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 https://www.rfc-editor.org/info/rfc9013.¶

Copyright Notice

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

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Table of Contents

1. Introduction

Networks use tunnels for a variety of reasons, such as:¶

• Partial deployment of IPv6 in IPv4 networks or IPv4 in IPv6 networks, as described in [RFC5565], where IPvx tunnels are used between IPvx-enabled routers so as to traverse non-IPvx routers.¶
• Remote Loop-Free Alternate (RLFA) repair tunnels as described in [RFC7490], where tunnels are used between the Point of Local Repair and the selected PQ node.¶

The tunnel encapsulator router needs to select a type of tunnel that is supported by the tunnel decapsulator router. This document defines how to advertise, in OSPF Router Information Link State Advertisements (LSAs), the list of tunnel encapsulations supported by the tunnel decapsulator. In this document, OSPF refers to both OSPFv2 [RFC2328] and OSPFv3 [RFC5340].¶

2. Terminology

This memo makes use of the terms defined in [RFC7770].¶

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.¶

3. Tunnel Encapsulations TLV

Routers advertise their supported tunnel encapsulation type(s) by advertising a new TLV of the OSPF Router Information (RI) Opaque LSA [RFC7770], referred to as the "Tunnel Encapsulations TLV". This TLV is applicable to both OSPFv2 and OSPFv3.¶

The Type code of the Tunnel Encapsulations TLV is 13, the Length value is variable, and the Value field contains one or more Tunnel Sub-TLVs, as defined in Section 4. Each Tunnel Sub-TLV indicates a particular encapsulation format that the advertising router supports, along with the parameters corresponding to the tunnel type.¶

The Tunnel Encapsulations TLV MAY appear more than once within a given OSPF Router Information (RI) Opaque LSA. If the Tunnel Encapsulations TLV appears more than once in an OSPF Router Information LSA, the set of all Tunnel Sub-TLVs from all Tunnel Encapsulations TLVs SHOULD be considered. The scope of the advertisement depends on the application, but it is recommended that it SHOULD be domain wide.¶

4. Tunnel Sub-TLV

The Tunnel Sub-TLV is structured as shown in Figure 1.¶

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Tunnel Type (2 octets)     |        Length (2 octets)      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |               Tunnel Parameter Sub-TLVs                       |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Tunnel Type (2 octets):

Identifies the type of tunneling technology signaled. Tunnel types are shared with the BGP extension [RFC9012] and hence are defined in the IANA registry "BGP Tunnel Encapsulation Attribute Tunnel Types". Unknown tunnel types are to be ignored upon receipt.¶

Length (2 octets):

Unsigned 16-bit integer indicating the total number of octets of the Tunnel Parameter Sub-TLVs field.¶

Tunnel Parameter Sub-TLVs (variable):

Zero or more Tunnel Parameter Sub-TLVs, as defined in Section 5.¶

If a Tunnel Sub-TLV is invalid, it MUST be ignored and skipped. However, other Tunnel Sub-TLVs MUST be considered.¶

5. Tunnel Parameter Sub-TLVs

A Tunnel Parameter Sub-TLV is structured as shown in Figure 2.¶

           +---------------------------------------------+
           |   Tunnel Parameter Sub-Type (2 octets)      |
           +---------------------------------------------+
           |   Tunnel Parameter Length (2 octets)        |
           +---------------------------------------------+
           |   Tunnel Parameter Value (variable)         |
           |                                             |
           +---------------------------------------------+

Tunnel Parameter Sub-Type (2 octets):

Each sub-type defines a parameter of the Tunnel Sub-TLV. Sub-types are registered in the IANA registry "OSPF Tunnel Parameter Sub-TLVs" (see Section 7.2).¶

Tunnel Parameter Length (2 octets):

Unsigned 16-bit integer indicating the total number of octets of the Tunnel Parameter Value field.¶

Tunnel Parameter Value (variable):

Encodings of the Value field depend on the sub-TLV type. The following subsections define the encoding in detail.¶

Any unknown Tunnel Parameter sub-type MUST be ignored and skipped upon receipt. When a reserved value (see Section 7.2) is seen in an LSA, it MUST be treated as an invalid Tunnel Parameter Sub-TLV. When a Tunnel Parameter Value has an incorrect syntax or semantics, it MUST be treated as an invalid Tunnel Parameter Sub-TLV. If a Tunnel Parameter Sub-TLV is invalid, its Tunnel Sub-TLV MUST be ignored. However, other Tunnel Sub-TLVs MUST be considered.¶

     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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Address Family           |           Address             ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               +
    ~                     (variable length)                         ~
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

6. Operation

The advertisement of a Tunnel Encapsulations Sub-TLV indicates that the advertising router supports a particular tunnel decapsulation along with the parameters to be used for the tunnel. The decision to use that tunnel is driven by the capability of the tunnel encapsulator router to support the encapsulation type and the policy on the tunnel encapsulator router. The Color Sub-TLV (see Section 5.4) may be used as an input to this policy. Note that some tunnel types may require the execution of an explicit tunnel setup protocol before they can be used to transit data.¶

A tunnel MUST NOT be used if there is no route toward the IP address specified in the Tunnel Egress Endpoint Sub-TLV (see Section 5.3) or if the route is not advertised in the same OSPF domain.¶

7. IANA Considerations

8. Security Considerations

Security considerations applicable to softwires can be found in the mesh framework [RFC5565]. In general, security issues of the tunnel protocols signaled through this OSPF capability extension are inherited.¶

If a third party is able to modify any of the information that is used to form encapsulation headers, choose a tunnel type, or choose a particular tunnel for a particular payload type, user data packets may end up getting misrouted, misdelivered, and/or dropped. However, since an OSPF routing domain is usually a well-controlled network under a single administrative domain, the possibility of the above attack is very low.¶

We note that the last paragraph of Section 6 forbids the establishment of a tunnel toward arbitrary destinations. It prohibits a destination outside of the OSPF domain. This prevents a third party that has gained access to an OSPF router from being able to send the traffic to other destinations, e.g., for inspection purposes.¶

Security considerations for the base OSPF protocol are covered in [RFC2328] and [RFC5340].¶

Acknowledgements

This document is partially inspired by [RFC5512].¶

The authors would like to thank Greg Mirsky, John E. Drake, Carlos Pignataro, and Karsten Thomann for their valuable comments on this document. Special thanks should be given to Acee Lindem for his multiple detailed reviews of this document and help. The authors would like to thank Pete Resnick, Joe Touch, David Mandelberg, Sabrina Tanamal, Tim Wicinski, and Amanda Baber for their Last Call reviews. The authors also thank Spencer Dawkins, Mirja Kühlewind, Ben Campbell, Benoit Claise, Alvaro Retana, Adam Roach, and Suresh Krishnan for their AD reviews.¶

Authors' Addresses