Advertising Layer 2 Bundle Member Link Attributes in OSPF Cisco Systems
India ketant.ietf@gmail.com
Cisco Systems
Apollo Business Center Mlynske nivy 43 Bratislava 821 09 Slovakia ppsenak@cisco.com
rtg lsr OSPF There are deployments where the Layer 3 (L3) interface on which OSPF operates is a Layer 2 (L2) interface bundle. Existing OSPF advertisements only support advertising link attributes of the L3 interface. If entities external to OSPF wish to control traffic flows on the individual physical links that comprise the L2 interface bundle, link attribute information for the bundle members is required. This document defines the protocol extensions for OSPF to advertise the link attributes of L2 bundle members. The document also specifies the advertisement of these OSPF extensions via the Border Gateway Protocol - Link State (BGP-LS) and thereby updates RFC 9085.
Status of This Memo This is an Internet Standards Track document. This document is a product of the Internet Engineering Task Force (IETF). It represents the consensus of the IETF community. It has received public review and has been approved for publication by the Internet Engineering Steering Group (IESG). Further information on Internet Standards is available in Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .
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Table of Contents
  • .  Introduction
    • .  Requirements Language
  • .  L2 Bundle Member Attributes
  • .  BGP-LS Advertisement
  • .  IANA Considerations
  • .  Operational Considerations
  • .  Security Considerations
  • .  References
    • .  Normative References
    • .  Informative References
  • Acknowledgements
  • Authors' Addresses
Introduction There are deployments where the L3 interface on which an OSPF adjacency is established is a L2 interface bundle, for instance, a Link Aggregation Group (LAG) . This reduces the number of adjacencies that need to be maintained by the OSPF protocol in cases where there are parallel links between the neighbors. Entities external to OSPF such as Path Computation Elements (PCEs) may wish to control traffic flows on individual L2 member links of the underlying bundle interface (e.g., LAG). To do so, link attribute information for individual bundle members is required. The protocol extensions defined in this document provide the means to advertise this information. This document defines sub-TLVs to advertise link attribute information for each of the L2 bundle members that comprise the L3 interface on which OSPF operates. Similar capabilities were introduced for IS-IS in . and introduced the Adjacency Segment Identifier (Adj-SID) link attribute for OSPFv2 and OSPFv3, respectively, which can be used as an instruction to forward traffic over a specific link . This document enables the advertisement of the Adj-SIDs using the same Adj-SID sub-TLV at the granularity level of each L2 bundle member link so that traffic may be steered over that specific member link. Note that the advertisements at the L2 bundle member link level defined in this document are intended to be provided to entities external to OSPF and do not alter or change the OSPF route computation. The following items are intentionally not defined in and are outside the scope of this document:
  • What link attributes will be advertised. This is determined by the needs of the external entities.
  • A minimum or default set of link attributes.
  • How these attributes are configured.
  • How the advertisements are used.
  • What impact the use of these advertisements may have on traffic flow in the network.
  • How the advertisements are passed to external entities.
BGP Link State (BGP-LS) was extended for the advertisement of L2 bundle members and their attributes in , which covered only IS-IS. This document updates by specifying the advertisement from OSPF (refer to ).
Requirements Language 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 when, and only when, they appear in all capitals, as shown here.
L2 Bundle Member Attributes A new L2 Bundle Member Attributes sub-TLV is introduced to advertise L2 bundle member attributes in both OSPFv2 and OSPFv3. In the case of OSPFv2, this sub-TLV is an optional sub-TLV of the OSPFv2 Extended Link TLV that is used to describe link attributes via the OSPFv2 Extended Link Opaque LSA (Link State Advertisement) . In the case of OSPFv3, this sub-TLV is an optional sub-TLV of the Router-Link TLV of the OSPFv3 E-Router-LSA . When the OSPF adjacency is associated with an L2 bundle interface, this sub-TLV is used to advertise the underlying L2 bundle member links along with their respective link attributes. The inclusion of this information implies that the identified link is a member of the L2 bundle associated with an OSPF L3 link and that the member link is operationally up. Therefore, advertisements of member links MUST NOT be done when the member link becomes operationally down or is no longer a member of the identified L2 bundle. The advertisement of the L2 Bundle Member Attributes sub-TLV may be asymmetric for an OSPF link, depending on the underlying L2 connectivity, i.e., advertised by the router on only one end. The L2 Bundle Member Attributes sub-TLV has the following format:
L2 Bundle Member Attributes Sub-TLV Format 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | L2 Bundle Member Descriptor | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Member Link Attribute sub-TLVs (variable) // +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Where:
Type:
24 for OSPFv2 and 29 for OSPFv3
Length:
The total length (in octets) of the value portion of the TLV including nested sub-TLVs.
