Internet DRAFT - draft-azimov-sidrops-aspa-verification
draft-azimov-sidrops-aspa-verification
Network Working Group A. Azimov
Internet-Draft E. Bogomazov
Intended status: Standards Track Qrator Labs
Expires: April 25, 2019 R. Bush
Internet Initiative Japan
K. Patel
Arrcus, Inc.
J. Snijders
NTT
October 22, 2018
Verification of AS_PATH Using the Resource Certificate Public Key
Infrastructure and Autonomous System Provider Authorization
draft-azimov-sidrops-aspa-verification-01
Abstract
This document defines the semantics of an Autonomous System Provider
Authorization object in the Resource Public Key Infrastructure to
verify the AS_PATH attribute of routes advertised in the Border
Gateway Protocol.
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.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
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Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 25, 2019.
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Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Anomaly Propagation . . . . . . . . . . . . . . . . . . . . . 3
3. Autonomous System Provider Authorization . . . . . . . . . . 4
4. Customer-Provider Verification Procedure . . . . . . . . . . 4
5. AS_PATH Verification . . . . . . . . . . . . . . . . . . . . 5
6. Disavowal of Provider Authorizaion . . . . . . . . . . . . . 6
7. Siblings (Complex Relations) . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The Border Gateway Protocol (BGP) was designed with no mechanisms to
validate BGP attributes. Two consequences are BGP Hijacks and BGP
Route Leaks [RFC7908]. BGP extensions are able to partially solve
these problems. For example, ROA-based Origin Validation [RFC6483]
can be used to detect and filter accidental mis-originations, and
[I-D.ymbk-idr-bgp-eotr-policy] can be used to detect accidental route
leaks. While these upgrades to BGP are quite useful, they still rely
on transitive BGP attributes, i.e. AS_PATH, that can be manipulated
by attackers.
BGPSec [RFC8205] was designed to solve the problem of AS_PATH
validation. Unfortunately, strict cryptographic validation brought
unaffordable computational overhead for BGP routers. BGPSec also
proved to be vulnerable to downgrade attacks that can nullify all the
work of AS_PATH signing. As a result, to abuse the AS_PATH or any
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other signed transit attribute, an attacker merely needs to downgrade
to 'old' BGP-4.
An alternative approach was introduced with soBGP
[I-D.white-sobgp-architecture]. Instead of strong cryptographic
AS_PATH validation, it was suggested to create an AS_PATH security
function based on a shared database of ASN adjacencies. While such
an approach has reasonable computational cost, the two side
adjacencies don't provide a way to automate anomaly detection without
high adoption rate - an attacker can easily up a one-way adjacency.
SO-BGP suggested sharing data about adjacencies using additional BGP
messages, which is recursively complex thus significantly increasing
adoption complexity. In addition, the general goal to verify all
AS_PATHs was not achievable given the indirect adjacencies at
internet exchange points.
Instead of the general goal of checking AS_PATH correctness, this
document focuses on solving real-world operational problems -
automatic detection of malicious hijacks and route leaks. To achieve
this goal a new AS_PATH verification procedure is defined which is
able to automatically detect invalid (malformed) AS_PATHs in
announcements that are received from customers and peers. This
procedure uses a shared signed database of customer-to-provider
relationships that is built using a new RPKI object - Autonomous
System Provider Authorization (ASPA). This technique provides
benefits for the participants even in a state of early adoption.
2. Anomaly Propagation
Both route leaks and hijacks have similar effects on ISP operations -
they redirect traffic, resulting in increased latency, packet loss,
or possible MiTM attacks. But the level of risk depends
significantly on the propagation of these BGP anomalies. For
example, a hijack that is propagated only to customers may
concentrate traffic in a particular ISP's customer cone; while if the
anomaly is propagated through peers, upstreams, or reaches Tier-1
networks, thus distributing globally, traffic may be redirected at
the level of entire countries and/or global providers.
The ability to constrain propagation of BGP anomalies to upstreams
and peers, without requiring support from the source of the anomaly
(which is critical if source has malicious intent), should
significantly improve the security of inter-domain routing and solve
the majority of problems.
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3. Autonomous System Provider Authorization
As described in [RFC6480], the RPKI is based on a hierarchy of
resource certificates that are aligned to the Internet Number
Resource allocation structure. Resource certificates are X.509
certificates that conform to the PKIX profile [RFC5280], and to the
extensions for IP addresses and AS identifiers [RFC3779]. A resource
certificate is a binding by an issuer of IP address blocks and
Autonomous System (AS) numbers to the subject of a certificate,
identified by the unique association of the subject's private key
with the public key contained in the resource certificate. The RPKI
is structured so that each current resource certificate matches a
current resource allocation or assignment.
