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Internet Engineering Task Force                            A. Khare, Ed.
Internet-Draft                                                J. Scudder
Intended status: Standards Track                  Juniper Networks, Inc.
Expires: November 2, 2019                                       L. Jalil
                                                            M. Gallagher
                                                                 Verizon
                                                          K. Kasavchenko
                                                                NetScout
                                                             May 1, 2019


                     BGP FlowSpec Payload Matching
             draft-khare-idr-bgp-flowspec-payload-match-03

Abstract

   The rise in frequency, volume, and pernicious effects of DDoS attacks
   has elevated them from fare for the specialist to generalist press.
   Numerous reports detail the taxonomy of DDoS types, the varying
   motivations of their attackers, as well as the resulting business and
   reputation loss of their targets.

   BGP FlowSpec (RFC 5575, "Dissemination of Flow Specification Rules")
   can be used to rapidly disseminate filters that thwart attacks, being
   particularly effective against the volumetric type.  Operators can
   use existing FlowSpec components to match on pre-defined packet
   header fields.  However recent enhancements to forwarding plane
   filter implementations allow matches at arbitary locations within the
   packet header and, to some extent, the payload.  This capability can
   be used to detect highly amplified attacks whose attack signature
   remains relatively constant while values in the packet header vary,
   as well as the burgeoning variety of tunneled traffic.

   We define a new FlowSpec component, "Flexible Match Conditions", with
   similar matching semantics to those of existing components.  This
   component will allow the operator to define bounded match conditions
   using bit offsets and a variety of match types.

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/.




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   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 2, 2019.

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
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Motivation  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Machine analysis of DDoS attacks  . . . . . . . . . . . .   4
       2.1.1.  Matching based on payload . . . . . . . . . . . . . .   4
       2.1.2.  Matching based on any protocol header field or across
               fields  . . . . . . . . . . . . . . . . . . . . . . .   4
     2.2.  Tunneled traffic  . . . . . . . . . . . . . . . . . . . .   5
     2.3.  Non-IP traffic  . . . . . . . . . . . . . . . . . . . . .   5
   3.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   5
   4.  Defining the Search Boundary  . . . . . . . . . . . . . . . .   6
     4.1.  Defining the Start of the Boundary  . . . . . . . . . . .   6
     4.2.  Defining the End of the Boundary  . . . . . . . . . . . .   7
   5.  Specification . . . . . . . . . . . . . . . . . . . . . . . .   8
     5.1.  Value . . . . . . . . . . . . . . . . . . . . . . . . . .   8
       5.1.1.  Match Boundary  . . . . . . . . . . . . . . . . . . .   8
       5.1.2.  Match Type  . . . . . . . . . . . . . . . . . . . . .   8
         5.1.2.1.  Bitmask match . . . . . . . . . . . . . . . . . .   9
         5.1.2.2.  Numeric range match . . . . . . . . . . . . . . .   9
         5.1.2.3.  ASCII-only regular expression string match  . . .   9
   6.  Error Handling  . . . . . . . . . . . . . . . . . . . . . . .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  10
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  10
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10



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   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  10
     10.2.  Informative References . . . . . . . . . . . . . . . . .  10
     10.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  11
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  11

1.  Introduction

   BGP FlowSpec [RFC5575] can be used to rapidly disseminate filters
   that thwart attacks, being particularly effective against the
   volumetric type.  Operators can use existing FlowSpec components to
   match on pre-defined packet header fields.  However recent
   enhancements to forwarding plane filter implementations allow matches
   at arbitary locations within the packet header and, to some extent,
   the payload.  This capability can be used to detect highly amplified
   attacks whose attack signature remains relatively constant, while
   values in packet header vary.  Varying values in packet headers
   generally make it challenging to mitigate such attacks.

   We define a new FlowSpec component, "Flexible Match Conditions", with
   similar matching semantics to those of existing components.  This
   component will allow the operator to define bounded match conditions
   using bit offsets and a variety of match types.

1.1.  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

   BGP FlowSpec couples both the advertisement of NLRI-specific match
   conditions, as well as the forwarding instance to which the filter is
   attached.  This makes sense since BGP FlowSpec advertisements are
   most commonly generated, or at least verified, by human operators.
   The operator finds it intuitive to configure match conditions as
   human-readable values, native to each address family.

   It is much friendlier, for instance, to define a filter that matches
   a source address of 192.168.1.1/32, than it is to work with the
   equivalent binary representation of that IPv4 address.  Further, it
   is easier to use field names such as 'IPv4 source address' as part of
   the match condition, than it is to demarc that field using byte and
   bit offsets.

   However, there are a number of use cases that benefit from the
   latter, more machine-readable approach.



