Problem Definition and Classification of BGP Route Leaks
A working definition of a BGP route leak and a taxonomy of the kinds that have caused outages.
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>.
@misc{rfc7908,
series = {Request for Comments},
number = 7908,
howpublished = {RFC 7908},
publisher = {RFC Editor},
doi = {10.17487/RFC7908},
url = {https://www.rfc-editor.org/info/rfc7908},
author = {K. Sriram and D. Montgomery and D. McPherson and E. Osterweil and B. Dickson},
title = {{Problem Definition and Classification of BGP Route Leaks}},
pagetotal = 11,
year = 2016,
month = jun,
} RFC text
Contents
Internet Engineering Task Force (IETF) K. Sriram
Request for Comments: 7908 D. Montgomery
Category: Informational US NIST
ISSN: 2070-1721 D. McPherson
E. Osterweil
Verisign, Inc.
B. Dickson
June 2016
Problem Definition and Classification of BGP Route Leaks
Abstract
A systemic vulnerability of the Border Gateway Protocol routing
system, known as "route leaks", has received significant attention in
recent years. Frequent incidents that result in significant
disruptions to Internet routing are labeled route leaks, but to date
a common definition of the term has been lacking. This document
provides a working definition of route leaks while keeping in mind
the real occurrences that have received significant attention.
Further, this document attempts to enumerate (though not
exhaustively) different types of route leaks based on observed events
on the Internet. The aim is to provide a taxonomy that covers
several forms of route leaks that have been observed and are of
concern to the Internet user community as well as the network
operator community.
Status of This Memo
This document is not an Internet Standards Track specification; it is
published for informational purposes.
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). Not all documents
approved by the IESG are a candidate for any level of Internet
Standard; see 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
http://www.rfc-editor.org/info/rfc7908.
Copyright Notice
Copyright (c) 2016 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
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Working Definition of Route Leaks . . . . . . . . . . . . . . 3
3. Classification of Route Leaks Based on Documented Events . . 4
3.1. Type 1: Hairpin Turn with Full Prefix . . . . . . . . . . 4
3.2. Type 2: Lateral ISP-ISP-ISP Leak . . . . . . . . . . . . 5
3.3. Type 3: Leak of Transit-Provider Prefixes to Peer . . . . 5
3.4. Type 4: Leak of Peer Prefixes to Transit Provider . . . . 5
3.5. Type 5: Prefix Re-origination with Data Path to
Legitimate Origin . . . . . . . . . . . . . . . . . . . . 6
3.6. Type 6: Accidental Leak of Internal Prefixes and More-
Specific Prefixes . . . . . . . . . . . . . . . . . . . . 6
4. Additional Comments about the Classification . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . 7
6. Informative References . . . . . . . . . . . . . . . . . . . 7
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
Frequent incidents [Huston2012] [Cowie2013] [Toonk2015-A]
[Toonk2015-B] [Cowie2010] [Madory] [Zmijewski] [Paseka] [LRL] [Khare]
that result in significant disruptions to Internet routing are
commonly called "route leaks". Examination of the details of some of
these incidents reveals that they vary in their form and technical
details. In order to pursue solutions to "the route-leak problem" it
is important to first provide a clear, technical definition of the
problem and enumerate its most common forms. Section 2 provides a
working definition of route leaks, keeping in view many recent
incidents that have received significant attention. Section 3
attempts to enumerate (though not exhaustively) different types of
route leaks based on observed events on the Internet. Further,
Section 3 provides a taxonomy that covers several forms of route
leaks that have been observed and are of concern to the Internet user
community as well as the network operator community. This document
builds on and extends earlier work in the IETF [ROUTE-LEAK-DEF]
[ROUTE-LEAK-REQ].
2. Working Definition of Route Leaks
A proposed working definition of "route leak" is as follows:
A route leak is the propagation of routing announcement(s) beyond
their intended scope. That is, an announcement from an Autonomous
System (AS) of a learned BGP route to another AS is in violation of
the intended policies of the receiver, the sender, and/or one of the
ASes along the preceding AS path. The intended scope is usually
defined by a set of local redistribution/filtering policies
distributed among the ASes involved. Often, these intended policies
are defined in terms of the pair-wise peering business relationship
between ASes (e.g., customer, transit provider, peer). For
literature related to AS relationships and routing policies, see
[Gao], [Luckie], and [Gill]. For measurements of valley-free
violations in Internet routing, see [Anwar], [Giotsas], and
[Wijchers].
