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Versions: (draft-hr-idr-rfc5575bis) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18

IDR Working Group                                               C. Loibl
Internet-Draft                                 Next Layer Communications
Obsoletes: 5575,7674 (if approved)                              S. Hares
Intended status: Standards Track                                  Huawei
Expires: May 7, 2020                                           R. Raszuk
                                                            Bloomberg LP
                                                            D. McPherson
                                                                Verisign
                                                               M. Bacher
                                                        T-Mobile Austria
                                                        November 4, 2019


               Dissemination of Flow Specification Rules
                      draft-ietf-idr-rfc5575bis-18

Abstract

   This document obsoletes both RFC5575 and RFC7674.

   This document defines a Border Gateway Protocol Network Layer
   Reachability Information (BGP NLRI) encoding format, that can be used
   to distribute traffic Flow Specifications.  This allows the routing
   system to propagate information regarding more specific components of
   the traffic aggregate defined by an IP destination prefix.

   It also specifies BGP Extended Community encoding formats, that can
   be used to propagate Traffic Filtering Actions along with the Flow
   Specification NLRI.  Those Traffic Filtering Actions encode actions a
   routing system can take if the packet matches the Flow Specification.

   Additionally, it defines two applications of that encoding format:
   one that can be used to automate inter-domain coordination of traffic
   filtering, such as what is required in order to mitigate
   (distributed) denial-of-service attacks, and a second application to
   provide traffic filtering in the context of a BGP/MPLS VPN service.
   Other applications (ie. centralized control of traffic in a SDN or
   NFV context) are also possible.  Other drafts specify IPv6, MPLS
   addresses, L2VPN addresses, and NV03 encapsulation of IP addresses as
   Flow Specification extensions.

   The information is carried via the BGP, thereby reusing protocol
   algorithms, operational experience, and administrative processes such
   as inter-provider peering agreements.







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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 May 7, 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
   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.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Definitions of Terms Used in This Memo  . . . . . . . . . . .   5
   3.  Flow Specifications . . . . . . . . . . . . . . . . . . . . .   5
   4.  Dissemination of IPv4 FLow Specification Information  . . . .   6
     4.1.  Length Encoding . . . . . . . . . . . . . . . . . . . . .   7
     4.2.  NLRI Value Encoding . . . . . . . . . . . . . . . . . . .   7
       4.2.1.  Operators . . . . . . . . . . . . . . . . . . . . . .   7
       4.2.2.  Components  . . . . . . . . . . . . . . . . . . . . .   9
     4.3.  Examples of Encodings . . . . . . . . . . . . . . . . . .  13
   5.  Traffic Filtering . . . . . . . . . . . . . . . . . . . . . .  16
     5.1.  Ordering of Flow Specifications . . . . . . . . . . . . .  17
   6.  Validation Procedure  . . . . . . . . . . . . . . . . . . . .  18
   7.  Traffic Filtering Actions . . . . . . . . . . . . . . . . . .  19
     7.1.  Traffic Rate in Bytes (traffic-rate-bytes) sub-type 0x06   20



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     7.2.  Traffic Rate in Packets (traffic-rate-packets) sub-type
           TBD . . . . . . . . . . . . . . . . . . . . . . . . . . .  21
     7.3.  Traffic-action (traffic-action) sub-type 0x07 . . . . . .  21
     7.4.  RT Redirect (rt-redirect) sub-type 0x08 . . . . . . . . .  22
     7.5.  Traffic Marking (traffic-marking) sub-type 0x09 . . . . .  22
     7.6.  Interaction with other Filtering Mechanisms in Routers  .  23
     7.7.  Considerations on Traffic Filtering Action Interference .  23
   8.  Dissemination of Traffic Filtering in BGP/MPLS VPN Networks .  24
   9.  Traffic Monitoring  . . . . . . . . . . . . . . . . . . . . .  25
   10. Error-Handling  . . . . . . . . . . . . . . . . . . . . . . .  25
   11. Future NLRI Extensions  . . . . . . . . . . . . . . . . . . .  25
   12. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26
     12.1.  AFI/SAFI Definitions . . . . . . . . . . . . . . . . . .  26
     12.2.  Flow Component Definitions . . . . . . . . . . . . . . .  26
     12.3.  Extended Community Flow Specification Actions  . . . . .  27
   13. Security Considerations . . . . . . . . . . . . . . . . . . .  30
   14. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  31
   15. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  31
   16. References  . . . . . . . . . . . . . . . . . . . . . . . . .  32
     16.1.  Normative References . . . . . . . . . . . . . . . . . .  32
     16.2.  Informative References . . . . . . . . . . . . . . . . .  33
     16.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  34
   Appendix A.  Python code: flow_rule_cmp . . . . . . . . . . . . .  34
   Appendix B.  Comparison with RFC 5575 . . . . . . . . . . . . . .  36
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  37

1.  Introduction

   This document obsoletes both
   "Dissemination of Flow Specification Rules" [RFC5575] and
   "Clarification of the Flowspec Redirect Extended Community"[RFC7674].

   Modern IP routers contain both the capability to forward traffic
   according to IP prefixes as well as to classify, shape, rate limit,
   filter, or redirect packets based on administratively defined
   policies.  These traffic policy mechanisms allow the operator to
   define match rules that operate on multiple fields of the packet
   header.  Actions such as the ones described above can be associated
   with each rule.

   The n-tuple consisting of the matching criteria defines an aggregate
   traffic Flow Specification.  The matching criteria can include
   elements such as source and destination address prefixes, IP
   protocol, and transport protocol port numbers.

   Section 4 of this document defines a general procedure to encode Flow
   Specification for aggregated traffic flows so that they can be
   distributed as a BGP [RFC4271] NLRI.  Additionally, Section 7 of this



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   document defines the required Traffic Filtering Actions BGP Extended
   Communities and mechanisms to use BGP for intra- and inter-provider
   distribution of traffic filtering rules to filter (distributed)
   denial-of-service (DoS) attacks.

   By expanding routing information with Flow Specifications, the
   routing system can take advantage of the ACL (Access Control List) or
   firewall capabilities in the router's forwarding path.  Flow
   Specifications can be seen as more specific routing entries to a
   unicast prefix and are expected to depend upon the existing unicast
   data information.

   A Flow Specification received from an external autonomous system will
   need to be validated against unicast routing before being accepted
   (Section 6).  The flow specification received from an internal BGP
   peer within the same autonomous system (per [RFC4271]) is assumed to
   have been validated prior to transmission within the iBGP mesh of an
   autonomous system.  If the aggregate traffic flow defined by the
   unicast destination prefix is forwarded to a given BGP peer, then the
   local system can install more specific Flow Specifications that may
   result in different forwarding behavior, as requested by this system.

   From an operational perspective, the utilization of BGP as the
   carrier for this information allows a network service provider to
   reuse both internal route distribution infrastructure (e.g., route
   reflector or confederation design) and existing external
   relationships (e.g., inter-domain BGP sessions to a customer
   network).

   While it is certainly possible to address this problem using other
   mechanisms, this solution has been utilized in deployments because of
   the substantial advantage of being an incremental addition to already
   deployed mechanisms.

   In current deployments, the information distributed by this extension
   is originated both manually as well as automatically.  The latter by
   systems that are able to detect malicious traffic flows.  When
   automated systems are used, care should be taken to ensure their
   correctness as well as the limitations of the systems that receive
   and process the advertised Flow Specifications (see also Section 13).

   This specification defines required protocol extensions to address
   most common applications of IPv4 unicast and VPNv4 unicast filtering.
   The same mechanism can be reused and new match criteria added to
   address similar filtering needs for other BGP address families such
   as IPv6 families [I-D.ietf-idr-flow-spec-v6].





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2.  Definitions of Terms Used in This Memo

   AFI -   Address Family Identifier.

   AS -   Autonomous System.

   Loc-RIB -   The Loc-RIB contains the routes that have been selected
      by the local BGP speaker's Decision Process.

   NLRI -   Network Layer Reachability Information.

   PE -   Provider Edge router.

   RIB -   Routing Information Base.

   SAFI -   Subsequent Address Family Identifier.

   VRF -   Virtual Routing and Forwarding instance.