L2 Bundle Member Descriptor:
A 4-octet link-local identifier for the member link. This identifier is described as "link local identifier" in and used as "Local Interface ID" in .
Link attributes for L2 bundle member links are advertised as sub-TLVs of the L2 Bundle Member Attributes sub-TLV. In the case of OSPFv2, the L2 Bundle Member Attributes sub-TLV shares the sub-TLV space of the Extended Link TLV, and the sub-TLVs of the Extended Link TLV MAY be used to describe the attributes of the member link. lists sub-TLVs and their applicability for L2 bundle member links. The sub-TLVs that are not applicable MUST NOT be used as sub-TLVs for the L2 Bundle Member Attributes sub-TLV. Specifications that introduce new sub-TLVs of the Extended Link TLV MUST indicate their applicability to the L2 Bundle Member Attributes sub-TLV. Typically, attributes that have L3 semantics would not be applicable, but L2 attributes would apply. An implementation MUST ignore any sub-TLVs received that are not applicable in the context of the L2 Bundle Member Attributes sub-TLV. Applicability of OSPFv2 Link Attribute Sub-TLVs for L2 Bundle Members
Value Description Applicability
1 SID/Label N
2 Adj-SID Y
3 LAN Adj-SID/Label Y
4 Network-to-Router Metric N
5 RTM Capability N
6 OSPFv2 Link MSD N
7 Graceful-Link-Shutdown N
8 Remote IPv4 Address N
9 Local/Remote Interface ID N
10 Application-Specific Link Attributes Y
11 Shared Risk Link Group Y
12 Unidirectional Link Delay Y
13 Min/Max Unidirectional Link Delay Y
14 Unidirectional Delay Variation Y
15 Unidirectional Link Loss Y
16 Unidirectional Residual Bandwidth Y
17 Unidirectional Available Bandwidth Y
18 Unidirectional Utilized Bandwidth Y
19 Administrative Group Y
20 Extended Administrative Group Y
22 TE Metric Y
23 Maximum Link Bandwidth Y
24 L2 Bundle Member Attributes N
Applicability:
Y:
This sub-TLV MAY appear in the L2 Bundle Member Attributes sub-TLV.
N:
This sub-TLV MUST NOT appear in the L2 Bundle Member Attributes sub-TLV.
In the case of OSPFv3, the L2 Bundle Member Attributes sub-TLV shares the sub-TLV space of the Router-Link TLV, and the sub-TLVs of the Router-Link TLV MAY be used to describe the attributes of the member link. lists sub-TLVs that are applicable to the Router-Link TLV and their applicability for L2 bundle member links. The sub-TLVs that are not applicable MUST NOT be used as sub-TLVs for the L2 Bundle Member Attributes sub-TLV. Specifications that introduce new sub-TLVs of the Router-Link TLV MUST indicate their applicability to the L2 Bundle Member Attributes sub-TLV. An implementation MUST ignore any sub-TLVs received that are not applicable in the context of the L2 Bundle Member Attributes sub-TLV. Applicability of OSPFv3 Link Attribute Sub-TLVs for L2 Bundle Members
Value Description Applicability
1 IPv6-Forwarding-Address X
2 IPv4-Forwarding-Address X
3 Route-Tag X
4 Prefix SID X
5 Adj-SID Y
6 LAN Adj-SID Y
7 SID/Label N
8 Graceful-Link-Shutdown N
9 OSPFv3 Link MSD N
11 Application-Specific Link Attributes Y
12 Shared Risk Link Group Y
13 Unidirectional Link Delay Y
14 Min/Max Unidirectional Link Delay Y
15 Unidirectional Delay Variation Y
16 Unidirectional Link Loss Y
17 Unidirectional Residual Bandwidth Y
18 Unidirectional Available Bandwidth Y
19 Unidirectional Utilized Bandwidth Y
20 Administrative Group Y
21 Extended Administrative Group Y
22 TE Metric Y
23 Maximum Link Bandwidth Y
24 Local Interface IPv6 Address N
25 Remote Interface IPv6 Address N
26 Flexible Algorithm Prefix Metric (FAPM) X
27 Prefix Source OSPF Router-ID X
28 Prefix Source Router Address X
29 L2 Bundle Member Attributes N
33 OSPF Flexible Algorithm ASBR Metric X
Applicability:
Y:
This sub-TLV MAY appear in the L2 Bundle Member Attributes sub-TLV.
