Internet DRAFT - draft-sriram-sidrops-drop-invalid-policy
draft-sriram-sidrops-drop-invalid-policy
SIDROPS Working Group K. Sriram
Internet-Draft O. Borchert
Intended status: Best Current Practice D. Montgomery
Expires: 31 May 2023 USA NIST
27 November 2022
Origin Validation Policy Considerations for Dropping Invalid Routes
draft-sriram-sidrops-drop-invalid-policy-10
Abstract
Deployment of Resource Public Key Infrastructure (RPKI) and Route
Origin Authorizations (ROAs) is expected to occur gradually over
several or many years. During the incremental deployment period,
network operators would wish to have a meaningful policy for dropping
Invalid routes. Their goal is to balance (A) dropping Invalid routes
so hijacked routes can be eliminated, versus (B) tolerance for
missing or erroneously created ROAs for customer prefixes. This
document considers a Drop Invalid if Still Routable (DISR) policy
that is based on these considerations. The key principle of DISR
policy is that an Invalid route can be dropped if a Valid or NotFound
route exists for a subsuming less specific prefix.
Status of This Memo
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Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Drop Invalid if Still Routable (DISR) Policy . . . . . . . . 3
2.1. Motivation for the DISR Policy . . . . . . . . . . . . . 3
3. Algorithm for Implementation of DISR Policy . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. Normative References . . . . . . . . . . . . . . . . . . . . 5
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
Deployment of Resource Public Key Infrastructure (RPKI) [RFC6481] and
Route Origin Authorizations (ROAs) [RFC6482] is expected to occur
gradually over several or many years. ROA-based BGP Origin
Validation (OV) process and the OV states are defined in [RFC6811].
During the incremental deployment period, network operators would
wish to have a meaningful policy for dropping Invalid routes. Their
goal is to balance (A) dropping Invalid routes so hijacked routes can
be eliminated, versus (B) tolerance for missing or erroneously
created ROAs for customer prefixes. This document considers a Drop
Invalid if Still Routable (DISR) policy that is based on these
considerations. The key principle of DISR policy is that an Invalid
route can be dropped if a Valid or NotFound route exists for a
subsuming less specific prefix.
The DISR policy applies in addition to (1) preferring Valid when more
than one route exists for the same prefix, and (2) always including
NotFound routes in the best path selection process. Note that for a
router performing OV, the existence of a NotFound route excludes the
possibility of an alternate Valid or Invalid route for the same
prefix or a subsuming less specific prefix.
This document also provides an algorithm for best path selection
policy that considers Origin Validation (OV) outcome and includes the
DISR policy.
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2. Drop Invalid if Still Routable (DISR) Policy
When BGP origin validation (OV) [RFC6811] is performed on a BGP
route, there are three possible outcomes: (1) Valid, (2) Invalid, or
(3) NotFound. During partial/incremental deployment of RPKI and
ROAs, it is natural to always include Valid and NotFound routes in
the path selection decision process. Note that Valid and NotFound
are mutually exclusive, i.e., at a validating router, there cannot be
two routes for a prefix where one is Valid and the other is NotFound.
Similarly, Invalid and NotFound are also mutually exclusive. If
Invalid routes are always dropped from consideration, then there
would be no tolerance for missing or erroneously created ROAs for
customer prefixes. Then the question arises whether the following
policy should be considered: Drop an Invalid route only if another
Valid or NotFound route exists for a subsuming less specific prefix?
This policy is called Drop Invalid if Still Routable (DISR).
The existence of an AS0 ROA for a prefix means that the prefix or any
more specific prefix subsumed in it are forbidden from routing except
when there exists a different ROA with a normal ASN for the prefix or
the more specific prefix. DISR policy MUST apply the following
exception: If a route is Invalid due to an AS0 ROA, then always drop
the route.
Any routes for 0.0.0.0/0 (IPv4) or ::/0 (IPv6) in the routing table
must be excluded from consideration in the DISR policy. (Author's
note: Think this through with help from the WG.)
2.1. Motivation for the DISR Policy
Consider these scenarios:
Scenario 1: A transit ISP A (AS A) created a ROA for a /22 prefix
they announce. They also announce a /24 prefix (subsumed in the /22)
that is owned by directly-connected customer X (has no AS). But ISP
A neglected to create a ROA for X's /24 prefix. Clearly, the
announcement of X's /24 will be Invalid. ISP A happens to propagate
to neighbors the /22 and the /24.
Scenario 2: Customer X (AS X) announces a /22 prefix only to transit
ISP A and a /24 prefix (subsumed in the /22) only to transit ISP B.
X is attempting to do traffic engineering (TE). X created a ROA for
the /22 but neglected to have ROA coverage for the /24. Clearly, X's
announcement of the /24 will be Invalid. ISP B does not participate
in OV and propagates the Invalid route to its neighbors.
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In each of the above scenarios, DISR policy (applied at routers
elsewhere in the Internet) ensures that traffic for the more specific
(/24) still reaches the correct destination, i.e., customer X (albeit
possibly via a suboptimal / non-TE path). Any actual hijacks of the
/24 prefix would be dropped at all eBGP routers that employ the DISR
policy. Please see [sriram-disr] for analysis of several more
scenarios.