   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 BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Flow Specifications

   A Flow Specification is an n-tuple consisting of several matching
   criteria that can be applied to IP traffic.  A given IP packet is
   said to match the defined Flow Specification if it matches all the
   specified criteria.  This n-tuple is encoded into a BGP NLRI defined
   below.

   A given Flow Specification may be associated with a set of
   attributes, depending on the particular application; such attributes
   may or may not include reachability information (i.e., NEXT_HOP).
   Well-known or AS-specific community attributes can be used to encode
   a set of predetermined actions.

   A particular application is identified by a specific (Address Family
   Identifier, Subsequent Address Family Identifier (AFI, SAFI)) pair
   [RFC4760] and corresponds to a distinct set of RIBs.  Those RIBs
   should be treated independently from each other in order to assure
   non-interference between distinct applications.

   BGP itself treats the NLRI as a key to an entry in its databases.
   Entries that are placed in the Loc-RIB are then associated with a
   given set of semantics, which is application dependent.  This is



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   consistent with existing BGP applications.  For instance, IP unicast
   routing (AFI=1, SAFI=1) and IP multicast reverse-path information
   (AFI=1, SAFI=2) are handled by BGP without any particular semantics
   being associated with them until installed in the Loc-RIB.

   Standard BGP policy mechanisms, such as UPDATE filtering by NLRI
   prefix as well as community matching and manipulation, must apply to
   the Flow Specification defined NLRI-type, especially in an inter-
   domain environment.  Network operators can also control propagation
   of such routing updates by enabling or disabling the exchange of a
   particular (AFI, SAFI) pair on a given BGP peering session.

4.  Dissemination of IPv4 FLow Specification Information

   This document defines a Flow Specification NLRI type (Figure 1) that
   may include several components such as destination prefix, source
   prefix, protocol, ports, and others (see Section 4.2 below).

   This NLRI information is encoded using MP_REACH_NLRI and
   MP_UNREACH_NLRI attributes as defined in [RFC4760].  Whenever the
   corresponding application does not require Next Hop information, this
   shall be encoded as a 0-octet length Next Hop in the MP_REACH_NLRI
   attribute (if a non 0-octet Next Hop is present it should be ignored
   on receipt).

   The NLRI field of the MP_REACH_NLRI and MP_UNREACH_NLRI is encoded as
   a 1- or 2-octet NLRI length field followed by a variable-length NLRI
   value.  The NLRI length is expressed in octets.

                     +-------------------------------+
                     |    length (0xnn or 0xfnnn)    |
                     +-------------------------------+
                     |    NLRI value   (variable)    |
                     +-------------------------------+

                Figure 1: Flow Specification NLRI for IPv4

   Implementations wishing to exchange Flow Specification MUST use BGP's
   Capability Advertisement facility to exchange the Multiprotocol
   Extension Capability Code (Code 1) as defined in [RFC4760].  The
   (AFI, SAFI) pair carried in the Multiprotocol Extension Capability
   MUST be (AFI=1, SAFI=133) for IPv4 Flow Specification, and (AFI=1,
   SAFI=134) for VPNv4 Flow Specification.








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4.1.  Length Encoding

   o  If the NLRI length is smaller than 240 (0xf0 hex) octets, the
      length field can be encoded as a single octet.

   o  Otherwise, it is encoded as an extended-length 2-octet value in
      which the most significant nibble of the first byte is all ones.

   In Figure 1 above, values less-than 240 are encoded using two hex
   digits (0xnn).  Values above 239 are encoded using 3 hex digits
   (0xfnnn).  The highest value that can be represented with this
   encoding is 4095.  For example the length value of 239 is encoded as
   0xef (single octet) while 240 is encoded as 0xf0f0 (2-octet).

4.2.  NLRI Value Encoding

   The Flow Specification NLRI value consists of a list of optional
   components and is encoded as follows:

   Encoding: <[component]+>

   A specific packet is considered to match the Flow Specification when
   it matches the intersection (AND) of all the components present in
   the Flow Specification.

   Components must follow strict type ordering by increasing numerical
   order.  A given component type may (exactly once) or may not be
   present in the Flow Specification.  If present, it MUST precede any
   component of higher numeric type value.

   All combinations of components within a single Flow Specification are
   allowed.  However, some combinations cannot match any packets (ie.
   "ICMP Type AND Port" will never match any packets), and thus SHOULD
   NOT be propagated by BGP.

4.2.1.  Operators

   Most of the components described below make use of comparison
   operators.  Which of the two operators is used is defined by the
   components in Section 4.2.2.  The operators are encoded as a single
   octet.

4.2.1.1.  Numeric Operator (numeric_op)

   This operator is encoded as shown in Figure 2.






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                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     | e | a |  len  | 0 |lt |gt |eq |
                     +---+---+---+---+---+---+---+---+

                  Figure 2: Numeric Operator (numeric_op)

   e -  end-of-list bit: Set in the last {op, value} pair in the list.

   a -  AND bit: If unset, the previous term is logically ORed with the
      current one.  If set, the operation is a logical AND.  In the
      first operator byte of a sequence it SHOULD be encoded as unset
      and and MUST be treated as always unset on decoding.  The AND
      operator has higher priority than OR for the purposes of
      evaluating logical expressions.

   len -  length: The length of the value field for this operator given
      as (1 << len).  This encodes 1 (len=00), 2 (len=01), 4 (len=10), 8
      (len=11) bytes.

   0 -  SHOULD be set to 0 on NLRI encoding, and MUST be ignored during
      decoding

   lt -  less than comparison between data and value.

   gt -  greater than comparison between data and value.

   eq -  equality between data and value.

   The bits lt, gt, and eq can be combined to produce common relational
   operators such as "less or equal", "greater or equal", and "not equal
   to" as shown in Table 1.

            +----+----+----+----------------------------------+
            | lt | gt | eq | Resulting operation              |
            +----+----+----+----------------------------------+
            | 0  | 0  | 0  | false (independent of the value) |
            | 0  | 0  | 1  | == (equal)                       |
            | 0  | 1  | 0  | > (greater than)                 |
            | 0  | 1  | 1  | >= (greater than or equal)       |
            | 1  | 0  | 0  | < (less than)                    |
            | 1  | 0  | 1  | <= (less than or equal)          |
            | 1  | 1  | 0  | != (not equal value)             |
            | 1  | 1  | 1  | true (independent of the value)  |
            +----+----+----+----------------------------------+

                Table 1: Comparison operation combinations




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4.2.1.2.  Bitmask Operator (bitmask_op)

   This operator is encoded as shown in Figure 3.

                       0   1   2   3   4   5   6   7
                     +---+---+---+---+---+---+---+---+
                     | e | a |  len  | 0 | 0 |not| m |
                     +---+---+---+---+---+---+---+---+

                  Figure 3: Bitmask Operator (bitmask_op)

   e, a, len - Most significant nibble:  (end-of-list bit, AND bit, and
      length field), as defined in the Numeric Operator format in
      Section 4.2.1.1.

   not - NOT bit:  If set, logical negation of operation.

   m - Match bit:  If set, this is a bitwise match operation defined as
      "(data AND value) == value"; if unset, (data AND value) evaluates
      to TRUE if any of the bits in the value mask are set in the data

   0 - all 0 bits:  SHOULD be set to 0 on NLRI encoding, and MUST be
      ignored during decoding

4.2.2.  Components

   The encoding of each of the components begins with a type field (1
   octet) followed by a variable length parameter.  The following
   sections define component types and parameter encodings for the IPv4
   IP layer and transport layer headers.  IPv6 NLRI component types are
   described in [I-D.ietf-idr-flow-spec-v6].

4.2.2.1.  Type 1 - Destination Prefix

   Encoding: <type (1 octet), length (1 octet), prefix (variable)>

   Defines the destination prefix to match.  The length and prefix
   fields are encoded as in BGP UPDATE messages [RFC4271]

4.2.2.2.  Type 2 - Source Prefix

   Encoding: <type (1 octet), length (1 octet), prefix (variable)>

   Defines the source prefix to match.  The length and prefix fields are
   encoded as in BGP UPDATE messages [RFC4271]






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4.2.2.3.  Type 3 - IP Protocol

   Encoding: <type (1 octet), [numeric_op, value]+>

   Contains a list of {numeric_op, value} pairs that are used to match
   the IP protocol value byte in IP packet header (see [RFC0791]
   Section 3.1).

