RFC 9455 BEST CURRENT PRACTICE RPKI · ROUTING · BEST PRACTICE
Single-prefix ROAs: Avoiding Route Origin Authorizations (ROAs) Containing Multiple IP Prefixes
Why each RPKI route authorization should cover one IP prefix, so one problem does not take down the rest.
RFC EDITOR
Yan, Z., Bush, R., Geng, G., de Kock, T., and J. Yao, "Avoiding Route Origin Authorizations (ROAs) Containing Multiple IP Prefixes", BCP 238, RFC 9455, DOI 10.17487/RFC9455, August 2023, <https://www.rfc-editor.org/info/rfc9455>.
BIBTEX
@misc{rfc9455,
series = {Request for Comments},
number = 9455,
howpublished = {RFC 9455},
publisher = {RFC Editor},
doi = {10.17487/RFC9455},
url = {https://www.rfc-editor.org/info/rfc9455},
author = {Z. Yan and R. Bush and G. Geng and T. de Kock and J. Yao},
title = {{Avoiding Route Origin Authorizations (ROAs) Containing Multiple IP Prefixes}},
pagetotal = 6,
year = 2023,
month = aug,
} RFC text
Contents
Internet Engineering Task Force (IETF) Z. Yan
Request for Comments: 9455 CNNIC
BCP: 238 R. Bush
Category: Best Current Practice IIJ Research Lab & Arrcus, Inc.
ISSN: 2070-1721 G. Geng
Jinan University
T. de Kock
RIPE NCC
J. Yao
CNNIC
August 2023
Avoiding Route Origin Authorizations (ROAs) Containing Multiple IP
Prefixes
Abstract
When using the Resource Public Key Infrastructure (RPKI), address
space holders need to issue Route Origin Authorization (ROA)
object(s) to authorize one or more Autonomous Systems (ASes) to
originate BGP routes to IP address prefix(es). This memo discusses
operational problems that may arise from ROAs containing multiple IP
prefixes and recommends that each ROA contain a single IP prefix.
Status of This Memo
This memo documents an Internet Best Current Practice.
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
BCPs 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/rfc9455.
Copyright Notice
Copyright (c) 2023 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) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
to this document. Code Components extracted from this document must
include Revised BSD License text as described in Section 4.e of the
Trust Legal Provisions and are provided without warranty as described
in the Revised BSD License.
Table of Contents
1. Introduction
2. Terminology
3. Problem Statement
4. Recommendations
5. Security Considerations
6. IANA Considerations
7. Normative References
Acknowledgements
Authors' Addresses
1. Introduction
In the RPKI, a ROA, which is a digitally signed object, identifies
that a single AS has been authorized by the address space holder to
originate BGP routes to one or more IP prefixes within the related
address space [RFC6482].
Each ROA contains an asID field and an ipAddrBlocks field. The asID
field contains a single AS number that is authorized to originate
routes to the given IP address prefix(es). The ipAddrBlocks field
contains one or more IP address prefixes to which the AS is
authorized to originate the routes.
If the address space holder needs to authorize more than one AS to
advertise the same set of IP prefixes, multiple ROAs must be issued
(one for each AS number [RFC6480]). Prior to this document, there
was no guidance recommending the issuance of a separate ROA for each
IP prefix or a single ROA containing multiple IP prefixes.
2. Terminology
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. Problem Statement
An address space holder can issue a separate ROA for each of its
routing announcements. Alternatively, for a given asID, it can issue
a single ROA for multiple routing announcements, or even for all of
its routing announcements. Since a given ROA is either valid or
invalid, the routing announcements for which that ROA was issued will
"share fate" when it comes to RPKI validation. Currently, no
existing RFCs provide recommendations about what kinds of ROAs to
issue: one per prefix or one for multiple routing announcements. The
problem of fate-sharing was not discussed or addressed.
In the RPKI trust chain, the Certification Authority (CA) certificate
issued by a parent CA to a delegatee of some resources may be revoked
by the parent at any time, which would result in changes to resources
specified in the certificate extensions defined in [RFC3779]. Any
ROA object that includes resources that are a) no longer entirely
contained in the new CA certificate or b) contained in a new CA
certificate that has not yet been discovered by Relying Party (RP)
software will be rejected as invalid. Since ROA invalidity affects
all routes specified in that ROA, unchanged resources with associated
routes via that asID cannot be separated from those affected by the
change in CA certificate validity. They will fall under this invalid
ROA even though there was no intent to change their validity. Had
these resources been in a separate ROA, there would be no change to
the issuing CA certificate and therefore no subsequent invalidity.
