Internet-Draft | A YANG Network Model for ACs | November 2023 |
Boucadair, et al. | Expires 9 May 2024 | [Page] |
- Workgroup:
- Operations and Management Area Working Group
- Internet-Draft:
- draft-ietf-opsawg-ntw-attachment-circuit-00
- Published:
- Intended Status:
- Standards Track
- Expires:
A Network YANG Data Model for Attachment Circuits
Abstract
This document specifies a network model for attachment circuits. The model can be used for the provisioning of attachment circuits prior or during service provisioning (e.g., Network Slice Service). A companion service model is specified in [I-D.boro-opsawg-teas-attachment-circuit].¶
The module augments the Service Attachment Point (SAP) model with the detailed information for the provisioning of attachment circuits in Provider Edges (PEs).¶
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 9 May 2024.¶
Copyright Notice
Copyright (c) 2023 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 Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License.¶
1. Introduction
Connectivity services are provided by networks to customers via dedicated terminating points, such as Service Functions [RFC7665], customer edges (CEs), peer Autonomous System Border Routers (ASBRs), data centers gateways, or Internet Exchange Points.¶
The procedure to provision a service in a service provider network may depend on the practices adopted by a service provider, including the flow put in place for the provisioning of advanced network services and how they are bound to an Attachment Circuit (AC). For example, the same AC may host multiple services (e.g., Layer 2 VPN, Slice Service, or Layer 3 VPN). In order to avoid service interference and redundant information in various locations, a service provider may expose an interface to manage ACs network-wide. Customers can then request a base AC to be put in place, and then refer to that AC when requesting services to be bound to that AC. [I-D.boro-opsawg-teas-attachment-circuit] specifies a data model for managing attachment circuits as a service.¶
This document specifies a network model for ACs ("ietf-ac-ntw"). The model can be used for the provisioning of ACs prior or during service provisioning.¶
The document leverages [RFC9182] and [RFC9291] by adopting an AC provisioning structure that uses data nodes that are defined in these RFCs. Some refinements were introduced to cover, not only conventional service provider networks, but also specifics of other target deployments (cloud, for example).¶
The AC network model is designed as an augmnetation to the Service Attachment Point (SAP) model [RFC9408]. An AC can be bound to a single or multiple SAPs. Likewise, the model is designed to accomdate deployments where a SAP can be bound to one or multiple ACs.¶
The AC network model uses the AC common model defined in [I-D.boro-opsawg-teas-common-ac].¶
The YANG data model in this document conforms to the Network Management Datastore Architecture (NMDA) defined in [RFC8342].¶
2. Conventions and Definitions
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.¶
The reader should be familiar with the terms defined in Section 2 of [RFC9408].¶
This document uses the term "network model" as defined in Section 2.1 of [RFC8969].¶
The meanings of the symbols in the YANG tree diagrams are defined in [RFC8340].¶
This document uses the following terms:¶
- Bearer:
-
A physical or logical link that connects a customer node (or site) to a provider network. A bearer can be a wireless or wired link. One or multiple technologies can be used to build a bearer. The bearer type can be specified by a customer.¶
-
The operator allocates a unique bearer reference to identify a bearer within its network (e.g., customer line identifier). Such a reference can be retrieved by a customer and used in subsequent service placement requests to unambiguously identify where a service is to be bound.¶
-
The concept of bearer can be generalized to refer to the required underlying connection for the provisioning of an attachment circuit. One or multiple attachment circuits may be hosted over the same bearer (e.g., multiple VLANs on the same bearer that is provided by a physical link).¶
- Network controller:
-
Denotes a functional entity responsible for the management of the service provider network.¶
- Service orchestrator:
-
Refers to a functional entity that interacts with the customer of a network service. The service orchestrator is typically responsible for the attachment circuits, the Provider Edge (PE) selection, and requesting the activation of the requested service to a network controller.¶
- Service provider network:
-
A network that is able to provide network services (e.g., Network Slice Services).¶
- Service provider:
-
A service provider that offers network services (e.g., Network Slice Services).¶
3. Sample Uses of the Attachment Circuit Data Models
Figure 2 shows the positioning of the AC network model in the overall service delivery process.¶
4. Description of the Attachment Circuit YANG Module
4.1. Overall Structure of the Module
The overall tree structure of the module is shown in Figure 3. A node can host one or more SAPs. As per [RFC9408], a SAP is an abstraction of the network reference points (the PE side of an AC, in the context of this document) where network services can be delivered and/or are delivered to customers. Each SAP terminates one or multiple ACs. Each AC in turn may be terminated by one or more peer SAPs. In order to expose such AC/SAP binding information, the SAP model [RFC9408] is augmented with required AC-related information. Also, in order to ease the correlation between the AC exposed at the service layer and the one that is actually provisioned in the network operation, a reference to the AC exposed to the customer ('ac-ref') is stored in the 'ac-ntw' module. A controller may, for example, indicate a filter based on the service type (e.g., Network Slice or L3VPN) to retrieve the list of available ACs for that service.¶
Unlike the AC service model, an AC is uniquely identified within the scope of a node, not a network. An AC can be characterized using Layer 2 connectivity, Layer 3 connectivity, routing protocols, OAM, and security considerations. In order to factorize a set of data that is provisioned for a set of ACs, a set of profiles can be defined at the network level, and then called under the node level. The information contained in a profile is thus inherited, unless the corresponding data node is refined at the AC level. In such a case, the value provided at the AC level takes precedence over the global one.¶