   This component uses the Numeric Operator (numeric_op) described in
   Section 4.2.1.1.  Type 3 component values SHOULD be encoded as single
   byte (numeric_op len=00).

4.2.2.4.  Type 4 - Port

   Encoding: <type (1 octet), [numeric_op, value]+>

   Defines a list of {numeric_op, value} pairs that matches source OR
   destination TCP/UDP ports (see [RFC0793] Section 3.1 and [RFC0768]
   Section "Format").  This component matches if either the destination
   port OR the source port of a IP packet matches the value.

   This component uses the Numeric Operator (numeric_op) described in
   Section 4.2.1.1.  Type 4 component values SHOULD be encoded as 1- or
   2-byte quantities (numeric_op len=00 or len=01).

   In case of the presence of the port (destination-port, source-port)
   component only TCP or UDP packets can match the entire Flow
   Specification.  The port component, if present, never matches when
   the packet's IP protocol value is not 6 (TCP) or 17 (UDP), if the
   packet is fragmented and this is not the first fragment, or if the
   system is unable to locate the transport header.  Different
   implementations may or may not be able to decode the transport header
   in the presence of IP options or Encapsulating Security Payload (ESP)
   NULL [RFC4303] encryption.

4.2.2.5.  Type 5 - Destination Port

   Encoding: <type (1 octet), [numeric_op, value]+>

   Defines a list of {numeric_op, value} pairs used to match the
   destination port of a TCP or UDP packet (see also [RFC0793]
   Section 3.1 and [RFC0768] Section "Format").

   This component uses the Numeric Operator (numeric_op) described in
   Section 4.2.1.1.  Type 5 component values SHOULD be encoded as 1- or
   2-byte quantities (numeric_op len=00 or len=01).

   The last paragraph of Section 4.2.2.4 also applies to this component.



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4.2.2.6.  Type 6 - Source Port

   Encoding: <type (1 octet), [numeric_op, value]+>

   Defines a list of {numeric_op, value} pairs used to match the source
   port of a TCP or UDP packet (see also [RFC0793] Section 3.1 and
   [RFC0768] Section "Format").

   This component uses the Numeric Operator (numeric_op) described in
   Section 4.2.1.1.  Type 6 component values SHOULD be encoded as 1- or
   2-byte quantities (numeric_op len=00 or len=01).

   The last paragraph of Section 4.2.2.4 also applies to this component.

4.2.2.7.  Type 7 - ICMP type

   Encoding: <type (1 octet), [numeric_op, value]+>

   Defines a list of {numeric_op, value} pairs used to match the type
   field of an ICMP packet (see also [RFC0792] Section "Message
   Formats").

   This component uses the Numeric Operator (numeric_op) described in
   Section 4.2.1.1.  Type 7 component values SHOULD be encoded as single
   byte (numeric_op len=00).

   In case of the presence of the ICMP type (code) component only ICMP
   packets can match the entire Flow Specification.  The ICMP type
   (code) component, if present, never matches when the packet's IP
   protocol value is not 1 (ICMP), if the packet is fragmented and this
   is not the first fragment, or if the system is unable to locate the
   transport header.  Different implementations may or may not be able
   to decode the transport header in the presence of IP options or
   Encapsulating Security Payload (ESP) NULL [RFC4303] encryption.

4.2.2.8.  Type 8 - ICMP code

   Encoding: <type (1 octet), [numeric_op, value]+>

   Defines a list of {numeric_op, value} pairs used to match the code
   field of an ICMP packet (see also [RFC0792] Section "Message
   Formats").

   This component uses the Numeric Operator (numeric_op) described in
   Section 4.2.1.1.  Type 8 component values SHOULD be encoded as single
   byte (numeric_op len=00).

   The last paragraph of Section 4.2.2.7 also applies to this component.



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4.2.2.9.  Type 9 - TCP flags

   Encoding: <type (1 octet), [bitmask_op, bitmask]+>

   Defines a list of {bitmask_op, bitmask} pairs used to match TCP
   Control Bits (see also [RFC0793] Section 3.1).

   This component uses the Bitmask Operator (bitmask_op) described in
   Section 4.2.1.2.  Type 9 component bitmasks MUST be encoded as 1- or
   2-byte bitmask (bitmask_op len=00 or len=01).

   When a single byte (bitmask_op len=00) is specified, it matches byte
   14 of the TCP header (see also [RFC0793] Section 3.1), which contains
   the TCP Control Bits.  When a 2-byte (bitmask_op len=01) encoding is
   used, it matches bytes 13 and 14 of the TCP header with the data
   offset (leftmost 4 bits) always treated as 0.

   In case of the presence of the TCP flags component only TCP packets
   can match the entire Flow Specification.  The TCP flags component, if
   present, never matches when the packet's IP protocol value is not 6
   (TCP), if the packet is fragmented and this is not the first
   fragment, or if the system is unable to locate the transport header.
   Different implementations may or may not be able to decode the
   transport header in the presence of IP options or Encapsulating
   Security Payload (ESP) NULL [RFC4303] encryption.

4.2.2.10.  Type 10 - Packet length

   Encoding: <type (1 octet), [numeric_op, value]+>

   Defines a list of {numeric_op, value} pairs used to match on the
   total IP packet length (excluding Layer 2 but including IP header).

   This component uses the Numeric Operator (numeric_op) described in
   Section 4.2.1.1.  Type 10 component values SHOULD be encoded as 1- or
   2-byte quantities (numeric_op len=00 or len=01).

4.2.2.11.  Type 11 - DSCP (Diffserv Code Point)

   Encoding: <type (1 octet), [numeric_op, value]+>

   Defines a list of {numeric_op, value} pairs used to match the 6-bit
   DSCP field (see also [RFC2474]).

   This component uses the Numeric Operator (numeric_op) described in
   Section 4.2.1.1.  Type 11 component values MUST be encoded as single
   byte (numeric_op len=00).




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   The six least significant bits contain the DSCP value.  All other
   bits SHOULD be treated as 0.

4.2.2.12.  Type 12 - Fragment

   Encoding: <type (1 octet), [bitmask_op, bitmask]+>

   Defines a list of {bitmask_op, bitmask} pairs used to match specific
   IP fragments.

   This component uses the Bitmask Operator (bitmask_op) described in
   Section 4.2.1.2.  The Type 12 component bitmask MUST be encoded as
   single byte bitmask (bitmask_op len=00).

                      0   1   2   3   4   5   6   7
                    +---+---+---+---+---+---+---+---+
                    | 0 | 0 | 0 | 0 |LF |FF |IsF|DF |
                    +---+---+---+---+---+---+---+---+

                    Figure 4: Fragment Bitmask Operand

   Bitmask values:

   DF -  Don't fragment - match if [RFC0791] IP Header Flags Bit-1 (DF)
      is 1

   IsF -  Is a fragment - match if [RFC0791] IP Header Fragment Offset
      is not 0

   FF -  First fragment - match if [RFC0791] IP Header Fragment Offset
      is 0 AND Flags Bit-2 (MF) is 1

   LF -  Last fragment - match if [RFC0791] IP Header Fragment Offset is
      not 0 AND Flags Bit-2 (MF) is 0

   0 -  SHOULD be set to 0 on NLRI encoding, and MUST be ignored during
      decoding

4.3.  Examples of Encodings

4.3.1.  Example 1

   An example of a Flow Specification NLRI encoding for: "all packets to
   192.0.2.0/24 and TCP port 25".







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          +--------+----------------+----------+----------+
          | length | destination    | protocol | port     |
          +--------+----------------+----------+----------+
          | 0x0b   | 01 18 c0 00 02 | 03 81 06 | 04 81 19 |
          +--------+----------------+----------+----------+

   Decoded:

          +-------+------------+------------------------------+
          | Value |            |                              |
          +-------+------------+------------------------------+
          |  0x0b | length     | 11 octets (len<240 1-octet)  |
          |  0x01 | type       | Type 1 - Destination Prefix  |
          |  0x18 | length     | 24 bit                       |
          |  0xc0 | prefix     | 192                          |
          |  0x00 | prefix     | 0                            |
          |  0x02 | prefix     | 2                            |
          |  0x03 | type       | Type 3 - IP Protocol         |
          |  0x81 | numeric_op | end-of-list, value size=1, = |
          |  0x06 | value      | IP Protocol 6 = TCP          |
          |  0x04 | type       | Type 4 - Port                |
          |  0x81 | numeric_op | end-of-list, value size=1, = |
          |  0x19 | value      | 25                           |
          +-------+------------+------------------------------+

   This constitutes a NLRI with a NLRI length of 11 octets.

