RFC 8920

OSPF Application-Specific Link Attributes

📅 published October 2020, from ietf

OSPF Application-Specific Link Attributes ✨

okay bestie, this is RFC 8920 and it is SO relevant to my life 💅🦋

Here's the title block tea ☕ This doc is by P. Psenak (editor), L. Ginsberg (Cisco Systems), W. Henderickx (Nokia), J. Tantsura (Apstra), and J. Drake (Juniper Networks). It's a Standards Track document, so it's an actual Internet standard, not just vibes 🎀. It's dated October 2020, lives in the ISSN 2070-1721 series, and it doesn't obsolete or update anything. It's brand new in the lore 🌸

Also: it's about OSPFv2 and OSPFv3, the routing protocols that help packets find their way around the Internet. Iconic. 👑

Abstract

okay so the big problem is this: link attribute advertisements for traffic engineering were made for RSVP-TE, but then other apps like Segment Routing Policy and Loop-Free Alternates started using them too 😭 Now if a link attribute is advertised and multiple apps want it, the current advertisements can't give each app its own value for the same attribute, and they can't say which apps are actually using a given link. It's giving confusion 💀 This document adds new link attribute advertisements in OSPFv2 and OSPFv3 that fix both problems ✨

Status of This Memo

This is an Internet Standards Track document 🎀

It's a product of the IETF, so it has the consensus of the IETF community, got public review, and was approved by the IESG. If you want more info on Internet Standards, check Section 2 of RFC 7841 💜

Errata, status, and feedback live at https://www.rfc-editor.org/info/rfc8920 🦋

Copyright Notice

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 in effect on the publication date. Read these carefully, because they spell out your rights and restrictions for this document 📜 Code Components pulled 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 🫶

Here's the full outline, so you can see where we're headed 🗺️

1.  Introduction
  1.1.  Requirements Language
2.  Requirements Discussion
3.  Existing Advertisement of Link Attributes
4.  Advertisement of Link Attributes
  4.1.  OSPFv2 Extended Link Opaque LSA and OSPFv3 E-Router-LSA
5.  Advertisement of Application-Specific Values
6.  Reused TE Link Attributes
  6.1.  Shared Risk Link Group (SRLG)
  6.2.  Extended Metrics
  6.3.  Administrative Group
  6.4.  Traffic Engineering Metric
7.  Maximum Link Bandwidth
8.  Considerations for Extended TE Metrics
9.  Local Interface IPv6 Address Sub-TLV
10. Remote Interface IPv6 Address Sub-TLV
11. Attribute Advertisements and Enablement
12. Deployment Considerations
  12.1.  Use of Legacy RSVP-TE LSA Advertisements
  12.2.  Interoperability, Backwards Compatibility, and Migration
         Concerns
    12.2.1.  Multiple Applications: Common Attributes with RSVP-TE
    12.2.2.  Multiple Applications: Some Attributes Not Shared with
             RSVP-TE
    12.2.3.  Interoperability with Legacy Routers
    12.2.4.  Use of Application-Specific Advertisements for RSVP-TE
13. Security Considerations
14. IANA Considerations
  14.1.  OSPFv2
  14.2.  OSPFv3
15. References
  15.1.  Normative References
  15.2.  Informative References
Acknowledgments
Contributors
Authors' Addresses

1. Introduction ✨

this is where the story starts 🧚

OSPFv2 [RFC2328] and OSPFv3 [RFC5340] first got link attribute advertisements for traffic engineering (TE) from [RFC3630] and [RFC5329], respectively. Then [RFC4203], [RFC7308], and [RFC7471] extended them. All of this was mostly for deployments doing Traffic Engineering over Multiprotocol Label Switching (MPLS) with the Resource Reservation Protocol (RSVP), which people shorten to RSVP-TE [RFC3209] 💅

For this document, an application is a technology that uses link attribute advertisements. Examples are listed in Section 5 🌸

Lately, newer applications want a lot of the same link attributes RSVP-TE used. Two examples are Segment Routing (SR) Policy [SEGMENT-ROUTING] and Loop-Free Alternates (LFAs) [RFC5286]. 😭 This causes ambiguity: if a network runs both RSVP-TE and SR Policy, you can't clearly tell which advertisements belong to RSVP-TE and which belong to SR Policy. If the two topologies are fully congruent, maybe it's fine, but any incongruence makes things messy 🙈

Here's a real example of the chaos. Say RSVP-TE is only enabled on some links, but an SR Policy attribute gets advertised for a link that doesn't have RSVP-TE on it. The RSVP-TE head-end router sees that attribute, assumes RSVP-TE is enabled on the link, and tries to set up a path over it. The path setup fails 💀

