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Versions: (draft-raszuk-idr-flow-spec-v6) 00 01 02 03 04 05 06 07 08 09 10

IDR Working Group                                          C. Loibl, Ed.
Internet-Draft                                 Next Layer Communications
Intended status: Standards Track                          R. Raszuk, Ed.
Expires: May 5, 2020                                        Bloomberg LP
                                                           S. Hares, Ed.
                                                                  Huawei
                                                        November 2, 2019


           Dissemination of Flow Specification Rules for IPv6
                     draft-ietf-idr-flow-spec-v6-10

Abstract

   Dissemination of Flow Specification Rules [I-D.ietf-idr-rfc5575bis]
   provides a protocol extension for propagation of traffic flow
   information for the purpose of rate limiting or filtering.  The
   [I-D.ietf-idr-rfc5575bis] specifies those extensions for IPv4
   protocol data packets only.

   This specification extends [I-D.ietf-idr-rfc5575bis] and defines
   changes to the original document in order to make it also usable and
   applicable to IPv6 data packets.

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 5, 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



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   (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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Definitions of Terms Used in This Memo  . . . . . . . . .   3
   2.  IPv6 Flow Specification encoding in BGP . . . . . . . . . . .   3
   3.  IPv6 Flow Specification components  . . . . . . . . . . . . .   4
     3.1.  Type 1 - Destination IPv6 Prefix  . . . . . . . . . . . .   4
     3.2.  Type 2 - Source IPv6 Prefix . . . . . . . . . . . . . . .   4
     3.3.  Type 3 - Next Header  . . . . . . . . . . . . . . . . . .   4
     3.4.  Type 7 - ICMPv6 type  . . . . . . . . . . . . . . . . . .   5
     3.5.  Type 8 - ICMPv6 code  . . . . . . . . . . . . . . . . . .   5
     3.6.  Type 12 - Fragment  . . . . . . . . . . . . . . . . . . .   5
     3.7.  Type 13 - Flow Label (new)  . . . . . . . . . . . . . . .   6
     3.8.  Encoding Example  . . . . . . . . . . . . . . . . . . . .   6
   4.  Ordering of Flow Specifications . . . . . . . . . . . . . . .   8
   5.  Validation Procedure  . . . . . . . . . . . . . . . . . . . .   8
   6.  IPv6 Traffic Filtering Action changes . . . . . . . . . . . .   8
     6.1.  Redirect IPv6 (rt-redirect-ipv6) Type/Sub-Type 0x80/TBD .   9
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .   9
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  10
   10. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  10
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  11
     11.2.  Informative References . . . . . . . . . . . . . . . . .  12
     11.3.  URIs . . . . . . . . . . . . . . . . . . . . . . . . . .  12
   Appendix A.  Python code: flow_rule_cmp_v6  . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   The growing amount of IPv6 traffic in private and public networks
   requires the extension of tools used in the IPv4 only networks to be
   also capable of supporting IPv6 data packets.

   In this document authors analyze the differences of IPv6 [RFC2460]
   flows description from those of traditional IPv4 packets and propose
   subset of new encoding formats to enable Dissemination of Flow
   Specification Rules [I-D.ietf-idr-rfc5575bis] for IPv6.




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   This specification should be treated as an extension of base
   [I-D.ietf-idr-rfc5575bis] specification and not its replacement.  It
   only defines the delta changes required to support IPv6 while all
   other definitions and operation mechanisms of Dissemination of Flow
   Specification Rules will remain in the main specification and will
   not be repeated here.

1.1.  Definitions of Terms Used in This Memo

   AFI -   Address Family Identifier.

   AS -   Autonomous System.

   NLRI -   Network Layer Reachability Information.

   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.

2.  IPv6 Flow Specification encoding in BGP

   The [I-D.ietf-idr-rfc5575bis] defines new SAFIs 133 (Dissemination of
   Flow Specification) and 134 (L3VPN Dissemination of Flow
   Specification) applications in order to carry corresponding to each
   such application Flow Specification.

   Implementations wishing to exchange IPv6 Flow Specifications MUST use
   BGP's Capability Advertisement facility to exchange the Multiprotocol
   Extension Capability Code (Code 1) as defined in [RFC4760].  While
   [I-D.ietf-idr-rfc5575bis] specifies Flow Specification for IPv4
   (AFI=1) only, the (AFI, SAFI) pair carried in the Multiprotocol
   Extension Capability MUST be: (AFI=2, SAFI=133) for IPv6 Flow
   Specification, and (AFI=2, SAFI=134) for VPNv6 Flow Specification.