4.3.2.  Example 2

   An example of a Flow Specification NLRI encoding for: "all packets to
   192.0.2.0/24 from 203.0.113.0/24 and port {range [137, 139] or
   8080}".

  +--------+----------------+----------------+-------------------------+
  | length | destination    | source         | port                    |
  +--------+----------------+----------------+-------------------------+
  |  0x12  | 01 18 c0 00 02 | 02 18 cb 00 71 | 04 03 89 45 8b 91 1f 90 |
  +--------+----------------+----------------+-------------------------+

   Decoded:











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          +--------+------------+------------------------------+
          | Value  |            |                              |
          +--------+------------+------------------------------+
          |   0x12 | length     | 18 octets (len<240 1-octet)  |
          |   0x01 | type       | Type 1 - Destination Prefix  |
          |   0x18 | length     | 24 bit                       |
          |   0xc0 | prefix     | 192                          |
          |   0x00 | prefix     | 0                            |
          |   0x02 | prefix     | 2                            |
          |   0x02 | type       | Type 2 - Source Prefix       |
          |   0x18 | length     | 24 bit                       |
          |   0xcb | prefix     | 203                          |
          |   0x00 | prefix     | 0                            |
          |   0x71 | prefix     | 113                          |
          |   0x04 | type       | Type 4 - Port                |
          |   0x03 | numeric_op | value size=1, >=             |
          |   0x89 | value      | 137                          |
          |   0x45 | numeric_op | "AND", value size=1, <=      |
          |   0x8b | value      | 139                          |
          |   0x91 | numeric_op | end-of-list, value size=2, = |
          | 0x1f90 | value      | 8080                         |
          +--------+------------+------------------------------+

   This constitutes a NLRI with a NLRI length of 18 octets.

4.3.3.  Example 3

   An example of a Flow Specification NLRI encoding for: "all packets to
   192.0.2.1/32 and fragment { DF or FF } (matching packet with DF bit
   set or First Fragments)

          +--------+-------------------+----------+
          | length | destination       | fragment |
          +--------+-------------------+----------+
          |  0x09  | 01 20 c0 00 02 01 | 0c 80 05 |
          +--------+-------------------+----------+

   Decoded:













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          +-------+------------+------------------------------+
          | Value |            |                              |
          +-------+------------+------------------------------+
          |  0x09 | length     | 9 octets (len<240 1-octet)   |
          |  0x01 | type       | Type 1 - Destination Prefix  |
          |  0x20 | length     | 32 bit                       |
          |  0xc0 | prefix     | 192                          |
          |  0x00 | prefix     | 0                            |
          |  0x02 | prefix     | 2                            |
          |  0x01 | prefix     | 1                            |
          |  0x0c | type       | Type 12 - Fragment           |
          |  0x80 | bitmask_op | end-of-list, value size=1    |
          |  0x05 | bitmask    | DF=1, FF=1                   |
          +-------+------------+------------------------------+

   This constitutes a NLRI with a NLRI length of 9 octets.

5.  Traffic Filtering

   Traffic filtering policies have been traditionally considered to be
   relatively static.  Limitations of these static mechanisms caused
   this new dynamic mechanism to be designed for the three new
   applications of traffic filtering:

   o  Prevention of traffic-based, denial-of-service (DOS) attacks.

   o  Traffic filtering in the context of BGP/MPLS VPN service.

   o  Centralized traffic control for SDN/NFV networks.

   These applications require coordination among service providers and/
   or coordination among the AS within a service provider.

   The Flow Specification NLRI defined in Section 4 conveys information
   about traffic filtering rules for traffic that should be discarded or
   handled in a manner specified by a set of pre-defined actions (which
   are defined in BGP Extended Communities).  This mechanism is
   primarily designed to allow an upstream autonomous system to perform
   inbound filtering in their ingress routers of traffic that a given
   downstream AS wishes to drop.

   In order to achieve this goal, this draft specifies two application
   specific NLRI identifiers that provide traffic filters, and a set of
   actions encoding in BGP Extended Communities.  The two application
   specific NLRI identifiers are:

   o  IPv4 Flow Specification identifier (AFI=1, SAFI=133) along with
      specific semantic rules for IPv4 routes, and



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   o  VPNv4 Flow Specification identifier (AFI=1, SAFI=134) value, which
      can be used to propagate traffic filtering information in a BGP/
      MPLS VPN environment.

   Encoding of the NLRI is described in Section 4 for IPv4 Flow
   Specification and in Section 8 for VPNv4 Flow Specification.  The
   filtering actions are described in Section 7.

5.1.  Ordering of Flow Specifications

   More than one Flow Specification may match a particular traffic flow.
   Thus, it is necessary to define the order in which Flow
   Specifications get matched and actions being applied to a particular
   traffic flow.  This ordering function is such that it does not depend
   on the arrival order of the Flow Specification via BGP and thus is
   consistent in the network.

   The relative order of two Flow Specifications is determined by
   comparing their respective components.  The algorithm starts by
   comparing the left-most components (lowest component type value) of
   the Flow Specifications.  If the types differ, the Flow Specification
   with lowest numeric type value has higher precedence (and thus will
   match before) than the Flow Specification that doesn't contain that
   component type.  If the component types are the same, then a type-
   specific comparison is performed (see below) if the types are equal
   the algorithm continues with the next component.

   For IP prefix values (IP destination or source prefix): If one of the
   two prefixes to compare is a more specific prefix of the other, the
   more specific prefix has higher precedence.  Otherwise the one with
   the lowest IP value has higher precedence.

   For all other component types, unless otherwise specified, the
   comparison is performed by comparing the component data as a binary
   string using the memcmp() function as defined by [ISO_IEC_9899].  For
   strings with equal lengths the lowest string (memcmp) has higher
   precedence.  For strings of different lengths, the common prefix is
   compared.  If the common prefix is not equal the string with the
   lowest prefix has higher precedence.  If the common prefix is equal,
   the longest string is considered to have higher precedence than the
   shorter one.

   The code in Appendix A shows a Python3 implementation of the
   comparison algorithm.  The full code was tested with Python 3.6.3 and
   can be obtained at https://github.com/stoffi92/flowspec-cmp [1].






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6.  Validation Procedure

   Flow Specifications received from a BGP peer that are accepted in the
   respective Adj-RIB-In are used as input to the route selection
   process.  Although the forwarding attributes of two routes for the
   same Flow Specification prefix may be the same, BGP is still required
   to perform its path selection algorithm in order to select the
   correct set of attributes to advertise.

   The first step of the BGP Route Selection procedure (Section 9.1.2 of
   [RFC4271] is to exclude from the selection procedure routes that are
   considered non-feasible.  In the context of IP routing information,
   this step is used to validate that the NEXT_HOP attribute of a given
   route is resolvable.

   The concept can be extended, in the case of the Flow Specification
   NLRI, to allow other validation procedures.

   The validation process described below validates Flow Specifications
   against unicast routes received over the same AFI but the associated
   unicast routing information SAFI:

      Flow specification received over SAFI=133 will be validated
      against routes received over SAFI=1

      Flow specification received over SAFI=134 will be validated
      against routes received over SAFI=128

   By default a Flow Specification NLRI MUST be validated such that it
   is considered feasible if and only if all of the below is true:

      a) A destination prefix component is embedded in the Flow
      Specification.

      b) 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 is the unicast route with
      the longest possible prefix length covering the destination prefix
      embedded in the Flow Specification).

      c) There are no more specific unicast routes, when compared with
      the flow destination prefix, that have been received from a
      different neighboring AS than the best-match unicast route, which
      has been determined in rule b).

   However, rule a) MAY be relaxed by explicit configuration, permitting
   Flow Specifications that include no destination prefix component.  If
   such is the case, rules b) and c) are moot and MUST be disregarded.



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   By originator of a BGP route, we mean either the address of the
   originator in the ORIGINATOR_ID Attribute [RFC4456], or the source IP
   address of the BGP peer, if this path attribute is not present.