Another issue: when both applications run on the same link but need different values for the same attribute, the current advertisements can't carry application-specific values for one attribute on one link 😤

This document defines extensions that fix these issues. Since use cases for link attributes will keep evolving, the solution is built to be easily extended for new applications and new use cases too 🦋

1.1. 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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. 🎀

2. Requirements Discussion 💜

Evolution of link attribute use cases is expected to keep going. So any discussion of existing use cases is limited to the requirements known when this was written. To figure out what OSPF needs beyond what it already has, we only need the use cases that justify the two key points from the introduction:

Support for indicating which applications are using the link attribute advertisements on a link
Support for advertising application-specific values for the same attribute on a link

[RFC7855] covers use cases and requirements for Segment Routing (SR). One of those use cases is SR Policy, defined in [SEGMENT-ROUTING]. If both RSVP-TE and SR Policy run in a network, link attribute advertisements can be used by one or both of them. The link attributes on a given link for SR Policy don't have to match the ones for RSVP-TE on that same link. So there's a clear requirement to indicate independently which advertisements each application should use 🫶

As more applications want link attributes, the extensions have to let new applications be associated with link attributes without changing the advertisement format or creating new backwards-compatibility issues 🌈

Also, lots of cases can share a single attribute value across multiple applications, so the solution must minimize advertising duplicate link/attribute pairs whenever possible ✨

3. Existing Advertisement of Link Attributes 🎀

Right now, existing advertisements support RSVP-TE. They're carried in the OSPFv2 TE Opaque Link State Advertisement (LSA) [RFC3630] and the OSPFv3 Intra-Area-TE-LSA [RFC5329]. [RFC4203], [RFC7308], and [RFC7471] defined extra RSVP-TE link attributes 💅

Extended Link Opaque LSAs, defined in [RFC7684] for OSPFv2, and E-Router-LSAs [RFC8362] for OSPFv3 carry link attributes used by applications other than RSVP-TE or GMPLS [RFC4203]. These LSAs were built as generic containers for distributing extended link attributes 🦋

4. Advertisement of Link Attributes 🌸

this section is the setup for the whole solution, so pay attention bestie 👀

This section outlines how to advertise link attributes that were originally defined for RSVP-TE or GMPLS when they're used by other applications 💖

Part 1 ends here, bestie. More is coming so stay tuned 🫶💅

4.1. OSPFv2 Extended Link Opaque LSA and OSPFv3 E-Router-LSA ✨

okay bestie, so Extended Link Opaque LSAs ([RFC7684]) for OSPFv2 and E-Router-LSAs ([RFC8362]) for OSPFv3 are lowkey iconic 💅 for advertising link attributes that were originally defined for RSVP-TE when they're used in packet networks and in GMPLS. here are the four big wins:

Advertising the link attributes does not make the link part of the RSVP-TE topology. No conflicts, and it's fully compatible with [RFC3630] and [RFC5329]. 🫶
The OSPFv2 TE Opaque LSA and OSPFv3 Intra-Area-TE-LSA stay truly opaque to OSPFv2 and OSPFv3, the way they were originally defined in [RFC3630] and [RFC5329] respectively. OSPF never pokes inside their contents and just acts as a pure transport 🚚
There's a clear split between link attributes used by RSVP-TE and link attributes used by other OSPFv2 or OSPFv3 applications. main character energy 👑
All link attributes used by other applications get advertised in the Extended Link Opaque LSA in OSPFv2 [RFC7684] or the OSPFv3 E-Router-LSA [RFC8362] in OSPFv3.

ngl there's one downside. In rare cases, the same link attribute ends up advertised in both the TE Opaque and Extended Link Attribute LSAs in OSPFv2, or in both the Intra-Area-TE-LSA and E-Router-LSA in OSPFv3. 🙈

The Extended Link Opaque LSA [RFC7684] and E-Router-LSA [RFC8362] are used to advertise any link attributes for non-RSVP-TE applications in OSPFv2 or OSPFv3, respectively. That includes the ones originally defined for RSVP-TE applications (see Section 6). 🍓

TE link attributes used for RSVP-TE/GMPLS keep using the OSPFv2 TE Opaque LSA [RFC3630] and OSPFv3 Intra-Area-TE-LSA [RFC5329]. 💜

The format of the link attribute TLVs that were defined for RSVP-TE applications stays unchanged, even when they're used for non-RSVP-TE applications. Unique codepoints get allocated for these link attribute TLVs from the "OSPFv2 Extended Link TLV Sub-TLVs" registry [RFC7684] and from the "OSPFv3 Extended-LSA Sub-TLVs" registry [RFC8362], as specified in Section 14. 🎀

5. Advertisement of Application-Specific Values 🦋

so this is where it gets spicy 🌶️ To let people advertise application-specific values of a link attribute, we're introducing a brand-new Application-Specific Link Attributes (ASLA) sub-TLV. It's a sub-TLV of the OSPFv2 Extended Link TLV [RFC7684] and the OSPFv3 Router-Link TLV [RFC8362].