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2.1.  Machine analysis of DDoS attacks

   Launching a DDoS is easier and more cost-effective than ever.  The
   will to attack matters more than wherewithal.  Those with the
   inclination can initiate one from the comfort of their homes [1], or
   even buy DDoS-as-a-Service [2], complete with 24x7 support and
   flexible payment plans.

   Despite their effectiveness, such attacks are easily thwarted - once
   identified.  The challenge lies in fishing out a generally unvarying
   attack signature from a data stream.  Machine analysis may prove
   superior here, given the size of input involved.  The resulting
   pattern may not lie within a well-defined field; even if it happens
   to, it may be a more straight-forward workflow to have machine
   analysis result in a machine-readable filter.

   Below we illustrate the need for the suggested approach with two use
   cases.

2.1.1.  Matching based on payload

   A vast majority of volumetric DDoS attacks are of reflection/
   amplification nature.  They can often be identified by the UDP source
   port of a service that reflects and amplifies the attack traffic.
   However, there exist DDoS attack methodologies such as SSDP
   Diffraction or Bittorent amplification where values in most of layer
   3 and layer 4 header fields, including source and destination UDP
   ports, are varied.  That makes it challenging if not impossible to
   classify and mitigate a DDoS attack based on existing Flow
   Specification components.  At the same time these attacks very often
   have a constant pattern in payload.  Using the pattern in payload as
   a matching criteria would help in mitigating such DDoS attacks.

2.1.2.  Matching based on any protocol header field or across fields

   BGP FlowSpec [RFC5575] defines 12 Flow Specification component types
   that can be used to match traffic.  However, a DDoS attack might
   result in illegitimate traffic of a specific pattern in a layer 3 or
   layer 4 header, and this pattern would not have a respective
   component type.  Examples are Time to Live field of IP header or
   Window field of TCP header.  In order to avoid extending BGP FlowSpec
   [RFC5575] with all theoretically possible component types, this
   document proposes divorcing the search boundary from having to align
   with header fields.  This allows flexibly matching patterns
   regardless of whether they have a currently matching component type
   as well as patterns that span fields.





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2.2.  Tunneled traffic

   Tunnels continue to proliferate due to the benefits they provide.
   They can help reduce state in the underlay network.  Tunnels allow
   bypassing routing decisions of the transit network.  Traffic that is
   tunneled is often done so to obscure or secure.  Common tunnel types
   include IPsec [RFC4301], Generic Routing Encapsulation (GRE)
   [RFC2890], Virtual eXtensible Local Area Network (VXLAN) [RFC7348],
   GPRS Tunneling Protocol (GTP) [GTPv1-U], et al.

   By definition, transit nodes that are not the endpoints of the tunnel
   hold no attendant control or management plane state.  These very
   qualities make it challenging to filter tunneled traffic at non-
   endpoints.  Often though, the forwarding hardware at these transit-
   only nodes is capable of reading the byte stream that comprises the
   protocol being tunneled.  Despite this capability, it is usually
   infeasible to filter based on the content of this passenger
   protocol's header since BGP FlowSpec does not provide the operator a
   way to address arbitrary locations within a packet.

2.3.  Non-IP traffic

   Not all traffic is forwarded as IP packets.  Layer 2 services abound,
   including flavors of BGP-signaled Ethernet VPNs such as BGP-EVPN,
   BGP-VPLS, FEC 129 VPWS (LDP-signaled VPWS with BGP Auto-Discovery).

   Ongoing efforts such as [I-D.ietf-idr-flowspec-l2vpn] offer one
   approach, which is to add layer 2 fields as additional match
   conditions.  This may suffice if a filter needs to be applied only to
   layer 2, or only to layer 3 header fields.

3.  Terminology

   Header  Subset of datagram or packet that contains information that
       is required for delivery from source to destination.

   Payload  Remaining subset of datagram or packet that contains the
       information that is being transported.

   Field  A priori defined subset of the header with established
       semantics, acceptable value type and length.

   Type  How the encoded bits that comprise a field are interpreted.  A
       well-defined type can be used to enforce notions of ordering,
       upper and lower bounds, and correctness.  For instance, using a
       signed integer type to count the number of packets received by a
       given forwarding element could result in negative values.  To
       avoid that, the field should be typed as a zero-based counter.



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       In order to avoid premature rollover, the counter should be sized
       appropriately.  To prevent retrogression, the values should
       always be accumulated as it is impossible to receive fewer
       packets in toto.  Defining this example field as an unsigned
       64-bit field with monotonically incrementing values ensure it
       meets the appropriate objectives.

   Maximum Readable Length  The packet length in bits that a forwarding
       implementation can parse and make available for filtering.
       Abbreviated as MRL.

