IDR Working Group J. Dong Internet-Draft Z. Hu Intended status: Standards Track Z. Li Expires: August 26, 2021 Huawei Technologies X. Tang R. Pang China Unicom February 22, 2021 BGP-LS Extensions for Segment Routing based Enhanced VPN draft-dong-idr-bgpls-sr-enhanced-vpn-03 Abstract Enhanced VPN (VPN+) aims to provide enhanced VPN services to support some applications' needs of enhanced isolation and stringent performance requirements. VPN+ requires integration between the overlay VPN connectivity and the characteristics provided by the underlay network. A Virtual Transport Network (VTN) is a virtual underlay network which consists of a customized network topology and a set of network resource allocated from the physical network. A VTN could be used as the underlay to support one or a group of VPN+ services. This document specifies the BGP-LS mechanisms with necessary extensions to advertise the information of Segment Routing (SR) based VTNs to a centralized network controller. Each VTN can have a customized topology and a set of network resources allocated. Multiple VTNs may shared the same topology, and multiple VTNs may share the same set of network resources on some network segments. This allows flexible combination of network topology and network resource attributes to build a large number of VTNs with a relatively small number of logical topologies. The proposed mechanism is applicable to both segment routing with MPLS data plane (SR-MPLS) and segment routing with IPv6 data plane (SRv6). Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Dong, et al. Expires August 26, 2021 [Page 1] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 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 August 26, 2021. 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 Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Advertisement of VTN Definition . . . . . . . . . . . . . . . 4 3. Advertisement of VTN Topology Attribute . . . . . . . . . . . 5 3.1. Intra-domain Topology Advertisement . . . . . . . . . . . 5 3.1.1. MTR based Topology Advertisement . . . . . . . . . . 6 3.1.2. Flex-Algo based Topology Advertisement . . . . . . . 7 3.2. Inter-Domain Topology Advertisement . . . . . . . . . . . 7 3.2.1. VTN ID TLV . . . . . . . . . . . . . . . . . . . . . 9 4. Advertisement of VTN Resource Attribute . . . . . . . . . . . 10 4.1. Link Attribute Flags TLV . . . . . . . . . . . . . . . . 10 5. Advertisement of VTN specific Data Plane Identifiers . . . . 11 5.1. VTN-specific SR-MPLS SIDs . . . . . . . . . . . . . . . . 11 5.1.1. VTN-specific Prefix-SID TLV . . . . . . . . . . . . . 11 5.1.2. VTN-specific Adj-SID TLV . . . . . . . . . . . . . . 12 5.2. VTN-specific SRv6 Locators . . . . . . . . . . . . . . . 13 5.3. Dedicated VTN ID in Data Plane . . . . . . . . . . . . . 14 6. Security Considerations . . . . . . . . . . . . . . . . . . . 14 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 15 Dong, et al. Expires August 26, 2021 [Page 2] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 15 9.1. Normative References . . . . . . . . . . . . . . . . . . 15 9.2. Informative References . . . . . . . . . . . . . . . . . 16 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 18 1. Introduction Enhanced VPN (VPN+) is an enhancement to VPN services to support the needs of new applications, particularly the applications that are associated with 5G services. These applications require enhanced isolation and have more stringent performance requirements than that can be provided with traditional overlay VPNs. These properties require integration between the underlay and the overlay networks. [I-D.ietf-teas-enhanced-vpn] specifies the framework of enhanced VPN and describes the candidate component technologies in different network planes and layers. An enhanced VPN can be used for 5G network slicing, and will also be of use in more generic scenarios. To meet the requirement of enhanced VPN services, a number of virtual underlay networks need to be created, each with a subset of the underlay network topology and a set of network resources allocated to meet the requirement of a specific VPN+ service or a group of VPN+ services. Such a virtual underlay network is called Virtual Transport Network (VTN) in [I-D.ietf-teas-enhanced-vpn]. [I-D.ietf-spring-resource-aware-segments] introduces resource- awareness to Segment Routing (SR) [RFC8402] by associating existing type of SIDs with network resource attributes (e.g. bandwidth, processing or storage resources). These resource-aware SIDs retain their original functionality, with the additional semantics