   For both SAFIs the indication to which address family they are
   referring to will be recognized by AFI value (AFI=1 for IPv4 or
   VPNv4, AFI=2 for IPv6 and VPNv6 respectively).

   It needs to be observed that such choice of proposed encoding is
   compatible with filter validation against routing reachability
   information as described in section 6 of [I-D.ietf-idr-rfc5575bis].




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3.  IPv6 Flow Specification components

   The following components are redefined or added for the purpose of
   accommodating the IPv6 header encoding.  Unless otherwise specified
   all other components defined in [I-D.ietf-idr-rfc5575bis]
   Section 4.2.2 also apply to IPv6 Flow Specification.

3.1.  Type 1 - Destination IPv6 Prefix

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

   Defines the destination prefix to match.  The offset has been defined
   to allow for flexible matching on part of the IPv6 address where it
   is required to skip (don't care) of N first bits of the address.
   This can be especially useful where part of the IPv6 address consists
   of an embedded IPv4 address and matching needs to happen only on the
   embedded IPv4 address.  The encoded prefix contains enough octets for
   the bits used in matching (length minus offset bits).

3.2.  Type 2 - Source IPv6 Prefix

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

   Defines the source prefix to match.  The length, offset and prefix
   are the same as in Section 3.1

3.3.  Type 3 - Next Header

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

   Contains a list of {numeric_op, value} pairs that are used to match
   the last Next Header ([RFC2460] Section 3) value octet in IPv6
   packets.

   This component uses the Numeric Operator (numeric_op) described in
   [I-D.ietf-idr-rfc5575bis] Section 4.2.1.1.  Type 3 component values
   SHOULD be encoded as single byte (numeric_op len=00).

   Note: While IPv6 allows for more then one Next Header field in the
   packet the main goal of Type 3 flow specification component is to
   match on the subsequent IP protocol value.  Therefor the definition
   is limited to match only on last Next Header field in the packet.







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3.4.  Type 7 - ICMPv6 type

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

   Defines a list of {numeric_op, value} pairs used to match the type
   field of an ICMPv6 packet (see also [RFC4443] Section 2.1).

   This component uses the Numeric Operator (numeric_op) described in
   [I-D.ietf-idr-rfc5575bis] 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 ICMPv6 type (code) component only
   ICMPv6 packets can match the entire Flow Specification.  The ICMPv6
   type (code) component, if present, never matches when the packet's
   last Next Header field value is not 58 (ICMPv6), 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.

3.5.  Type 8 - ICMPv6 code

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

   Defines a list of {numeric_op, value} pairs used to match the code
   field of an ICMPv6 packet (see also [RFC4443] Section 2.1).

   This component uses the Numeric Operator (numeric_op) described in
   [I-D.ietf-idr-rfc5575bis] Section 4.2.1.1.  Type 8 component values
   SHOULD be encoded as single byte (numeric_op len=00).

   The last paragraph of Section 3.4 also applies to this component.

3.6.  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
   [I-D.ietf-idr-rfc5575bis] Section 4.2.1.2.  The Type 12 component
   bitmask MUST be encoded as single byte bitmask (bitmask_op len=00).









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

                    Figure 1: Fragment Bitmask Operand

   Bitmask values:

   IsF -  Is a fragment - match if IPv6 Fragment Header ([RFC2460]
      Section 4.5) Fragment Offset is not 0

   FF -  First fragment - match if IPv6 Fragment Header ([RFC2460]
      Section 4.5) Fragment Offset is 0 AND M flag is 1

   LF -  Last fragment - match if IPv6 Fragment Header ([RFC2460]
      Section 4.5) Fragment Offset is not 0 AND M flag is 0

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

3.7.  Type 13 - Flow Label (new)

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

   Contains a list of {numeric_op, value} pairs that are used to match
   the 20-bit Flow Label IPv6 header field ([RFC2460] Section 3).

   This component uses the Numeric Operator (numeric_op) described in
   [I-D.ietf-idr-rfc5575bis] Section 4.2.1.1.  Type 13 component values
   SHOULD be encoded as 1-, 2-, or 4-byte quantities (numeric_op len=00,
   len=01 or len=10).

3.8.  Encoding Example

3.8.1.  Example 1

   The following example demonstrates the prefix encoding for: "all
   packets to ::1234:5678:9A00:0/64-104 from 100::/8 and port 25".

