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Network Working Group                                      James Uttaro
Internet Draft                                                     AT&T
Intended status: Standards Track                        Matthieu Texier
Nov 26, 2012                                             Arbor Networks
Expires: May 26, 2013                                       David Smith
                                                      Pradosh Mohapatra
                                                          Cisco Systems
                                                         Wim Henderickx
                                                           Adam Simpson
                                                         Alcatel-Lucent

   BGP Flow-Spec Extended Community for Traffic Redirect to IP Next Hop
                draft-simpson-idr-flowspec-redirect-02.txt


Status of this Memo

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   Section 4.e of the Trust Legal Provisions and are provided without
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Abstract

   Flow-spec is an extension to BGP that allows for the dissemination
   of traffic flow specification rules. This has many possible
   applications but the primary one for many network operators is the
   distribution of traffic filtering actions for DDoS mitigation. The
   flow-spec standard [RFC 5575] defines a redirect-to-VRF action for
   policy-based forwarding but this mechanism can be difficult to use,
   particularly in networks without L3 VPNs.

   This draft proposes a new redirect-to-IP flow-spec action that
   provides a simpler method of policy-based forwarding. This action is
   indicated by the presence of a new BGP extended community in the
   flow-spec route. Many routers already support a redirect-to-IP
   filter action and, in this case, the only new functionality implied
   by this draft is the ability to signal the action using flow-spec.

Table of Contents


   1. Introduction...................................................3
   2. Terminology....................................................3
   3. Redirect to IP Extended Community..............................3
   4. Security Considerations........................................5
   5. IANA Considerations............................................6
   6. References.....................................................6
      6.1. Normative References......................................6
      6.2. Informative References....................................6
   7. Acknowledgments................................................6

















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1. Introduction

   Flow-spec is an extension to BGP that allows for the dissemination
   of traffic flow specification rules. This has many possible
   applications but the primary one for many network operators is the
   distribution of traffic filtering actions for DDoS mitigation.

   Every flow-spec route is effectively a rule, consisting of a
   matching part (encoded in the NLRI field) and an action part
   (encoded as a BGP extended community). The flow-spec standard [RFC
   5575] defines widely-used filter actions such as discard and rate
   limit; it also defines a redirect-to-VRF action for policy-based
   forwarding. Using the redirect-to-VRF action for redirecting traffic
   towards an alternate destination is useful for DDoS mitigation but
   it can be complex and cumbersome, particularly in networks without
   L3 VPNs.

   This draft proposes a new redirect-to-IP flow-spec action that
   provides a simpler method of policy-based forwarding. This action is
   indicated by the presence of a new BGP extended community in the
   flow-spec route. Many routers already support a redirect-to-IP
   filter action and, in this case, the only new functionality implied
   by this draft is the ability to signal the action using flow-spec.

2. Terminology

   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].

3. Redirect to IP Extended Community

   This document proposes a new BGP extended community called "Flow
   spec redirect/mirror to IP next-hop" with type value 0x0800
   (assigned from the "BGP Extended Communities Type - extended,
   transitive" registry). The new extended community, simply called
   "redirect to IP" in the remainder of this document, can be added to
   any UPDATE message announcing the reachability of one or more flow-
   spec NLRI. The encoding of the attribute is shown in Figure 1. In
   the 6 bytes of data after the 2-byte type value the least-
   significant bit is the 'C' (copy) bit. If 'C' is equal to 1 the
   originator of the flow-spec route is requesting a mirror action:
   routers that install this flow-spec route should create a copy of
   every matching packet and forward the copies towards a specified
   next-hop address while still forwarding the original packets
   normally (i.e. based on longest-prefix-match forwarding table
   lookups). If 'C' is equal to 0 the originator of the flow-spec route


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   is requesting a simple redirect action: routers that install this
   flow-spec route should forward the matching packets (the original
   versions, not copies) towards a new next-hop address. All bits other
   than the 'C' bit in the 6-byte data portion of the extended
   community should be set to 0 by the originating BGP speaker and
   ignored by receiving BGP speakers.


    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     0x08      |     0x00      |     Reserved                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+     (Set to zero and          |
   |                                     ignored on receipt)     |C|
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

        Flow-spec Redirect/Mirror to IP Next-hop Extended Community

                                 Figure 1



   The redirect-to-IP extended community is valid with any other set of
   flow-spec extended communities except if that set includes a
   redirect-to-VRF extended community (type 0x8008) and in that case
   the redirect-to-IP extended community should be ignored.

   When a BGP speaker receives an UPDATE message with the redirect-to-
   IP extended community it is expected to create a traffic filtering
   rule for every flow-spec NLRI in the message that has this path as
   its best path. The filter entry matches the IP packets described in
   the NLRI field and redirects them (C=0) or copies them (C=1) towards
   the IPv4 or IPv6 address specified in the 'Network Address of Next-
   Hop' field of the associated MP_REACH_NLRI. More specifically: if an
   IPv4 [or IPv6] packet with destination address D that is normally
   forwarded to a next-hop A matches a filter entry of the type
   described above it MUST instead be redirected (C=0) or mirrored
   (C=1) to next-hop B, where B is found by FIB lookup of the IPv4 [or
   IPv6] address contained in the MP_REACH_NLRI next-hop field (i.e. a
   longest-prefix-match lookup). Signaling and applying constraints
   beyond longest-prefix-match on the types of interfaces or tunnels
   that can be used as the redirection next-hop B are not precluded by
   this specification but are nevertheless outside its scope.