of identifying the set of network resources available for the packet processing action. [I-D.ietf-spring-sr-for-enhanced-vpn] describes the use of resource-aware segments to build SR based VTNs. To allow the network controller and network nodes to perform VTN-specific explicit path computation and/or shortest path computation, the group of resource-aware SIDs allocated by network nodes to each VTN and the associated topology and resource attributes need to be distributed in the control plane. When a VTN spans multiple IGP areas or multiple Autonomous Systems (ASes), BGP-LS is needed to advertise the VTN information in each IGP area or AS to the network controller, so that the controller could use the collected information to build the view of inter-area or inter-AS SR VTNs. This document describes BGP-LS [RFC7752] based mechanism with necessary extensions to advertise the topology and resource attribute of inter-area and inter-domain SR based VTNs. Each VTN can have a Dong, et al. Expires August 26, 2021 [Page 3] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 customized topology and a set of network resources allocated. Multiple VTNs may shared the same topology, and multiple VTNs may share the same set of network resources on some network segments. This allows flexible combination of network topology and network resource attributes to build a large number of VTNs with a relatively small number of logical topologies. The definition of VTN is advertised as a node attribute using BGP-LS. The associated network topology and resources attributes of a VTN are advertised as link attributes using BGP-LS. 2. Advertisement of VTN Definition According to [I-D.ietf-teas-enhanced-vpn], a VTN has a customized network topology and a set of dedicated or shared network resources. Thus a VTN can be defined as the combination of a set of network attributes, which include the topology attribute and other attributes, such as the associated network resources. The Virtual Transport Network Definition (VTND) TLV is a new TLV of the optional BGP-LS Attribute which is associated with the node NLRI. The format of VTND TLV is as follows: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VTN ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MT-ID | Algorithm | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sub-TLVs | ~ ... ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: o Type: TBD o Length: the length of the value field of the TLV. It is variable dependent on the included Sub-TLVs. o VTN ID: A global significant 32-bit identifier which is used to identify a virtual transport network. Dong, et al. Expires August 26, 2021 [Page 4] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 o MT-ID: 16-bit identifier which indicates the multi-topology identifier of the IGP topology. o Algorithm: 8-bit identifier which indicates the algorithm which applies to this virtual transport network. It can be either a normal algorithm in [RFC8402] or a Flex-Algorithm [I-D.ietf-lsr-flex-algo]. o Flags: 8-bit flags. Currently all the flags are reserved for future use. They SHOULD be set to zero on transmission and MUST be ignored on receipt. o Sub-TLVs: optional sub-TLVs to specify the additional attributes of a virtual transport network. Currently no sub-TLV is defined in this document. 3. Advertisement of VTN Topology Attribute [I-D.dong-lsr-sr-enhanced-vpn] describes the IGP mechanisms to distribute the topology attributes of SR based VTNs. This section describes the BGP-LS mechanism to distribute both the intra-domain and inter-domain topology attributes of SR based VTNs. 3.1. Intra-domain Topology Advertisement The intra-domain topology attribute of a VTN can be determined by the MT-ID and/or the algorithm ID included in the VTN definition. In practice, it could be described using two optional approaches. The first approach is to use Multi-Topology Routing (MTR) [RFC4915] [RFC5120] with the segment routing extensions to advertise the topology associated with the SR based VTNs. Different algorithms MAY be used to further specify the computation algorithm or the metric type used for path computation within the topology. Multiple VTNs can be associated with the same , and the IGP computation with the tuple can be shared by these VTNs. The second approach is to use Flex-Algo [I-D.ietf-lsr-flex-algo] to describe the topological constraints of SR based VTNs on a shared network topology (e.g. the default topology). Multiple VTNs can be associated with the same Flex-Algo, and the IGP computation with this Flex-Algo can be shared. This section describes the