Extensions to the Access Control Lists (ACLs) YANG Model
draft-dbb-netmod-acl-00

Document Type Active Internet-Draft (individual)
Authors Oscar de Dios  , samier barguil  , Mohamed Boucadair 
Last updated 2021-10-18
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Netmod WG                                            O. Gonzalez de Dios
Internet-Draft                                                S. Barguil
Intended status: Standards Track                              Telefonica
Expires: 21 April 2022                                      M. Boucadair
                                                                  Orange
                                                         18 October 2021

        Extensions to the Access Control Lists (ACLs) YANG Model
                        draft-dbb-netmod-acl-00

Abstract

   RFC 8519 defines a YANG data model for Access Control Lists (ACLs).
   This document discusses a set of extensions that fix many of the
   limitations of the ACL model as initially defined in RFC 8519.

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
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   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 21 April 2022.

Copyright Notice

   Copyright (c) 2021 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   Please review these documents carefully, as they describe your rights
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   provided without warranty as described in the Simplified BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Approach  . . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Problem Statement & Gap Analysis  . . . . . . . . . . . . . .   4
     3.1.  Suboptimal Configuration: Lack of Manipulating Lists of
           Prefixes  . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Manageability: Impossibility to Use Aliases or Defined
           Sets  . . . . . . . . . . . . . . . . . . . . . . . . . .   8
     3.3.  Bind ACLs to Devices, Not Only Interfaces . . . . . . . .   9
     3.4.  Partial or Lack of IPv4/IPv6 Fragment Handling  . . . . .   9
     3.5.  Suboptimal TCP Flags Handling . . . . . . . . . . . . . .  13
     3.6.  Rate-Limit Action . . . . . . . . . . . . . . . . . . . .  13
     3.7.  Payload-based Filtering . . . . . . . . . . . . . . . . .  14
     3.8.  Reuse the ACLs Content Across Several Devices . . . . . .  15
   4.  Overall Module Structure (TBC)  . . . . . . . . . . . . . . .  15
   5.  YANG Module (TBC) . . . . . . . . . . . . . . . . . . . . . .  15
   6.  Security Considerations (TBC) . . . . . . . . . . . . . . . .  15
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     7.1.  URI Registration (TBC)  . . . . . . . . . . . . . . . . .  16
     7.2.  YANG Module Name Registration (TBC) . . . . . . . . . . .  16
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  16
   9.  Normative References  . . . . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  17

1.  Introduction

   [RFC8519] defines Acces control lists (ACLs) as a user-ordered set of
   filtering rules.  The model targets the configuration of the
   filtering behaviour of a device.  However, the model structure, as
   defined in [RFC8519], suffers from a set of limitations.  This
   document describes these limitations and proposes an enhanced ACL
   structure.

   The motivation of such enhanced ACL structure is discussed in detail
   in Section 3.

   When managing ACLs, it is common for network operators to group
   matching elements in pre-defined sets.  The consolidation into
   matches allows reducing the number of rules, especially in large
   scale networks.  If it is needed, for example, to find a match
   against 100 IP addresses (or prefixes), a single rule will suffice
   rather than creating individual Access Control Entries (ACEs) for
   each IP address (or prefix).  In doing so, implementations would
   optimize the performance of matching lists vs multiple rules
   matching.

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   The enhanced ACL structure is also meant to facilitate the management
   of network operators.  Instead of entering the IP address or port
   number literals, using user-named lists decouples the creation of the
   rule from the management of the sets.  Hence, it is possible to
   remove/add entries to the list without redefining the (parent) ACL
   rule.

   In addition, the notion of Access Control List (ACL) and defined sets
   is generalized so that it is not device-specific as per [RFC8519].
   ACLs and defined sets may be defined at network / administrative
   domain level and associated to devices.  This approach facilitates
   the reusability across multiple network elements.  For example,
   managing the IP prefix sets from a network level makes it easier to
   maintain by the security groups.

   Network operators maintain sets of IP prefixes that are related to
   each other, e.g., deny-lists or accept-lists that are associated with
   those provided by a VPN customer.  These lists are maintained and
   manipulated by security expert teams.

   Note that ACLs are used locally in devices but are triggered by other
   tools such as DDoS mitigation [RFC9132] or BGP Flow Spec [RFC8955]
   [RFC8956].  Therefore, supporting means to easily map to the
   filtering rules conveyed in messages triggered by hese tools is
   valuable from a network operation standpoint.