The full tree of the 'ac-ntw' is provided in [AC-Ntw-Tree].¶
4.2. L2 Connection
The Layer 2 connection tree structure is shown in Figure 4.¶
4.3. IP Connection
The Layer 3 connection tree structure is shown in Figure 5.¶
5. YANG Module
This module uses types defined in [RFC6991], [RFC8177], [RFC8294], [RFC8343], [RFC9181], [I-D.boro-opsawg-teas-common-ac], and IEEE Std 802.1Qcp.¶
<CODE BEGINS> file "ietf-ac-ntw@2022-11-30.yang" module ietf-ac-ntw { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-ac-ntw"; prefix ac-ntw; import ietf-vpn-common { prefix vpn-common; reference "RFC 9181: A Common YANG Data Model for Layer 2 and Layer 3 VPNs"; } import ietf-inet-types { prefix inet; reference "RFC 6991: Common YANG Data Types, Section 4"; } import ietf-key-chain { prefix key-chain; reference "RFC 8177: YANG Data Model for Key Chains"; } import ietf-routing-types { prefix rt-types; reference "RFC 8294: Common YANG Data Types for the Routing Area"; } import ietf-interfaces { prefix if; reference "RFC 8343: A YANG Data Model for Interface Management"; } import ieee802-dot1q-types { prefix dot1q-types; reference "IEEE Std 802.1Qcp: Bridges and Bridged Networks-- Amendment 30: YANG Data Model"; } import ietf-network { prefix nw; reference "RFC 8345: A YANG Data Model for Network Topologies, Section 6.1"; } import ietf-sap-ntw { prefix sap; reference "RFC SSSS: A YANG Network Model for Service Attachment Points (SAPs)"; } import ietf-ac-common { prefix ac-common; reference "RFC CCCC: A Common YANG Data Model for Attachment Circuits"; } import ietf-ac-svc { prefix ac-svc; reference "RFC SSSS: YANG Service Data Models for Attachment Circuits"; } organization "IETF OPSAWG (Operations and Management Area Working Group)"; contact "WG Web: <https://datatracker.ietf.org/wg/opsawg/> WG List: <mailto:opsawg@ietf.org> Editor: Mohamed Boucadair <mailto:mohamed.boucadair@orange.com> Author: Richard Roberts <mailto:rroberts@juniper.net>"; description "This YANG module defines a YANG model for the management of attachment circuits. Copyright (c) 2023 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 Revised BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). This version of this YANG module is part of RFC xxx; see the RFC itself for full legal notices."; revision 2022-11-30 { description "Initial revision."; reference "RFC xxxx: A YANG Network Data Model for Attachment Circuits"; } // L2 conenction grouping l2-connection { description "Defines Layer 2 protocols and parameters that are required to enable AC connectivity."; container encapsulation { description "Container for Layer 2 encapsulation."; leaf encap-type { type identityref { base vpn-common:encapsulation-type; } description "Tagged interface type."; } container dot1q { when "derived-from-or-self(../encap-type, " + "'vpn-common:dot1q')" { description "Only applies when the type of the tagged interface is 'dot1q'."; } description "Tagged interface."; uses ac-common:dot1q; container tag-operations { description "Sets the tag manipulation policy for this AC. It defines a set of tag manipulations that allow for the insertion, removal, or rewriting of 802.1Q VLAN tags. These operations are indicated for the CE-PE direction. By default, tag operations are symmetric. As such, the reverse tag operation is assumed on the PE-CE direction."; choice op-choice { description "Selects the tag rewriting policy for an AC."; leaf pop { type empty; description "Pop the outer tag."; } leaf push { type empty; description "Pushes one or two tags defined by the tag-1 and tag-2 leaves. It is assumed that, absent any policy, the default value of 0 will be used for the PCP setting."; } leaf translate { type empty; description "Translates the outer tag to one or two tags. PCP bits are preserved."; } } leaf tag-1 { when 'not(../pop)'; type dot1q-types:vlanid; description "A first tag to be used for push or translate operations. This tag will be used as the outermost tag as a result of the tag operation."; } leaf tag-1-type { type dot1q-types:dot1q-tag-type; default "dot1q-types:s-vlan"; description "Specifies a specific 802.1Q tag type of tag-1."; } leaf tag-2 { when '(../translate)'; type dot1q-types:vlanid; description "A second tag to be used for translation."; } leaf tag-2-type { type dot1q-types:dot1q-tag-type; default "dot1q-types:c-vlan"; description "Specifies a specific 802.1Q tag type of tag-2."; } } } container priority-tagged { when "derived-from-or-self(../encap-type, " + "'vpn-common:priority-tagged')" { description "Only applies when the type of the tagged interface is 'priority-tagged'."; } description "Priority tagged container."; uses ac-common:priority-tagged; } container qinq { when "derived-from-or-self(../encap-type, " + "'vpn-common:qinq')" { description "Only applies when the type of the tagged interface is 'QinQ'."; } description "Includes QinQ parameters."; uses ac-common:qinq; container tag-operations { description "Sets the tag manipulation policy for this AC. It defines a set of tag manipulations that allow for the insertion, removal, or rewriting of 802.1Q VLAN tags. These operations are indicated for the CE-PE direction. By default, tag operations are symmetric. As such, the reverse tag operation is assumed on the PE-CE direction."; choice op-choice { description "Selects the tag rewriting policy for a AC."; leaf pop { type uint8 { range "1|2"; } description "Pops one or two tags as a function of the indicated pop value."; } leaf push { type empty; description "Pushes one or two tags defined by the tag-1 and tag-2 leaves. It is assumed that, absent any policy, the default value of 0 will be used for PCP setting."; } leaf translate { type uint8 { range "1|2"; } description "Translates one or two outer tags. PCP bits are preserved. The following operations are supported: - translate 1 with tag-1 leaf is provided: only the outermost tag is translated to the value in tag-1. - translate 2 with both tag-1 and tag-2 leaves are provided: both outer and inner tags are translated to the values in tag-1 and tag-2, respectively. - translate 2 with tag-1 leaf is provided: the outer tag is popped while the inner tag is translated to the value in tag-1."; } } leaf tag-1 { when 'not(../pop)'; type dot1q-types:vlanid; description "A first tag to be used for push or translate operations. This tag will be used as the outermost tag as a result of the tag operation."; } leaf tag-1-type { type dot1q-types:dot1q-tag-type; default "dot1q-types:s-vlan"; description "Specifies a specific 802.1Q tag type of tag-1."; } leaf tag-2 { when 'not(../pop)'; type dot1q-types:vlanid; description "A second tag to be used