two optional approaches to advertise the intra-domain topology of a VTN using BGP-LS. Dong, et al. Expires August 26, 2021 [Page 5] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 3.1.1. MTR based Topology Advertisement In section 4.2.2.1 of [I-D.ietf-idr-rfc7752bis], Multi-Topology Identifier (MT-ID) TLV is defined, which can contain one or more IS- IS or OSPF Multi-Topology IDs. The MT-ID TLV MAY be present in a Link Descriptor, a Prefix Descriptor, or the BGP-LS Attribute of a Node NLRI. [I-D.ietf-idr-bgp-ls-segment-routing-ext] defines the BGP-LS extensions to carry the segment routing information using TLVs of BGP-LS Attribute. When MTR is used with SR-MPLS data plane, topology-specific prefix-SIDs and topology-specific Adj-SIDs can be carried in the BGP-LS Attribute associated with the prefix NLRI and link NLRI respectively, the MT-ID TLV is carried in the prefix descriptor or link descriptor to identify the corresponding topology of the SIDs. [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions to advertise SRv6 segments along with their functions and attributes. When MTR is used with SRv6 data plane, the SRv6 Locator TLV is carried in the BGP-LS Attribute associated with the prefix-NLRI, the MT-ID TLV can be carried in the prefix descriptor to identify the corresponding topology of the SRv6 Locator. The SRv6 End.X SIDs are carried in the BGP-LS Attribute associated with the link NLRI, the MT-ID TLV can be carried in the link descriptor to identify the corresponding topology of the End.X SIDs. The SRv6 SID NLRI is defined to advertise other types of SRv6 SIDs, in which the SRv6 SID Descriptors can include the MT-ID TLV so as to advertise topology- specific SRv6 SIDs. [I-D.ietf-idr-rfc7752bis] also defines the rules of the usage of MT- ID TLV: "In a Link or Prefix Descriptor, only a single MT-ID TLV containing the MT-ID of the topology where the link or the prefix is reachable is allowed. In case one wants to advertise multiple topologies for a given Link Descriptor or Prefix Descriptor, multiple NLRIs MUST be generated where each NLRI contains a single unique MT-ID." Editor's note: the above rules indicates that only one MT-ID is allowed to be carried the Link or Prefix descriptors. When a link or prefix needs to be advertised in multiple topologies, multiple NLRIs needs to be generated to report all the topologies the link or prefix participates in, together with the topology-specific segment routing information and link attributes. This may increase the number of BGP Updates needed for advertising MT-specific topology attributes, and may introduce additional processing burden to both the sending BGP speaker and the receiving network controller. When the number of Dong, et al. Expires August 26, 2021 [Page 6] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 topologies in a network is not a small number, some optimization may be needed for the reporting of multi-topology information and the associated segment routing information in BGP-LS. Based on the WG's opinion, this will be elaborated in a future version. 3.1.2. Flex-Algo based Topology Advertisement The Flex-Algo definition [I-D.ietf-lsr-flex-algo] can be used to describe the calculation-type, the metric-type and the topological constraints for path computation on a network topology. As specified in [I-D.dong-lsr-sr-enhanced-vpn], the topology of a VTN can be determined by applying Flex-Algo constraints on a particular topology. BGP-LS extensions for Flex-Algo [I-D.ietf-idr-bgp-ls-flex-algo] provide the mechanisms to advertise the Flex-Algo definition information. BGP-LS extensions for SR-MPLS [I-D.ietf-idr-bgp-ls-segment-routing-ext] and SRv6 [I-D.ietf-idr-bgpls-srv6-ext] provide the mechanism to advertise the algorithm-specific segment routing information. In[I-D.ietf-idr-bgp-ls-segment-routing-ext], algorithm-specific prefix-SIDs can be advertised in BGP-LS attribute associated with Prefix NLRI. In [I-D.ietf-idr-bgpls-srv6-ext], algorithm-specific SRv6 Locators can be advertised in BGP-LS Attribute associated with the corresponding Prefix NLRI, and algorithm-specific End.X SID can be advertised in BGP-LS Attribute associated with the corresponding Link NLRI. Other types of SRv6 SIDs can also be algorithm-specific and are advertised using the SRv6 SID NLRI. 3.2. Inter-Domain Topology Advertisement In some network scenarios, a VTNs which span multiple areas or ASes needs to be created. The multi-domain VTN could have different inter-domain connectivity, and may be associated with different set of network resources in each domain and also on the inter-domain