Link attributes can be advertised for non-standardized applications too, not just standardized ones. We call these a "user-defined application" or "UDA". UDAs aren't subject to standardization and are outside the scope of this specification. 🌈

The ASLA sub-TLV is optional inside the OSPFv2 Extended Link TLV and OSPFv3 Router-Link TLV. You can have multiple ASLA sub-TLVs in one parent TLV when different applications want to control different link attributes, or when a different value of the same attribute needs to be advertised by multiple applications. ✨ The ASLA sub-TLV MUST be used for advertising the link attributes listed at the end of this section if they're advertised inside the OSPFv2 Extended Link TLV and OSPFv3 Router-Link TLV. Here's the 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            |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  SABM Length  |  UDABM Length |            Reserved           |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           Standard Application Identifier Bit Mask            |
+-                                                             -+
|                            ...                                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|           User-Defined Application Identifier Bit Mask        |
+-                                                             -+
|                            ...                                |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                      Link Attribute sub-sub-TLVs              |
+-                                                             -+
|                            ...                                |

Here's what each field means:

Type: 10 (OSPFv2), 11 (OSPFv3)
Length: Variable
SABM Length: Standard Application Identifier Bit Mask Length in octets. The value MUST be 0, 4, or 8. If the Standard Application Identifier Bit Mask is not present, the SABM Length MUST be set to 0.
UDABM Length: User-Defined Application Identifier Bit Mask Length in octets. The value MUST be 0, 4, or 8. If the User-Defined Application Identifier Bit Mask is not present, the UDABM Length MUST be set to 0.
Standard Application Identifier Bit Mask: An optional set of bits, where each bit represents a single standard application. The bits are defined in the "Link Attribute Applications" registry, which is defined in [RFC8919]. The current assignments are repeated here for informational purposes:

                 0 1 2 3 4 5 6 7 ...
                +-+-+-+-+-+-+-+-+...
                |R|S|F|          ...
                +-+-+-+-+-+-+-+-+...

Bit 0 (R-bit): RSVP-TE.
Bit 1 (S-bit): Segment Routing Policy.
Bit 2 (F-bit): Loop-Free Alternate (LFA). Includes all LFA types.

User-Defined Application Identifier Bit Mask: An optional set of bits, where each bit represents a single user-defined application.

If the SABM or UDABM Length is other than 0, 4, or 8, the ASLA sub-TLV MUST be ignored by the receiver. 🙅‍♀️

Standard Application Identifier Bits are defined and sent starting with bit 0. Undefined bits that are transmitted MUST be transmitted as 0 and MUST be ignored on receipt. Bits that are not transmitted MUST be treated as if they are set to 0 on receipt. Bits that are not supported by an implementation MUST be ignored on receipt. 💖

User-Defined Application Identifier Bits have no relationship to Standard Application Identifier Bits, and they aren't managed by IANA or any other standards body. It is recommended that these bits be used starting with bit 0, so as to minimize the number of octets required to advertise all UDAs. Undefined bits that are transmitted MUST be transmitted as 0 and MUST be ignored on receipt. Bits that are not transmitted MUST be treated as if they are set to 0 on receipt. Bits that are not supported by an implementation MUST be ignored on receipt. 🧚

If the link attribute advertisement is only meant to be used by a specific set of applications, the corresponding bit masks MUST be present, and the application-specific bit(s) MUST be set for all applications that use the link attributes advertised in the ASLA sub-TLV. 🎯

Application Identifier Bit Masks apply to all link attributes that support application-specific values and are advertised in the ASLA sub-TLV.

The nice thing about not putting the Application Identifier Bit Masks inside the attribute advertisement itself is that the format of any previously defined link attributes can be kept and reused when they're advertised in the ASLA sub-TLV. 🫶

If the same attribute is advertised in more than one ASLA sub-TLV, with the application listed in the Application Identifier Bit Masks, the application SHOULD use the first instance of the advertisement and ignore any subsequent advertisements of that attribute. 🙈

If link attributes are advertised with zero-length Application Identifier Bit Masks for both standard and user-defined applications, then any standard application and/or any user-defined application is permitted to use that set of link attributes. If support for a new application is introduced on any node in a network in the presence of such advertisements, these advertisements are permitted to be used by the new application. If that's not what's intended, the existing advertisements MUST be readvertised with an explicit set of applications specified before a new application is introduced. 😭