1.1.  Terminology

   The keywords MUST, MUST NOT, REQUIRED, SHALL, SHALL NOT, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL, when they appear in this
   document, are to be interpreted as described in [RFC2119].

   The terminology for describing YANG modules is defined in [RFC7950].
   The meaning of the symbols in the tree diagrams is defined in
   [RFC8340].

   In adition to the terms defined in [RFC8519], this document makes use
   of the following terms:

   *  Defined set: Refers to reusable description of one or multiple
      information elements (e.g., IP address, IP prefix, port number,
      ICMP type).

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2.  Approach

   This first version of the document does not include on purpose any
   YANG module.  This is because the authors are seeking a work
   direction from the netmod WG whether the missing features can be
   accomplished by means of augmentations or whether an ACL-bis document
   is more appropriate.

   Future versions of the document will include a YANG module that will
   reflect the WG feedback.  A network wide module, in adition to the
   device module, might be required.  The decision on whether a single
   module is sufficient to handle both device and network levels or two
   separate ones will be based on WG feedback.

3.  Problem Statement & Gap Analysis

3.1.  Suboptimal Configuration: Lack of Manipulating Lists of Prefixes

   IP prefix related data nodes, e.g., "destination-ipv4-network" or
   "destination-ipv6-network", do not allow manipulating a list of IP
   prefixes, which may lead to manipulating large files.  The same issue
   is encountered when ACLs have to be in place to mitigate DDoS attacks
   (e.g., [RFC9132]) when a set of sources are involved in such an
   attack.  The situation is even worse when both a list of sources and
   destination prefixes are involved.

   Figure 1 shows an example of the required ACL configuration for
   filtering traffic from two prefixes.

   {
     "ietf-access-control-list:acls": {
       "acl": [
         {
           "name": "first-prefix",
           "type": "ipv6-acl-type",
           "aces": {
             "ace": [
               {
                 "name": "my-test-ace",
                 "matches": {
                   "ipv6": {
                     "destination-ipv6-network":
                       "2001:db8:6401:1::/64",
                     "source-ipv6-network":
                       "2001:db8:1234::/96",
                     "protocol": 17,
                     "flow-label": 10000
                   },

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                   "udp": {
                     "source-port": {
                       "operator": "lte",
                       "port": 80
                     },
                     "destination-port": {
                       "operator": "neq",
                       "port": 1010
                     }
                   }
                 },
                 "actions": {
                   "forwarding": "accept"
                 }
               }
             ]
           }
         },
         {
           "name": "second-prefix",
           "type": "ipv6-acl-type",
           "aces": {
             "ace": [
               {
                 "name": "my-test-ace",
                 "matches": {
                   "ipv6": {
                     "destination-ipv6-network":
                       "2001:db8:6401:c::/64",
                     "source-ipv6-network":
                       "2001:db8:1234::/96",
                     "protocol": 17,
                     "flow-label": 10000
                   },
                   "udp": {
                     "source-port": {
                       "operator": "lte",
                       "port": 80
                     },
                     "destination-port": {
                       "operator": "neq",
                       "port": 1010
                     }
                   }
                 },
                 "actions": {
                   "forwarding": "accept"
                 }

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               }
             ]
           }
         }
       ]
     }
   }

      Figure 1: Example Illustrating Sub-optimal Use of the ACL Model
                            with a Prefix List.

   Such configuration is suboptimal for both: - Network controllers that
   need to manipulate large files.  All or a subset fo this
   configuration will need to be passed to the undelrying network
   devices. - Devices may receive such confirguration and thus will need
   to maintain it locally.

   Figure 2 depicts an example of an optimized strcuture:

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   {
     "ietf-access-control-list:acls": {
       "acl": [
         {
           "name": "prefix-list-support",
           "type": "ipv6-acl-type",
           "aces": {
             "ace": [
               {
                 "name": "my-test-ace",
                 "matches": {
                   "ipv6": {
                     "destination-ipv6-network": [
                       "2001:db8:6401:1::/64",
                       "2001:db8:6401:c::/64"
                     ],
                     "source-ipv6-network":
                       "2001:db8:1234::/96",
                     "protocol": 17,
                     "flow-label": 10000
                   },
                   "udp": {
                     "source-port": {
                       "operator": "lte",
                       "port": 80
                     },
                     "destination-port": {
                       "operator": "neq",
                       "port": 1010
                     }
                   }
                 },
                 "actions": {
                   "forwarding": "accept"
                 }
               }
             ]
           }
         }
       ]
     }
   }

      Figure 2: Example Illustrating Optimal Use of the ACL Model in a
                              Network Context.