N:
This sub-TLV MUST NOT appear in the L2 Bundle Member Attributes sub-TLV.
X:
This is not a sub-TLV of the Router-Link TLV; it MUST NOT appear in the L2 Bundle Member Attributes sub-TLV.
BGP-LS Advertisement The BGP-LS extensions for the advertisement of L2 bundle members and their attributes were specified in . Using the OSPF L2 Bundle Member Attributes sub-TLV defined in this document, the L2 bundle member information can now be advertised from OSPF into BGP-LS on the same lines as discussed for IS-IS in .
IANA Considerations IANA has allocated the following code point in the "OSPFv2 Extended Link TLV Sub-TLVs" subregistry under the "Open Shortest Path First v2 (OSPFv2) Parameters" registry:
Value:
24
Designation:
L2 Bundle Member Attributes
IANA has allocated the following code point in the "OSPFv3 Extended-LSA Sub-TLVs" subregistry under the "Open Shortest Path First v3 (OSPFv3) Parameters" registry:
Value:
29
Description:
L2 Bundle Member Attributes
IANA has also introduced a column titled "L2BM" in the "OSPFv2 Extended Link TLV Sub-TLVs" registry. The "L2BM" column indicates applicability to the L2 Bundle Attributes Member sub-TLV. The initial allocations (Y/N) for this column are indicated in . The following explanatory note has been added to the registry:
The "L2BM" column indicates applicability to the L2 Bundle Attributes Member sub-TLV. The options for the "L2BM" column are: Y - This sub-TLV MAY appear in the L2 Bundle Member Attributes sub-TLV. N - This sub-TLV MUST NOT appear in the L2 Bundle Member Attributes sub-TLV.
Similarly, IANA has introduced a column titled "L2BM" in the "OSPFv3 Extended-LSA Sub-TLVs" registry. The "L2BM" column indicates applicability to the L2 Bundle Attributes Member sub-TLV. The initial allocations (Y/N/X) for this column are indicated in . The following explanatory note has been added to the registry:
The "L2BM" column indicates applicability to the L2 Bundle Attributes Member sub-TLV. The options for the "L2BM" column are: Y - This sub-TLV MAY appear in the L2 Bundle Member Attributes sub-TLV. N - This sub-TLV MUST NOT appear in the L2 Bundle Member Attributes sub-TLV. X - This is not a sub-TLV of the Router-Link TLV; it MUST NOT appear in the L2 Bundle Member Attributes sub-TLV.
Future allocations in these two registries are required to indicate the applicability of the introduced sub-TLV to the L2 Bundle Member Attributes sub-TLV. IANA has added this document as a reference for both registries.
Operational Considerations Implementations MUST NOT enable the advertisement of L2 bundle member links and their attributes in OSPF LSAs by default and MUST provide a configuration option to enable their advertisement on specific links. specifies the base YANG data model for OSPF. The required configuration and operational elements for this feature are expected to be introduced as augmentation to this base YANG data model for OSPF.
Security Considerations The OSPF protocol has supported the advertisement of link attribute information, including link identifiers, for many years. The advertisements defined in this document are identical to the existing advertisements defined in , , , , , and , but they are associated with L2 links that are part of a bundle interface on which the OSPF protocol operates. Therefore, the security considerations of these documents are applicable, and there are no new security issues introduced by the extensions in this document. As always, if the protocol is used in an environment where unauthorized access to the physical links on which OSPF packets are sent occurs, then attacks are possible. The use of authentication as defined in , , , and is recommended for preventing such attacks.