   BGP implementations MUST also enforce that the 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.  While this rule is optional in the BGP specification, it
   becomes necessary to enforce it for security reasons.

   The best-match unicast route may change over the time independently
   of the Flow Specification NLRI.  Therefore, a revalidation of the
   Flow Specification NLRI MUST be performed whenever unicast routes
   change.  Revalidation is defined as retesting that clause a and
   clause b above are true.

   Explanation:

   The underlying concept is that the neighboring AS that advertises the
   best unicast route for a destination is allowed to advertise Flow
   Specification information that conveys a more or equally specific
   destination prefix.  Thus, as long as there are no more specific
   unicast routes, received from a different neighboring AS, which would
   be affected by that Flow Specification.

   The neighboring AS is the immediate destination of the traffic
   described by the Flow Specification.  If it requests these flows to
   be dropped, that request can be honored without concern that it
   represents a denial of service in itself.  Supposedly, the traffic is
   being dropped by the downstream autonomous system, and there is no
   added value in carrying the traffic to it.

7.  Traffic Filtering Actions

   This document defines a minimum set of Traffic Filtering Actions that
   it standardizes as BGP extended community values [RFC4360].  This is
   not meant to be an inclusive list of all the possible actions, but
   only a subset that can be interpreted consistently across the
   network.  Additional actions can be defined as either requiring
   standards or as vendor specific.

   The default action for a matching Flow Specification is to accept the
   packet (treat the packet according to the normal forwarding behaviour
   of the system).

   This document defines the following extended communities values shown
   in Table 2 in the form 0xttss where tt indicates the type and ss




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   indicates the sub-type of the extended community.  Encodings for
   these extended communities are described below.

   +--------------+--------------------------+-------------------------+
   | community    | action                   | encoding                |
   | 0xttss       |                          |                         |
   +--------------+--------------------------+-------------------------+
   | 0x8006       | traffic-rate-bytes       | 2-byte ASN, 4-byte      |
   |              | (Section 7.1)            | float                   |
   | TBD          | traffic-rate-packets     | 2-byte ASN, 4-byte      |
   |              | (Section 7.1)            | float                   |
   | 0x8007       | traffic-action (Section  | bitmask                 |
   |              | 7.3)                     |                         |
   | 0x8008       | rt-redirect AS-2byte     | 2-octet AS, 4-octet     |
   |              | (Section 7.4)            | value                   |
   | 0x8108       | rt-redirect IPv4         | 4-octet IPv4 address,   |
   |              | (Section 7.4)            | 2-octet value           |
   | 0x8208       | rt-redirect AS-4byte     | 4-octet AS, 2-octet     |
   |              | (Section 7.4)            | value                   |
   | 0x8009       | traffic-marking (Section | DSCP value              |
   |              | 7.5)                     |                         |
   +--------------+--------------------------+-------------------------+

          Table 2: Traffic Filtering Action Extended Communities

   Multiple Traffic Filtering Actions defined in this document may be
   present for a single Flow Specification and SHOULD be applied to the
   traffic flow (for example traffic-rate-bytes and rt-redirect can be
   applied to packets at the same time).  If not all of the Traffic
   Filtering Actions can be applied to a traffic flow they should be
   treated as interfering Traffic filtering actions (see below).

   Some Traffic Filtering Actions may interfere with each other even
   contradict.  Section 7.7 of this document provides general
   considerations on such Traffic Filtering Action interference.  Any
   additional definition of Traffic Filtering Actions SHOULD specify the
   action to take if those Traffic Filtering Actions interfere (also
   with existing Traffic Filtering Actions).

   All Traffic Filtering Actions are specified as transitive BGP
   Extended Communities.

7.1.  Traffic Rate in Bytes (traffic-rate-bytes) sub-type 0x06

   The traffic-rate-bytes extended community uses the following extended
   community encoding:





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   The first two octets carry the 2-octet id, which can be assigned from
   a 2-byte AS number.  When a 4-byte AS number is locally present, the
   2 least significant bytes of such an AS number can be used.  This
   value is purely informational and SHOULD NOT be interpreted by the
   implementation.

   The remaining 4 octets carry the maximum rate information in IEEE
   floating point [IEEE.754.1985] format, units being bytes per second.
   A traffic-rate of 0 should result on all traffic for the particular
   flow to be discarded.  On encoding the traffic-rate MUST NOT be
   negative.  On decoding negative values MUST be treated as zero
   (discard all traffic).

   Interferes with: No other BGP Flow Specification Traffic Filtering
   Action in this document.

7.2.  Traffic Rate in Packets (traffic-rate-packets) sub-type TBD

   The traffic-rate-packets extended community uses the same encoding as
   the traffic-rate-bytes extended community.  The floating point value
   carries the maximum packet rate in packets per second.  A traffic-
   rate-packets of 0 should result in all traffic for the particular
   flow to be discarded.  On encoding the traffic-rate-packets MUST NOT
   be negative.  On decoding negative values MUST be treated as zero
   (discard all traffic).

   Interferes with: No other BGP Flow Specification Traffic Filtering
   Action in this document.

7.3.  Traffic-action (traffic-action) sub-type 0x07

   The traffic-action extended community consists of 6 bytes of which
   only the 2 least significant bits of the 6th byte (from left to
   right) are defined by this document as shown in Figure 5.

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Traffic Action Field                                          |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     | Tr. Action Field (cont.)  |S|T|
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 5: Traffic-action Extended Community Encoding

   where S and T are defined as:





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   o  T: Terminal Action (bit 47): When this bit is set, the traffic
      filtering engine will evaluate any subsequent Flow Specifications
      (as defined by the ordering procedure).  If not set, the
      evaluation of the traffic filters stops when this Flow
      Specification is evaluated.

   o  S: Sample (bit 46): Enables traffic sampling and logging for this
      Flow Specification (only effective when set).

   o  Traffic Action Field: Other Traffic Action Field (see Section 12)
      bits unused in this specification.

   The use of the Terminal Action (bit 47) may result in more than one
   Flow Specification matching a particular traffic flow.  All the
   Traffic Filtering Actions from these Flow Specifications shall be
   collected and applied.  In case of interfering Traffic Filtering
   Actions it is an implementation decision which Traffic Filtering
   Actions are selected.  See also Section 7.7.

   Interferes with: No other BGP Flow Specification Traffic Filtering
   Action in this document.

7.4.  RT Redirect (rt-redirect) sub-type 0x08

   The redirect extended community allows the traffic to be redirected
   to a VRF routing instance that lists the specified route-target in
   its import policy.  If several local instances match this criteria,
   the choice between them is a local matter (for example, the instance
   with the lowest Route Distinguisher value can be elected).

   This Extended Community allows 3 different encodings formats for the
   route-target (type 0x80, 0x81, 0x82).  It uses the same encoding as
   the Route Target Extended Community in Sections 3.1 (type 0x80:
   2-octet AS, 4-octet value), 3.2 (type 0x81: 4-octet IPv4 address,
   2-octet value) and 4 of [RFC4360] and Section 2 (type 0x82: 4-octet
   AS, 2-octet value) of [RFC5668] with the high-order octet of the Type
   field 0x80, 0x81, 0x82 respectively and the low-order of the Type
   field (Sub-Type) always 0x08.

   Interferes with: No other BGP Flow Specification Traffic Filtering
   Action in this document.

7.5.  Traffic Marking (traffic-marking) sub-type 0x09

   The traffic marking extended community instructs a system to modify
   the DSCP bits in the IP header ([RFC2474] Section 3) of a transiting
   IP packet to the corresponding value encoded in the 6 least




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   significant bits of the extended community value as shown in
   Figure 6.

   The extended is encoded as follows:

      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
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   reserved    |   reserved    |   reserved    |   reserved    |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |   reserved    | r.|    DSCP   |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

           Figure 6: Traffic Marking Extended Community Encoding

   o  DSCP: new DSCP value for the transiting IP packet.

   o  reserved, r.: SHOULD be set to 0 on encoding, and MUST be ignored
      during decoding.

   Interferes with: No other BGP Flow Specification Traffic Filtering
   Action in this document.