An application-specific advertisement (an Application Identifier Bit Mask with a matching Application Identifier Bit set) for an attribute MUST always be preferred over the advertisement of the same attribute with zero-length Application Identifier Bit Masks for both standard and user-defined applications on the same link.主 priority, bestie 👑

This document defines the initial set of link attributes that MUST use the ASLA sub-TLV if they're advertised in the OSPFv2 Extended Link TLV or in the OSPFv3 Router-Link TLV. Documents that define new link attributes MUST state whether the new attributes support application-specific values and, as such, are advertised in an ASLA sub-TLV. The standard link attributes that are advertised in ASLA sub-TLVs are:

Shared Risk Link Group [RFC4203]
Unidirectional Link Delay [RFC7471]
Min/Max Unidirectional Link Delay [RFC7471]
Unidirectional Delay Variation [RFC7471]
Unidirectional Link Loss [RFC7471]
Unidirectional Residual Bandwidth [RFC7471]
Unidirectional Available Bandwidth [RFC7471]
Unidirectional Utilized Bandwidth [RFC7471]
Administrative Group [RFC3630]
Extended Administrative Group [RFC7308]
TE Metric [RFC3630]

6. Reused TE Link Attributes 🌸

this section explains the use case and points out the codepoints (Section 14) from the "OSPFv2 Extended Link TLV Sub-TLVs" registry and the "OSPFv3 Extended-LSA Sub-TLVs" registry for some of the link attributes that were originally defined for RSVP-TE or GMPLS. 🧠

6.1. Shared Risk Link Group (SRLG) 🔥

The SRLG of a link can be used in OSPF-calculated IPFRR (IP Fast Reroute) [RFC5714] to compute a backup path that doesn't share any SRLG group with the protected link. 🛡️

To advertise the SRLG of the link in the OSPFv2 Extended Link TLV, the same format for the sub-TLV defined in Section 1.3 of [RFC4203] is used, with TLV type 11. Similarly, to advertise the SRLG in the OSPFv3 Router-Link TLV, TLV type 12 is used. 💅

6.2. Extended Metrics 📈✨

okay so [RFC3630] defines several link bandwidth types 🦋. Then [RFC7471] comes in with extended link metrics based on bandwidth, delay, and loss characteristics 💅. All of these can be used to compute primary and backup paths within an OSPF area, so you can cover requirements for bandwidth, delay (nominal or worst case), or loss 🔥

To advertise extended link metrics in the OSPFv2 Extended Link TLV, you reuse the same format for the sub-TLVs defined in [RFC7471], just with these TLV types:

12:  Unidirectional Link Delay
13:  Min/Max Unidirectional Link Delay
14:  Unidirectional Delay Variation
15:  Unidirectional Link Loss
16:  Unidirectional Residual Bandwidth
17:  Unidirectional Available Bandwidth
18:  Unidirectional Utilized Bandwidth

To advertise extended link metrics in the Router-Link TLV inside the OSPFv3 E-Router-LSA, it's the same format for the sub-TLVs defined in [RFC7471], but the numbers shift up by one 🌸

13:  Unidirectional Link Delay
14:  Min/Max Unidirectional Link Delay
15:  Unidirectional Delay Variation
16:  Unidirectional Link Loss
17:  Unidirectional Residual Bandwidth
18:  Unidirectional Available Bandwidth
19:  Unidirectional Utilized Bandwidth

6.3. Administrative Group 🎀

[RFC3630] and [RFC7308] define the Administrative Group and Extended Administrative Group sub-TLVs, respectively 🧚

To advertise the Administrative Group and Extended Administrative Group in the OSPFv2 Extended Link TLV, the same format for the sub-TLVs defined in [RFC3630] and [RFC7308] is used, with these TLV types:

19:  Administrative Group
20:  Extended Administrative Group

To advertise the Administrative Group and Extended Administrative Group in the OSPFv3 Router-Link TLV, the same format for the sub-TLVs defined in [RFC3630] and [RFC7308] is used, with these TLV types:

20:  Administrative Group
21:  Extended Administrative Group

6.4. Traffic Engineering Metric 💜

[RFC3630] defines the Traffic Engineering Metric, and it's literally iconic 👑

To advertise the Traffic Engineering Metric in the OSPFv2 Extended Link TLV, the same format for the sub-TLV defined in Section 2.5.5 of [RFC3630] is used with TLV type 22. Similarly, for OSPFv3 to advertise the Traffic Engineering Metric in the OSPFv3 Router-Link TLV, TLV type 22 is used 🦋

7. Maximum Link Bandwidth 🌈

Maximum link bandwidth is an application-independent attribute of the link, defined in [RFC3630] 🔥 Because it's application-independent, it MUST NOT be advertised in the ASLA sub-TLV 🙈 Instead, it MAY be advertised as a sub-TLV of the Extended Link TLV in the Extended Link Opaque LSA in OSPFv2 [RFC7684], or as a sub-TLV of the Router-Link TLV in the E-Router-LSA Router-Link TLV in OSPFv3 [RFC8362] 💅

To advertise the maximum link bandwidth in the OSPFv2 Extended Link TLV, the same format for the sub-TLV defined in [RFC3630] is used with TLV type 23.

