RFC 9013
OSPF Advertisement of Tunnel Encapsulations
RFC 9013: OSPF Advertisement of Tunnel Encapsulations 🦋
okay bestie, let's get into it. RFC 9013 is an IETF Standards Track document from April 2021, published as ISSN 2070-1721. The editors are X. Xu (Capitalonline) and B. Decraene (Orange), with R. Raszuk (NTT Network Innovations), L. Contreras (Telefonica I+D), and L. Jalil (Verizon). Its header doesn't list any Obsoletes or Updates entries, so it isn't replacing or amending anything else. 💅
Abstract
Networks use tunnels for all kinds of reasons 🌈 and there are SO many tunnel types. So the tunnel encapsulator router has to pick a type that the tunnel decapsulator router actually supports. This document explains how to advertise that list of supported tunnel encapsulations in OSPF Router Information Link State Advertisements (LSAs) 🧚
Status of This Memo
This is an Internet Standards Track document. ✨
It's a product of the Internet Engineering Task Force (IETF), it represents the consensus of the IETF community, it got public review, and the Internet Engineering Steering Group (IESG) approved it for publication. If you want more on Internet Standards, check out Section 2 of RFC 7841. 📚
For the current status, any errata, and how to send feedback, head to 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. 🎀
This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) as they stand on the publication date. Please actually read these, because they spell out your rights and restrictions for 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 they come without warranty as described in the Simplified BSD License. 💜
Table of Contents 🗂️
1. Introduction
2. Terminology
3. Tunnel Encapsulations TLV
4. Tunnel Sub-TLV
5. Tunnel Parameter Sub-TLVs
5.1. Encapsulation Sub-TLV
5.2. Protocol Type Sub-TLV
5.3. Tunnel Egress Endpoint Sub-TLV
5.4. Color Sub-TLV
5.5. Load-Balancing Block Sub-TLV
5.6. DS Field Sub-TLV
5.7. UDP Destination Port Sub-TLV
6. Operation
7. IANA Considerations
7.1. OSPF Router Information (RI) TLVs Registry
7.2. OSPF Tunnel Parameter Sub-TLVs Registry
8. Security Considerations
9. References
9.1. Normative References
9.2. Informative References
Acknowledgements
Contributors
Authors' Addresses1. Introduction 🌷
Okay so networks use tunnels for lots of reasons, like these two:
- Partial IPv6 deployment in IPv4 networks (or the other way around), as described in [RFC5565]. IPvx tunnels run between IPvx-enabled routers so the traffic can get across routers that don't speak IPvx. 🦋
- Remote Loop-Free Alternate (RLFA) repair tunnels, as described in [RFC7490]. These tunnels run between the Point of Local Repair and the selected PQ node. 🔥
The tunnel encapsulator router has to pick a tunnel type the tunnel decapsulator router supports, and this doc is the how-to for advertising that list of supported encapsulations inside OSPF Router Information Link State Advertisements (LSAs) ✨. Here, "OSPF" means both OSPFv2 [RFC2328] and OSPFv3 [RFC5340]. 💖
2. Terminology 📖
This memo uses the terms defined in [RFC7770]. 🧚
Now the important bit 👑: the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" are interpreted as described in BCP 14 [RFC2119] [RFC8174], but only when they show up in all capitals, like they do here. 💅
3. Tunnel Encapsulations TLV 🎀
Routers advertise their supported tunnel encapsulation types by sending a new TLV inside the OSPF Router Information (RI) Opaque LSA [RFC7770]. This one's called the "Tunnel Encapsulations TLV", and it works for both OSPFv2 and OSPFv3. 🌈
The Type code is 13. The Length is variable. The Value field holds one or more Tunnel Sub-TLVs (defined in Section 4), and each Tunnel Sub-TLV names a specific encapsulation format the advertising router supports, along with the parameters for that tunnel type. 🫶
The Tunnel Encapsulations TLV MAY show up more than once in the same OSPF Router Information (RI) Opaque LSA 🌸. If it does, you SHOULD consider the full set of Tunnel Sub-TLVs from all of those Tunnel Encapsulations TLVs together. How far the advertisement reaches depends on the application, but it's recommended that it SHOULD be domain wide 🌍.