The result of a route leak can be redirection of traffic through an
unintended path that may enable eavesdropping or traffic analysis and
may or may not result in an overload or black hole. Route leaks can
be accidental or malicious but most often arise from accidental
misconfigurations.
The above definition is not intended to be all encompassing. Our aim
here is to have a working definition that fits enough observed
incidents so that the IETF community has a basis for developing
solutions for route-leak detection and mitigation.
3. Classification of Route Leaks Based on Documented Events
As illustrated in Figure 1, a common form of route leak occurs when a
multihomed customer AS (such as AS3 in Figure 1) learns a prefix
update from one transit provider (ISP1) and leaks the update to
another transit provider (ISP2) in violation of intended routing
policies, and further, the second transit provider does not detect
the leak and propagates the leaked update to its customers, peers,
and transit ISPs.
/\ /\
\ route leak(P)/
\ propagated /
\ /
+------------+ peer +------------+
______| ISP1 (AS1) |----------->| ISP2 (AS2)|---------->
/ ------------+ prefix(P) +------------+ route leak(P)
| prefix | \ update /\ \ propagated
\ (P) / \ / \
------- prefix(P) \ / \
update \ / \
\ /route leak(P) \/
\/ /
+---------------+
| customer(AS3) |
+---------------+
Figure 1: Basic Notion of a Route Leak
This document proposes the following taxonomy to cover several types
of observed route leaks while acknowledging that the list is not
meant to be exhaustive. In what follows, the AS that announces a
route that is in violation of the intended policies is referred to as
the "offending AS".
3.1. Type 1: Hairpin Turn with Full Prefix
Description: A multihomed AS learns a route from one upstream ISP and
simply propagates it to another upstream ISP (the turn essentially
resembling a hairpin). Neither the prefix nor the AS path in the
update is altered. This is similar to a straightforward path-
poisoning attack [Kapela-Pilosov], but with full prefix. It should
be noted that leaks of this type are often accidental (i.e., not
malicious). The update basically makes a hairpin turn at the
offending AS's multihomed AS. The leak often succeeds (i.e., the
leaked update is accepted and propagated) because the second ISP
prefers customer announcement over peer announcement of the same
prefix. Data packets would reach the legitimate destination, albeit
via the offending AS, unless they are dropped at the offending AS due
to its inability to handle resulting large volumes of traffic.
o Example incidents: Examples of Type 1 route-leak incidents are (1)
the Dodo-Telstra incident in March 2012 [Huston2012], (2) the
VolumeDrive-Atrato incident in September 2014 [Madory], and (3)
the massive Telekom Malaysia route leak of about 179,000 prefixes,
which in turn Level3 accepted and propagated [Toonk2015-B].
3.2. Type 2: Lateral ISP-ISP-ISP Leak
Description: The term "lateral" here is synonymous with "non-transit"
or "peer-to-peer". This type of route leak typically occurs when,
for example, three sequential ISP peers (e.g., ISP-A, ISP-B, and
ISP-C) are involved, and ISP-B receives a route from ISP-A and in
turn leaks it to ISP-C. The typical routing policy between laterally
(i.e., non-transit) peering ISPs is that they should only propagate
to each other their respective customer prefixes.
o Example incidents: In [Mauch-nanog] and [Mauch], route leaks of
this type are reported by monitoring updates in the global BGP
system and finding three or more very large ISPs' Autonomous
System Numbers (ASNs) in a sequence in a BGP update's AS path.
[Mauch] observes that its detection algorithm detects for these
anomalies and potentially route leaks because very large ISPs do
not, in general, buy transit services from each other. However,
it also notes that there are exceptions when one very large ISP
does indeed buy transit from another very large ISP, and
accordingly, exceptions are made in its detection algorithm for
known cases.