ASPAs are digitally signed objects that bind a selected AFI Provider
AS number to a Customer AS number (in terms of BGP announcements not
business), and are signed by the holder of the Customer AS. An ASPA
attests that a Customer AS holder (CAS) has authorized a particular
Provider AS (PAS) to propagate the Customer's IPv4/IPv6 announcements
onward, e.g. to the Provider's upstream providers or peers. The ASPA
record profile is described in [I-D.azimov-sidrops-aspa-profile].
4. Customer-Provider Verification Procedure
This section describes an abstract procedure that checks that pair of
ASNs (AS1, AS2) is included in the set of signed ASPAs. The
semantics of its usa are defined in next section. The procedure
takes (AS1, AS2, ROUTE_AFI) as input parameters and returns three
types of results: "valid", "invalid" and "unknown".
A relying party (RP) must have access to a local cache of the
complete set of cryptographically valid ASPAs when performing
customer-provider verification procedure.
1. Retrieve all cryptographically valid ASPAs in a selected AFI with
a customer value of AS1. This selection forms the set of
"candidate ASPAs."
2. If the set of candidate ASPAs is empty, then the procedure exits
with an outcome of "unknown."
3. If there is at least one candidate ASPA where the provider field
is AS2, then the procedure exits with an outcome of "valid."
4. Otherwise, the procedure exits with an outcome of "invalid."
Since an AS1 may have different set providers in different AFI, it
should also have different set of corresponding ASPAs. In this case,
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the output of this procedure with input (AS1, AS2, ROUTE_AFI) may
have different output for different ROUTE_AFI values.
5. AS_PATH Verification
The AS_PATH attribute identifies the autonomous systems through which
an UPDATE message has passed. AS_PATH may contain two types of
components: ordered AS_SEQes and unordered AS_SETs, as defined in
[RFC4271].
The value of each AS_SEQ component can be described as set of pairs
{(AS(I), prepend(I)), (AS(I-1), prepend(I-1))...}. In this case, the
sequence {AS(I), AS(I-1),...} represents different ASNs, that packet
should pass towards the destination. When a route is received from a
customer or a literal peer, each pair (AS(I-1), AS(I)) MUST belong to
customer-provider or sibling relationship. If there are other types
of relationships, it means that the route was leaked or the AS_PATH
attribute was malformed. The goal of the above procedure is to check
the correctness of this statement.
For 32-bit AS number compatible BGP speakers, if a route from
ROUTE_AFI address family is received from a customer or peer, its
AS_PATH MUST be verified as follows:
1. If the closest AS in the AS_PATH is not the receiver's neighbor
ASN then procedure halts with the outcome "invalid";
2. If in one of AS_SEQ segments there is a pair (AS(I-1), AS(I)),
and customer-provider verification procedure (Section 4) with
parameters (AS(I-1), AS(I), ROUTE_AFI) returns "invalid" then the
procedure also halts with the outcome "invalid";
3. If the AS_PATH has at least one AS_SET segment then procedure
halts with the outcome "unverifiable";
4. Otherwise, the procedure halts with an outcome of "valid".
For BGP speakers that are not 32-bit AS compatible, the above
procedure is slightly different. In point 2 if at least one AS(I-1),
AS(I) is equal to AS_TRANS(23456), the corresponding pair must be
passed without check using the customer-provider verification
procedure.
If the output of the AS_PATH verification procedure is "invalid" the
LOCAL_PREF SHOULD be set to 0 or the route MAY be dropped. If an
"invalid" route has no alternative route(s) and it is propagated to
other ASes despite the above, it MUST be marked with the
GRACEFUL_SHUTDOWN community to avoid possible stable oscillations,
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when an unchecked route received from a provider becomes preferred
over an invalid route received from a customer. This also allows
customers to detect malformed routes received from upstream
providers.
If the output of the AS_PATH verification procedure is 'unverifiable'
it means that AS_PATH can't be fully verified. Such routes should be
treated with caution and SHOULD be processed the same way as
"invalid" routes. This policy goes with full correspondence to
[I-D.kumari-deprecate-as-set-confed-set].
The above AS_PATH verification procedure is able to check routes
received from customers and peers. The ASPA mechanism combined with
BGP Roles [I-D.ietf-idr-bgp-open-policy] and ROA-based Origin
Validation [RFC6483] provide a fully automated solution to detect and
filter hijacks and route leaks, including malicious ones.
6. Disavowal of Provider Authorizaion
An ASPA is a positive attestation that an AS holder has authorized
its provider to redistribute received routes to the provider's
providers and peers. This does not preclude the provider AS from
redistribution to its other customers. By creating an ASPA where the
provider AS is 0, the customer indicates that no provider should
further announce its routes. Specifically, AS 0 is reserved to
identify provider-free networks, Internet exchange meshes, etc.