for push or translate operations."; } leaf tag-2-type { type dot1q-types:dot1q-tag-type; default "dot1q-types:c-vlan"; description "Specifies a specific 802.1Q tag type of tag-2."; } } } } choice l2-service { description "The Layer 2 connectivity service can be provided by indicating a pointer to an L2VPN or by specifying a Layer 2 tunnel service."; container l2-tunnel-service { description "Defines a Layer 2 tunnel termination."; uses ac-common:l2-tunnel-service; } case l2vpn { leaf l2vpn-id { type vpn-common:vpn-id; description "Indicates the L2VPN service associated with an Integrated Routing and Bridging (IRB) interface."; } } } } grouping l2-connection-if-ref { description "Specifies Layer 2 connection paramters with interface references."; uses l2-connection; leaf l2-termination-point { type string; description "Specifies a reference to a local Layer 2 termination point, such as a Layer 2 sub-interface."; } leaf local-bridge-reference { type string; description "Specifies a local bridge reference to accommodate, e.g., implementations that require internal bridging. A reference may be a local bridge domain."; } leaf bearer-reference { if-feature "vpn-common:bearer-reference"; type string; description "This is an internal reference for the service provider to identify the bearer associated with this AC."; } container lag-interface { if-feature "vpn-common:lag-interface"; description "Container for configuration of Link Aggregation Group (LAG) interface attributes."; leaf lag-interface-id { type string; description "LAG interface identifier."; } container member-link-list { description "Container for the member link list."; list member-link { key "name"; description "Member link."; leaf name { type string; description "Member link name."; } } } } } // IPv4 connection grouping ipv4-connection { description "IPv4-specific parameters."; leaf local-address { type inet:ipv4-address; description "The IP address used at the provider's interface."; } uses ac-common:ipv4-allocation-type; choice allocation-type { description "Choice of the IPv4 address allocation."; case dynamic { description "When the addresses are allocated by DHCP or other dynamic means local to the infrastructure."; choice address-assign { default "number"; description "A choice for how IPv4 addresses are assigned."; case number { leaf number-of-dynamic-address { type uint16; description "Specifies the number of IP addresses to be assigned to the customer on this access."; } } case explicit { container customer-addresses { description "Container for customer addresses to be allocated using DHCP."; list address-pool { key "pool-id"; description "Describes IP addresses to be dyncamically allocated. When only 'start-address' is present, it represents a single address. When both 'start-address' and 'end-address' are specified, it implies a range inclusive of both addresses."; leaf pool-id { type string; description "A pool identifier for the address range from 'start-address' to 'end-address'."; } leaf start-address { type inet:ipv4-address; mandatory true; description "Indicates the first address in the pool."; } leaf end-address { type inet:ipv4-address; description "Indicates the last address in the pool."; } } } } } choice provider-dhcp { description "Parameters related to DHCP-allocated addresses. IP addresses are allocated by DHCP, which is provided by the operator."; leaf dhcp-service-type { type enumeration { enum server { description "Local DHCP server."; } enum relay { description "Local DHCP relay. DHCP requests are relayed to a provider's server."; } } description "Indicates the type of DHCP service to be enabled on this access."; } choice service-type { description "Choice based on the DHCP service type."; case relay { description "Container for a list of the provider's DHCP servers (i.e., 'dhcp-service-type' is set to 'relay')."; leaf-list server-ip-address { type inet:ipv4-address; description "IPv4 addresses of the provider's DHCP server, for use by the local DHCP relay."; } } } } choice dhcp-relay { description "The DHCP relay is provided by the operator."; container customer-dhcp-servers { description "Container for a list of the customer's DHCP servers."; leaf-list server-ip-address { type inet:ipv4-address; description "IPv4 addresses of the customer's DHCP server."; } } } } case static-addresses { description "Lists the IPv4 addresses that are used."; list address { key "address-id"; ordered-by user; description "Lists the IPv4 addresses that are used. The first address of the list is the primary address of the connection."; leaf address-id { type string; description "An identifier of the static IPv4 address."; } leaf customer-address { type inet:ipv4-address; description "An IPv4 address of the customer side."; } } } } } grouping ipv6-connection { description "IPv6-specific parameters."; leaf local-address { type inet:ipv6-address; description "IPv6 address of the provider side."; } uses ac-common:ipv6-allocation-type; choice allocation-type { description "Choice of the IPv6 address allocation."; case dynamic { description "When the addresses are allocated by DHCP or other dynamic means local to the infrastructure."; choice address-assign { default "number"; description "A choice for how IPv6 addresses are assigned."; case number { leaf number-of-dynamic-address { type uint16; default "1"; description "Specifies the number of IP addresses to be assigned to the customer on this access."; } } case explicit { container customer-addresses { description "Container for customer addresses to be allocated using DHCP."; list address-pool { key "pool-id"; description "Describes IP addresses to be dyncamically allocated. When only 'start-address' is present, it represents a single address. When both 'start-address' and 'end-address' are specified, it implies a range inclusive of both addresses."; leaf pool-id { type string; description "A pool identifier for the address range from 'start-address' to 'end-address'."; } leaf start-address { type inet:ipv6-address; mandatory true; description "Indicates the first address in the pool."; } leaf end-address { type inet:ipv6-address; description "Indicates the last address in the pool."; } } } } } choice provider-dhcp { description "Parameters related to DHCP-allocated addresses. IP addresses are allocated by DHCP, which is provided by the operator."; leaf dhcp-service-type { type enumeration { enum server { description "Local DHCP server."; } enum relay { description "Local DHCP relay. DHCP requests are relayed to a provider's server."; } } description "Indicates the type of DHCP service to be enabled