CAs have to carefully coordinate ROA updates with updates to a
resource certificate. This process may be automated if a single
entity manages both the parent CA and the CA issuing the ROAs
(Scenario D in [RFC8211], Section 3.4). However, in other deployment
scenarios, this coordination becomes more complex.
As there is a single expiration time for the entire ROA, expiration
will affect all prefixes in the ROA. Thus, changes to the ROA for
any of the prefixes must be synchronized with changes to other
prefixes, especially when authorization for a prefix is time bounded.
Had these prefixes been in separately issued ROAs, the validity
interval would be unique to each ROA, and invalidity would only be
affected by reissuance of the specific issuing parent CA certificate.
A prefix could be allowed to originate from an AS only for a specific
period of time, for example, if the IP prefix was leased out
temporarily. If a ROA with multiple IP prefixes was used, this would
be more difficult to manage, and potentially be more error-prone.
Similarly, more complex routing may require changes in asID or routes
for a subset of prefixes. Reissuance of a ROA might result in
changes to the validity of previously received BGP routes covered by
the ROA's prefixes. There will be no change to the validity of
unaffected routes if a) the time-limited resources are in separate
ROAs, or b) for more complex routing, each change in asID or a change
in routes for a given prefix is reflected in a change to a discrete
ROA.
The use of ROA with a single IP prefix can minimize these side
effects. It avoids fate-sharing irrespective of the cause, where the
parent CA issuing each ROA remains valid and where each ROA itself
remains valid.
4. Recommendations
Unless the CA has good reasons to the contrary, an issued ROA SHOULD
contain a single IP prefix.
5. Security Considerations
Issuing separate ROAs for independent IP prefixes may increase the
file-fetch burden on the RP during validation.
6. IANA Considerations
This document has no IANA actions.
7. 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>.
[RFC3779] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779,
DOI 10.17487/RFC3779, June 2004,
<https://www.rfc-editor.org/info/rfc3779>.
[RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, DOI 10.17487/RFC6480,
February 2012, <https://www.rfc-editor.org/info/rfc6480>.
[RFC6482] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
Origin Authorizations (ROAs)", RFC 6482,
DOI 10.17487/RFC6482, February 2012,
<https://www.rfc-editor.org/info/rfc6482>.
[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>.
[RFC8211] Kent, S. and D. Ma, "Adverse Actions by a Certification
Authority (CA) or Repository Manager in the Resource
Public Key Infrastructure (RPKI)", RFC 8211,
DOI 10.17487/RFC8211, September 2017,
<https://www.rfc-editor.org/info/rfc8211>.
Acknowledgements
The authors wish to thank the following people for their reviews and
contributions to this document: George Michaelson, Tim Bruijnzeels,
Job Snijders, Di Ma, Geoff Huston, Tom Harrison, Rob Austein, Stephen
Kent, Christopher Morrow, Russ Housley, Ching-Heng Ku, Keyur Patel,
Cuiling Zhang, and Kejun Dong. Thanks are also due to Sean Turner
for the Security Area Directorate review.
This work was supported by the Beijing Nova Program of Science and
Technology under grant Z191100001119113.
Authors' Addresses
Zhiwei Yan
CNNIC
No.4 South 4th Street, Zhongguancun
Beijing
100190
China
Email: yanzhiwei@cnnic.cn
Randy Bush
IIJ Research Lab & Arrcus, Inc.
5147 Crystal Springs
Bainbridge Island, Washington 98110
United States of America
Email: randy@psg.com
Guanggang Geng
Jinan University
No.601, West Huangpu Avenue
Guangzhou
510632
China
Email: gggeng@jnu.edu.cn
Ties de Kock
RIPE NCC
Stationsplein 11
Amsterdam
Netherlands
Email: tdekock@ripe.net
Jiankang Yao
CNNIC
No.4 South 4th Street, Zhongguancun
Beijing
100190
China
Email: yaojk@cnnic.cn
AI ELI5
On this page
PROBLEMA ROA with several IP prefixes is either valid or invalid as a whole, so unrelated routes share fate. A certificate change, an expiry or a reissuance for one prefix can invalidate the others.