3.3. Type 3: Leak of Transit-Provider Prefixes to Peer
Description: This type of route leak occurs when an offending AS
leaks routes learned from its transit provider to a lateral (i.e.,
non-transit) peer.
o Example incidents: The incidents reported in [Mauch] include
Type 3 leaks.
3.4. Type 4: Leak of Peer Prefixes to Transit Provider
Description: This type of route leak occurs when an offending AS
leaks routes learned from a lateral (i.e., non-transit) peer to its
(the AS's) own transit provider. These leaked routes typically
originate from the customer cone of the lateral peer.
o Example incidents: Examples of Type 4 route-leak incidents are (1)
the Axcelx-Hibernia route leak of Amazon Web Services (AWS)
prefixes causing disruption of AWS and a variety of services that
run on AWS [Kephart], (2) the Hathway-Airtel route leak of 336
Google prefixes causing widespread interruption of Google services
in Europe and Asia [Toonk2015-A], (3) the Moratel-PCCW route leak
of Google prefixes causing Google's services to go offline
[Paseka], and (4) some of the example incidents cited for Type 1
route leaks above are also inclusive of Type 4 route leaks. For
instance, in the Dodo-Telstra incident [Huston2012], the leaked
routes from Dodo to Telstra included routes that Dodo learned from
its transit providers as well as lateral peers.
3.5. Type 5: Prefix Re-origination with Data Path to Legitimate Origin
Description: A multihomed AS learns a route from one upstream ISP and
announces the prefix to another upstream ISP as if it is being
originated by it (i.e., strips the received AS path and re-originates
the prefix). This can be called re-origination or mis-origination.
However, somehow a reverse path to the legitimate origination AS may
be present and data packets reach the legitimate destination albeit
via the offending AS. (Note: The presence of a reverse path here is
not attributable to the use of a path-poisoning trick by the
offending AS.) But sometimes the reverse path may not be present,
and data packets destined for the leaked prefix may be simply
discarded at the offending AS.
o Example incidents: Examples of Type 5 route leak include (1) the
China Telecom incident in April 2010 [Hiran] [Cowie2010]
[Labovitz], (2) the Belarusian GlobalOneBel route-leak incidents
in February-March 2013 and May 2013 [Cowie2013], (3) the Icelandic
Opin Kerfi-Simmin route-leak incidents in July-August 2013
[Cowie2013], and (4) the Indosat route-leak incident in April 2014
[Zmijewski]. The reverse paths (i.e., data paths from the
offending AS to the legitimate destinations) were present in
incidents #1, #2, and #3 cited above, but not in incident #4. In
incident #4, the misrouted data packets were dropped at Indosat's
AS.
3.6. Type 6: Accidental Leak of Internal Prefixes and More-Specific
Prefixes
Description: An offending AS simply leaks its internal prefixes to
one or more of its transit-provider ASes and/or ISP peers. The
leaked internal prefixes are often more-specific prefixes subsumed by
an already announced, less-specific prefix. The more-specific
prefixes were not intended to be routed in External BGP (eBGP).
Further, the AS receiving those leaks fails to filter them.
Typically, these leaked announcements are due to some transient
failures within the AS; they are short-lived and typically withdrawn
quickly following the announcements. However, these more-specific
prefixes may momentarily cause the routes to be preferred over other
aggregate (i.e., less specific) route announcements, thus redirecting
traffic from its normal best path.
o Example incidents: Leaks of internal routes occur frequently
(e.g., multiple times in a week), and the number of prefixes
leaked range from hundreds to thousands per incident. One highly
conspicuous and widely disruptive leak of internal routes happened
in August 2014 when AS701 and AS705 leaked about 22,000 more-
specific prefixes of already-announced aggregates [Huston2014]
[Toonk2014].
4. Additional Comments about the Classification
It is worth noting that Types 1 through 4 are similar in that a route
is leaked in violation of policy in each case, but what varies is the
context of the leaked-route source AS and destination AS roles.
A Type 5 route leak (i.e., prefix mis-origination with data path to
legitimate origin) can also happen in conjunction with the AS
relationship contexts in Types 2, 3, and 4. While these
possibilities are acknowledged, simply enumerating more types to
consider all such special cases does not add value as far as solution
development for route leaks is concerned. Hence, the special cases
mentioned here are not included in enumerating route-leak types.
