Advertising Tunneling Capability in OSPF
draft-ietf-ospf-encapsulation-cap-05

Abstract

Networks use tunnels for a variety of reasons. A large variety of tunnel types are defined and the ingress needs to select a type of tunnel which is supported by the egress and itself. This document defines how to advertise egress tunnel capabilities in OSPF Router Information Link State Advertisement (LSAs).

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.

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 http://datatracker.ietf.org/drafts/current/.

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This Internet-Draft will expire on January 4, 2018.

Copyright Notice

Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. Terminology
• 3. Advertising Encapsulation Capability
• 4. Tunnel Encapsulation Type
• 5. Tunnel Encapsulation Attribute
• 6. Tunnel Encapsulation Attribute Sub-TLVs
• 6.1. Encapsulation Sub-TLV
• 6.2. Protocol Type Sub-TLV
• 6.3. Endpoint Sub-TLV
• 6.4. Color Sub-TLV
• 6.5. IP QoS Field
• 6.6. UDP Destination Port
• 6.7. future sub-TLV allocations
• 7. Usage of the Tunnel Encapsulation attribute
• 8. IANA Considerations
• 8.1. OSPF Router Information
• 8.2. IGP Tunnel Encapsulation Attribute Sub-TLVs Registry
• 9. Security Considerations
• 10. Contributors
• 11. Acknowledgements
• 12. References
• 12.1. Normative References
• 12.2. Informative References
• Authors' Addresses

1. Introduction

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

• Partial deployment of MPLS-SPRING as described in [I-D.xu-mpls-unified-source-routing-instruction], where IP tunnels are used between MPLS-SPRING-enabled routers to traverse non-MPLS routers.
• Partial deployment of MPLS-BIER as described in [I-D.ietf-bier-architecture], where IP tunnels are used between MPLS-BIER-capable routers to traverse non MPLS-BIER [I-D.ietf-bier-mpls-encapsulation] routers.
• 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 ingress needs to select a type of tunnel which is supported by the egress and itself. This document describes how to use OSPF Router Information Link State Advertisements (LSAs) to advertise the egress tunneling capabilities of OSPF routers. In this document, OSPF refers to both OSPFv2 [RFC2328] and OSPFv3 [RFC5340].

2. Terminology

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

3. Advertising Encapsulation Capability

Routers advertise their supported encapsulation type(s) by advertising a new TLV of the OSPF Router Information (RI) Opaque LSA [RFC7770], referred to as the Encapsulation Capability TLV. This TLV is applicable to both OSPFv2 and OSPFv3. The Encapsulation Capability TLV SHOULD NOT appear more than once within a given OSPF Router Information (RI) Opaque LSA. If the Encapsulation Capability TLV appears more than once in an OSPF Router Information LSA, only the first occurrence MUST be processed and others MUST be ignored. The scope of the advertisement depends on the application but it is recommended that it SHOULD be domain- wide. The Type code of the Encapsulation Capability TLV is TBD1, the Length value is variable, and the Value field contains one or more Tunnel Encapsulation Type Sub-TLVs. Each Encapsulation Type Sub-TLVs indicates a particular encapsulation format that the advertising router supports along with the parameters to be used for the tunnel.

4. Tunnel Encapsulation Type

The Tunnel Encapsulation Type Sub-TLV is structured 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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    Tunnel Type (2 Octets)     |        Length (2 Octets)      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   |                            Sub-TLVs                           |
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
        

• Tunnel Type (2 octets): Identifies the type of tunneling technology being signaled. Tunnel types are shared with the BGP extension [RFC5512] and hence are defined in the IANA registry "BGP Tunnel Encapsulation Attribute Tunnel Types". Unknown types are to be ignored and skipped upon receipt.
• Length (2 octets): Unsigned 16-bit integer indicating the total number of octets of the value field.
• Value (variable): Zero or more Tunnel Encapsulation Attribute Sub-TLVs as defined in Section 5.

5. Tunnel Encapsulation Attribute

The Tunnel Encapsulation Attribute Sub-TLV is structured as follows:

                        
           +-----------------------------------+
           |      Sub-TLV Type (1 Octet)       |
           +-----------------------------------+
           |     Sub-TLV Length (1 Octet)      |
           +-----------------------------------+
           |     Sub-TLV Value (Variable)      |
           |                                   |
           +-----------------------------------+
         

• Sub-TLV Type (1 octet): Each Sub-TLV type defines a certain property of the tunnel TLV that contains this Sub-TLV. This document defines such types Section 6 )
• Sub-TLV Length (1 octet): Unsigned 8-bit integer indicating the total number of octets of the Sub-TLV value field.
• Sub-TLV Value (variable): Encodings of the value field depend on the Sub-TLV type as enumerated above. The following sub-sections define the encoding in detail.