To advertise the maximum link bandwidth in the OSPFv3 Router-Link TLV, the same format for the sub-TLV defined in [RFC3630] is used with TLV type 23.

8. Considerations for Extended TE Metrics 🧠

[RFC7471] defines a number of dynamic performance metrics associated with a link. It's conceivable that such metrics could be measured specifically for traffic tied to one application ✨ So this document supports advertising these link attributes for a given application. However, in practice it may well be more practical to have these metrics reflect the performance of all traffic on the link, regardless of application 🫶 In that case, advertisements for these attributes can be associated with all of the applications using that link. You can do this either by explicitly listing the applications in the Application Identifier Bit Mask, or by using a zero-length Application Identifier Bit Mask 🍓

9. Local Interface IPv6 Address Sub-TLV 🦋

The Local Interface IPv6 Address sub-TLV is an application-independent attribute of the link, defined in [RFC5329]. Because it's application-independent, it MUST NOT be advertised in the ASLA sub-TLV 😭 Instead, it MAY be advertised as a sub-TLV of the Router-Link TLV inside the OSPFv3 E-Router-LSA [RFC8362].

To advertise the Local Interface IPv6 Address sub-TLV in the OSPFv3 Router-Link TLV, the same format for the sub-TLV defined in [RFC5329] is used with TLV type 24.

10. Remote Interface IPv6 Address Sub-TLV 🌸

The Remote Interface IPv6 Address sub-TLV is an application-independent attribute of the link, defined in [RFC5329]. Because it's application-independent, it MUST NOT be advertised in the ASLA sub-TLV 💀 Instead, it MAY be advertised as a sub-TLV of the Router-Link TLV inside the OSPFv3 E-Router-LSA [RFC8362].

To advertise the Remote Interface IPv6 Address sub-TLV in the OSPFv3 Router-Link TLV, the same format for the sub-TLV defined in [RFC5329] is used with TLV type 25.

11. Attribute Advertisements and Enablement 🔑

This document defines extensions to support advertising application-specific link attributes ✨

There are applications where enablement on the link matters. For example, with RSVP-TE, you need to make sure RSVP is enabled on the link before you send an RSVP-TE signaling message over it 🚦

There are also applications where enabling the application on the link is irrelevant, and has nothing to do with the fact that some link attributes are advertised for it. LFA is an example of this 🙃

Whether the presence of link attribute advertisements for a given application indicates that the application is enabled on that link depends on the application. Similarly, whether the absence of link attribute advertisements indicates that the application is not enabled also depends on the application 🤔

For RSVP-TE, advertising application-specific link attributes has no implication of RSVP-TE being enabled on that link. RSVP-TE enablement is derived solely from the information carried in the OSPFv2 TE Opaque LSA [RFC3630] and the OSPFv3 Intra-Area-TE-LSA [RFC5329] 💜

For SR Policy, advertising application-specific link attributes does not indicate enablement of SR Policy. The advertisements are only used to support constraints that may be applied when specifying an explicit path. SR Policy is implicitly enabled on all links that are part of the SR-enabled topology, whether or not any link attribute advertisements exist 🧚

For LFA, advertising application-specific link attributes does not indicate enablement of LFA on that link. Enablement is controlled by local configuration ⚙️

In the future, if additional standard applications are defined to use this mechanism, the specification defining that use MUST define the relationship between application-specific link attribute advertisements and enablement for that application 📜

This document allows advertising application-specific link attributes with no application identifiers, meaning both the Standard Application Identifier Bit Mask and the User-Defined Application Identifier Bit Mask are absent (see Section 5). This supports using the link attribute with any application 🌈 But if an application uses link attribute advertisements to infer enablement on that link (RSVP-TE, for example), then the absence of the application identifier leaves it ambiguous whether that application is enabled on such a link. Keep this in mind whenever you use the "any application" encoding 👀

12. Deployment Considerations 🎀

12.1. Use of Legacy RSVP-TE LSA Advertisements 🕰️

Bit identifiers for standard applications are defined in Section 5. Every identifier defined in this document is tied to applications that were already deployed in some networks before this document was written, so those applications were deployed using the RSVP-TE LSA advertisements. The standard applications defined here may continue to use RSVP-TE LSA advertisements for a given link, so long as at least one of the following conditions is true:

The application is RSVP-TE.
The application is SR Policy or LFA, and RSVP-TE is not deployed anywhere in the network.
The application is SR Policy or LFA, RSVP-TE is deployed in the network, and both the set of links on which SR Policy and/or LFA advertisements are required and the attribute values used by SR Policy and/or LFA on all such links are fully congruent with the links and attribute values used by RSVP-TE.