       +--------+-------------------------+-------------+----------+
       | length | destination             | source      | port     |
       +--------+-------------------------+-------------+----------+
       | 0x0f   | 01 68 40 12 34 56 78 9A | 02 08 00 01 | 04 81 19 |
       +--------+-------------------------+-------------+----------+

   Decoded:




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       +-------+------------+------------------------------+
       | Value |            |                              |
       +-------+------------+------------------------------+
       |  0x0f | length     | 16 octets (len<240 1-octet)  |
       |  0x01 | type       | Type 1 - Dest. IPv6 Prefix   |
       |  0x68 | length     | 104 bit                      |
       |  0x40 | offset     | 64 bit                       |
       |  0x12 | prefix     |                              |
       |  0x34 | prefix     |                              |
       |  0x56 | prefix     |                              |
       |  0x78 | prefix     |                              |
       |  0x9A | prefix     |                              |
       |  0x02 | type       | Type 2 - Source IPv6 Prefix  |
       |  0x08 | length     | 8 bit                        |
       |  0x00 | offset     | 0 bit                        |
       |  0x01 | prefix     |                              |
       |  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 16 octets.

3.8.2.  Example 2

   The following example demonstrates the prefix encoding for: "all
   packets to ::1234:5678:9A00:0/65-104".

       +--------+-------------------------+
       | length | destination             |
       +--------+-------------------------+
       | 0x08   | 01 68 41 24 68 ac f1 34 |
       +--------+-------------------------+

   Decoded:
















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       +-------+------------+------------------------------+
       | Value |            |                              |
       +-------+------------+------------------------------+
       |  0x08 | length     | 8 octets (len<240 1-octet)   |
       |  0x01 | type       | Type 1 - Dest. IPv6 Prefix   |
       |  0x68 | length     | 104 bit                      |
       |  0x41 | offset     | 65 bit                       |
       |  0x24 | prefix     | starting with the 66ths bit  |
       |  0x68 | prefix     |                              |
       |  0xac | prefix     |                              |
       |  0xf1 | prefix     |                              |
       |  0x34 | prefix     |                              |
       +-------+------------+------------------------------+

   This constitutes a NLRI with a NLRI length of 8 octets.

4.  Ordering of Flow Specifications

   The definition for the order of traffic filtering rules from
   [I-D.ietf-idr-rfc5575bis] Section 5.1 can be reused with new
   consideration for the IPv6 prefix offset.  As long as the offsets are
   equal, the comparison is the same, retaining longest-prefix-match
   semantics.  If the offsets are not equal, the lowest offset has
   precedence, as this flow matches the most significant bit.

   The code in Appendix A shows a Python3 implementation of the
   resulting comparison algorithm.  The full code was tested with Python
   3.7.2 and can be obtained at https://github.com/stoffi92/flowspec-
   cmp-v6 [1].

5.  Validation Procedure

   The validation procedure is the same as specified in
   [I-D.ietf-idr-rfc5575bis] Section 6 with the exception that item a)
   of the validation procedure should now read as follows:

      a) A destination prefix component with offset=0 is embedded in the
      Flow Specification

6.  IPv6 Traffic Filtering Action changes

   Traffic Filtering Actions from [I-D.ietf-idr-rfc5575bis] Section 7
   can also be applied to IPv6 Flow Specifications.  To allow an IPv6
   address specific route-target, a new Traffic Filtering Action IPv6
   address specific extended community is specified in Section 6.1
   below:





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6.1.  Redirect IPv6 (rt-redirect-ipv6) Type/Sub-Type 0x80/TBD

   The redirect IPv6 address specific extended community allows the
   traffic to be redirected to a VRF routing instance that lists the
   specified IPv6 address specific 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 uses the same encoding as the IPv6 address
   specific Route Target extended community [RFC5701] Section 2 with the
   high-order octet of the Type always set to 0x80 and the Sub-Type
   always TBD.

   Interferes with: All BGP Flow Specification redirect Traffic
   Filtering Actions (with itself and those specified in
   [I-D.ietf-idr-rfc5575bis] Section 7.4).

7.  Security Considerations

   No new security issues are introduced to the BGP protocol by this
   specification over the security considerations in
   [I-D.ietf-idr-rfc5575bis]

8.  IANA Considerations

   This section complies with [RFC7153]

   IANA is requested to create and maintain a new registry entitled:
   "Flow Spec IPv6 Component Types" containing the initial entries as
   specified in Table 1.




