Measurements show that if OV were performed, there are 10,417 Invalid
routes in the global Internet based on analysis of Routeviews/RPKI/
ROA data from February 2018. Of these, 6846 routes are Invalid due
to exceeding the maxlength. 6027 of the 6846 Invalid prefixes are
seen to be routable via alternate Valid or NotFound routes for either
the same prefix (as in the Invalid route) or a subsuming less
specific prefix. Again, 5987 of the 6027 are routes for which the
corresponding Valid or NotFound routes (with the same or subsuming
less specific prefix) have the exact same origin AS as in the Invalid
route in question. These measurements show that Scenarios 1 and 2
described above do occur in significant numbers currently. So, the
data lends support to the efficacy of the DISR policy in terms of
delivering the data traffic to the right destination though not
necessarily via the optimal/TE path. Please see [sriram-disr] for
more detailed results from the Routeviews/RPKI/ROA data measurement
study.
The following is recommended in BCP 185 [RFC7115]: "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." However, as seen by the
above measurement data, there are lapses in following this
recommendation.
Network operators who do not wish to drop Invalid routes outright in
partial deployment SHOULD consider employing the DISR policy. It
helps eliminate actual prefix hijacks, while incentivizing creation
of required ROAs and the adherence to the above recommendation from
BCP 185. The stick used here is the possibility of data traveling
via a suboptimal path, while the more aggressive stick of dropping
all Invalid routes is held in abeyance.
3. Algorithm for Implementation of DISR Policy
An algorithm for implementation of the DISR policy is as follows.
Perform the following steps when a route is received:
1. Perform BGP Origin Validation (OV) [RFC6811] on the routes in the
Adj-RIB-ins.
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2. Apply best path decision process including the results of OV.
Include NotFound routes in the decision process. When there is a
choice, prefer Valid over Invalid routes.
3. Store the selected routes in the Loc-RIB.
4. Apply the DISR policy. Process routes in the order of least
specific to most specific. If a selected route in the Loc-RIB is
Valid/NotFound, then add the route to FIB and Adj-RIB-outs; Else,
if Invalid, then add the route to FIB and Adj-RIB-outs only if
there is no existing Valid/NotFound route in the Loc-RIB for a
subsuming Less Specific prefix.
Additional steps in the algorithm that are performed in reaction to
addition/withdrawal of routes that influence DISR policy decisions
and due to changes in RPKI:
a. When a Valid/NotFound route is added to Loc-RIB, check if there
are any more specific prefixes in the FIB and Adj-RIB-Outs
subsumed by the route prefix; If such more specific prefix route
is Invalid, then remove it from the FIB and Adj-RIB-Outs.
b. When a Valid/NotFound route is withdrawn from Loc-RIB, check if
there are any more specifics prefixes in the Loc-RIB subsumed by
the route prefix; If such more specific prefix route is Invalid,
then add the route to FIB and Adj-RIB-outs.
c. When the router is notified of RPKI state change, then list all
the prefixes effected by it. Rerun route selection decision and
DISR policy for those prefixes.
4. Security Considerations
This document addresses some aspects of best common practices for
origin validation and related BGP policy. The security
considerations provided in RFC 6811 [RFC6811] and BCP 185 [RFC7115]
also apply here.
5. Normative References
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>.
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[RFC6481] Huston, G., Loomans, R., and G. Michaelson, "A Profile for
Resource Certificate Repository Structure", RFC 6481,
DOI 10.17487/RFC6481, February 2012,
<https://www.rfc-editor.org/info/rfc6481>.
[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>.
[RFC6811] Mohapatra, P., Scudder, J., Ward, D., Bush, R., and R.
Austein, "BGP Prefix Origin Validation", RFC 6811,
DOI 10.17487/RFC6811, January 2013,
<https://www.rfc-editor.org/info/rfc6811>.
[RFC7115] Bush, R., "Origin Validation Operation Based on the
Resource Public Key Infrastructure (RPKI)", BCP 185,
RFC 7115, DOI 10.17487/RFC7115, January 2014,
<https://www.rfc-editor.org/info/rfc7115>.
[sriram-disr]
Sriram et al., K., "Origin Validation Policy
Considerations for Dropping Invalid Routes", Presented at
the SIDROPS WG Meeting, IETF-101, London , March 2018,
<https://datatracker.ietf.org/meeting/101/materials/
slides-101-sidrops-origin-validation-policy-
considerations-for-dropping-invalid-routes-00>.
Acknowledgements
The authors wish to thank Sebastian Spies, Saku Ytti, Jeffrey Haas,
Tim Bruijnzeels, Keyur Patel, Warren Kumari, John Scudder, and Jay
Borkenhagen for comments and discussion related to this work. Also,
thanks are due to Lilia Hannachi for her insightful analysis of
global RPKI and BGP data that has been helpful in this work.
Authors' Addresses
Kotikalapudi Sriram
USA National Institute of Standards and Technology
Email: ksriram@nist.gov
Oliver Borchert
USA National Institute of Standards and Technology
Email: oliver.borchert@nist.gov
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Doug Montgomery
USA National Institute of Standards and Technology
Email: dougm@nist.gov
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