MECHANISMThe RFC recommends that, unless the CA has good reasons to the contrary, an issued ROA SHOULD contain a single IP prefix.
THE TRADE-OFFSingle-prefix ROAs avoid fate-sharing, at the cost of more files for relying parties to fetch.
§1What a ROA Contains
In the RPKI, a ROA is a digitally signed object. It says that a single AS has been authorized by the address space holder to originate BGP routes to one or more IP prefixes within that address space (RFC 6482).
Each ROA has an asID field, holding one AS number, and an ipAddrBlocks field, holding one or more prefixes. To authorize more than one AS for the same prefixes, the holder must issue one ROA per AS number (RFC 6480).
Before this document there was no guidance on whether to issue a separate ROA for each prefix or one ROA containing several.
A ROA is a signed note saying which network may announce which addresses. One note can list one address block or many, and nobody had said which is better.
§3The Fate-Sharing Problem
A holder can issue a ROA per routing announcement, or one ROA for several announcements, or even for all of them under a given asID. A ROA is either valid or invalid, so every announcement it covers shares fate in RPKI validation. The RFC notes that no existing RFC discussed this.
The text gives three concrete ways this hurts.
- A parent CA can revoke a delegated certificate at any time, changing its resources. Any ROA with resources no longer entirely inside the new certificate, or inside a certificate the relying party has not yet discovered, is rejected. Unchanged prefixes in that ROA fall with it.
- A ROA has a single expiration time, so it affects all its prefixes. Changes for one prefix must be synchronized with the others.
- If a prefix is authorized only for a period, for example when leased out temporarily, or routing changes for a subset of prefixes, reissuing a multi-prefix ROA is harder and more error-prone. It can change the validity of previously received BGP routes it covers.
Imagine one ticket that covers five rides. If the ticket expires or tears, you lose all five rides, even if only one ride had a problem.
§3Coordination Burden on CAs
CAs have to carefully coordinate ROA updates with updates to a resource certificate. This can be automated when a single entity manages both the parent CA and the CA issuing the ROAs (Scenario D in RFC 8211, Section 3.4). In other deployment scenarios the coordination becomes more complex.
With separate ROAs, each ROA has its own validity interval. Invalidity is then affected only by reissuance of the specific issuing parent CA certificate.
Keeping many things on one form means everyone must agree before any change. Separate forms let each be changed on its own schedule.
§4The Recommendation
The recommendation is one sentence: unless the CA has good reasons to the contrary, an issued ROA SHOULD contain a single IP prefix.
Using a ROA with a single prefix minimizes the side effects above. It avoids fate-sharing whatever the cause, provided the parent CA issuing each ROA remains valid and each ROA itself remains valid. Because it is a SHOULD, a CA with a good reason can still issue multi-prefix ROAs.
The document is a Best Current Practice (BCP 238) and defines no new protocol elements.
The advice is simple: one note for each address block, unless you have a good reason not to.
| Concern | Single-prefix ROAs | Multi-prefix ROA |
|---|---|---|
| Fate-sharing THIS RFC | Avoided | All prefixes share one valid or invalid result |
| Expiration time | One per ROA | Single time for all prefixes |
| Relying party file fetches | May increase | Fewer files |
§5Security and IANA Considerations
The only cost the RFC names is that issuing separate ROAs for independent prefixes may increase the file-fetch burden on the relying party during validation. There are no IANA actions.
More small notes means the checker has more papers to pick up and read.
§6References
[RFC3779]RFC 3779Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP Addresses and AS Identifiers", RFC 3779, June 2004.June 2004[RFC6480]RFC 6480Lepinski, M. and S. Kent, "An Infrastructure to Support Secure Internet Routing", RFC 6480, February 2012.February 2012[RFC6482]RFC 6482Lepinski, M., Kent, S., and D. Kong, "A Profile for Route Origin Authorizations (ROAs)", RFC 6482, February 2012.February 2012[RFC8211]RFC 8211Kent, S. and D. Ma, "Adverse Actions by a Certification Authority (CA) or Repository Manager in the Resource Public Key Infrastructure (RPKI)", RFC 8211, September 2017.September 2017