on this access."; } choice service-type { description "Choice based on the DHCP service type."; case relay { description "Container for a list of the provider's DHCP servers (i.e., 'dhcp-service-type' is set to 'relay')."; leaf-list server-ip-address { type inet:ipv6-address; description "IPv6 addresses of the provider's DHCP server, for use by the local DHCP relay."; } } } } choice dhcp-relay { description "The DHCP relay is provided by the operator."; container customer-dhcp-servers { description "Container for a list of the customer's DHCP servers."; leaf-list server-ip-address { type inet:ipv6-address; description "IPv6 addresses of the customer's DHCP server."; } } } } case static-addresses { description "Lists the IPv4 addresses that are used."; list address { key "address-id"; ordered-by user; description "Lists the IPv6 addresses that are used. The first address of the list is the primary address of the connection."; leaf address-id { type string; description "An identifier of the static IPv4 address."; } leaf customer-address { type inet:ipv6-address; description "An IPv6 address of the customer side."; } } } } } grouping ip-connection { description "Defines IP connection parameters."; leaf l3-termination-point { type string; description "Specifies a reference to a local Layer 3 termination point, such as a bridge domain interface."; } container ipv4 { if-feature "vpn-common:ipv4"; description "IPv4-specific parameters."; uses ipv4-connection; } container ipv6 { if-feature "vpn-common:ipv6"; description "IPv6-specific parameters."; uses ipv6-connection; } } /* Routing */ //BGP base parameters grouping bgp-base { description "Configuration specific to BGP."; leaf description { type string; description "Includes a description of the BGP session. This description is meant to be used for diagnostic purposes. The semantic of the description is local to an implementation."; } leaf local-as { type inet:as-number; description "Indicates a local AS Number (ASN), if an ASN distinct from the ASN configured at the AC level is needed."; } leaf peer-as { type inet:as-number; mandatory true; description "Indicates the customer's ASN when the customer requests BGP routing."; } leaf address-family { type identityref { base vpn-common:address-family; } description "This node contains the address families to be activated. 'dual-stack' means that both IPv4 and IPv6 will be activated."; } leaf multihop { type uint8; description "Describes the number of IP hops allowed between a given BGP neighbor and the PE."; } leaf as-override { type boolean; default "false"; description "Defines whether ASN override is enabled, i.e., replacing the ASN of the customer specified in the AS_PATH attribute with the local ASN."; } leaf allow-own-as { type uint8; default "0"; description "If set, specifies the maximum number of occurrences of the provider's ASN that are permitted within the AS_PATH before it is rejected."; } leaf prepend-global-as { type boolean; default "false"; description "In some situations, the ASN that is provided at the node level may be distinct from the ASN configured at the AC. When such ASNs are provided, they are both prepended to the BGP route updates for this AC. To disable that behavior, 'prepend-global-as' must be set to 'false'. In such a case, the ASN that is provided at the node level is not prepended to the BGP route updates for this access."; } leaf send-default-route { type boolean; default "false"; description "Defines whether default routes can be advertised to a peer. If set, the default routes are advertised to a peer."; } leaf site-of-origin { when "../address-family = 'vpn-common:ipv4' " + "or 'vpn-common:dual-stack'" { description "Only applies if IPv4 is activated."; } type rt-types:route-origin; description "The Site of Origin attribute is encoded as a Route Origin Extended Community. It is meant to uniquely identify the set of routes learned from a site via a particular AC and is used to prevent routing loops."; reference "RFC 4364: BGP/MPLS IP Virtual Private Networks (VPNs), Section 7"; } leaf ipv6-site-of-origin { when "../address-family = 'vpn-common:ipv6' " + "or 'vpn-common:dual-stack'" { description "Only applies if IPv6 is activated."; } type rt-types:ipv6-route-origin; description "The IPv6 Site of Origin attribute is encoded as an IPv6 Route Origin Extended Community. It is meant to uniquely identify the set of routes learned from a site."; reference "RFC 5701: IPv6 Address Specific BGP Extended Community Attribute"; } list redistribute-connected { key "address-family"; description "Indicates, per address family, the policy to follow for connected routes."; leaf address-family { type identityref { base vpn-common:address-family; } description "Indicates the address family."; } leaf enable { type boolean; description "Enables the redistribution of connected routes."; } } container bgp-max-prefix { description "Controls the behavior when a prefix maximum is reached."; leaf max-prefix { type uint32; default "5000"; description "Indicates the maximum number of BGP prefixes allowed in the BGP session. It allows control of how many prefixes can be received from a neighbor. If the limit is exceeded, the action indicated in 'violate-action' will be followed."; reference "RFC 4271: A Border Gateway Protocol 4 (BGP-4), Section 8.2.2"; } leaf warning-threshold { type decimal64 { fraction-digits 5; range "0..100"; } units "percent"; default "75"; description "When this value is reached, a warning notification will be triggered."; } leaf violate-action { type enumeration { enum warning { description "Only a warning message is sent to the peer when the limit is exceeded."; } enum discard-extra-paths { description "Discards extra paths when the limit is exceeded."; } enum restart { description "The BGP session restarts after the indicated time interval."; } } description "If the BGP neighbor 'max-prefix' limit is reached, the action indicated in 'violate-action' will be followed."; } leaf restart-timer { type uint32; units "seconds"; description "Time interval after which the BGP session will be reestablished."; } } container bgp-timers { description "Includes two BGP timers."; leaf keepalive { type uint16 { range "0..21845"; } units "seconds"; default "30"; description "This timer indicates the KEEPALIVE messages' frequency between a PE and a BGP peer. If set to '0', it indicates that KEEPALIVE messages are disabled. It is suggested that the maximum time between KEEPALIVE messages be one-third of the Hold Time interval."; reference "RFC 4271: A Border Gateway Protocol 4 (BGP-4), Section 4.4"; } leaf