BGP Support for Four-Octet
              Autonomous System (AS) Number Space", RFC 6793,
              DOI 10.17487/RFC6793, December 2012,
              <http://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


   Clarence Filsfils
   Cisco

   Email: cf@cisco.com







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   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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