References Normative References IEEE Standard for Local and Metropolitan Area Networks--Link Aggregation IEEE Key words for use in RFCs to Indicate Requirement Levels In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. Routing Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS) This document specifies routing extensions in support of carrying link state information for Generalized Multi-Protocol Label Switching (GMPLS). This document enhances the routing extensions required to support MPLS Traffic Engineering (TE). [STANDARDS-TRACK] OSPFv2 Prefix/Link Attribute Advertisement OSPFv2 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisements (LSAs) as described in RFC 2328. This document defines OSPFv2 Opaque LSAs based on Type-Length-Value (TLV) tuples that can be used to associate additional attributes with prefixes or links. Depending on the application, these prefixes and links may or may not be advertised in the fixed-format LSAs. The OSPFv2 Opaque LSAs are optional and fully backward compatible. Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. OSPFv3 Link State Advertisement (LSA) Extensibility OSPFv3 requires functional extension beyond what can readily be done with the fixed-format Link State Advertisement (LSA) as described in RFC 5340. Without LSA extension, attributes associated with OSPFv3 links and advertised IPv6 prefixes must be advertised in separate LSAs and correlated to the fixed-format LSAs. This document extends the LSA format by encoding the existing OSPFv3 LSA information in Type-Length-Value (TLV) tuples and allowing advertisement of additional information with additional TLVs. Backward-compatibility mechanisms are also described. This document updates RFC 5340, "OSPF for IPv6", and RFC 5838, "Support of Address Families in OSPFv3", by providing TLV-based encodings for the base OSPFv3 unicast support and OSPFv3 address family support. OSPF Extensions for Segment Routing Segment Routing (SR) allows a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological subpaths called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This document describes the OSPFv2 extensions required for Segment Routing. OSPFv3 Extensions for Segment Routing Segment Routing (SR) allows a flexible definition of end-to-end paths within IGP topologies by encoding paths as sequences of topological subpaths called "segments". These segments are advertised by the link-state routing protocols (IS-IS and OSPF). This document describes the OSPFv3 extensions required for Segment Routing with the MPLS data plane. Border Gateway Protocol - Link State (BGP-LS) Extensions for Segment Routing Segment Routing (SR) allows for a flexible definition of end-to-end paths by encoding paths as sequences of topological subpaths, called "segments". These segments are advertised by routing protocols, e.g., by the link-state routing protocols (IS-IS, OSPFv2, and OSPFv3) within IGP topologies. This document defines extensions to the Border Gateway Protocol - Link State (BGP-LS) address family in order to carry SR information via BGP. Informative References Traffic Engineering (TE) Extensions to OSPF Version 2 This document describes extensions to the OSPF protocol version 2 to support intra-area Traffic Engineering (TE), using Opaque Link State Advertisements. OSPF Extensions in Support of Generalized Multi-Protocol Label Switching (GMPLS) This document specifies encoding of extensions to the OSPF routing protocol in support of Generalized Multi-Protocol Label Switching (GMPLS). [STANDARDS-TRACK] Authentication/Confidentiality for OSPFv3 This document describes means and mechanisms to provide authentication/confidentiality to OSPFv3 using an IPv6 Authentication Header/Encapsulating Security Payload (AH/ESP) extension header. [STANDARDS-TRACK] A Path Computation Element (PCE)-Based Architecture Constraint-based path computation is a fundamental building block for traffic engineering systems such as Multiprotocol Label Switching (MPLS) and Generalized Multiprotocol Label Switching (GMPLS) networks. Path computation in large, multi-domain, multi-region, or multi-layer networks is complex and may require special computational components and cooperation between the different network domains. This document specifies the architecture for a Path Computation Element (PCE)-based model to address this problem space. This document does not attempt to provide a detailed description of all the architectural components, but rather it describes a set of building blocks for the PCE architecture from which solutions may be constructed. This memo provides information for the Internet community. Traffic Engineering Extensions to OSPF Version 3 This document describes extensions to OSPFv3 to support intra-area Traffic Engineering (TE). This document extends OSPFv2 TE to handle IPv6 networks. A new TLV and several new sub-TLVs are defined to support IPv6 networks. [STANDARDS-TRACK] OSPFv2 HMAC-SHA Cryptographic Authentication This document describes how the National Institute of Standards and Technology (NIST) Secure Hash Standard family of algorithms can be used with OSPF version 2's built-in, cryptographic authentication mechanism. This updates, but does not supercede, the cryptographic authentication mechanism specified in RFC 2328. [STANDARDS-TRACK] Supporting Authentication Trailer for OSPFv3 Currently, OSPF for IPv6 (OSPFv3) uses IPsec as the only mechanism for authenticating protocol packets. This behavior is different from authentication mechanisms present in other routing protocols (OSPFv2, Intermediate System to Intermediate System (IS-IS), RIP, and Routing Information Protocol Next Generation (RIPng)). In some environments, it has been found that IPsec is difficult to configure and maintain and thus cannot be used. This document defines an alternative mechanism to authenticate OSPFv3 protocol packets so that OSPFv3 does not depend only upon IPsec for authentication. The OSPFv3 