4.  Defining the Search Boundary

   Based on this set of definitions, the flexible match operator
   requires three inputs to demarcate the search extents and the search
   term itself:

   o  Where the match should begin: Where in the datagram or packet the
      search for matching values is initiated.  This allows skipping
      over parts of the packet that are not of interest.

   o  Where the match should end: Where in the datagram or packet the
      search ends.

   o  What should be matched: A variety of search types, including exact
      numeric matches, matching a range of numeric values, and string-
      based matches.

4.1.  Defining the Start of the Boundary

   While intuitive to grasp, determining the search boundary requires
   explication.  A canonical forwarding engine parses an incoming packet
   header and identifies it as belonging to a single Network Layer
   Reachability Information (NLRI), or address family.  The contents of
   the header are parsed with address family specificity, in order to
   extract a forwarding lookup key.  In the case of IPv4 unicast
   forwarding, this key is the IPv4 destination address.  The key is
   used to look up the corresponding action in an address family
   specific forwarding table.

   This does not preclude implementations from exposing additional
   packet headers to the operator, both encapsulating and encapsulated,
   to provide additional forwarding functionality.  For instance, common
   stateless load balancing techniques involve reading fields in
   additional headers in order to increase entropy and preserve flow
   ordering.  As another example, in the case of Ethernet encapsulated
   IPv4 packets, a forwarding engine could allow filtering using the




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   source or destination MAC address even though the forwarding decision
   is ultimately based only on the IPv4 header.

   As yet another example, consider that a Virtual eXtensible Local Area
   Network (VXLAN) [RFC7348] packet has the following headers:

   o  Outer Ethernet Header: Source MAC address of the originating VXLAN
      Tunnel End Point (VTEP). - Outer IPv4/IPv6 Header: Source IP
      address of the originating VXLAN Tunnel End Point (VTEP).

   o  Outer UDP Header: Random source port used to generate entropy for
      load balancing, and destined to the IANA-assigned VXLAN port 4789.

   o  VXLAN Header: Used to identify a specific VXLAN overlay network.

   o  Inner Ethernet Header and payload: Original MAC frame
      encapsulated.

   Forwarding at the tunnel midpoints, i.e., not the where tunnel
   imposition or disposition occur, makes use of the outer IPv4 header.
   In order to differentiate itself, a midpoint may provide the ability
   to parse and take the VXLAN header into account.  This functionality
   could be used to implement access control or perform traffic
   telemetry.

   In order to normalize behavior across forwarding implementations, the
   beginning of the search space MUST be aligned with the FlowSpec AFI/
   SAFI to which the flexible match rule belongs.  For instance, with
   FlowSpec for IPv4 traffic, the match can only start at the first bit
   of the IPv4 header.  Even if the forwarding implementation has the
   capability to read outer and inner headers, the start of the search
   extent is anchored at the IPv4 header.

4.2.  Defining the End of the Boundary

   Similarly, the end of the search boundary MUST be the lesser of
   either the last bit in a packet or the Maximum Readable Length
   (Section 3) that a forwarding implementation can parse from a packet
   and make available for filtering.  As the MRL will be implementation-
   dependent, it needs to be known to the flexible filtering rules
   engine.  That can be communicated out-of-band via configuration or
   signaled using future BGP or IGP extensions.

   It is not required that all nodes in a flexible filtering domain be
   required to have a common or minimum MRL.  This does not obviate the
   need for a rules engine to take MRL into account when creating
   flexible filters.  This is especially important as the rules engine
   may not have direct BGP peering with all FlowSpec enforcers and may



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   not receive a BGP Notification if it advertises a flexible match that
   exceeds the MRL of a given node.

5.  Specification

   We define a new FlowSpec component, Type TBD, named "Flexible Match
   Conditions".

   Encoding: <type (1 octet), length (1 octet), value>

5.1.  Value

   The Value field contains the match boundary, match type, and term to
   match.

   Encoding: <match boundary (2 octets), match type (1 octet), match
   term>

5.1.1.  Match Boundary

   The match boundary is encoded as:

                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                     |u|bit o|      byte offset      |
                     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   u - Currently unused.  MUST be zero.

   bit offset -  The number of bits to ignore in the packet being
       matched, from the start of the search boundary.

   byte offset -  The number of bytes to ignore.

5.1.2.  Match Type

   Currently the following match types are defined:

            +-------+-----------------------------------------+
            | Value | Match Type                              |
            +-------+-----------------------------------------+
            |   0   | Bitmask match                           |
            |   1   | Numeric range match                     |
            |   2   | Regular expression (regex) string match |
            +-------+-----------------------------------------+

                                Match Types





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   Match types 0 and 1 MUST be implemented.  All other types are
   optional.