An ASPA with a provider AS of 0 is a statement by the customer AS
that the its routes should not be received by any relying party AS
from any of its customers or peers.
By convention, an ASPA with a provider AS of 0 should be the only
ASPA issued by a given AS holder; although this is not a strict
requirement. A provider 0 ASPA may coexist with ASPAs that have
different provider AS values; though in such cases, the presence or
absence of the provider AS 0 ASPA does not alter the AS_PATH
verification procedure.
7. Siblings (Complex Relations)
There are peering relationships which can not be described as
strictly simple peer-peer or customer-provider; e.g. when both
parties are intentionally sending prefixes received from each other
to their peers and/or upstreams.
In this case, two symmetric ASPAs records {(AS1, AS2), (AS2, AS1)}
must be created by AS1 and AS2 respectively.
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8. Security Considerations
ASPA issuers should be aware of the verification implication in
issuing an ASPA - an ASPA implicitly invalidates all routes passed to
upstream providers other than the provider ASs listed in the
collection of ASPAs. It is the Customer AS's duty to maintain a
correct set of ASPAs.
While the ASPA provides a check of an AS_PATH for routes received
from customers and peers, it doesn't provide full support for routes
that are received from upstream providers. So, this mechanism
guarantees detection of both malicious and accidental route leaks and
provides partial support for detection of malicious hijacks: upstream
transit ISPs will still be able to send hijacked prefixes with
malformed AS_PATHs to their customers.
9. Acknowledgments
The authors wish to thank authors of [RFC6483] since its text was
used as an example while writing this document.
10. References
10.1. 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>.
[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>.
10.2. Informative References
[I-D.azimov-sidrops-aspa-profile]
Azimov, A., Uskov, E., Bush, R., Patel, K., Snijders, J.,
and R. Housley, "A Profile for Autonomous System Provider
Authorization", draft-azimov-sidrops-aspa-profile-00 (work
in progress), June 2018.
[I-D.ietf-idr-bgp-open-policy]
Azimov, A., Bogomazov, E., Bush, R., Patel, K., and K.
Sriram, "Route Leak Prevention using Roles in Update and
Open messages", draft-ietf-idr-bgp-open-policy-02 (work in
progress), January 2018.
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[I-D.kumari-deprecate-as-set-confed-set]
Kumari, W. and K. Sriram, "Deprecation of AS_SET and
AS_CONFED_SET in BGP", draft-kumari-deprecate-as-set-
confed-set-12 (work in progress), July 2018.
[I-D.white-sobgp-architecture]
White, R., "Architecture and Deployment Considerations for
Secure Origin BGP (soBGP)", draft-white-sobgp-
architecture-02 (work in progress), June 2006.
[I-D.ymbk-idr-bgp-eotr-policy]
Azimov, A., Bogomazov, E., Bush, R., and K. Patel, "Route
Leak Detection and Filtering using Roles in Update and
Open messages", draft-ymbk-idr-bgp-eotr-policy-02 (work in
progress), March 2018.
[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>.
[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>.
[RFC5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC 5280, DOI 10.17487/RFC5280, May 2008,
<https://www.rfc-editor.org/info/rfc5280>.
[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>.
[RFC6483] Huston, G. and G. Michaelson, "Validation of Route
Origination Using the Resource Certificate Public Key
Infrastructure (PKI) and Route Origin Authorizations
(ROAs)", RFC 6483, DOI 10.17487/RFC6483, February 2012,
<https://www.rfc-editor.org/info/rfc6483>.
[RFC7908] Sriram, K., Montgomery, D., McPherson, D., Osterweil, E.,
and B. Dickson, "Problem Definition and Classification of
BGP Route Leaks", RFC 7908, DOI 10.17487/RFC7908, June
2016, <https://www.rfc-editor.org/info/rfc7908>.
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[RFC8205] Lepinski, M., Ed. and K. Sriram, Ed., "BGPsec Protocol
Specification", RFC 8205, DOI 10.17487/RFC8205, September
2017, <https://www.rfc-editor.org/info/rfc8205>.
Authors' Addresses
Alexander Azimov
Qrator Labs
Email: aa@qrator.net
Eugene Bogomazov
Qrator Labs
Email: eb@qrator.net
Randy Bush
Internet Initiative Japan
Email: randy@psg.com
Keyur Patel
Arrcus, Inc.
Email: keyur@arrcus.com
Job Snijders
NTT Communications
Theodorus Majofskistraat 100
Amsterdam 1065 SZ
The Netherlands
Email: job@ntt.net
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