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           +-------+-------------------------+-----------------+
           | Value | Name                    | Reference       |
           +-------+-------------------------+-----------------+
           | 1     | Destination IPv6 Prefix | [this document] |
           | 2     | Source IPv6 Prefix      | [this document] |
           | 3     | Next Header             | [this document] |
           | 4     | Port                    | [this document] |
           | 5     | Destination port        | [this document] |
           | 6     | Source port             | [this document] |
           | 7     | ICMPv6 type             | [this document] |
           | 8     | ICMPv6 code             | [this document] |
           | 9     | TCP flags               | [this document] |
           | 10    | Packet length           | [this document] |
           | 11    | DSCP                    | [this document] |
           | 12    | Fragment                | [this document] |
           | 13    | Flow Label              | [this document] |
           +-------+-------------------------+-----------------+

             Table 1: Registry: Flow Spec IPv6 Component Types

   IANA maintains a registry entitled "Generic Transitive Experimental
   Use Extended Community Sub-Types".  For the purpose of this work,
   IANA is requested to assign a new value:

   +----------------+--------------------------------+-----------------+
   | Sub-Type Value | Name                           | Reference       |
   +----------------+--------------------------------+-----------------+
   | TBD            | Flow spec rt-redirect-ipv6     | [this document] |
   |                | format                         |                 |
   +----------------+--------------------------------+-----------------+

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

9.  Acknowledgements

   Authors would like to thank Pedro Marques, Hannes Gredler and Bruno
   Rijsman, Brian Carpenter, and Thomas Mangin for their valuable input.

10.  Contributors

   Danny McPherson
   Verisign, Inc.

   Email: dmcpherson@verisign.com






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   Burjiz Pithawala
   Individual

   Email: burjizp@gmail.com


   Andy Karch
   Cisco Systems
   170 West Tasman Drive
   San Jose, CA  95134
   USA

   Email: akarch@cisco.com


11.  References

11.1.  Normative References

   [I-D.ietf-idr-rfc5575bis]
              Loibl, C., Hares, S., Raszuk, R., McPherson, D., and M.
              Bacher, "Dissemination of Flow Specification Rules",
              draft-ietf-idr-rfc5575bis-17 (work in progress), June
              2019.

   [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>.

   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
              December 1998, <https://www.rfc-editor.org/info/rfc2460>.

   [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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   [RFC4443]  Conta, A., Deering, S., and M. Gupta, Ed., "Internet
              Control Message Protocol (ICMPv6) for the Internet
              Protocol Version 6 (IPv6) Specification", STD 89,
              RFC 4443, DOI 10.17487/RFC4443, March 2006,
              <https://www.rfc-editor.org/info/rfc4443>.

   [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>.

   [RFC5492]  Scudder, J. and R. Chandra, "Capabilities Advertisement
              with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
              2009, <https://www.rfc-editor.org/info/rfc5492>.

   [RFC5701]  Rekhter, Y., "IPv6 Address Specific BGP Extended Community
              Attribute", RFC 5701, DOI 10.17487/RFC5701, November 2009,
              <https://www.rfc-editor.org/info/rfc5701>.

   [RFC6437]  Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme,
              "IPv6 Flow Label Specification", RFC 6437,
              DOI 10.17487/RFC6437, November 2011,
              <https://www.rfc-editor.org/info/rfc6437>.

   [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>.

   [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>.

11.2.  Informative References

   [RFC5095]  Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
              of Type 0 Routing Headers in IPv6", RFC 5095,
              DOI 10.17487/RFC5095, December 2007,
              <https://www.rfc-editor.org/info/rfc5095>.

11.3.  URIs

   [1] https://github.com/stoffi92/flowspec-cmp-v6

Appendix A.  Python code: flow_rule_cmp_v6

  <CODE BEGINS>
  """
  Copyright (c) 2019 IETF Trust and the persons identified as authors of



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  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_v6(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
          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):
              if comp_a.offset < comp_b.offset:
                  return A_HAS_PRECEDENCE
              if comp_a.offset < comp_b.offset:
                  return B_HAS_PRECEDENCE
              # both components have the same offset
              # assuming comp_a.value, comp_b.value of type
              # ipaddress.IPv6Network
              # and the offset bits are reset to 0 (since they are not
              # represented in the NLRI)
              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



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          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>

Authors' Addresses

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

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


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

   Email: robert@raszuk.net










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   Susan Hares (editor)
   Huawei
   7453 Hickory Hill
   Saline, MI  48176
   USA

   Email: shares@ndzh.com












































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