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.
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Provisions Relating to IETF Documents (https://trustee.ietf.org/
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Please review these documents carefully, as they describe your rights
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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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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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