Any unknown Sub-TLVs MUST be ignored and skipped upon receipt. However, if the TLV is understood, the entire TLV MUST NOT be ignored just because it contains an unknown Sub-TLV.

If a Sub-TLV is invalid, this specific Tunnel Encapsulation MUST be ignored and skipped. However, other Tunnel Encapsulations MUST be considered.

6. Tunnel Encapsulation Attribute Sub-TLVs

6.1. Encapsulation Sub-TLV

This Sub-TLV is defined in section 3.2 "Encapsulation Sub-TLVs for Particular Tunnel Types" of [I-D.ietf-idr-tunnel-encaps] from both a syntax and semantic standpoint. Usage is defined in Section 7.

6.2. Protocol Type Sub-TLV

This Sub-TLV is defined in section 3.4.1 "Protocol Type sub-TLV" of [I-D.ietf-idr-tunnel-encaps] from a syntactic, semantic, and usage standpoint.

6.3. Endpoint Sub-TLV

The value field carries the Network Address to be used as tunnel destination address.

If length is 4, the tunnel endpoint is an IPv4 address.

If length is 16, the tunnel endpoint is an IPv6 address.

6.4. Color Sub-TLV

The valued field is a 4-octet opaque unsigned integer.

The color value is user-defined and configured locally on the advertising routers. It may be used by service providers to define policies on the ingress routers, for example, to control the selection of the tunnel to use.

This color value can be referenced by BGP routes carrying Color Extended Community [I-D.ietf-idr-tunnel-encaps]. If the tunnel is used to reach the BGP Next-Hop of BGP routes, then attaching a Color Extended Community attached to those routes express the willingness of the BGP speaker to use a tunnel of the same color.

6.5. IP QoS Field

This Sub-TLV is defined in section 3.3.1 "IPv4 DS Field" of [I-D.ietf-idr-tunnel-encaps] from a syntactic, semantic and usage standpoint.

6.6. UDP Destination Port

This Sub-TLV is defined in section 3.3.2 "UDP Destination Port" of [I-D.ietf-idr-tunnel-encaps] from a syntactic, semantic and usage standpoint.

6.7. future sub-TLV allocations

[I-D.ietf-idr-tunnel-encaps] similarly defines Tunnel Encapsulation Attribute Sub-TLVs. IGP and BGP have separate IANA registries allowing for separate sub-TLV definitions. If the same information is to be advertised for both IGP and BGP tunnel encapsulation, it is RECOMMENDED to use the same code point, semantic and syntax. However, it is to be noted that the "BGP Tunnel Encapsulation Attribute Sub-TLVs" registry, allows for sub-TLV with two octets of length, while the "IGP Tunnel Encapsulation Attribute Sub-TLVs" registry only allows for one octet of length. Hence two-octets BGP Tunnel Encapsulation Attribute Sub-TLVs won't be able to be defined for IGP Tunnels. Eventually, their information may be split over multiple sub-TLVs.

7. Usage of the Tunnel Encapsulation attribute

The advertisement of an Encapsulation Type Sub-TLVs indicates that the advertising router support a particular tunnel encapsulation along with the parameters to be used for the tunnel. The decision to use that tunnel is driven by the capability of the ingress router to support the encapsulation type and the policy on the ingress router. The color sub-TLV 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 carry data.

A tunnel MUST NOT be used if there is no route toward the IP address specified in the Endpoint Sub-TLV or if the route is not advertised by the router advertising the Tunnel Encapsulation attribute for the tunnel.

8. IANA Considerations

8.1. OSPF Router Information

This document requests IANA to allocate a new code point from the OSPF Router Information (RI) registry.

    Value   TLV Name                               Reference
    -----   ------------------------------------   -------------
    TBD1    Tunnel Capabilities                    This document

8.2. IGP Tunnel Encapsulation Attribute Sub-TLVs Registry

This document requests IANA to create a new registry "IGP Tunnel Encapsulation Attribute Sub-TLVs" with the following registration procedure:

           Registry Name: IGP Tunnel Encapsulation Attribute Sub-TLVs

Value      Name                                      Reference
-------    ------------------------------------      -------------
      0    Reserved                                  This document
      1    Encapsulation                             This document
      2    Protocol Type                             This document
      3    Endpoint                                  This document
      4    Color                                     This document
      5    Unassigned
      6    IP QoS                                    This document
      7    UDP Destination Port                      This document
  8-250    Unassigned
251-254    Experimental                              This document
    255    Reserved                                  This document

Assignments of Encapsulation Attribute Types are via Standards Action [RFC5226].

9. 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, to choose a tunnel type, or to choose a particular tunnel for a particular payload type, user data packets may end up getting misrouted, misdelivered, and/or dropped.

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

10. Contributors

Uma Chunduri
Huawei
Email: uma.chunduri@gmail.com

11. 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 detailed reviews of this document.

12. References

12.1. Normative References

12.2. Informative References

Authors' Addresses