5. Security Considerations
No security considerations apply since this is a problem definition
document.
6. Informative References
[Anwar] Anwar, R., Niaz, H., Choffnes, D., Cunha, I., Gill, P.,
and N. Katz-Bassett, "Investigating Interdomain Routing
Policies in the Wild", In Proceedings of the 2015
ACM Internet Measurement Conference (IMC),
DOI 10.1145/2815675.2815712, October 2015,
<http://www.cs.usc.edu/assets/007/94928.pdf>.
[Cowie2010]
Cowie, J., "China's 18 Minute Mystery", Dyn Research: The
New Home of Renesys Blog, November 2010,
<http://research.dyn.com/2010/11/
chinas-18-minute-mystery/>.
[Cowie2013]
Cowie, J., "The New Threat: Targeted Internet Traffic
Misdirection", Dyn Research: The New Home of Renesys Blog,
November 2013, <http://research.dyn.com/2013/11/
mitm-internet-hijacking/>.
[Gao] Gao, L. and J. Rexford, "Stable Internet Routing Without
Global Coordination", IEEE/ACM Transactions on Networking
(TON), Volume 9, Issue 6, pp 689-692,
DOI 10.1109/90.974523, December 2001,
<http://www.cs.princeton.edu/~jrex/papers/
sigmetrics00.long.pdf>.
[Gill] Gill, P., Schapira, M., and S. Goldberg, "A Survey of
Interdomain Routing Policies", ACM SIGCOMM Computer
Communication Review, Volume 44, Issue 1, pp 28-34,
DOI 10.1145/2567561.2567566, January 2014,
<http://www.cs.bu.edu/~goldbe/papers/survey.pdf>.
[Giotsas] Giotsas, V. and S. Zhou, "Valley-free violation in
Internet routing - Analysis based on BGP Community data",
2012 IEEE International Conference on
Communications (ICC), DOI 10.1109/ICC.2012.6363987, June
2012.
[Hiran] Hiran, R., Carlsson, N., and P. Gill, "Characterizing
Large-Scale Routing Anomalies: A Case Study of the China
Telecom Incident", In Proceedings of the 14th
International Conference on Passive and Active Measurement
(PAM) 2013, DOI 10.1007/978-3-642-36516-4_23, March 2013,
<http://www3.cs.stonybrook.edu/~phillipa/papers/
CTelecom.html>.
[Huston2012]
Huston, G., "Leaking Routes", Asia Pacific Network
Information Centre (APNIC) Blog, March 2012,
<http://labs.apnic.net/blabs/?p=139/>.
[Huston2014]
Huston, G., "What's so special about 512?", Asia Pacific
Network Information Centre (APNIC) Blog, September 2014,
<http://labs.apnic.net/blabs/?p=520/>.
[Kapela-Pilosov]
Pilosov, A. and T. Kapela, "Stealing the Internet: An
Internet-Scale Man in the Middle Attack", 16th
Defcon Conference, August 2008,
<https://www.defcon.org/images/defcon-16/
dc16-presentations/defcon-16-pilosov-kapela.pdf>.
[Kephart] Kephart, N., "Route Leak Causes Amazon and AWS Outage",
ThousandEyes Blog, June 2015,
<https://blog.thousandeyes.com/
route-leak-causes-amazon-and-aws-outage>.
[Khare] Khare, V., Ju, Q., and B. Zhang, "Concurrent Prefix
Hijacks: Occurrence and Impacts", In Proceedings of the
2013 ACM Internet Measurement Conference (IMC),
DOI 10.1145/2398776.2398780, November 2012,
<http://www.cs.arizona.edu/~bzhang/
paper/12-imc-hijack.pdf>.
[Labovitz] Labovitz, C., "Additional Discussion of the April China
BGP Hijack Incident", Arbor Networks IT Security Blog,
November 2010,
<http://www.arbornetworks.com/asert/2010/11/additional-
discussion-of-the-april-china-bgp-hijack-incident/>.