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3.2.  Manageability: Impossibility to Use Aliases or Defined Sets

   The same approach as the one discussed for IP prefixes can be
   generalized by introduing the concept of "aliases" or "defined sets".

   The defined sets are reusable definitions across several ACLs.  Each
   category is modelled in YANG as a list of parameters related to the
   class it represents.  The following sets can be considered:

   *  Prefix sets: Used to create lists of IPv4 or IPv6 prefixes.

   *  Protocol sets: Used to create a list of protocols.

   *  Port number sets: Used to create lists of TCP or UDP port values
      (or any other transport protocol that makes uses of port numbers).
      The identity of the protcols is identified by the protocol set, if
      present.  Otherwise, a set apply to any protocol.

   *  ICMP sets: Uses to create lists of ICMP-based filters.  This
      applies only when the protocol is set to ICMP or ICMPv6.

   A candidate structure is shown in #example_sets:

        +--rw defined-sets
        |  +--rw prefix-sets
        |  |  +--rw prefix-set* [name mode]
        |  |     +--rw name        string
        |  |     +--rw mode        enumeration
        |  |     +--rw ip-prefix*   inet:ip-prefix
        |  +--rw port-sets
        |  |  +--rw port-set* [name]
        |  |     +--rw name    string
        |  |     +--rw port*   inet:port-number
        |  +--rw protocol-sets
        |  |  +--rw protocol-set* [name]
        |  |     +--rw name             string
        |  |     +--rw protocol-name*   identityref
        |  +--rw icmp-type-sets
        |     +--rw icmp-type-set* [name]
        |        +--rw name     string
        |        +--rw types* [type]
        |           +--rw type              uint8
        |           +--rw code?             uint8
        |           +--rw rest-of-header?   binary

                    Figure 3: Examples of Defined Sets.

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3.3.  Bind ACLs to Devices, Not Only Interfaces

   In the context of network management, an ACL may be enforced in many
   network locations.  As such, the ACL module should allow binding an
   ACL to multiple devices, not only (abstract) interfaces.

   The ACL name must, thus, be unique at the scale of the network, but
   still the same name may be used in many devices when enforcing node-
   specific ACLs.

3.4.  Partial or Lack of IPv4/IPv6 Fragment Handling

   [RFC8519] does not support fragment handling capability for IPv6 but
   offers a partial support for IPv4 by means of 'flags'.  Nevertheless,
   the use of 'flags' is problematic since it does not allow a bitmask
   to be defined.  For example, setting other bits not covered by the
   'flags' filtering clause in a packet will allow that packet to get
   through (because it won't match the ACE).

   Defining a new IPv4/IPv6 matching field called 'fragment' is thus
   required to efficiently handle fragment-related filtering rules.
   Some examples to illustrate how 'fragment' can be used are provided
   below.

   Figure 4 shows the content of a candidate POST request to allow the
   traffic destined to 198.51.100.0/24 and UDP port number 53, but to
   drop all fragmented packets.  The following ACEs are defined (in this
   order):

   *  "drop-all-fragments" ACE: discards all fragments.

   *  "allow-dns-packets" ACE: accepts DNS packets destined to
      198.51.100.0/24.

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      {
        "ietf-access-control-list:acls": {
          "acl": [
            {
              "name": "dns-fragments",
              "type": "ipv4-acl-type",
              "aces": {
                "ace": [
                  {
                    "name": "drop-all-fragments",
                    "matches": {
                      "ipv4": {
                        "fragment": {
                          "operator": "match",
                          "type": "isf"
                        }
                      }
                    },
                    "actions": {
                      "forwarding": "drop"
                    }
                  },
                  {
                    "name": "allow-dns-packets",
                    "matches": {
                      "ipv4": {
                        "destination-ipv4-network": "198.51.100.0/24"
                      },
                      "udp": {
                        "destination-port": {
                          "operator": "eq",
                          "port": 53
                        }
                      },
                      "actions": {
                        "forwarding": "accept"
                      }
                    }
                  }
                ]
              }
            }
          ]
        }
      }

         Figure 4: Example Illustrating Canddiate Filtering of IPv4
                            Fragmented Packets.

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   Figure 5 shows an example of the body of a candidate POST request to
   allow the traffic destined to 2001:db8::/32 and UDP port number 53,
   but to drop all fragmented packets.  The following ACEs are defined
   (in this order):

   *  "drop-all-fragments" ACE: discards all fragments (including atomic
      fragments).  That is, IPv6 packets that include a Fragment header
      (44) are dropped.