5.1.2.1.  Bitmask match

   This is encoded as {prefix, mask}, of equal length.

   prefix -  Provides a bit string to be matched.  The prefix and mask
       fields are bitwise AND'ed to create a resulting pattern.

   mask -  Paired with the prefix field to create a bit string match.
       An unset bit is treated as a 'do not care' bit in the
       corresponding position in the prefix field.  When a bit is set in
       the mask, the value of the bit in the corresponding location in
       the prefix field must match exactly.

5.1.2.2.  Numeric range match

   This is encoded as {low value, high value}, treated as an inclusive
   range.

   low -  The low value of the desired numeric range.  This value MUST
       be numerically lower than the high value.

   high -  The high value of the desired numeric range.  This value MUST
       be numerically higher than the low value.

5.1.2.3.  ASCII-only regular expression string match

   Not every forwarding plane that supports filtering via FlowSpec is a
   hardware-accelerated Network Processor Unit (NPU) or Application-
   Specific Integrated Circuit (ASIC).  Software-only forwarding planes,
   while less performant, may be able to filter on more complex match
   types.

   There is a plethora of regular expression engines and their supported
   flavor.  The specific flavor this match type refers to is the
   extended regular expression (ERE) as defined by [IEEE.1003-2.1992].

6.  Error Handling

   Malicious, misbehaving, or misunderstanding implementations could
   advertise semantically incorrect values.  Care must be taken to
   minimize fallout from attempting to parse such data.  Any well-
   behaved implementation SHOULD verify that the minimum packet length
   undergoing a match equals (match start header length + byte offset +
   bit offset + value length).




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7.  Security Considerations

   This document introduces no additional security considerations beyond
   those already covered in [RFC5575] .

8.  IANA Considerations

   IANA is requested to assign a type from the First Come First Served
   range of the "Flow Spec Component Types" registry:

        +------------+---------------------------+---------------+
        | Type Value |            Name           |   Reference   |
        +------------+---------------------------+---------------+
        |    TBD     | Flexible Match Conditions | this document |
        +------------+---------------------------+---------------+

9.  Acknowledgements

   Thanks to Rafal Jan Szarecki, Sudipto Nandi, Ron Bonica, and Jeff
   Haas for their valuable comments and suggestions on this document.

10.  References

10.1.  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>.

   [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,
              <https://www.rfc-editor.org/info/rfc5575>.

10.2.  Informative References

   [GTPv1-U]  3GPP, "General Packet Radio System (GPRS) Tunnelling
              Protocol User Plane (GTPv1-U)", 3GPP TS 29.281 10.3.0,
              September 2011.

   [I-D.ietf-idr-flowspec-l2vpn]
              Weiguo, H., Eastlake, D., Uttaro, J., Litkowski, S., and
              S. Zhuang, "BGP Dissemination of L2VPN Flow Specification
              Rules", draft-ietf-idr-flowspec-l2vpn-09 (work in
              progress), January 2019.





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   [IEEE.1003-2.1992]
              Institute of Electrical and Electronics Engineers,
              "Information Technology - Portable Operating System
              Interface (POSIX) - Part 2: Shell and Utilities (Vol. 1)",
              IEEE Standard 1003.2, 1992.

   [RFC2890]  Dommety, G., "Key and Sequence Number Extensions to GRE",
              RFC 2890, DOI 10.17487/RFC2890, September 2000,
              <https://www.rfc-editor.org/info/rfc2890>.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, DOI 10.17487/RFC4301,
              December 2005, <https://www.rfc-editor.org/info/rfc4301>.

   [RFC7348]  Mahalingam, M., Dutt, D., Duda, K., Agarwal, P., Kreeger,
              L., Sridhar, T., Bursell, M., and C. Wright, "Virtual
              eXtensible Local Area Network (VXLAN): A Framework for
              Overlaying Virtualized Layer 2 Networks over Layer 3
              Networks", RFC 7348, DOI 10.17487/RFC7348, August 2014,
              <https://www.rfc-editor.org/info/rfc7348>.

10.3.  URIs

   [1] https://github.com/649/Memcrashed-DDoS-Exploit

   [2] https://www.facebook.com/PutinStresser/photos/
       a.1687498801469198/2024483917770683/?type=3

Authors' Addresses

   Anurag Khare (editor)
   Juniper Networks, Inc.
   2251 Corporate Park Drive
   Herndon, Virginia  20171
   US

   Email: anuragk@juniper.net


   John Scudder
   Juniper Networks, Inc.
   1133 Innovation Way
   Sunnyvale, CA  94089
   US

   Email: jgs@juniper.net





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   Luay Jalil
   Verizon

   Email: luay.jalil@one.verizon.com


   Michael Gallagher
   Verizon

   Email: michael.gallagher@verizon.com


   Kirill Kasavchenko
   NetScout

   Email: Kirill.Kasavchenko@netscout.com



































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