Internet Engineering Task Force (IETF) R. Bush
Request for Comments: 7115 Internet Initiative Japan
BCP: 185 January 2014
Category: Best Current Practice
ISSN: 2070-1721
Origin Validation Operation
Based on the Resource Public Key Infrastructure (RPKI)
Abstract
Deployment of BGP origin validation that is based on the Resource
Public Key Infrastructure (RPKI) has many operational considerations.
This document attempts to collect and present those that are most
critical. It is expected to evolve as RPKI-based origin validation
continues to be deployed and the dynamics are better understood.
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 has been approved for publication by the Internet
Engineering Steering Group (IESG). Further information on BCPs is
available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7115.
Copyright Notice
Copyright (c) 2014 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 2 3
2. Suggested Reading . . . . . . . . . . . . . . . . . . . . . . 3
3. RPKI Distribution and Maintenance . . . . . . . . . . . . . . 3
4. Within a Network . . . . . . . . . . . . . . . . . . . . . . 6
5. Routing Policy . . . . . . . . . . . . . . . . . . . . . . . 6
6. Notes and Recommendations . . . . . . . . . . . . . . . . . . 8
7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
9.1. Normative References . . . . . . . . . . . . . . . . . . 10
9.2. Informative References . . . . . . . . . . . . . . . . . 10
1. Introduction
RPKI-based origin validation relies on widespread deployment of the
Resource Public Key Infrastructure (RPKI) [RFC6480]. How the RPKI is
distributed and maintained globally is a serious concern from many
aspects.
While the global RPKI is in the early stages of deployment, there is
no single root trust anchor, initial testing is being done by the
Regional Internet Registries (RIRs), and there are technical
testbeds. It is thought that origin validation based on the RPKI
will continue to be deployed incrementally over the next few years.
It is assumed that eventually there must be a single root trust
anchor for the public address space, see [iab].
Origin validation needs to be done only by an AS's border routers and
is designed so that it can be used to protect announcements that are
originated by any network participating in Internet BGP routing:
large providers, upstream and downstream routers, and by edge
networks (e.g., small stub or enterprise networks).
Origin validation has been designed to be deployed on current routers
without significant hardware upgrades. It should be used in border
routers by operators from large backbones to small stub/enterprise/
edge networks.
RPKI-based origin validation has been designed so that, with prudent
local routing policies, there is little risk that what is seen as
today's normal Internet routing is threatened by imprudent deployment
of the global RPKI; see Section 5.
1.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
be interpreted as described in RFC 2119 [RFC2119] only when they
appear in all upper case. They may also appear in lower or mixed
case as English words, without normative meaning.
2. Suggested Reading
It is assumed that the reader understands BGP [RFC4271], the RPKI
[RFC6480], the RPKI Repository Structure [RFC6481], Route Origin
Authorizations (ROAs) [RFC6482], the RPKI to Router Protocol
[RFC6810], RPKI-based Prefix Validation [RFC6811], and Ghostbusters
Records [RFC6493].
3. RPKI Distribution and Maintenance
The RPKI is a distributed database containing certificates,
Certificate Revocation Lists (CRLs), manifests, ROAs, and
Ghostbusters Records as described in [RFC6481]. Policies and
considerations for RPKI object generation and maintenance are
discussed elsewhere.
The RPKI repository design [RFC6481] anticipated a hierarchic
organization of repositories, as this seriously improves the
performance of relying parties that gather data over a non-hierarchic
organization. Publishing parties MUST implement hierarchic directory
structures.
A local relying party's valid cache containing all RPKI data may be
gathered from the global distributed database using the rsync
protocol [RFC5781] and a validation tool such as rcynic [rcynic].
A validated cache contains all RPKI objects that the RP has verified
to be valid according to the rules for validation RPKI certificates
and signed objects; see [RFC6487] and [RFC6488]. Entities that trust
the cache can use these RPKI objects without further validation.
Validated caches may also be created and maintained from other
validated caches. Network operators SHOULD take maximum advantage of
this feature to minimize load on the global distributed RPKI
database. Of course, the recipient relying parties should re-
validate the data.
As Trust Anchor Locators (TALs) [RFC6490] are critical to the RPKI
trust model, operators should be very careful in their initial
selection and vigilant in their maintenance.
Timing of inter-cache synchronization, and synchronization between
caches and the global RPKI, is outside the scope of this document,
and depends on things such as how often routers feed from the caches,
how often the operator feels the global RPKI changes significantly,
etc.
As inter-cache synchronization within an operator's network does not
impact global RPKI resources, an operator may choose to synchronize
quite frequently.