   *  "allow-dns-packets" ACE: accepts DNS packets destined to
      2001:db8::/32.

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     {
        "ietf-access-control-list:acls": {
          "acl": [
            {
              "name": "dns-fragments",
              "type": "ipv6-acl-type",
              "aces": {
                "ace": [
                  {
                    "name": "drop-all-fragments",
                    "matches": {
                      "ipv6": {
                        "fragment": {
                          "operator": "match",
                          "type": "isf"
                        }
                      }
                    },
                    "actions": {
                      "forwarding": "drop"
                    }
                  },
                  {
                    "name": "allow-dns-packets",
                    "matches": {
                      "ipv6": {
                        "destination-ipv6-network": "2001:db8::/32"
                      },
                      "udp": {
                        "destination-port": {
                          "operator": "eq",
                          "port": 53
                        }
                      }
                    },
                    "actions": {
                      "forwarding": "accept"
                    }
                  }
                ]
              }
            }
          ]
        }
      }

         Figure 5: Example Illustrating Canddiate Filtering of IPv6
                            Fragmented Packets.

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3.5.  Suboptimal TCP Flags Handling

   [RFC8519] allows including flags in the TCP match fields, however
   that strcuture does not support matching operations as those
   supported in BGP Flow Spec.  Definig this field to be defined as a
   flag bitmask together with a set of operations is meant to
   efficiently handle TCP flags filtering rules.  Some examples to
   illustrate the use of such field are discussed below.

   Figure 6 shows an example of a candidate request to install a filter
   to discard incoming TCP messages having all flags unset.

     {
        "ietf-access-control-list:acls": {
          "acl": [{
            "name": "tcp-flags-example",
            "aces": {
              "ace": [{
                "name": "null-attack",
                "matches": {
                  "tcp": {
                    "flags-bitmask": {
                      "operator": "not any",
                      "bitmask": 4095
                    }
                  }
                },
                "actions": {
                  "forwarding": "drop"
                }
              }]
            }
          }]
        }
      }

             Figure 6: Example to Deny TCP Null Attack Messages

3.6.  Rate-Limit Action

   [RFC8519] specifies that forwarding actions can be 'accept' (i.e.,
   accept matching traffic), 'drop' (i.e., drop matching traffic without
   sending any ICMP error message), or 'reejct' (i.e., drop matching
   traffic and send an ICMP error message to the source).  Howover,
   there are situations where the matching traffic can be accepted, but
   with a rate-limit policy.  Such capability is not currently supported
   by the ACL model.

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   Figure 7 shows a candidate ACL example to rate-limit incoming SYNs
   during a SYN flood attack.

     {
        "ietf-access-control-list:acls": {
          "acl": [{
            "name": "tcp-flags-example-with-rate-limit",
            "aces": {
              "ace": [{
                "name": "rate-limit-syn",
                "matches": {
                  "tcp": {
                    "flags-bitmask": {
                      "operator": "match",
                      "bitmask": 2
                    }
                  }
                },
                "actions": {
                  "forwarding": "accept",
                  "rate-limit": "20.00"
                }
              }]
            }
          }]
        }
      }

               Figure 7: Example Rate-Limit Incoming TCP SYNs

3.7.  Payload-based Filtering

   Some transport protocols use existing protocols (e.g., TCP or UDP) as
   substrate.  The match criteria for such protocols may rely upon the
   'protocol' under 'l3', TCP/UDP match criteria, part of the TCP/UDP
   payload, or a combination thereof.  [RFC8519] does not support
   matching based on the payload.

   Likewise, the current version of the ACL model does not support
   filetering of encapsulated traffic.

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3.8.  Reuse the ACLs Content Across Several Devices

   Having a global network view of the ACLs is highly valuable for
   service providers.  An ACL could be defined and applied following the
   hierarchy of the network topology.  So, an ACL can be defined at the
   network level and, then, that same ACL can be used (or referenced to)
   in several devices (including termination points) within the same
   network.

   This network/device ACLs differentiation introduces several new
   requirements, e.g.:

   *  An ACL name can be used at both network and device levels.

   *  An ACL content updated at the network level should imply a
      transaction that updates the relevant content in all the nodes
      using this ACL.

   *  ACLs defined at the device level have a local meaning for the
      specific node.

   *  A device can be associated with a router, a VRF, a logical system,
      or a virtual node.  ACLs can be applied in physical and logical
      infrastructure.