links. In order to build the multi-domain VTNs using segment routing, it is necessary to advertise the topology and resource attribute of VTN on the inter-domain links and the associated BGP Peering SIDs. [I-D.ietf-idr-bgpls-segment-routing-epe] and [I-D.ietf-idr-bgpls-srv6-ext] defines the BGP-LS extensions for advertisement of BGP topology information between ASes and the associated BGP Peering Segment Identifiers. Such information could be used by a network controller for the computation and instantiation of inter-AS traffic engineering SR paths. Dong, et al. Expires August 26, 2021 [Page 7] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 Depending on the network scenarios and the requirement of inter- domain VTNs, different mechanisms can be used to specify the inter- domain connections of VTNs. o One EBGP session between two ASes can be established over multiple underlying links. In this case, different underlying links can be used for different inter-domain VTNs which requires link isolation between each other. In another similar case, the EBGP session is established over a single link, while the network resource (e.g. bandwidth) on this link can be partitioned into several pieces, each of which can be considered as a virtual member link. In both cases, different BGP Peer-Adj-SIDs SHOULD be allocated to each underlying physical or virtual member link, and ASBRs SHOULD advertise the VTN identifier associated with each BGP Peer-Adj- SID. o For inter-domain connection between two ASes, multiple EBGP sessions can be established between different set of peering ASBRs. It is possible that some of these BGP sessions are used for one multi-domain VTN, while some other BGP sessions are used for another multi-domain VTN. In this case, different BGP peer- node-SIDs are allocated to each BGP session, and ASBRs SHOULD advertise the VTN identifier associated with each BGP Peer-node- SIDs. o At the AS-level topology, different multi-domain VTNs may have different inter-domain connectivity. Different BGP Peer-Set-SIDs can be allocated to represent the groups of BGP peers which can be used for load-balancing in each multi-domain VTN. In network scenarios where the MT-ID or Flex-Algo is used consistently in multiple areas or ASes covered by a VTN. the approaches to advertise topology-specific BGP peering SIDs are described as below: o Using MT-based mechanism, the topology-specific BGP peering SIDs can be advertised with the MT-ID associated with the VTN carried in the corresponding link NLRI. This can be supported with the existing mechanisms defined in [RFC7752][I-D.ietf-idr-bgpls-segment-routing-epe] and [I-D.ietf-idr-bgpls-srv6-ext]. o Using Flex-Algo based mechanism, the topology-specific BGP peering SIDs can be advertised together with the Admin Group (color) of the corresponding Flex-Algo in the BGP-LS attribute. In network scenarios where consistent usage of MT-ID or Flex-Algo among multiple ASes can not be expected, then the global-significant Dong, et al. Expires August 26, 2021 [Page 8] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 VTN-ID can be used to define the AS level topologies. Within each domain, the MT or Flex-Algo based mechanism could still be used for topology advertisement. 3.2.1. VTN ID TLV A new VTN ID TLV is defined to describe the identifiers of one or more VTNs an intra-domain or inter-domain link belongs to. It can be carried in BGP-LS attribute which is associated with a Link NLRI, or it could be carried as a sub-TLV in the L2 Bundle Member Attribute TLV. The format of VTN ID TLV is as below: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VTN ID-1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ... ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VTN ID-n | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: o Type: TBD o Length: The length of the value field of the sub-TLV. It is variable dependent on the number of VTN IDs included. o Flags: 16 bit flags. All the bits are reserved, which MUST be set to 0 on transmission and ignored on receipt. o Reserved: this field is reserved for future use. MUST be set to 0 on transmission and ignored on receipt. o VTN IDs: One or more 32-bit identifiers to specify the VTNs this link or member link belongs to. Dong, et al. Expires August 26, 2021 [Page 9] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 4. Advertisement of VTN Resource Attribute [I-D.dong-lsr-sr-enhanced-vpn] specifies the mechanism to advertise the resource information associated with each VTN. It is based on the extensions to the advertisement of L2 bundle member links information[RFC8668]. This section defines the corresponding BGP-LS extensions. Two new TLVs are defined to carry the VTN ID and the link attribute flags of either a Layer-3 link or the L2 bundle member links. The VTN ID TLV is defined in section 3.2.1 of this document, and a new Link Attribute Flags TLV is defined in this section. The TE attributes of each Layer 3 link or the L2 bundle member link, such as the bandwidth and the SR SIDs, can be advertised using the mechanism as defined in [I-D.ietf-idr-bgp-ls-segment-routing-ext][I-D .ietf-idr-bgpls-segment-routing-epe] and [I-D.ietf-idr-bgpls-srv6-ext]. 