Under the conditions above, implementations that support the extensions in this document can choose between RSVP-TE LSA advertisements or application-specific advertisements to support SR Policy and/or LFA 🔀 This will require implementations to provide controls specifying which types of advertisements are sent and processed on receipt for these applications. More on the associated issues in Section 12.2 📚

New applications that future documents define to use the advertisements in this document MUST NOT make use of RSVP-TE LSA advertisements 🚫 This keeps deployment simple, since there's no need to support multiple ways of advertising attributes for the new applications 💅

12.2. Interoperability, Backwards Compatibility, and Migration Concerns 🔄

Existing deployments of RSVP-TE, SR Policy, and/or LFA use the legacy advertisements listed in Section 3. Routers that don't support the extensions in this document will only process legacy advertisements, and they're likely to infer that RSVP-TE is enabled on links where legacy advertisements exist 🫣 Deployments using legacy advertisements are expected to stick around for a significant period of time. So deployments using the extensions in this document, in the presence of routers that don't support them, need to interoperate with the legacy advertisements sent by those legacy routers 🤝 The following subsections discuss interoperability and backwards-compatibility concerns for a number of deployment scenarios.

12.2.1. Multiple Applications: Common Attributes with RSVP-TE 🧩

When multiple applications use a given link, one of them is RSVP-TE, and all link attributes for that link are common to every application using it, interoperability is achieved by using legacy advertisements for RSVP-TE. Attributes for applications other than RSVP-TE MUST be advertised using application-specific advertisements 📣 This results in duplicate advertisements for those attributes 👯

12.2.2. Multiple Applications: Some Attributes Not Shared with RSVP-TE 🌗

When one or more applications other than RSVP-TE use a given link, and one or more link attribute values are not shared with RSVP-TE, interoperability is achieved by using legacy advertisements for RSVP-TE. Attributes for applications other than RSVP-TE MUST be advertised using application-specific advertisements 🎯 When some link attributes are shared with RSVP-TE, this requires duplicate advertisements for those attributes 🥹

12.2.3. Interoperability with Legacy Routers ✨

okay so routers that don't support the extensions in this doc will only send and receive the legacy link attribute advertisements, no cap 🫠. That means as long as there's even ONE legacy router in the network with any of these applications turned on, every router MUST keep advertising link attributes the old way 🫶.

Also, the link attribute values for the apps legacy routers support (RSVP-TE, SR Policy, and/or LFA) are always shared, bc legacy routers literally have no way to advertise or process app-specific values 💀. Once every legacy router has been upgraded, you can move from the legacy ads to the app-specific ones in these steps 🦋:

Send the new app-specific advertisements while still advertising with the legacy one (so everything gets duplicated for a sec 👯). Receiving routers keep using the legacy advertisements.
Turn on the use of the app-specific advertisements on all routers 🔥.
Keep the legacy advertisements if you still need them for RSVP-TE purposes 🎀.

Once the migration is done, it becomes possible to advertise incongruent values per application on a given link 💜. Lowkey iconic.

Any document that defines a new application using the app-specific advertisements from this doc MUST talk about the interoperability and backwards-compatibility issues that could pop up when routers that don't support that new application are around 📝. Don't skip this, bestie 🙈.

12.2.4. Use of Application-Specific Advertisements for RSVP-TE 🌸

This doc supports RSVP-TE as one of the supported applications, periodt ✨. That said, it is RECOMMENDED to advertise all link attributes for RSVP-TE in the existing OSPFv2 TE Opaque LSA [RFC3630] and OSPFv3 Intra-Area-TE-LSA [RFC5329] to keep backwards compatibility 🫶. Eventually RSVP-TE can use the app-specific advertisements for newly defined link attributes that are defined as app specific 🧚.

Link attributes that aren't allowed in the ASLA sub-TLV, like maximum reservable link bandwidth and unreserved bandwidth, MUST use the OSPFv2 TE Opaque LSA [RFC3630] and OSPFv3 Intra-Area-TE-LSA [RFC5329], and they MUST NOT be advertised in the ASLA sub-TLV 🚫 (so don't even try, bestie 💅).

13. Security Considerations 🔐

Okay the existing security extensions from [RFC2328], [RFC5340], and [RFC8362] all apply to the extensions in this doc 🛡️. OSPF is meant to live in a single administrative domain, BUT there can be deployments where sketchy attackers have access to one or more networks in the OSPF routing domain 👀. In those deployments, stronger authentication mechanisms like the ones in [RFC5709], [RFC7474], [RFC4552], or [RFC7166] SHOULD be used 🔒. Do not let the bad guys in, fr fr.