4.  Overall Module Structure (TBC)

   To be completed.

5.  YANG Module (TBC)

   To be completed.

6.  Security Considerations (TBC)

   The YANG modules specified in this document define a schema for data
   that is designed to be accessed via network management protocol such
   as NETCONF [RFC6241] or RESTCONF [RFC8040].  The lowest NETCONF layer
   is the secure transport layer, and the mandatory-to-implement secure
   transport is Secure Shell (SSH) [RFC6242].  The lowest RESTCONF layer
   is HTTPS, and the mandatory-to-implement secure transport is TLS
   [RFC8446].

   The Network Configuration Access Control Model (NACM) [RFC8341]
   provides the means to restrict access for particular NETCONF or
   RESTCONF users to a preconfigured subset of all available NETCONF or
   RESTCONF protocol operations and content.

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   There are a number of data nodes defined in this YANG module that are
   writable/creatable/deletable (i.e., config true, which is the
   default).  These data nodes may be considered sensitive or vulnerable
   in some network environments.  Write operations (e.g., edit-config)
   to these data nodes without proper protection can have a negative
   effect on network operations.  These are the subtrees and data nodes
   and their sensitivity/vulnerability:

   *  TBC

   Some of the readable data nodes in this YANG module may be considered
   sensitive or vulnerable in some network environments.  It is thus
   important to control read access (e.g., via get, get-config, or
   notification) to these data nodes.  These are the subtrees and data
   nodes and their sensitivity/vulnerability:

   *  TBC

7.  IANA Considerations

7.1.  URI Registration (TBC)

   This document requests IANA to register the following URI in the "ns"
   subregistry within the "IETF XML Registry" [RFC3688]:

            URI: urn:ietf:params:xml:ns:yang:xxx
            Registrant Contact: The IESG.
            XML: N/A; the requested URI is an XML namespace.

7.2.  YANG Module Name Registration (TBC)

   This document requests IANA to register the following YANG module in
   the "YANG Module Names" subregistry [RFC6020] within the "YANG
   Parameters" registry.

            name: xxxx
            namespace: urn:ietf:params:xml:ns:yang:ietf-xxx
            maintained by IANA: N
            prefix: xxxx
            reference: RFC XXXX

8.  Acknowledgements

   Many thanks to Jon Shallow and Miguel Cros for the discussion when
   preparing this draft.

9.  Normative References

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   [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>.

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              DOI 10.17487/RFC3688, January 2004,
              <https://www.rfc-editor.org/info/rfc3688>.

   [RFC6020]  Bjorklund, M., Ed., "YANG - A Data Modeling Language for
              the Network Configuration Protocol (NETCONF)", RFC 6020,
              DOI 10.17487/RFC6020, October 2010,
              <https://www.rfc-editor.org/info/rfc6020>.

   [RFC6241]  Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed.,
              and A. Bierman, Ed., "Network Configuration Protocol
              (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011,
              <https://www.rfc-editor.org/info/rfc6241>.

   [RFC6242]  Wasserman, M., "Using the NETCONF Protocol over Secure
              Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011,
              <https://www.rfc-editor.org/info/rfc6242>.

   [RFC8040]  Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF
              Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017,
              <https://www.rfc-editor.org/info/rfc8040>.

   [RFC8341]  Bierman, A. and M. Bjorklund, "Network Configuration
              Access Control Model", STD 91, RFC 8341,
              DOI 10.17487/RFC8341, March 2018,
              <https://www.rfc-editor.org/info/rfc8341>.

   [RFC8446]  Rescorla, E., "The Transport Layer Security (TLS) Protocol
              Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018,
              <https://www.rfc-editor.org/info/rfc8446>.

   [RFC8519]  Jethanandani, M., Agarwal, S., Huang, L., and D. Blair,
              "YANG Data Model for Network Access Control Lists (ACLs)",
              RFC 8519, DOI 10.17487/RFC8519, March 2019,
              <https://www.rfc-editor.org/info/rfc8519>.

Authors' Addresses

   Oscar Gonzalez de Dios
   Telefonica
   Distrito T
   Madrid

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Internet-Draft                Enhanced ACLs                 October 2021

   Email: oscar.gonzalezdedios@telefonica.com

   Samier Barguil
   Telefonica
   Distrito T
   Madrid

   Email: samier.barguilgiraldo.ext@telefonica.com

   Mohamed Boucadair
   Orange
   Rennes

   Email: mohamed.boucadair@orange.com

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