4.1. Link Attribute Flags TLV A new Link attribute Flags TLV is defined to specify the characteristics of a link. It can be carried in BGP-LS attribute which is associated with a Link NLRI, or it could be carried as a sub-TLV in the L2 Bundle Member Attribute TLV. The format of the sub-TLV is as below: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: Type: TBD Length: 4 octets. Flags: 16-bit flags. This field is consistent with the Flag field in IS-IS Link Attribute sub-TLV in [RFC5029]. In addition to the flags defined in [RFC5029], A new Flag V is defined in this document. When the V flag is set, it indicates this link is a virtual link. Dong, et al. Expires August 26, 2021 [Page 10] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 5. Advertisement of VTN specific Data Plane Identifiers In network scenarios where each VTN is associated with an independent network topology or Flex-Algo, the topology or Flex-Algo specific SIDs or Locators could be used as the identifier of the VTN in data plane. In network scenarios where multiple VTNs share the same topology or Flex-Algo, additional data plane identifiers would be needed to identify different VTNs. This section describes the mechanisms to advertise the VTN identifiers with different data plane encapsulations. 5.1. VTN-specific SR-MPLS SIDs With SR-MPLS data plane, the VTN identification information is implicitly carried in the SR SIDs of the corresponding VTN. Each node SHOULD allocate VTN-specific Prefix-SIDs for each VTN it participates in. Similarly, VTN-specific Adj-SIDs MAY be allocated for each link which participates in the VTN. 5.1.1. VTN-specific Prefix-SID TLV A new VTN-specific Prefix-SID TLV is defined to advertise the prefix- SID and its associated VTN. It is derived from VTN specific Prefix- SID sub-TLV of IS-IS [I-D.dong-lsr-sr-enhanced-vpn]. The format of the sub-TLV is as below: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VTN ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Index/Label(Variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: o Type: TBD o Length: The length of the value field of the sub-TLV. It is variable dependent on the length of the SID/Index/Label field. o Flags: 16-bit flags. The high-order 8 bits are the same as in the Prefix-SID sub-TLV defined in [RFC8667]. The lower-order 8 bits are reserved for future use, which SHOULD be set to 0 on transmission and MUST be ignored on receipt. Dong, et al. Expires August 26, 2021 [Page 11] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 o VTN ID: A 32-bit local identifier to identify the VTN this prefix- SID associates with. o SID/Index/Label: The same as defined in [RFC8667]. One or more of VTN-specific Prefix-SID TLVs MAY be carried in BGP-LS attribute of the associated Prefix NLRI. The MT-ID in the Prefix descriptors SHOULD be the same as the MT-ID in the definition of these VTNs. 5.1.2. VTN-specific Adj-SID TLV A new VTN-specific Adj-SID TLV is defined to advertise the Adj-SID and its associated VTN. It is derived from VTN specific Adj-SID sub- TLV of IS-IS [I-D.dong-lsr-sr-enhanced-vpn]. The format of the sub- TLV is as below: 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VTN ID | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SID/Index/Label(Variable) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: o Type: TBD o Length: The length of the value field of the sub-TLV. It is variable dependent on the length of the SID/Index/Label field. o Flags: 16-bit flags. The high-order 8 bits are the same as in the Adj-SID sub-TLV defined in [RFC8667]. The lower-order 8 bits are reserved for future use, which SHOULD be set to 0 on transmission and MUST be ignored on receipt. o VTN ID: A 32-bit local identifier to identify the VTN this Adj-SID associates with. o SID/Index/Label: The same as defined in [RFC8667]. Multiple VTN-specific Adj-SID TLVs MAY be carried in BGP-LS attribute of the associated Link NLRI. The MT-ID in the Link descriptors SHOULD be the same as the