hold-time { type uint16 { range "0 | 3..65535"; } units "seconds"; default "90"; description "Indicates the maximum number of seconds that may elapse between the receipt of successive KEEPALIVE and/or UPDATE messages from the peer. The Hold Time must be either zero or at least three seconds."; reference "RFC 4271: A Border Gateway Protocol 4 (BGP-4), Section 4.2"; } } } // RIP base parameters grouping rip-base { description "Configuration specific to RIP routing."; leaf address-family { type identityref { base vpn-common:address-family; } description "Indicates whether IPv4, IPv6, or both address families are to be activated."; } container timers { description "Indicates the RIP timers."; reference "RFC 2453: RIP Version 2"; leaf update-interval { type uint16 { range "1..32767"; } units "seconds"; description "Indicates the RIP update time, i.e., the amount of time for which RIP updates are sent."; } leaf invalid-interval { type uint16 { range "1..32767"; } units "seconds"; description "The interval before a route is declared invalid after no updates are received. This value is at least three times the value for the 'update-interval' argument."; } leaf holddown-interval { type uint16 { range "1..32767"; } units "seconds"; description "Specifies the interval before better routes are released."; } leaf flush-interval { type uint16 { range "1..32767"; } units "seconds"; description "Indicates the RIP flush timer, i.e., the amount of time that must elapse before a route is removed from the routing table."; } } leaf default-metric { type uint8 { range "0..16"; } description "Sets the default metric."; } } // routing profile grouping routing-profile { description "Defines routing protocols."; list routing-protocol { key "id"; description "List of routing protocols used on the AC."; leaf id { type string; description "Unique identifier for the routing protocol."; } leaf type { type identityref { base vpn-common:routing-protocol-type; } description "Type of routing protocol."; } container bgp { when "derived-from-or-self(../type, " + "'vpn-common:bgp-routing')" { description "Only applies when the protocol is BGP."; } description "Configuration specific to BGP."; uses bgp-base; } container ospf { when "derived-from-or-self(../type, " + "'vpn-common:ospf-routing')" { description "Only applies when the protocol is OSPF."; } description "Configuration specific to OSPF."; uses ac-common:ospf-basic; leaf max-lsa { type uint32 { range "1..4294967294"; } description "Maximum number of allowed Link State Advertisements (LSAs) that the OSPF instance will accept."; } } container isis { when "derived-from-or-self(../type, " + "'vpn-common:isis-routing')" { description "Only applies when the protocol is IS-IS."; } description "Configuration specific to IS-IS."; uses ac-common:isis-basic; leaf level { type identityref { base vpn-common:isis-level; } description "Can be 'level-1', 'level-2', or 'level-1-2'."; reference "RFC 9181: A Common YANG Data Model for Layer 2 and Layer 3 VPNs"; } leaf metric { type uint16; description "Metric of the AC. It is used in the routing state calculation and path selection."; } leaf mode { type enumeration { enum active { description "The interface sends or receives IS-IS protocol control packets."; } enum passive { description "Suppresses the sending of IS-IS updates through the specified interface."; } } description "IS-IS interface mode type."; } } container rip { when "derived-from-or-self(../type, " + "'vpn-common:rip-routing')" { description "Only applies when the protocol is RIP."; } description "Configuration specific to RIP routing."; uses rip-base; } container vrrp { when "derived-from-or-self(../type, " + "'vpn-common:vrrp-routing')" { description "Only applies when the protocol is the Virtual Router Redundancy Protocol (VRRP)."; } description "Configuration specific to VRRP."; reference "RFC 5798: Virtual Router Redundancy Protocol (VRRP) Version 3 for IPv4 and IPv6"; leaf address-family { type identityref { base vpn-common:address-family; } description "Indicates whether IPv4, IPv6, or both address families are to be enabled."; } leaf ping-reply { type boolean; description "Controls whether the VRRP speaker should reply to ping requests."; } } } } grouping routing { description "Defines routing protocols."; list routing-protocol { key "id"; description "List of routing protocols used on the AC."; leaf id { type string; description "Unique identifier for the routing protocol."; } leaf type { type identityref { base vpn-common:routing-protocol-type; } description "Type of routing protocol."; } list routing-profiles { key "id"; description "Routing profiles."; leaf id { type leafref { path "/nw:networks/nw:network" + "/ac-ntw:specific-provisioning-profiles" + "/valid-provider-identifiers" + "/routing-profile-identifier/id"; } description "Routing profile to be used."; } leaf type { type identityref { base vpn-common:ie-type; } description "Import, export, or both."; } } container static { when "derived-from-or-self(../type, " + "'vpn-common:static-routing')" { description "Only applies when the protocol is a static routing protocol."; } description "Configuration specific to static routing."; container cascaded-lan-prefixes { description "LAN prefixes from the customer."; list ipv4-lan-prefixes { if-feature "vpn-common:ipv4"; key "lan next-hop"; description "List of LAN prefixes for the site."; uses ac-common:ipv4-static-rtg-entry; leaf bfd-enable { if-feature "vpn-common:bfd"; type boolean; description "Enables BFD."; } leaf preference { type uint32; description "Indicates the preference associated with the static route."; } uses vpn-common:service-status; } list ipv6-lan-prefixes { if-feature "vpn-common:ipv6"; key "lan next-hop"; description "List of LAN prefixes for the site."; uses ac-common:ipv4-static-rtg-entry; leaf bfd-enable { if-feature "vpn-common:bfd"; type boolean; description "Enables BFD."; } leaf preference { type uint32; description "Indicates the preference associated with the static route."; } uses vpn-common:service-status; } } } container bgp { when "derived-from-or-self(../type, " + "'vpn-common:bgp-routing')" { description "Only applies when the protocol is BGP."; } description "Configuration specific to BGP."; container peer-groups { description "Configuration for BGP peer-groups"; list peer-group { key "name"; description "List of BGP peer-groups configured on the local system - uniquely identified by peer-group name"; leaf name { type string; description "Name of the BGP peer-group"; } leaf local-address { type union { type inet:ip-address; type if:interface-ref; } description "Sets the local IP address to use for the BGP transport session. This may be expressed as either an IP address or a reference to an interface."; } uses bgp-base; uses ac-common:bgp-authentication; } } list neighbor { key "remote-address"; description "List of BGP neighbors."; leaf remote-address { type inet:ip-address; description "The remote IP address of this entry's BGP peer."; } leaf local-address { type union { type inet:ip-address; type if:interface-ref; } description "Sets the local IP address to use for the BGP transport session. This may be expressed as either an IP address or a reference to an interface."; } leaf peer-group { type leafref { path "../../peer-groups/peer-group/name"; } description "The peer-group with which this neighbor is associated."; } uses bgp-base; uses ac-common:bgp-authentication; uses vpn-common:service-status; } } container ospf { when "derived-from-or-self(../type, " + "'vpn-common:ospf-routing')" { description "Only applies when the protocol is OSPF."; } description "Configuration specific to OSPF."; uses ac-common:ospf-basic; container sham-links { if-feature "vpn-common:rtg-ospf-sham-link"; description "List of sham links."; reference "RFC 4577: OSPF as the Provider/Customer Edge Protocol for BGP/MPLS IP Virtual Private Networks (VPNs), Section 4.2.7 RFC 6565: OSPFv3 as a Provider Edge to Customer Edge (PE-CE) Routing Protocol, Section 5"; list sham-link { key "target-site"; description "Creates a sham link with another site."; leaf target-site { type string; description "Target site for the sham link connection. The site is referred to by its identifier."; } leaf metric { type uint16; default "1"; description "Metric of the sham link. It is used in the routing state calculation and path selection."; reference "RFC 4577: OSPF as the Provider/Customer Edge Protocol for BGP/MPLS IP Virtual Private Networks (VPNs), Section 4.2.7.3 RFC 6565: OSPFv3 as a Provider Edge to Customer Edge (PE-CE) Routing Protocol, Section 5.2"; } } } leaf max-lsa { type uint32 { range "1..4294967294"; } description "Maximum number of allowed Link State Advertisements (LSAs) that the OSPF instance will accept."; } uses ac-common:ospf-authentication; uses vpn-common:service-status; } container isis { when "derived-from-or-self(../type, " + "'vpn-common:isis-routing')" { description "Only applies when the protocol is IS-IS."; } description "Configuration specific to IS-IS."; uses ac-common:isis-basic; leaf level { type identityref { base vpn-common:isis-level; } description "Can be 'level-1', 'level-2', or 'level-1-2'."; reference "RFC 9181: A Common YANG Data Model for Layer 2 and Layer 3 VPNs"; } leaf metric { type uint16; default "1"; description "Metric of the PE-CE link. It is used in the routing state calculation and path selection."; } leaf mode { type enumeration { enum active { description "The interface sends or receives IS-IS protocol control packets."; } enum passive { description "Suppresses the sending of IS-IS updates through the specified interface."; } } default "active"; description "IS-IS interface mode type."; } uses ac-common:isis-authentication; uses vpn-common:service-status; } container rip { when "derived-from-or-self(../type, " + "'vpn-common:rip-routing')" { description "Only applies when the protocol is RIP. For IPv4, the model assumes that RIP version 2 is used."; } description "Configuration specific to RIP routing."; uses rip-base; uses ac-common:rip-authentication; uses vpn-common:service-status; } container vrrp { when "derived-from-or-self(../type, " + "'vpn-common:vrrp-routing')" { description "Only applies when the protocol is the VRRP."; } description "Configuration specific to VRRP."; reference "RFC 5798: Virtual Router Redundancy Protocol (VRRP) Version 3 for IPv4 and IPv6"; leaf address-family { type identityref { base vpn-common:address-family; } description "Indicates whether IPv4, IPv6, or both address families are to be enabled."; } leaf vrrp-group { type uint8 { range "1..255"; } description "Includes the VRRP group identifier."; } leaf backup-peer { type inet:ip-address; description "Indicates the IP address of the peer."; } leaf-list virtual-ip-address { type inet:ip-address; description "Virtual IP addresses for a single VRRP group."; reference "RFC 5798: Virtual Router Redundancy Protocol (VRRP) Version 3 for IPv4 and IPv6, Sections 1.2 and 1.3"; } leaf priority { type uint8 { range "1..254"; } default "100"; description "Sets the local priority of the VRRP speaker."; } leaf ping-reply { type boolean; default "false"; description "Controls whether the VRRP speaker should reply to ping requests."; } uses vpn-common:service-status; } } } // OAM grouping bfd { description "Grouping for BFD."; leaf session-type { type identityref { base vpn-common:bfd-session-type; } default "vpn-common:classic-bfd"; description "Specifies the BFD session type."; } leaf desired-min-tx-interval { type uint32; units "microseconds"; default "1000000"; description "The minimum interval between transmissions of BFD Control packets, as desired by the operator."; reference "RFC 5880: Bidirectional Forwarding Detection (BFD), Section 6.8.7"; } leaf required-min-rx-interval { type uint32; units "microseconds"; default "1000000"; description "The minimum interval between received BFD Control packets that the PE should support."; reference "RFC 5880: Bidirectional Forwarding Detection (BFD), Section 6.8.7"; } leaf local-multiplier { type uint8 { range "1..255"; } default "3"; description "Specifies the detection multiplier that is transmitted to a BFD peer. The detection interval for the receiving BFD peer is calculated by multiplying the value of the negotiated transmission interval by the received detection multiplier value."; reference "RFC 5880: Bidirectional Forwarding Detection (BFD), Section 6.8.7"; } leaf holdtime { type uint32; units "milliseconds"; description "Expected BFD holdtime. The customer may impose some fixed values for the holdtime period if the provider allows the customer to use this function."; reference "RFC 5880: Bidirectional Forwarding Detection (BFD), Section 6.8.18"; } } // OAM grouping oam { description "Defines the Operations, Administration, and Maintenance (OAM) mechanisms used."; container bfd { description "Container for BFD."; leaf profile { type leafref { path "/nw:networks/nw:network" + "/ac-ntw:specific-provisioning-profiles" + "/valid-provider-identifiers" + "/bfd-profile-identifier/id"; } description "Well-known service provider profile name."; } uses bfd; container authentication { presence "Enables BFD authentication"; description "Parameters for BFD authentication."; leaf key-chain { type key-chain:key-chain-ref; description "Name of the key chain."; } leaf meticulous { type boolean; description "Enables meticulous mode."; reference "RFC 5880: Bidirectional Forwarding Detection (BFD), Section 6.7"; } } uses vpn-common:service-status; } } // security grouping security { description "Security parameters for an AC."; container encryption { if-feature "vpn-common:encryption"; description "Container for AC encryption."; leaf enabled { type boolean; default "false"; description "If set to 'true', traffic encryption on the connection is required. Otherwise, it is disabled."; } leaf layer { when "../enabled = 'true'" { description "Included only when encryption is enabled."; } type enumeration { enum layer2 { description "Encryption occurs at Layer 2."; } enum layer3 { description "Encryption occurs at Layer 3. For example, IPsec may be used when a customer requests Layer 3 encryption."; } } description "Indicates the layer on which encryption is applied."; } } container encryption-profile { when "../encryption/enabled = 'true'" { description "Indicates the layer on which encryption is enabled."; } description "Container for the encryption profile."; choice profile { description "Choice for the encryption profile."; case provider-profile { leaf profile-name { type leafref { path "/nw:networks/nw:network" + "/ac-ntw:specific-provisioning-profiles" + "/valid-provider-identifiers" + "/encryption-profile-identifier/id"; } description "Name of the provider's profile to be applied."; } } case customer-profile { leaf customer-key-chain { type key-chain:key-chain-ref; description "Customer-supplied key chain."; } } } } } // AC profile grouping ac-profile { description "Grouping for attachment circuit profiles."; container l2-connection { description "Defines Layer 2 protocols and parameters that are required to enable AC connectivity."; //uses l2-connection; } container ip-connection { description "Defines IP connection parameters."; //uses l3-connection; } container routing-protocols { description "Defines routing protocols."; uses routing-profile; } container oam { description "Defines the OAM mechanisms used for the AC profile."; container bfd { if-feature "vpn-common:bfd"; description "Container for BFD."; uses bfd; } } } //AC network provisioning grouping ac { description "Grouping for attachment circuits."; leaf description { type string; description "Associates a description with an AC."; } container l2-connection { description "Defines Layer 2 protocols and parameters that are required to enable AC connectivity."; uses l2-connection-if-ref; } container ip-connection { description "Defines IP connection parameters."; uses ip-connection; } container routing-protocols { description "Defines routing protocols."; uses routing; } container oam { description "Defines the OAM mechanisms used for the AC."; uses oam; } container security { description "AC-specific security parameters."; uses security; } } augment "/nw:networks/nw:network" { description "Add a list of profiles."; container specific-provisioning-profiles { description "Contains a set of valid profiles to reference in the AC activation."; uses vpn-common:vpn-profile-cfg; } list ac-profile { key "name"; description "Specifies a list of AC profiles."; leaf name { type string; description "Name of the AC."; } uses ac-ntw:ac-profile; } } augment "/nw:networks/nw:network/nw:node" + "/sap:service/sap:sap" { when '../../../nw:network-types/sap:sap-network' { description "Augmentation parameters apply only for SAP networks."; } description "Augments SAPs with AC provisioning details."; list ac { key "name"; description "List of ACs."; leaf name { type string; description "A local AC identifier."; } leaf ac-ref { type ac-svc:attachment-circuit-reference; description "A reference to the AC as exposed at the service level."; } list ac-profile { key "profile-id"; description "List of AC profiles."; leaf profile-id { type leafref { path "/nw:networks/nw:network/ac-profile/name"; } description "A reference to an AC profile."; } } leaf-list peer-sap-id { type string; description "One or more peer SAPs can be indicated."; } list group { key "group-id"; description "List of group-ids."; leaf group-id { type string; description "Indicates the group-id to which the AC belongs."; } leaf precedence { type identityref { base ac-common:precedence-type; } description "Defines redundancy of an AC."; } } uses vpn-common:service-status; uses ac-ntw:ac; } } } <CODE ENDS>¶
6. Security Considerations
The YANG module specified in this document defines a schema for data that is designed to be accessed via network management protocols 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.¶
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) and delete operations to these data nodes without proper protection or authentication can have a negative effect on network operations. These are the subtrees and data nodes and their sensitivity/ vulnerability in the "ietf-ac-ntw" module:¶
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 in the "ietf-ac-svc" module:¶
Several data nodes ('bgp', 'ospf', 'isis', and 'rip') rely upon [RFC8177] for authentication purposes. As such, the AC network module inherits the security considerations discussed in Section 5 of [RFC8177]. Also, these data nodes support supplying explicit keys as strings in ASCII format. The use of keys in hexadecimal string format would afford greater key entropy with the same number of key-string octets. However, such a format is not included in this version of the AC network model, because it is not supported by the underlying device modules (e.g., [RFC8695]).¶
7. IANA Considerations
IANA is requested to register the following URI in the "ns" subregistry within the "IETF XML Registry" [RFC3688]:¶
URI: urn:ietf:params:xml:ns:yang:ietf-ac-ntw Registrant Contact: The IESG. XML: N/A; the requested URI is an XML namespace.¶
IANA is requested to register the following YANG module in the "YANG Module Names" subregistry [RFC6020] within the "YANG Parameters" registry.¶
Name: ietf-ac-ntw Maintained by IANA? N Namespace: urn:ietf:params:xml:ns:yang:ietf-ac-ntw Prefix: ac-ntw Reference: RFC xxxx¶
8. References
8.1. Normative References
- [I-D.boro-opsawg-teas-attachment-circuit]
- Boucadair, M., Roberts, R., de Dios, O. G., Barguil, S., and B. Wu, "YANG Data Models for 'Attachment Circuits'-as-a-Service (ACaaS)", Work in Progress, Internet-Draft, draft-boro-opsawg-teas-attachment-circuit-07, , <https://datatracker.ietf.org/doc/html/draft-boro-opsawg-teas-attachment-circuit-07>.