4. Tunnel Sub-TLV 🧁
Here's how the Tunnel Sub-TLV is laid out, 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 |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Tunnel Sub-TLVHere's what each field does:
- Tunnel Type (2 octets): This says which tunneling technology is being signaled. Tunnel types are shared with the BGP extension [RFC9012], so they live in the IANA registry "BGP Tunnel Encapsulation Attribute Tunnel Types". Unknown tunnel types are to be ignored when received. 🙈
- Length (2 octets): An unsigned 16-bit integer counting the total octets in the Tunnel Parameter Sub-TLVs field. 🔢
- Tunnel Parameter Sub-TLVs (variable): Zero or more Tunnel Parameter Sub-TLVs, defined in Section 5. ✨
If a Tunnel Sub-TLV is invalid, it MUST be ignored and skipped. But the other Tunnel Sub-TLVs MUST still be considered. 💀
5. Tunnel Parameter Sub-TLVs 🌟
A Tunnel Parameter Sub-TLV is laid out as shown in Figure 2 🦋
+---------------------------------------------+
| Tunnel Parameter Sub-Type (2 octets) |
+---------------------------------------------+
| Tunnel Parameter Length (2 octets) |
+---------------------------------------------+
| Tunnel Parameter Value (variable) |
| |
+---------------------------------------------+
Figure 2: Tunnel Parameter Sub-TLVBreaking it down:
- Tunnel Parameter Sub-Type (2 octets): Each sub-type defines one parameter of the Tunnel Sub-TLV. They're registered in the IANA registry "OSPF Tunnel Parameter Sub-TLVs" (see Section 7.2). 🗝️
- Tunnel Parameter Length (2 octets): An unsigned 16-bit integer counting the total octets in the Tunnel Parameter Value field. 🔢
- Tunnel Parameter Value (variable): How the Value field is encoded depends on the sub-TLV type. The subsections below spell out each encoding. 💜
Now the rules for getting these right 👑:
Any unknown Tunnel Parameter sub-type MUST be ignored and skipped when received. If a reserved value (see Section 7.2) shows up in an LSA, it MUST be treated as an invalid Tunnel Parameter Sub-TLV. If a Tunnel Parameter Value has incorrect syntax or semantics, it MUST be treated as an invalid Tunnel Parameter Sub-TLV. And if a Tunnel Parameter Sub-TLV is invalid, its Tunnel Sub-TLV MUST be ignored. Once again, the other Tunnel Sub-TLVs MUST still be considered. 🫶
5.1. Encapsulation Sub-TLV 🎀
This sub-TLV type is 1. Its Value field's syntax, semantics, and usage are defined in Section 3.2 ("Encapsulation Sub-TLVs for Particular Tunnel Types") of [RFC9012]. 🌸
5.2. Protocol Type Sub-TLV 🧚
This sub-TLV type is 2. Its Value field's syntax, semantics, and usage are defined in Section 3.4.1 ("Protocol Type Sub-TLV") of [RFC9012]. 💅
5.3. Tunnel Egress Endpoint Sub-TLV 🌈
The Tunnel Egress Endpoint Sub-TLV tells you the address of the tunnel's egress endpoint, meaning the router that's going to decapsulate the payload. 📍
This sub-TLV type is 3. It MUST be present once and only once in a given Tunnel Sub-TLV. Its Value field has two subfields:
- a two-octet Address Family subfield
- an Address subfield, whose length depends on the Address Family
Here's the layout, shown in Figure 3 👇
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) ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Tunnel Egress Endpoint Sub-TLVThe Address Family subfield holds a value from IANA's "Address Family Numbers" registry. In this document we assume the Address Family is either IPv4 or IPv6, and any other address family is outside the scope of this doc. 🌍
Here's where the details get real 🔍:
If the Address Family subfield holds the IPv4 value, the Address subfield MUST contain an IPv4 address (a /32 IPv4 prefix). In that case, the Length field of the Tunnel Egress Endpoint Sub-TLV MUST contain the value 6. 🌟
If the Address Family subfield holds the IPv6 value, the Address subfield MUST contain an IPv6 address (a /128 IPv6 prefix). In that case, the Length field of the Tunnel Egress Endpoint Sub-TLV MUST contain the value 18 (0x12). And IPv6 link-local addresses are not valid values for the IP address field. 🚫
5.4. Color Sub-TLV 🎨
This sub-TLV type is 4. It may appear zero or more times in a given Tunnel Sub-TLV. Its Value field is a 4-octet opaque unsigned integer. 🔮
The color value is user-defined and configured locally on the advertising routers. Service providers can use it to define policies on the tunnel encapsulator routers, for example to control which tunnel gets picked. 🍓
This color value can be referenced by BGP routes that carry the Color Extended Community [RFC9012]. If the tunnel is used to reach the BGP next hop of BGP routes, attaching a Color Extended Community to those routes says the BGP speaker is willing to use a tunnel of the same color. It's giving "we're on the same page" 💜
5.5. Load-Balancing Block Sub-TLV ⚖️
This sub-TLV type is 5. Its Value field's syntax, semantics, and usage are defined in [RFC5640]. ✨
Part 1 is done, bestie 🫶 Part 2 is coming with the rest of the tunnel sub-TLVs, Operation, IANA, Security (very dramatic, very important), and References 🌈💖
5.6. DS Field Sub-TLV
bestie, this one's a little cameo 🎀 The sub-TLV type is 6 ✨ and the syntax, semantics, and usage of its Value field aren't in this doc at all. They're defined in Section 3.3.1 ("DS Field") of [RFC9012] 💅
5.7. UDP Destination Port Sub-TLV
same energy 🦋 The type is 7 💖 and the Value field lives in Section 3.3.2 ("UDP Destination Port") of [RFC9012] 🌸
6. Operation ✨
okay this is the heart of it 💜 Advertising a Tunnel Encapsulations Sub-TLV basically says "hey, I can do this tunnel decapsulation, and here are the params to use" 🎀 Whether anyone actually picks that tunnel is up to the tunnel encapsulator router. It has to be able to support the encapsulation type, and then its own policy gets a say 👑 The Color Sub-TLV (see Section 5.4) can be an input to that policy, ooh 🌈 Also, heads up: some tunnel types need an explicit tunnel setup protocol before they can actually carry 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 🎀
7.1. OSPF Router Information (RI) TLVs Registry
IANA has allocated the following new code point in the "OSPF Router Information (RI) TLVs" registry 🦋
+=======+=======================+===========+
| Value | TLV Name | Reference |
+=======+=======================+===========+
| 13 | Tunnel Encapsulations | RFC 9013 |
+-------+-----------------------+-----------+
Table 1: Addition to OSPF Router
Information (RI) TLVs Registry7.2. OSPF Tunnel Parameter Sub-TLVs Registry
IANA has created a new subregistry called the "OSPF Tunnel Parameter Sub-TLVs" registry under the "Open Shortest Path First (OSPF) Parameters" registry 🌸 The registration procedures are as follows:
- The values in the range 1-34999 are to be allocated using the "Standards Action" registration procedure defined in [RFC8126].