Implementations must ensure that if any of the TLVs and sub-TLVs defined in this doc are malformed, the malformed ones get detected and don't create a vulnerability that lets attackers crash the OSPF router or routing process 😭💀. Receiving a malformed TLV or sub-TLV SHOULD be counted and/or logged for further analysis 📊. And logging malformed TLVs and sub-TLVs SHOULD be rate-limited so a denial-of-service (DoS) attack (distributed or otherwise) can't overload the OSPF control plane 🚨. This is serious, not a vibe, okay?

This doc defines a new way to advertise link attributes 🦋. Messing with the info defined here may affect applications that use it, including traffic engineering, which uses various link attributes for its path computation 🛤️. This is similar in nature to the impacts associated with, for example, [RFC3630] 🤝. Because the advertisements in this doc limit their scope to specific applications, the impact of tampering is similarly limited in scope 💖. Phew, contained 🫧.

14. IANA Considerations 🎀

This spec updates two existing registries 📚:

the "OSPFv2 Extended Link TLV Sub-TLVs" registry
the "OSPFv3 Extended-LSA Sub-TLVs" registry

The new values defined in this doc were allocated using the IETF Review procedure from [RFC8126] 🌈.

14.1. OSPFv2

The "OSPFv2 Extended Link TLV Sub-TLVs" registry [RFC7684] defines sub-TLVs at any level of nesting for OSPFv2 Extended Link TLVs 🧩. IANA assigned the following sub-TLV types from the "OSPFv2 Extended Link TLV Sub-TLVs" registry 💅:

10:  Application-Specific Link Attributes

11:  Shared Risk Link Group

12:  Unidirectional Link Delay

13:  Min/Max Unidirectional Link Delay

14:  Unidirectional Delay Variation

15:  Unidirectional Link Loss

16:  Unidirectional Residual Bandwidth

17:  Unidirectional Available Bandwidth

18:  Unidirectional Utilized Bandwidth

19:  Administrative Group

20:  Extended Administrative Group

22:  TE Metric

23:  Maximum link bandwidth

14.2. OSPFv3

The "OSPFv3 Extended-LSA Sub-TLVs" registry [RFC8362] defines sub-TLVs at any level of nesting for OSPFv3 Extended LSAs 🦋. IANA assigned the following sub-TLV types from the "OSPFv3 Extended-LSA Sub-TLVs" registry 🫶:

11:  Application-Specific Link Attributes

12:  Shared Risk Link Group

13:  Unidirectional Link Delay

14:  Min/Max Unidirectional Link Delay

15:  Unidirectional Delay Variation

16:  Unidirectional Link Loss

17:  Unidirectional Residual Bandwidth

18:  Unidirectional Available Bandwidth

19:  Unidirectional Utilized Bandwidth

20:  Administrative Group

21:  Extended Administrative Group

22:  TE Metric

23:  Maximum link bandwidth

24:  Local Interface IPv6 Address

25:  Remote Interface IPv6 Address

15. References 📖

15.1. 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>.

[RFC2328]  Moy, J., "OSPF Version 2", STD 54, RFC 2328,
           DOI 10.17487/RFC2328, April 1998,
           <https://www.rfc-editor.org/info/rfc2328>.

[RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
           (TE) Extensions to OSPF Version 2", RFC 3630,
           DOI 10.17487/RFC3630, September 2003,
           <https://www.rfc-editor.org/info/rfc3630>.

[RFC4203]  Kompella, K., Ed. and Y. Rekhter, Ed., "OSPF Extensions in
           Support of Generalized Multi-Protocol Label Switching
           (GMPLS)", RFC 4203, DOI 10.17487/RFC4203, October 2005,
           <https://www.rfc-editor.org/info/rfc4203>.

[RFC5329]  Ishiguro, K., Manral, V., Davey, A., and A. Lindem, Ed.,
           "Traffic Engineering Extensions to OSPF Version 3",
           RFC 5329, DOI 10.17487/RFC5329, September 2008,
           <https://www.rfc-editor.org/info/rfc5329>.

[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>.

[RFC7308]  Osborne, E., "Extended Administrative Groups in MPLS
           Traffic Engineering (MPLS-TE)", RFC 7308,
           DOI 10.17487/RFC7308, July 2014,
           <https://www.rfc-editor.org/info/rfc7308>.

[RFC7471]  Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
           Previdi, "OSPF Traffic Engineering (TE) Metric
           Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
           <https://www.rfc-editor.org/info/rfc7471>.