To relieve routers of the load of performing certificate validation,
cryptographic operations, etc., the RPKI-Router protocol [RFC6810]
does not provide object-based security to the router. That is, the
router cannot validate the data cryptographically from a well-known
trust anchor. The router trusts the cache to provide correct data
and relies on transport-based security for the data received from the
cache. Therefore, the authenticity and integrity of the data from
the cache should be well protected; see Section 7 of [RFC6810].
As RPKI-based origin validation relies on the availability of RPKI
data, operators SHOULD locate RPKI caches close to routers that
require these data and services in order to minimize the impact of
likely failures in local routing, intermediate devices, long
circuits, etc. One should also consider trust boundaries, routing
bootstrap reachability, etc.
For example, a router should bootstrap from a cache that is reachable
with minimal reliance on other infrastructure such as DNS or routing
protocols. If a router needs its BGP and/or IGP to converge for the
router to reach a cache, once a cache is reachable, the router will
then have to reevaluate prefixes already learned via BGP. Such
configurations should be avoided if reasonably possible.
If insecure transports are used between an operator's cache and their
router(s), the Transport Security recommendations in [RFC6810] SHOULD
be followed. In particular, operators MUST NOT use insecure
transports between their routers and RPKI caches located in other
Autonomous Systems.
For redundancy, a router should peer with more than one cache at the
same time. Peering with two or more, at least one local and others
remote, is recommended.
If an operator trusts upstreams to carry their traffic, they may also
trust the RPKI data those upstreams cache and SHOULD peer with caches
made available to them by those upstreams. Note that this places an
obligation on those upstreams to maintain fresh and reliable caches
and to make them available to their customers. And, as usual, the
recipient SHOULD re-validate the data.
A transit provider or a network with peers SHOULD validate origins in
announcements made by upstreams, downstreams, and peers. They still
should trust the caches provided by their upstreams.
Before issuing a ROA for a super-block, an operator MUST ensure that
all sub-allocations from that block that are announced by other ASes,
e.g., customers, have correct ROAs in the RPKI. Otherwise, issuing a
ROA for the super-block will cause the announcements of sub-
allocations with no ROAs to be viewed as Invalid; see [RFC6811].
While waiting for all recipients of sub-allocations to register ROAs,
the owner of the super-block may use live BGP data to populate ROAs
as a proxy, and then safely issue a ROA for the super-block.
Use of RPKI-based origin validation removes any need to inject more
specifics into BGP to protect against mis-origination of a less
specific prefix. Having a ROA for the covering prefix will protect
it.
To aid translation of ROAs into efficient search algorithms in
routers, ROAs should be as precise as possible, i.e., match prefixes
as announced in BGP. For example, software and operators SHOULD
avoid use of excessive max length values in ROAs unless they are
operationally necessary.
One advantage of minimal ROA length is that the forged origin attack
does not work for sub-prefixes that are not covered by overly long
max length. For example, if, instead of 10.0.0.0/16-24, one issues
10.0.0.0/16 and 10.0.42.0/24, a forged origin attack cannot succeed
against 10.0.666.0/24. They must attack the whole /16, which is more
likely to be noticed because of its size.
Therefore, ROA generation software MUST use the prefix length as the
max length if the user does not specify a max length.
Operators should be conservative in use of max length in ROAs. For
example, if a prefix will have only a few sub-prefixes announced,
multiple ROAs for the specific announcements should be used as
opposed to one ROA with a long max length.
Operators owning prefix P should issue ROAs for all ASes that may
announce P. If a prefix is legitimately announced by more than one
AS, ROAs for all of the ASes SHOULD be issued so that all are
considered Valid.
In an environment where private address space is announced in
External BGP (eBGP), the operator may have private RPKI objects that
cover these private spaces. This will require a trust anchor created
and owned by that environment; see [LTA-USE].
Operators issuing ROAs may have customers that announce their own
prefixes and ASes into global eBGP, but who do not wish to go though
the work to manage the relevant certificates and ROAs. Operators
SHOULD offer to provision the RPKI data for these customers just as
they provision many other things for them.
An operator using RPKI data MAY choose any polling frequency they
wish for ensuring they have a fresh RPKI cache. However, if they use
RPKI data as an input to operational routing decisions, they SHOULD
ensure local caches inside their AS are synchronized with each other
at least every four to six hours.
Operators should use tools that warn them of any impending ROA or
certificate expiry that could affect the validity of their own data.
Ghostbusters Records [RFC6493] can be used to facilitate contact with
upstream Certification Authorities (CAs) to effect repair.
4. Within a Network
Origin validation need only be done by edge routers in a network,
those which border other networks or ASes.