- The values in the range 35000-65499 are to be allocated using the "First Come First Served" registration procedure.
The initial contents of the registry are as follows 💜
+=============+======================+=====================+
| Value | TLV Name | Reference |
+=============+======================+=====================+
| 0 | Reserved | RFC 9013 |
+-------------+----------------------+---------------------+
| 1 | Encapsulation | RFC 9013 & RFC 9012 |
+-------------+----------------------+---------------------+
| 2 | Protocol Type | RFC 9013 & RFC 9012 |
+-------------+----------------------+---------------------+
| 3 | Endpoint | RFC 9013 |
+-------------+----------------------+---------------------+
| 4 | Color | RFC 9013 |
+-------------+----------------------+---------------------+
| 5 | Load-Balancing Block | RFC 9013 & RFC 5640 |
+-------------+----------------------+---------------------+
| 6 | DS Field | RFC 9013 & RFC 9012 |
+-------------+----------------------+---------------------+
| 7 | UDP Destination Port | RFC 9013 & RFC 9012 |
+-------------+----------------------+---------------------+
| 8-65499 | Unassigned | |
+-------------+----------------------+---------------------+
| 65500-65534 | Experimental | RFC 9013 |
+-------------+----------------------+---------------------+
| 65535 | Reserved | RFC 9013 |
+-------------+----------------------+---------------------+
Table 2: Initial Contents of OSPF Tunnel Parameter Sub-
TLVs Registry8. Security Considerations 🔥
okay bestie, this section is SERIOUS 😭 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. 👑 Lowkey the most important part of this whole doc, fr fr.
Security considerations for the base OSPF protocol are covered in [RFC2328] and [RFC5340].
9. References 📚
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5640] Filsfils, C., Mohapatra, P., and C. Pignataro, "Load-
Balancing for Mesh Softwires", RFC 5640,
DOI 10.17487/RFC5640, August 2009,
<https://www.rfc-editor.org/info/rfc5640>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", RFC 9012,
DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>.9.2. Informative References
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation
Subsequent Address Family Identifier (SAFI) and the BGP
Tunnel Encapsulation Attribute", RFC 5512,
DOI 10.17487/RFC5512, April 2009,
<https://www.rfc-editor.org/info/rfc5512>.
[RFC5565] Wu, J., Cui, Y., Metz, C., and E. Rosen, "Softwire Mesh
Framework", RFC 5565, DOI 10.17487/RFC5565, June 2009,
<https://www.rfc-editor.org/info/rfc5565>.
[RFC7490] Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
RFC 7490, DOI 10.17487/RFC7490, April 2015,
<https://www.rfc-editor.org/info/rfc7490>.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. 💖
Contributors 🧚
Uma Chunduri
Huawei
Email: uma.chunduri@gmail.comAuthors' Addresses 🍓
Xiaohu Xu (editor)
Capitalonline
Email: xiaohu.xu@capitalonline.net
Bruno Decraene (editor)
Orange
Email: bruno.decraene@orange.com
Robert Raszuk
NTT Network Innovations
940 Stewart Dr
Sunnyvale, CA 94085
United States of America
Email: robert@raszuk.net
Luis M. Contreras
Telefonica I+D
Email: luismiguel.contrerasmurillo@telefonica.com
Luay Jalil
Verizon
Email: luay.jalil@verizon.com📦 where this page comes from
- ietf: rfc9013 2021-04
- 💖 girlified by claude-haiku-5-5 on : a language model's rewrite of the original, under its terms