7.6.  Interaction with other Filtering Mechanisms in Routers

   Implementations SHOULD provide mechanisms that map an arbitrary BGP
   community value (normal or extended) to Traffic Filtering Actions
   that require different mappings in different systems in the network.
   For instance, providing packets with a worse-than-best-effort, per-
   hop behavior is a functionality that is likely to be implemented
   differently in different systems and for which no standard behavior
   is currently known.  Rather than attempting to define it here, this
   can be accomplished by mapping a user-defined community value to
   platform-/network-specific behavior via user configuration.

7.7.  Considerations on Traffic Filtering Action Interference

   Since Traffic Filtering Actions are represented as BGP extended
   community values, Traffic Filtering Actions may interfere with each
   other (e.g. there may be more than one conflicting traffic-rate-bytes
   Traffic Filtering Action associated with a single Flow
   Specification).  Traffic Filtering Action interference has no impact
   on BGP propagation of Flow Specifications (all communities are
   propagated according to policies).

   If a Flow Specification associated with interfering Traffic Filtering
   Actions is selected for packet forwarding, it is an implementation
   decision which of the interfering Traffic Filtering Actions are



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   selected.  Implementors of this specification SHOULD document the
   behaviour of their implementation in such cases.

   Operators are encouraged to make use of the BGP policy framework
   supported by their implementation in order to achieve a predictable
   behaviour (ie. match - replace - delete communities on administrative
   boundaries).  See also Section 13.

8.  Dissemination of Traffic Filtering in BGP/MPLS VPN Networks

   Provider-based Layer 3 VPN networks, such as the ones using a BGP/
   MPLS IP VPN [RFC4364] control plane, may have different traffic
   filtering requirements than Internet service providers.  But also
   Internet service providers may use those VPNs for scenarios like
   having the Internet routing table in a VRF, resulting in the same
   traffic filtering requirements as defined for the global routing
   table environment within this document.  This document defines an
   additional BGP NLRI type (AFI=1, SAFI=134) value, which can be used
   to propagate Flow Specification in a BGP/MPLS VPN environment.

   The NLRI format for this address family consists of a fixed-length
   Route Distinguisher field (8 bytes) followed by the Flow
   Specification NLRI value Section 4.2.  The NLRI length field shall
   include both the 8 bytes of the Route Distinguisher as well as the
   subsequent Flow Specification NLRI value.  The resulting encoding is
   shown in Figure 7.

                     +------------------------------+
                     | length (0xnn or 0xfn nn)     |
                     +------------------------------+
                     | Route Distinguisher (8 bytes)|
                     +------------------------------+
                     |    NLRI value  (variable)    |
                     +------------------------------+

                Figure 7: Flow Specification NLRI for MPLS

   Propagation of this NLRI is controlled by matching Route Target
   extended communities associated with the BGP path advertisement with
   the VRF import policy, using the same mechanism as described in BGP/
   MPLS IP VPNs [RFC4364].

   Flow Specifications received via this NLRI apply only to traffic that
   belongs to the VRF(s) in which it is imported.  By default, traffic
   received from a remote PE is switched via an MPLS forwarding decision
   and is not subject to filtering.





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   Contrary to the behavior specified for the non-VPN NLRI, Flow
   Specifications are accepted by default, when received from remote PE
   routers.

   The validation procedure (Section 6) and Traffic Filtering Actions
   (Section 7) are the same as for IPv4.

9.  Traffic Monitoring

   Traffic filtering applications require monitoring and traffic
   statistics facilities.  While this is an implementation specific
   choice, implementations SHOULD provide:

   o  A mechanism to log the packet header of filtered traffic.

   o  A mechanism to count the number of matches for a given Flow
      Specification.

10.  Error-Handling

   Error handling according to [RFC7606] SHOULD apply to this
   specification.

   This document introduces Traffic Filtering Action Extended
   Communities.  Malformed Traffic Filtering Action Extended Communities
   in the sense of [RFC7606] Section 7.14. are Extended Community values
   that cannot be decoded according to Section 7 of this document.

11.  Future NLRI Extensions

   Future Flow Specification extensions may introduce new Flow
   Specification components.  In order to facilitate such extensions of
   the Flow Specification NLRI, in addition to the cases described in
   [RFC7606], if BGP encounters an unknown Flow Specification component
   in an UPDATE message, it SHOULD also treat this message as Treat-as-
   withdraw as specified in [RFC7606] Section 2.

   The specification of a new Flow Specification Component Type SHOULD
   clearly identify what the criteria used to match packets forwarded by
   the router is.  This criteria should be meaningful across router hops
   and not depend on values that change hop-by-hop such as TTL or Layer
   2 encapsulation.

   Such extensions SHOULD also specify a way to encode an "always-match"
   match condition within the newly introduced components (this is a
   match condition, encoded with the newly introduced components: If
   present on its own, matches all flows).  This match condition can be




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   used to propagate (and apply) certain Flow Specifications only if a
   specific extension is known to the implementation.

12.  IANA Considerations

   This section complies with [RFC7153].

12.1.  AFI/SAFI Definitions

   IANA maintains a registry entitled "SAFI Values".  For the purpose of
   this work, IANA is requested to update the following SAFIs to read
   according to the table below (Note: This document obsoletes both
   RFC7674 and RFC5575 and all references to those documents should be
   deleted from the registry below):

   +-------+------------------------------------------+----------------+
   | Value | Name                                     | Reference      |
   +-------+------------------------------------------+----------------+
   | 133   | Dissemination of Flow Specification      | [this          |
   |       | rules                                    | document]      |
   | 134   | L3VPN Dissemination of Flow              | [this          |
   |       | Specification rules                      | document]      |
   +-------+------------------------------------------+----------------+

                      Table 3: Registry: SAFI Values

12.2.  Flow Component Definitions

   A Flow Specification consists of a sequence of flow components, which
   are identified by a an 8-bit component type.  IANA has created and
   maintains a registry entitled "Flow Spec Component Types".  IANA is
   requested to update the reference for this registry to [this
   document].  Furthermore the references to the values should be
   updated according to the table below (Note: This document obsoletes
   both RFC7674 and RFC5575 and all references to those documents should
   be deleted from the registry below).















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             +-------+--------------------+-----------------+
             | Value | Name               | Reference       |
             +-------+--------------------+-----------------+
             | 1     | Destination Prefix | [this document] |
             | 2     | Source Prefix      | [this document] |
             | 3     | IP Protocol        | [this document] |
             | 4     | Port               | [this document] |
             | 5     | Destination port   | [this document] |
             | 6     | Source port        | [this document] |
             | 7     | ICMP type          | [this document] |
             | 8     | ICMP code          | [this document] |
             | 9     | TCP flags          | [this document] |
             | 10    | Packet length      | [this document] |
             | 11    | DSCP               | [this document] |
             | 12    | Fragment           | [this document] |
             +-------+--------------------+-----------------+

               Table 4: Registry: Flow Spec Component Types

   In order to manage the limited number space and accommodate several
   usages, the following policies defined by [RFC8126] are used:

             +--------------+-------------------------------+
             | Type Values  | Policy                        |
             +--------------+-------------------------------+
             | 0            | Specification required        |
             | [1 .. 12]    | Defined by this specification |
             | [13 .. 127]  | Specification required        |
             | [128 .. 255] | First Come First Served       |
             +--------------+-------------------------------+

                Table 5: Flow Spec Component Types Policies

12.3.  Extended Community Flow Specification Actions

   The Extended Community Flow Specification Action types defined in
   this document consist of two parts:

      Type (BGP Transitive Extended Community Type)

      Sub-Type

   For the type-part, IANA maintains a registry entitled "BGP Transitive
   Extended Community Types".  For the purpose of this work (Section 7),
   IANA is requested to update the references to the following entries
   according to the table below (Note: This document obsoletes both
   RFC7674 and RFC5575 and all references to those documents should be
   deleted in the registry below):



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   +-------+-----------------------------------------------+-----------+
   | Type  | Name                                          | Reference |
   | Value |                                               |           |
   +-------+-----------------------------------------------+-----------+
   | 0x81  | Generic Transitive Experimental Use Extended  | [this     |
   |       | Community Part 2 (Sub-Types are defined in    | document] |
   |       | the "Generic Transitive Experimental Use      |           |
   |       | Extended Community Part 2 Sub-Types"          |           |
   |       | Registry)                                     |           |
   | 0x82  | Generic Transitive Experimental Use Extended  | [this     |
   |       | Community Part 3 (Sub-Types are defined in    | document] |
   |       | the "Generic Transitive Experimental Use      |           |
   |       | Extended Community Part 3 Sub-Types"          |           |
   |       | Registry)                                     |           |
   +-------+-----------------------------------------------+-----------+

        Table 6: Registry: BGP Transitive Extended Community Types

   For the sub-type part of the extended community Traffic Filtering
   Actions IANA maintains the following registries.  IANA is requested
   to update all names and references according to the tables below and
   assign a new value for the "Flow spec traffic-rate-packets" Sub-Type
   (Note: This document obsoletes both RFC7674 and RFC5575 and all
   references to those documents should be deleted from the registries
   below).