A validating router will use the result of origin validation to
influence local policy within its network; see Section 5. In
deployment, this policy should fit into the AS's existing policy,
preferences, etc. This allows a network to incrementally deploy
validation-capable border routers.
The operator should be aware that RPKI-based origin validation, as
any other policy change, can cause traffic shifts in their network.
And, as with normal policy shift practice, a prudent operator has
tools and methods to predict, measure, modify, etc.
5. Routing Policy
Origin validation based on the RPKI marks a received announcement as
having an origin that is Valid, NotFound, or Invalid; see [RFC6811].
How this is used in routing should be specified by the operator's
local policy.
Local policy using relative preference is suggested to manage the
uncertainty associated with a system in early deployment; local
policy can be applied to eliminate the threat of unreachability of
prefixes due to ill-advised certification policies and/or incorrect
certification data. For example, until the community feels
comfortable relying on RPKI data, routing on Invalid origin validity,
though at a low preference, MAY occur.
Operators should be aware that accepting Invalid announcements, no
matter how de-preferenced, will often be the equivalent of treating
them as fully Valid. Consider having a ROA for AS 42 for prefix
10.0.0.0/16-24. A BGP announcement for 10.0.666.0/24 from AS 666
would be Invalid. But if policy is not configured to discard it,
then longest-match forwarding will send packets toward AS 666, no
matter the value of local preference.
As origin validation will be rolled out incrementally, coverage will
be incomplete for a long time. Therefore, routing on NotFound
validity state SHOULD be done for a long time. As the transition
moves forward, the number of BGP announcements with validation state
NotFound should decrease. Hence, an operator's policy should not be
overly strict and should prefer Valid announcements; it should attach
a lower preference to, but still use, NotFound announcements, and
drop or give a very low preference to Invalid announcements. Merely
de-preferencing Invalid announcements is ill-advised; see previous
paragraph.
Some providers may choose to set Local-Preference based on the RPKI
validation result. Other providers may not want the RPKI validation
result to be more important than AS_PATH length -- these providers
would need to map the RPKI validation result to some BGP attribute
that is evaluated in BGP's path selection process after the AS_PATH
is evaluated. Routers implementing RPKI-based origin validation MUST
provide such options to operators.
Local-Preference may be used to carry both the validity state of a
prefix along with its traffic engineering (TE) characteristic(s). It
is likely that an operator already using Local-Preference will have
to change policy so they can encode these two separate
characteristics in the same BGP attribute without negative impact or
opening privilege escalation attacks. For example, do not encode
validation state in higher bits than used for TE.
When using a metric that is also influenced by other local policy, an
operator should be careful not to create privilege-upgrade
vulnerabilities. For example, if Local Pref is set depending on
validity state, peer community signaling SHOULD NOT upgrade an
Invalid announcement to Valid or better.
Announcements with Valid origins should be preferred over those with
NotFound or Invalid origins, if Invalid origins are accepted at all.
Announcements with NotFound origins should be preferred over those
with Invalid origins.
Announcements with Invalid origins SHOULD NOT be used, but may be
used to meet special operational needs. In such circumstances, the
announcement should have a lower preference than that given to Valid
or NotFound.
When first deploying origin validation, it may be prudent not to drop
announcements with Invalid origins until inspection of logs, SNMP, or
other data indicates that the correct result would be obtained.
Validity state signaling SHOULD NOT be accepted from a neighbor AS.
The validity state of a received announcement has only local scope
due to issues such as scope of trust, RPKI synchrony, and management
of local trust anchors [LTA-USE].
6. Notes and Recommendations
Like the DNS, the global RPKI presents only a loosely consistent
view, depending on timing, updating, fetching, etc. Thus, one cache
or router may have different data about a particular prefix than
another cache or router. There is no 'fix' for this, it is the
nature of distributed data with distributed caches.
Operators should beware that RPKI caches are loosely synchronized,
even within a single AS. Thus, changes to the validity state of
prefixes could be different within an operator's network. In
addition, there is no guaranteed interval from when an RPKI cache is
updated to when that new information may be pushed or pulled into a
set of routers via this protocol. This may result in sudden shifts
of traffic in the operator's network, until all of the routers in the
AS have reached equilibrium with the validity state of prefixes
reflected in all of the RPKI caches.
It is hoped that testing and deployment will produce advice on cache
loading and timing for relying parties.
There is some uncertainty about the origin AS of aggregates and what,
if any, ROA can be used. The long-range solution to this is the
deprecation of AS_SETs; see [RFC6472].