MT-ID in the definition of these VTNs. Dong, et al. Expires August 26, 2021 [Page 12] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 5.2. VTN-specific SRv6 Locators With SRv6 data plane, the VTN identification information can be implicitly or explicitly carried in the SRv6 Locator of the corresponding VTN, this is to ensure that all network nodes (including both the SRv6 End nodes and Transit nodes) can identify the VTN to which a packet belongs to. Network nodes SHOULD allocate VTN-specific Locators for each VTN it participates in. The VTN- specific Locators are used as the covering prefix of VTN-specific SRv6 End SIDs, End.X SIDs and other types of SIDs. Each VTN-specific SRv6 Locator MAY be advertised in a separate Prefix NLRI. If multiple VTNs share the same topology/algorithm, the topology/algorithm specific Locator is the covering prefix of a group of VTN-specific Locators. Then the advertisement of VTN-specific locators can be optimized to reduce the amount of information advertised in the control plane. A new VTN locator-block sub-TLV under the SRv6 Locator TLV is defined to advertise a set of sub-blocks which follows the topology/algorithm specific Locator. Each VTN locator-block value is assigned to one of the VTNs which share the same topology/algorithm. 0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Number of VTNs| Block Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VTN ID #1 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Locator Block Value ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ ... ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | VTN ID #n | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Locator Block Value ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Where: o Type: TBD o Length: The length of the value field of the sub-TLV. It is variable dependent on the number of VTNs and the Block Length. Dong, et al. Expires August 26, 2021 [Page 13] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 o Number of VTNs: The number of VTNs which share the same topology/ algorithm specific Locator as the covering prefix. o Block Length: The length of the VTN locator-block which follows the length of the topology/algorithm specific Locator. o VTN ID: A 32-bit identifier to identify the VTN the locator-block is associates with. o Block Value: The value of the VTN locator-block for each VTN. With the VTN locator-block sub-TLV, the VTN-specific Locator can be obtained by concatenating the topology/algorithm specific locator and the locator-block value advertised for the VTN. 5.3. Dedicated VTN ID in Data Plane As the number of VTNs increases, with the mechanism described in [I-D.ietf-spring-sr-for-enhanced-vpn], the number of SR SIDs and SRv6 Locators allocated for different VTNs would also increase. In network scenarios where the number of SIDs or Locators becomes a concern, some data plane optimization may be needed to reduce the amount of SR SIDs and Locators allocated. As described in [I-D.dong-teas-enhanced-vpn-vtn-scalability], one approach is to decouple the data plane identifiers used for topology based forwarding and the identifiers used for the VTN-specific processing. Thus a dedicated data plane VTN-ID could be introduced and encapsulated in the packet. One possible encapsulation of VTN-ID in IPv6 data plane is proposed in [I-D.dong-6man-enhanced-vpn-vtn-id]. One possible encapsulation of VTN-ID in MPLS data plane is proposed in [I-D.li-mpls-enhanced-vpn-vtn-id]. In that case, the VTN ID encapsulated in data plane can be the same value as the VTN ID in the control plane, so that the overhead of advertising the mapping between the VTN IDs in the control plane and the corresponding data plane identifiers could be saved. 6. Security Considerations This document introduces no additional security vulnerabilities to BGP-LS. The mechanism proposed in this document is subject to the same vulnerabilities as any other protocol that relies on BGP-LS. Dong, et al. Expires August 26, 2021 [Page 14] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 7. IANA Considerations TBD 8. Acknowledgments The authors would like to thank Shunwan Zhuang and Zhenbin Li for the review and discussion of this document. 