Authentication Trailer was originally defined in RFC 6506. This document obsoletes RFC 6506 by providing a revised definition, including clarifications and refinements of the procedures. OSPF Traffic Engineering (TE) Metric Extensions In certain networks, such as, but not limited to, financial information networks (e.g., stock market data providers), network performance information (e.g., link propagation delay) is becoming critical to data path selection. This document describes common extensions to RFC 3630 "Traffic Engineering (TE) Extensions to OSPF Version 2" and RFC 5329 "Traffic Engineering Extensions to OSPF Version 3" to enable network performance information to be distributed in a scalable fashion. The information distributed using OSPF TE Metric Extensions can then be used to make path selection decisions based on network performance. Note that this document only covers the mechanisms by which network performance information is distributed. The mechanisms for measuring network performance information or using that information, once distributed, are outside the scope of this document. Security Extension for OSPFv2 When Using Manual Key Management The current OSPFv2 cryptographic authentication mechanism as defined in RFCs 2328 and 5709 is vulnerable to both inter-session and intra- session replay attacks when using manual keying. Additionally, the existing cryptographic authentication mechanism does not cover the IP header. This omission can be exploited to carry out various types of attacks. This document defines changes to the authentication sequence number mechanism that will protect OSPFv2 from both inter-session and intra- session replay attacks when using manual keys for securing OSPFv2 protocol packets. Additionally, we also describe some changes in the cryptographic hash computation that will eliminate attacks resulting from OSPFv2 not protecting the IP header. North-Bound Distribution of Link-State and Traffic Engineering (TE) Information Using BGP In a number of environments, a component external to a network is called upon to perform computations based on the network topology and current state of the connections within the network, including Traffic Engineering (TE) information. This is information typically distributed by IGP routing protocols within the network. This document describes a mechanism by which link-state and TE information can be collected from networks and shared with external components using the BGP routing protocol. This is achieved using a new BGP Network Layer Reachability Information (NLRI) encoding format. The mechanism is applicable to physical and virtual IGP links. The mechanism described is subject to policy control. Applications of this technique include Application-Layer Traffic Optimization (ALTO) servers and Path Computation Elements (PCEs). Segment Routing Architecture Segment Routing (SR) leverages the source routing paradigm. A node steers a packet through an ordered list of instructions, called "segments". A segment can represent any instruction, topological or service based. A segment can have a semantic local to an SR node or global within an SR domain. SR provides a mechanism that allows a flow to be restricted to a specific topological path, while maintaining per-flow state only at the ingress node(s) to the SR domain. SR can be directly applied to the MPLS architecture with no change to the forwarding plane. A segment is encoded as an MPLS label. An ordered list of segments is encoded as a stack of labels. The segment to process is on the top of the stack. Upon completion of a segment, the related label is popped from the stack. SR can be applied to the IPv6 architecture, with a new type of routing header. A segment is encoded as an IPv6 address. An ordered list of segments is encoded as an ordered list of IPv6 addresses in the routing header. The active segment is indicated by the Destination Address (DA) of the packet. The next active segment is indicated by a pointer in the new routing header. OSPF Link-Local Signaling (LLS) Extensions for Local Interface ID Advertisement Every OSPF interface is assigned an Interface ID that uniquely identifies the interface on the router. In some cases, it is useful to know the assigned Interface ID on the remote side of the adjacency (Remote Interface ID). This document describes the extensions to OSPF link-local signaling (LLS) to advertise the Local Interface ID. Advertising Layer 2 Bundle Member Link Attributes in IS-IS There are deployments where the Layer 3 interface on which IS-IS operates is a Layer 2 interface bundle. Existing IS-IS advertisements only support advertising link attributes of the Layer 3 interface. If entities external to IS-IS wish to control traffic flows on the individual physical links that comprise the Layer 2 interface bundle, link attribute information about the bundle members is required. This document introduces the ability for IS-IS to advertise the link attributes of Layer 2 (L2) Bundle Members. YANG Data Model for the OSPF Protocol This document defines a YANG data model that can be used to configure and manage OSPF. The model is based on YANG 1.1 as defined in RFC 7950 and conforms to the Network Management Datastore Architecture (NMDA) as described in RFC 8342.
Acknowledgements This document leverages similar work done for IS-IS, and the authors of this document would like to acknowledge the contributions of the authors of . The authors would like to thank , , , and for their review and feedback on this document. The authors would also like to thank for his detailed shepherd review of this document. The authors would also like to thank for his AD review and the discussion related to the applicability of TLVs/sub-TLVs to the L2 Bundle Member Attributes sub-TLV.
Authors' Addresses Cisco Systems
India ketant.ietf@gmail.com
Cisco Systems
Apollo Business Center Mlynske nivy 43 Bratislava 821 09 Slovakia ppsenak@cisco.com