   If an MP_REACH_NLRI containing one or more flow-spec NLRI does not
   have a valid IPv4 or IPv6 address in its next-hop field, or the


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   length of the next-hop is 0, then the redirect-to-IP extended
   community, if present, should be ignored.

   The scope of application (in terms of router interfaces/contexts) of
   the filter rules derived from the redirect-to-IP extended community
   is outside the scope of this specification except for noting that
   filter rules derived from VPNv4 and VPNv6 flow-spec routes should
   only be installed in the VRF contexts that import the routes.

   The redirect-to-IP extended community is transitive across AS
   boundaries. When a flow-spec route with this community is advertised
   to an EBGP peer the next-hop address in the MP_REACH_NLRI SHOULD be
   reset to an address of the advertising router by default, per normal
   BGP procedures. Alternatively, the advertising router MAY be
   configured to keep the next-hop unchanged, if it is known that the
   destination AS has a valid route to the next-hop address.

   The validation check described in [RFC 5575] and revised in
   [VALIDATE] SHOULD be applied by default to received flow-spec routes
   with the redirect-to-IP extended community, as it is to all types of
   flow-spec routes. This means that a flow-spec route with a
   destination prefix subcomponent SHOULD NOT be accepted from an EBGP
   peer unless that peer also advertised the best path for the matching
   unicast route. BGP speakers that support the redirect-to-IP extended
   community MUST also, by default, enforce the following check when
   receiving a flow-spec route from an EBGP peer:

        . If the flow-spec route has an IP next-hop X and includes a
           redirect-to-IP extended community, then the BGP speaker
           SHOULD discard the redirect-to-ip extended community (and
           not propagate it further with the flow-spec route) if the
           last AS in the AS_PATH or AS4_PATH attribute of the longest
           prefix match for X does not match the AS of the EBGP peer.

   It MUST be possible to disable this additional validation check on a
   per-EBGP session basis.

4. Security Considerations

   A system that originates a flow-spec route with a redirect-to-IP
   extended community can cause many receivers of the flow-spec route
   to send traffic to a single next-hop, overwhelming that next-hop and
   resulting in inadvertent or deliberate denial-of-service. This is
   particularly a concern when the redirect-to-IP extended community is
   allowed to cross AS boundaries. The validation check described in
   section 3 significantly reduces this risk.



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5. IANA Considerations

   IANA is requested to update the reference for the following
   assignment in the "BGP Extended Communities Type - extended,
   transitive" registry:



   Type value  Name                                      Reference
   ----------  ----------------------------------------  ---------
   0x0800      Flow spec redirect/mirror to IP next-hop  [this
   document]

6. References

   6.1. Normative References

   [RFC2119]        Bradner, S., "Key words for use in RFCs to Indicate
                    Requirement Levels", BCP 14, RFC 2119, March 1997.

   6.2. Informative References

   [RFC5575]        P. Marques, N. Sheth, R. Raszuk, B. Greene, J.
                    Mauch, D. McPherson, "Dissemination of Flow
                    Specification Rules", RFC 5575, August 2009.

   [IPV6-FLOW]      R. Raszuk, B. Pithawala, D. McPherson,
                    "Dissemination of Flow Specification Rules for
                    IPv6", draft-ietf-idr-flow-spec-v6-00, June 2011.

   [VALIDATE]       Uttaro, J., Filsfils, C., Mohapatra, P., Smith, D.,
                    "Revised Validation Procedure for BGP Flow
                    Specifications", draft-ietf-idr-bgp-flowspec-oid-
                    00, June 2012.

7. Acknowledgments

   The authors would like to thank Han Nguyen and Robert Raszuk for
   their feedback and suggestions.

   This document was prepared using 2-Word-v2.0.template.dot.







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Authors' Addresses

   James Uttaro
   AT&T
   200 S. Laurel Avenue
   Middletown, NJ  07748
   USA
   Email: ju1738@att.com

   Pradosh Mohapatra
   Cisco
   170 W. Tasman Drive
   San Jose, CA  95134
   USA
   Email: pmohapat@cisco.com

   David Smith
   Cisco
   111 Wood Avenue South
   Iselin, NJ  08830
   USA
   E-mail: djsmith@cisco.com

   Wim Henderickx
   Alcatel-Lucent
   Copernicuslaan 50
   2018 Antwerp, Belgium
   Email: wim.henderickx@alcatel-lucent.be

   Adam Simpson
   Alcatel-Lucent
   600 March Road
   Ottawa, Ontario K2K 2E6
   Canada
   Email: adam.simpson@alcatel-lucent.com

   Matthieu Texier
   Arbor Networks
   38 Rue de Berri
   75008 Paris
   Email: mtexier@arbor.net








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