9. References 9.1. Normative References [I-D.ietf-idr-bgp-ls-flex-algo] Talaulikar, K., Psenak, P., Zandi, S., and G. Dawra, "Flexible Algorithm Definition Advertisement with BGP Link-State", draft-ietf-idr-bgp-ls-flex-algo-05 (work in progress), November 2020. [I-D.ietf-idr-bgp-ls-segment-routing-ext] Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H., and M. Chen, "BGP Link-State extensions for Segment Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16 (work in progress), June 2019. [I-D.ietf-idr-bgpls-segment-routing-epe] Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray, S., and J. Dong, "BGP-LS extensions for Segment Routing BGP Egress Peer Engineering", draft-ietf-idr-bgpls- segment-routing-epe-19 (work in progress), May 2019. [I-D.ietf-idr-bgpls-srv6-ext] Dawra, G., Filsfils, C., Talaulikar, K., Chen, M., daniel.bernier@bell.ca, d., and B. Decraene, "BGP Link State Extensions for SRv6", draft-ietf-idr-bgpls- srv6-ext-05 (work in progress), November 2020. [I-D.ietf-idr-rfc7752bis] Talaulikar, K., "Distribution of Link-State and Traffic Engineering Information Using BGP", draft-ietf-idr- rfc7752bis-05 (work in progress), November 2020. [I-D.ietf-spring-resource-aware-segments] Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, Z., and F. Clad, "Introducing Resource Awareness to SR Segments", draft-ietf-spring-resource-aware-segments-01 (work in progress), January 2021. Dong, et al. Expires August 26, 2021 [Page 15] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 [I-D.ietf-spring-sr-for-enhanced-vpn] Dong, J., Bryant, S., Miyasaka, T., Zhu, Y., Qin, F., Li, Z., and F. Clad, "Segment Routing based Virtual Transport Network (VTN) for Enhanced VPN", February 2021, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC5029] Vasseur, JP. and S. Previdi, "Definition of an IS-IS Link Attribute Sub-TLV", RFC 5029, DOI 10.17487/RFC5029, September 2007, . [RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and S. Ray, "North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP", RFC 7752, DOI 10.17487/RFC7752, March 2016, . [RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L., Decraene, B., Litkowski, S., and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018, . 9.2. Informative References [I-D.dong-6man-enhanced-vpn-vtn-id] Dong, J., Li, Z., Xie, C., and C. Ma, "Carrying Virtual Transport Network Identifier in IPv6 Extension Header", draft-dong-6man-enhanced-vpn-vtn-id-02 (work in progress), November 2020. [I-D.dong-lsr-sr-enhanced-vpn] Dong, J., Hu, Z., Li, Z., Tang, X., Pang, R., JooHeon, L., and S. Bryant, "IGP Extensions for Segment Routing based Enhanced VPN", draft-dong-lsr-sr-enhanced-vpn-04 (work in progress), June 2020. [I-D.dong-teas-enhanced-vpn-vtn-scalability] Dong, J., Li, Z., Qin, F., and G. Yang, "Scalability Considerations for Enhanced VPN (VPN+)", draft-dong-teas- enhanced-vpn-vtn-scalability-01 (work in progress), November 2020. Dong, et al. Expires August 26, 2021 [Page 16] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 [I-D.ietf-lsr-flex-algo] Psenak, P., Hegde, S., Filsfils, C., Talaulikar, K., and A. Gulko, "IGP Flexible Algorithm", draft-ietf-lsr-flex- algo-13 (work in progress), October 2020. [I-D.ietf-lsr-isis-srv6-extensions] Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and Z. Hu, "IS-IS Extension to Support Segment Routing over IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-11 (work in progress), October 2020. [I-D.ietf-teas-enhanced-vpn] Dong, J., Bryant, S., Li, Z., Miyasaka, T., and Y. Lee, "A Framework for Enhanced Virtual Private Networks (VPN+) Service", draft-ietf-teas-enhanced-vpn-06 (work in progress), July 2020. [I-D.li-mpls-enhanced-vpn-vtn-id] Li, Z. and J. Dong, "Carrying Virtual Transport Network Identifier in MPLS Packet", February 2021, . [RFC4915] Psenak, P., Mirtorabi, S., Roy, A., Nguyen, L., and P. Pillay-Esnault, "Multi-Topology (MT) Routing in OSPF", RFC 4915, DOI 10.17487/RFC4915, June 2007, . [RFC5120] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi Topology (MT) Routing in Intermediate System to Intermediate Systems (IS-ISs)", RFC 5120, DOI 10.17487/RFC5120, February 2008, . [RFC8667] Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., Bashandy, A., Gredler, H., and B. Decraene, "IS-IS Extensions for Segment Routing", RFC 8667, DOI 10.17487/RFC8667, December 2019, . [RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri, M., and E. Aries, "Advertising Layer 2 Bundle Member Link Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668, December 2019, . Dong, et al. Expires August 26, 2021 [Page 17] Internet-Draft BGP-LS Extensions for SR VPN+ February 2021 Authors' Addresses Jie Dong Huawei Technologies Email: jie.dong@huawei.com Zhibo Hu Huawei Technologies Email: huzhibo@huawei.com Zhenbin Li Huawei Technologies Email: lizhenbin@huawei.com Xiongyan Tang China Unicom Email: tangxy@chinaunicom.cn Ran Pang China Unicom Email: pangran@chinaunicom.cn Dong, et al. Expires August 26, 2021 [Page 18]