[RFC7684]  Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
           Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
           Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
           2015, <https://www.rfc-editor.org/info/rfc7684>.

[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>.

[RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
           F. Baker, "OSPFv3 Link State Advertisement (LSA)
           Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
           2018, <https://www.rfc-editor.org/info/rfc8362>.

[RFC8919]  Ginsberg, L., Psenak, P., Previdi, S., Henderickx, W., and
           J. Drake, "IS-IS Application-Specific Link Attributes",
           RFC 8919, DOI 10.17487/RFC8919, October 2020,
           <https://www.rfc-editor.org/info/rfc8919>.

15.2. Informative References

[RFC3209]  Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
           and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
           Tunnels", RFC 3209, DOI 10.17487/RFC3209, December 2001,
           <https://www.rfc-editor.org/info/rfc3209>.

[RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
           for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
           <https://www.rfc-editor.org/info/rfc4552>.

[RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
           IP Fast Reroute: Loop-Free Alternates", RFC 5286,
           DOI 10.17487/RFC5286, September 2008,
           <https://www.rfc-editor.org/info/rfc5286>.

[RFC5709]  Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
           Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
           Authentication", RFC 5709, DOI 10.17487/RFC5709, October
           2009, <https://www.rfc-editor.org/info/rfc5709>.

[RFC5714]  Shand, M. and S. Bryant, "IP Fast Reroute Framework",
           RFC 5714, DOI 10.17487/RFC5714, January 2010,
           <https://www.rfc-editor.org/info/rfc5714>.

[RFC7166]  Bhatia, M., Manral, V., and A. Lindem, "Supporting
           Authentication Trailer for OSPFv3", RFC 7166,
           DOI 10.17487/RFC7166, March 2014,
           <https://www.rfc-editor.org/info/rfc7166>.

[RFC7474]  Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
           "Security Extension for OSPFv2 When Using Manual Key
           Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
           <https://www.rfc-editor.org/info/rfc7474>.

[RFC7855]  Previdi, S., Ed., Filsfils, C., Ed., Decraene, B.,
           Litkowski, S., Horneffer, M., and R. Shakir, "Source
           Packet Routing in Networking (SPRING) Problem Statement
           and Requirements", RFC 7855, DOI 10.17487/RFC7855, May
           2016, <https://www.rfc-editor.org/info/rfc7855>.

[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>.

[SEGMENT-ROUTING]
           Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
           P. Mattes, "Segment Routing Policy Architecture", Work in
           Progress, Internet-Draft, draft-ietf-spring-segment-
           routing-policy-08, 8 July 2020,
           <https://tools.ietf.org/html/draft-ietf-spring-segment-
           routing-policy-08>.

Acknowledgments 🙏

Thanks to Chris Bowers for his review and comments 💕.

Thanks to Alvaro Retana for his detailed review and comments 🫶.

Contributors 🌟

The following people contributed to the content of this document and should be considered as coauthors 👯‍♀️:

Acee Lindem
Cisco Systems
301 Midenhall Way
Cary, NC 27513
United States of America

Email: acee@cisco.com


Ketan Talaulikar
Cisco Systems, Inc.
India

Email: ketant@cisco.com


Hannes Gredler
RtBrick Inc.
Austria

Email: hannes@rtbrick.com

Authors' Addresses ✨

okay bestie, here are the humans who made this whole thing happen 🫶 these are the people you'd email if something in the spec makes you cry 😭

Peter Psenak (editor) 💖 is our editor and the one who kept everything organized. Here's where to find him 🦋

Peter Psenak (editor)
Cisco Systems
Eurovea Centre, Central 3
Pribinova Street 10
81109 Bratislava
Slovakia

Email: ppsenak@cisco.com

Les Ginsberg 💜 is also at Cisco, so you know he's serious 💅

Les Ginsberg
Cisco Systems
821 Alder Drive
Milpitas, CA 95035
United States of America

Email: ginsberg@cisco.com

Wim Henderickx 🌸 is at Nokia, and his address is written exactly as the original has it, typo and all 🙈

Wim Henderickx
Nokia
Copernicuslaan 50
2018 94089 Antwerp
Belgium

Email: wim.henderickx@nokia.com

Jeff Tantsura 🍓 is at Apstra. This is the one entry with no street address, just the country, so no cap, it's a little mysterious 🧚

Jeff Tantsura
Apstra
United States of America

Email: jefftant.ietf@gmail.com

Last but definitely not least, John Drake 🎀 is at Juniper Networks, and he's giving very "Sunnyvale and proud" energy ⭐

John Drake
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, California 94089
United States of America

Email: jdrake@juniper.net

That's the whole squad, periodt 🌈👑

📦 where this page comes from

ietf: rfc8920 2020-10
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