- [I-D.boro-opsawg-teas-common-ac]
- Boucadair, M., Roberts, R., de Dios, O. G., Barguil, S., and B. Wu, "A Common YANG Data Model for Attachment Circuits", Work in Progress, Internet-Draft, draft-boro-opsawg-teas-common-ac-02, , <https://datatracker.ietf.org/doc/html/draft-boro-opsawg-teas-common-ac-02>.
- [RFC2119]
- Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/rfc/rfc2119>.
- [RFC3688]
- Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, , <https://www.rfc-editor.org/rfc/rfc3688>.
- [RFC6020]
- Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, , <https://www.rfc-editor.org/rfc/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, , <https://www.rfc-editor.org/rfc/rfc6241>.
- [RFC6242]
- Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, , <https://www.rfc-editor.org/rfc/rfc6242>.
- [RFC6991]
- Schoenwaelder, J., Ed., "Common YANG Data Types", RFC 6991, DOI 10.17487/RFC6991, , <https://www.rfc-editor.org/rfc/rfc6991>.
- [RFC8040]
- Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, , <https://www.rfc-editor.org/rfc/rfc8040>.
- [RFC8174]
- Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/rfc/rfc8174>.
- [RFC8177]
- Lindem, A., Ed., Qu, Y., Yeung, D., Chen, I., and J. Zhang, "YANG Data Model for Key Chains", RFC 8177, DOI 10.17487/RFC8177, , <https://www.rfc-editor.org/rfc/rfc8177>.
- [RFC8294]
- Liu, X., Qu, Y., Lindem, A., Hopps, C., and L. Berger, "Common YANG Data Types for the Routing Area", RFC 8294, DOI 10.17487/RFC8294, , <https://www.rfc-editor.org/rfc/rfc8294>.
- [RFC8341]
- Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, , <https://www.rfc-editor.org/rfc/rfc8341>.
- [RFC8342]
- Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, , <https://www.rfc-editor.org/rfc/rfc8342>.
- [RFC8343]
- Bjorklund, M., "A YANG Data Model for Interface Management", RFC 8343, DOI 10.17487/RFC8343, , <https://www.rfc-editor.org/rfc/rfc8343>.
- [RFC8446]
- Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, , <https://www.rfc-editor.org/rfc/rfc8446>.
- [RFC9181]
- Barguil, S., Gonzalez de Dios, O., Ed., Boucadair, M., Ed., and Q. Wu, "A Common YANG Data Model for Layer 2 and Layer 3 VPNs", RFC 9181, DOI 10.17487/RFC9181, , <https://www.rfc-editor.org/rfc/rfc9181>.
- [RFC9182]
- Barguil, S., Gonzalez de Dios, O., Ed., Boucadair, M., Ed., Munoz, L., and A. Aguado, "A YANG Network Data Model for Layer 3 VPNs", RFC 9182, DOI 10.17487/RFC9182, , <https://www.rfc-editor.org/rfc/rfc9182>.
- [RFC9291]
- Boucadair, M., Ed., Gonzalez de Dios, O., Ed., Barguil, S., and L. Munoz, "A YANG Network Data Model for Layer 2 VPNs", RFC 9291, DOI 10.17487/RFC9291, , <https://www.rfc-editor.org/rfc/rfc9291>.
- [RFC9408]
- Boucadair, M., Ed., Gonzalez de Dios, O., Barguil, S., Wu, Q., and V. Lopez, "A YANG Network Data Model for Service Attachment Points (SAPs)", RFC 9408, DOI 10.17487/RFC9408, , <https://www.rfc-editor.org/rfc/rfc9408>.
8.2. Informative References
- [AC-Ntw-Tree]
- "Full Network Attachment Circuit Tree Structure", , <https://github.com/boucadair/attachment-circuit-model/blob/main/yang/full-trees/ac-ntw-without-groupings.txt>.
- [RFC7665]
- Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, , <https://www.rfc-editor.org/rfc/rfc7665>.
- [RFC8340]
- Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, , <https://www.rfc-editor.org/rfc/rfc8340>.
- [RFC8695]
- Liu, X., Sarda, P., and V. Choudhary, "A YANG Data Model for the Routing Information Protocol (RIP)", RFC 8695, DOI 10.17487/RFC8695, , <https://www.rfc-editor.org/rfc/rfc8695>.
- [RFC8969]
- Wu, Q., Ed., Boucadair, M., Ed., Lopez, D., Xie, C., and L. Geng, "A Framework for Automating Service and Network Management with YANG", RFC 8969, DOI 10.17487/RFC8969, , <https://www.rfc-editor.org/rfc/rfc8969>.
Acknowledgments
Thanks to Moti Morgenstern for the review and comments.¶