As reliable access to the global RPKI and an operator's caches (and
possibly other hosts, e.g., DNS root servers) is important, an
operator should take advantage of relying-party tools that report
changes in BGP or RPKI data that would negatively affect validation
of such prefixes.
Operators should be aware that there is a trade-off in placement of
an RPKI repository in address space for which the repository's
content is authoritative. On one hand, an operator will wish to
maximize control over the repository. On the other hand, if there
are reachability problems to the address space, changes in the
repository to correct them may not be easily accessed by others.
Operators who manage certificates should associate RPKI Ghostbusters
Records (see [RFC6493]) with each publication point they control.
These are publication points holding the CRL, ROAs, and other signed
objects issued by the operator, and made available to other ASes in
support of routing on the public Internet.
Routers that perform RPKI-based origin validation must support Four-
octet AS Numbers (see [RFC6793]), as, among other things, it is not
reasonable to generate ROAs for AS 23456.
Software that produces filter lists or other control forms for
routers where the target router does not support Four-octet AS
Numbers (see [RFC6793]) must be prepared to accept four-octet AS
Numbers and generate the appropriate two-octet output.
As a router must evaluate certificates and ROAs that are time
dependent, routers' clocks MUST be correct to a tolerance of
approximately an hour.
Servers should provide time service, such as NTPv4 [RFC5905], to
client routers.
7. Security Considerations
As the BGP origin AS of an update is not signed, origin validation is
open to malicious spoofing. Therefore, RPKI-based origin validation
is expected to deal only with inadvertent mis-advertisement.
Origin validation does not address the problem of AS_PATH validation.
Therefore, paths are open to manipulation, either malicious or
accidental.
As BGP does not ensure that traffic will flow via the paths it
advertises, the data plane may not follow the control plane.
Be aware of the class of privilege escalation issues discussed in
Section 5 above.
8. Acknowledgments
The author wishes to thank Shane Amante, Rob Austein, Steve Bellovin,
Jay Borkenhagen, Wes George, Seiichi Kawamura, Steve Kent, Pradosh
Mohapatra, Chris Morrow, Sandy Murphy, Eric Osterweil, Keyur Patel,
Heather and Jason Schiller, John Scudder, Kotikalapudi Sriram,
Maureen Stillman, and Dave Ward.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC6481] Huston, G., Loomans, R., and G. Michaelson, "A Profile for
Resource Certificate Repository Structure", RFC 6481,
February 2012.
[RFC6482] Lepinski, M., Kent, S., and D. Kong, "A Profile for Route
Origin Authorizations (ROAs)", RFC 6482, February 2012.
[RFC6490] Huston, G., Weiler, S., Michaelson, G., and S. Kent,
"Resource Public Key Infrastructure (RPKI) Trust Anchor
Locator", RFC 6490, February 2012.
[RFC6493] Bush, R., "The Resource Public Key Infrastructure (RPKI)
Ghostbusters Record", RFC 6493, February 2012.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793, December
2012.
[RFC6810] Bush, R. and R. Austein, "The Resource Public Key
Infrastructure (RPKI) to Router Protocol", RFC 6810,
January 2013.
[RFC6811] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
Austein, "BGP Prefix Origin Validation", RFC 6811, January
2013.
9.2. Informative References
[LTA-USE] Bush, R., "RPKI Local Trust Anchor Use Cases", Work in
Progress, September 2013.
[RFC4271] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway
Protocol 4 (BGP-4)", RFC 4271, January 2006.
[RFC5781] Weiler, S., Ward, D., and R. Housley, "The rsync URI
Scheme", RFC 5781, February 2010.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010.
[RFC6472] Kumari, W. and K. Sriram, "Recommendation for Not Using
AS_SET and AS_CONFED_SET in BGP", BCP 172, RFC 6472,
December 2011.
[RFC6480] Lepinski, M. and S. Kent, "An Infrastructure to Support
Secure Internet Routing", RFC 6480, February 2012.
[RFC6487] Huston, G., Michaelson, G., and R. Loomans, "A Profile for
X.509 PKIX Resource Certificates", RFC 6487, February
2012.
[RFC6488] Lepinski, M., Chi, A., and S. Kent, "Signed Object
Template for the Resource Public Key Infrastructure
(RPKI)", RFC 6488, February 2012.
[iab] IAB, "IAB statement on the RPKI", January 2010,
<http://www.iab.org/documents/
correspondence-reports-documents/docs2010/
iab-statement-on-the-rpki/>.
[rcynic] "rcynic RPKI validator", November 2013,
<http://rpki.net/rcynic>.
Author's Address
Randy Bush
Internet Initiative Japan
5147 Crystal Springs
Bainbridge Island, Washington 98110
US
EMail: randy@psg.com