   +----------+--------------------------------------------+-----------+
   | Sub-Type | Name                                       | Reference |
   | Value    |                                            |           |
   +----------+--------------------------------------------+-----------+
   | 0x06     | Flow spec traffic-rate-bytes               | [this     |
   |          |                                            | document] |
   | TBD      | Flow spec traffic-rate-packets             | [this     |
   |          |                                            | document] |
   | 0x07     | Flow spec traffic-action (Use of the       | [this     |
   |          | "Value" field is defined in the "Traffic   | document] |
   |          | Action Fields" registry)                   |           |
   | 0x08     | Flow spec rt-redirect AS-2byte format      | [this     |
   |          |                                            | document] |
   | 0x09     | Flow spec traffic-remarking                | [this     |
   |          |                                            | document] |
   +----------+--------------------------------------------+-----------+

      Table 7: Registry: Generic Transitive Experimental Use Extended
                            Community Sub-Types






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   +----------------+--------------------------------+-----------------+
   | Sub-Type Value | Name                           | Reference       |
   +----------------+--------------------------------+-----------------+
   | 0x08           | Flow spec rt-redirect IPv4     | [this document] |
   |                | format                         |                 |
   +----------------+--------------------------------+-----------------+

      Table 8: Registry: Generic Transitive Experimental Use Extended
                        Community Part 2 Sub-Types

   +---------------+----------------------------------+----------------+
   | Sub-Type      | Name                             | Reference      |
   | Value         |                                  |                |
   +---------------+----------------------------------+----------------+
   | 0x08          | Flow spec rt-redirect AS-4byte   | [this          |
   |               | format                           | document]      |
   +---------------+----------------------------------+----------------+

      Table 9: Registry: Generic Transitive Experimental Use Extended
                        Community Part 3 Sub-Types

   Furthermore IANA is requested to update the reference for the
   registries "Generic Transitive Experimental Use Extended Community
   Part 2 Sub-Types" and "Generic Transitive Experimental Use Extended
   Community Part 3 Sub-Types" to [this document].

   The "traffic-action" extended community (Section 7.3) defined in this
   document has 46 unused bits, which can be used to convey additional
   meaning.  IANA created and maintains a registry entitled: "Traffic
   Action Fields".  IANA is requested to update the reference for this
   registry to [this document].  Furthermore IANA is requested to update
   the references according to the table below.  These values should be
   assigned via IETF Review rules only (Note: This document obsoletes
   both RFC7674 and RFC5575 and all references to those documents should
   be deleted from the registry below).

                +-----+-----------------+-----------------+
                | Bit | Name            | Reference       |
                +-----+-----------------+-----------------+
                | 47  | Terminal Action | [this document] |
                | 46  | Sample          | [this document] |
                +-----+-----------------+-----------------+

                 Table 10: Registry: Traffic Action Fields







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13.  Security Considerations

   As long as Flow Specifications are restricted to match the
   corresponding unicast routing paths for the relevant prefixes
   (Section 6), the security characteristics of this proposal are
   equivalent to the existing security properties of BGP unicast
   routing.  Any relaxation of the validation procedure described in
   Section 6 may allow unwanted Flow Specifications to be propagated and
   thus unwanted Traffic Filtering Actions may be applied to flows.

   Where the above mechanisms are not in place, this could open the door
   to further denial-of-service attacks such as unwanted traffic
   filtering, remarking or redirection.

   Deployment of specific relaxations of the validation within an
   administrative boundary of a network, defined by an AS or an AS-
   Confederation boundary, may be useful in some networks for quickly
   distributing filters to prevent denial-of-service attacks.  For a
   network to utilize this relaxation, the BGP policies must support
   additional filtering since the origin AS field is empty.
   Specifications relaxing the validation restrictions SHOULD contain
   security considerations that provide details on the required
   additional filtering.  For example, the use of [RFC6811] to enhance
   filtering within an AS confederation.

   Inter-provider routing is based on a web of trust.  Neighboring
   autonomous systems are trusted to advertise valid reachability
   information.  If this trust model is violated, a neighboring
   autonomous system may cause a denial-of-service attack by advertising
   reachability information for a given prefix for which it does not
   provide service (unfiltered address space hijack).  Since validation
   of the Flow Specification is tied to the announcement of the best
   unicast route, this may also cause this validation to fail and
   consequently prevent Flow Specifications from being accepted by a
   peer.  Possible mitigations are [RFC6811] and [RFC8205].

   Enabling firewall-like capabilities in routers without centralized
   management could make certain failures harder to diagnose.  For
   example, it is possible to allow TCP packets to pass between a pair
   of addresses but not ICMP packets.  It is also possible to permit
   packets smaller than 900 or greater than 1000 bytes to pass between a
   pair of addresses, but not packets whose length is in the range 900-
   1000.  Such behavior may be confusing and these capabilities should
   be used with care whether manually configured or coordinated through
   the protocol extensions described in this document.

   Flow Specification BGP speakers (e.g. automated DDoS controllers) not
   properly programmed, algorithms that are not performing as expected,



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   or simply rogue systems may announce unintended Flow Specifications,
   send updates at a high rate or generate a high number of Flow
   Specifications.  This may stress the receiving systems, exceed their
   maximum capacity or may lead to unwanted Traffic Filtering Actions
   being applied to flows.

   While the general verification of the Flow Specification NLRI is
   specified in this document (Section 6) the Traffic Filtering Actions
   received by a third party may need custom verification or filtering.
   In particular all non traffic-rate actions may allow a third party to
   modify packet forwarding properties and potentially gain access to
   other routing-tables/VPNs or undesired queues.  This can be avoided
   by proper filtering/screening of the Traffic Filtering Action
   communities at network borders and only exposing a predefined subset
   of Traffic Filtering Actions (see Section 7) to third parties.  One
   way to achieve this is by mapping user-defined communities, that can
   be set by the third party, to Traffic Filtering Actions and not
   accepting Traffic Filtering Action extended communities from third
   parties.

   This extension adds additional information to Internet routers.
   These are limited in terms of the maximum number of data elements
   they can hold as well as the number of events they are able to
   process in a given unit of time.  Service providers need to consider
   the maximum capacity of their devices and may need to limit the
   number of Flow Specifications accepted and processed.

14.  Contributors

   Barry Greene, Pedro Marques, Jared Mauch, Danny McPherson, and
   Nischal Sheth were authors on [RFC5575], and therefore are
   contributing authors on this document.

15.  Acknowledgements

   The authors would like to thank Yakov Rekhter, Dennis Ferguson, Chris
   Morrow, Charlie Kaufman, and David Smith for their comments for the
   comments on the original [RFC5575].  Chaitanya Kodeboyina helped
   design the flow validation procedure; and Steven Lin and Jim Washburn
   ironed out all the details necessary to produce a working
   implementation in the original [RFC5575].

   A packet rate Traffic Filtering Action was also described in a Flow
   Specification extension draft and the authors like to thank Wesley
   Eddy, Justin Dailey and Gilbert Clark for their work.






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   Additionally, the authors would like to thank Alexander Mayrhofer,
   Nicolas Fevrier, Job Snijders, Jeffrey Haas and Adam Chappell for
   their comments and review.

16.  References

16.1.  Normative References

   [IEEE.754.1985]
              IEEE, "Standard for Binary Floating-Point Arithmetic",
              IEEE 754-1985, August 1985.

   [ISO_IEC_9899]
              ISO, "Information technology -- Programming languages --
              C", ISO/IEC 9899:2018, June 2018.

   [RFC0768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,
              DOI 10.17487/RFC0768, August 1980,
              <https://www.rfc-editor.org/info/rfc768>.

   [RFC0791]  Postel, J., "Internet Protocol", STD 5, RFC 791,
              DOI 10.17487/RFC0791, September 1981,
              <https://www.rfc-editor.org/info/rfc791>.

   [RFC0792]  Postel, J., "Internet Control Message Protocol", STD 5,
              RFC 792, DOI 10.17487/RFC0792, September 1981,
              <https://www.rfc-editor.org/info/rfc792>.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,
              <https://www.rfc-editor.org/info/rfc793>.

   [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>.

   [RFC2474]  Nichols, K., Blake, S., Baker, F., and D. Black,
              "Definition of the Differentiated Services Field (DS
              Field) in the IPv4 and IPv6 Headers", RFC 2474,
              DOI 10.17487/RFC2474, December 1998,
              <https://www.rfc-editor.org/info/rfc2474>.

   [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>.




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   [RFC4360]  Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
              Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
              February 2006, <https://www.rfc-editor.org/info/rfc4360>.

   [RFC4364]  Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
              Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
              2006, <https://www.rfc-editor.org/info/rfc4364>.

   [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>.

   [RFC4760]  Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
              "Multiprotocol Extensions for BGP-4", RFC 4760,
              DOI 10.17487/RFC4760, January 2007,
              <https://www.rfc-editor.org/info/rfc4760>.

   [RFC5668]  Rekhter, Y., Sangli, S., and D. Tappan, "4-Octet AS
              Specific BGP Extended Community", RFC 5668,
              DOI 10.17487/RFC5668, October 2009,
              <https://www.rfc-editor.org/info/rfc5668>.

   [RFC7153]  Rosen, E. and Y. Rekhter, "IANA Registries for BGP
              Extended Communities", RFC 7153, DOI 10.17487/RFC7153,
              March 2014, <https://www.rfc-editor.org/info/rfc7153>.

   [RFC7606]  Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
              Patel, "Revised Error Handling for BGP UPDATE Messages",
              RFC 7606, DOI 10.17487/RFC7606, August 2015,
              <https://www.rfc-editor.org/info/rfc7606>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.

   [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>.

16.2.  Informative References

   [I-D.ietf-idr-flow-spec-v6]
              McPherson, D., Raszuk, R., Pithawala, B.,
              akarch@cisco.com, a., and S. Hares, "Dissemination of Flow
              Specification Rules for IPv6", draft-ietf-idr-flow-spec-
              v6-09 (work in progress), November 2017.



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   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <https://www.rfc-editor.org/info/rfc4303>.

   [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>.

   [RFC6811]  Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
              Austein, "BGP Prefix Origin Validation", RFC 6811,
              DOI 10.17487/RFC6811, January 2013,
              <https://www.rfc-editor.org/info/rfc6811>.

   [RFC7674]  Haas, J., Ed., "Clarification of the Flowspec Redirect
              Extended Community", RFC 7674, DOI 10.17487/RFC7674,
              October 2015, <https://www.rfc-editor.org/info/rfc7674>.

   [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>.

16.3.  URIs

   [1] https://github.com/stoffi92/flowspec-cmp

Appendix A.  Python code: flow_rule_cmp

  <CODE BEGINS>
  """
  Copyright (c) 2019 IETF Trust and the persons identified as authors of
  the code. All rights reserved.

  Redistribution and use in source and binary forms, with or without
  modification, is permitted pursuant to, and subject to the license
  terms contained in, the Simplified BSD License set forth in Section
  4.c of the IETF Trust's Legal Provisions Relating to IETF Documents
  (http://trustee.ietf.org/license-info).
  """

  import itertools
  import ipaddress

  def flow_rule_cmp(a, b):
      for comp_a, comp_b in itertools.zip_longest(a.components,
                                             b.components):
          # If a component type does not exist in one rule
          # this rule has lower precedence



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          if not comp_a:
              return B_HAS_PRECEDENCE
          if not comp_b:
              return A_HAS_PRECEDENCE
          # higher precedence for lower component type
          if comp_a.component_type < comp_b.component_type:
              return A_HAS_PRECEDENCE
          if comp_a.component_type > comp_b.component_type:
              return B_HAS_PRECEDENCE
          # component types are equal -> type specific comparison
          if comp_a.component_type in (IP_DESTINATION, IP_SOURCE):
              # assuming comp_a.value, comp_b.value of type
              # ipaddress.IPv4Network
              if comp_a.value.overlaps(comp_b.value):
                  # longest prefixlen has precedence
                  if comp_a.value.prefixlen > comp_b.value.prefixlen:
                      return A_HAS_PRECEDENCE
                  if comp_a.value.prefixlen < comp_b.value.prefixlen:
                      return B_HAS_PRECEDENCE
                  # components equal -> continue with next component
              elif comp_a.value > comp_b.value:
                  return B_HAS_PRECEDENCE
              elif comp_a.value < comp_b.value:
                  return A_HAS_PRECEDENCE
          else:
              # assuming comp_a.value, comp_b.value of type bytearray
              if len(comp_a.value) == len(comp_b.value):
                  if comp_a.value > comp_b.value:
                      return B_HAS_PRECEDENCE
                  if comp_a.value < comp_b.value:
                      return A_HAS_PRECEDENCE
                  # components equal -> continue with next component
              else:
                  common = min(len(comp_a.value), len(comp_b.value))
                  if comp_a.value[:common] > comp_b.value[:common]:
                      return B_HAS_PRECEDENCE
                  elif comp_a.value[:common] < comp_b.value[:common]:
                      return A_HAS_PRECEDENCE
                  # the first common bytes match
                  elif len(comp_a.value) > len(comp_b.value):
                      return A_HAS_PRECEDENCE
                  else:
                      return B_HAS_PRECEDENCE
      return EQUAL
  <CODE ENDS>






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Appendix B.  Comparison with RFC 5575

   This document includes numerous editorial changes to [RFC5575].  It
   also completely incorporates the redirect action clarification
   document [RFC7674].  It is recommended to read the entire document.
   The authors, however want to point out the following technical
   changes to [RFC5575]:

      Section 1 introduces the Flow Specification NLRI.  In [RFC5575]
      this NLRI was defined as an opaque-key in BGPs database.  This
      specification has removed all references to a opaque-key property.
      BGP is able to understand the NLRI encoding.  This change also
      resulted in a new section regarding error-handling and
      extensibility (Section 10 and Section 11).

      Section 4.2.2.3 defines a numeric operator and comparison bit
      combinations.  In [RFC5575] the meaning of those bit combination
      was not explicitly defined and left open to the reader.

      Section 4.2.2.3 - Section 4.2.2.8, Section 4.2.2.10,
      Section 4.2.2.11 make use of the above numeric operator.  The
      allowed length of the comparison value was not consistently
      defined in [RFC5575].

      Section 7 defines all Traffic Filtering Action Extended
      communities as transitive extended communities.  [RFC5575] defined
      the traffic-rate action to be non-transitive and did not define
      the transitivity of the other Traffic Filtering Action communities
      at all.

      Section 7.2 introduces a new Traffic Filtering Action (traffic-
      rate-packets).  This action did not exist in [RFC5575].

      Section 7.4 contains the same redirect actions already defined in
      [RFC5575] however, these actions have been renamed to "rt-
      redirect" to make it clearer that the redirection is based on
      route-target.  This section also completely incorporates the
      [RFC7674] clarifications of the Flowspec Redirect Extended
      Community.

      Section 7.7 contains general considerations on interfering traffic
      actions.  Section 7.3 also cross-references this section.
      [RFC5575] did not mention this.

      Section 10 contains new error handling.

      Section 11 describes graceful handling of unknown Flow
      Specification components to allow future extensions.



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Authors' Addresses

   Christoph Loibl
   Next Layer Communications
   Mariahilfer Guertel 37/7
   Vienna  1150
   AT

   Phone: +43 664 1176414
   Email: cl@tix.at


   Susan Hares
   Huawei
   7453 Hickory Hill
   Saline, MI  48176
   USA

   Email: shares@ndzh.com


   Robert Raszuk
   Bloomberg LP
   731 Lexington Ave
   New York City, NY  10022
   USA

   Email: robert@raszuk.net


   Danny McPherson
   Verisign
   USA

   Email: dmcpherson@verisign.com


   Martin Bacher
   T-Mobile Austria
   Rennweg 97-99
   Vienna  1030
   AT

   Email: mb.ietf@gmail.com







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