[LRL] Khare, V., Ju, Q., and B. Zhang, "Large Route Leaks",
University of Arizona (UA) Network Research Lab: Projects
Webpage, 2012, <http://nrl.cs.arizona.edu/projects/
lsrl-events-from-2003-to-2009/>.
[Luckie] Luckie, M., Huffaker, B., Dhamdhere, A., Giotsas, V., and
kc. claffy, "AS Relationships, Customer Cones, and
Validation", In Proceedings of the 2013 ACM Internet
Measurement Conference (IMC), DOI 10.1145/2504730.2504735,
October 2013,
<http://www.caida.org/~amogh/papers/asrank-IMC13.pdf>.
[Madory] Madory, D., "Why Far-Flung Parts of the Internet Broke
Today", Dyn Research: The New Home of Renesys Blog,
September 2014, <http://research.dyn.com/2014/09/
why-the-internet-broke-today/>.
[Mauch] Mauch, J., "BGP Routing Leak Detection System", Project
web page, 2014,
<http://puck.nether.net/bgp/leakinfo.cgi/>.
[Mauch-nanog]
Mauch, J., "Detecting Routing Leaks by Counting", 41st
NANOG Conference, October 2007,
<https://www.nanog.org/meetings/nanog41/presentations/
mauch-lightning.pdf>.
[Paseka] Paseka, T., "Why Google Went Offline Today and a Bit about
How the Internet Works", CloudFlare Blog, November 2012,
<http://blog.cloudflare.com/
why-google-went-offline-today-and-a-bit-about/>.
[ROUTE-LEAK-DEF]
Dickson, B., "Route Leaks -- Definitions", Work in
Progress, draft-dickson-sidr-route-leak-def-03, October
2012.
[ROUTE-LEAK-REQ]
Dickson, B., "Route Leaks -- Requirements for Detection
and Prevention thereof", Work in Progress, draft-dickson-
sidr-route-leak-reqts-02, March 2012.
[Toonk2014]
Toonk, A., "What caused today's Internet hiccup",
BGPMON Blog, August 2014, <http://www.bgpmon.net/
what-caused-todays-internet-hiccup/>.
[Toonk2015-A]
Toonk, A., "What caused the Google service interruption",
BGPMON Blog, March 2015, <http://www.bgpmon.net/
what-caused-the-google-service-interruption/>.
[Toonk2015-B]
Toonk, A., "Massive route leak causes Internet slowdown",
BGPMON Blog, June 2015, <http://www.bgpmon.net/
massive-route-leak-cause-internet-slowdown/>.
[Wijchers] Wijchers, B. and B. Overeinder, "Quantitative Analysis of
BGP Route Leaks", Reseaux IP Europeens (RIPE) 69th
Meeting, November 2014, <http://ripe69.ripe.net/
presentations/157-RIPE-69-Routing-WG.pdf>.
[Zmijewski]
Zmijewski, E., "Indonesia Hijacks the World", Dyn
Research: The New Home of Renesys Blog, April 2014,
<http://research.dyn.com/2014/04/
indonesia-hijacks-world/>.
Acknowledgements
The authors wish to thank Jared Mauch, Jeff Haas, Warren Kumari,
Amogh Dhamdhere, Jakob Heitz, Geoff Huston, Randy Bush, Job Snijders,
Ruediger Volk, Andrei Robachevsky, Charles van Niman, Chris Morrow,
and Sandy Murphy for comments, suggestions, and critique. The
authors are also thankful to Padma Krishnaswamy, Oliver Borchert, and
Okhee Kim for their comments and review.
Authors' Addresses
Kotikalapudi Sriram
US NIST
Email: ksriram@nist.gov
Doug Montgomery
US NIST
Email: dougm@nist.gov
Danny McPherson
Verisign, Inc.
Email: dmcpherson@verisign.com
Eric Osterweil
Verisign, Inc.
Email: eosterweil@verisign.com
Brian Dickson
Email: brian.peter.dickson@gmail.com
ISO Plain Language
On this page
§1Why a Definition Was Needed
Frequent incidents that result in significant disruptions to Internet routing are commonly called route leaks. Examination of the details of some of these incidents reveals that they vary in their form and technical details. In order to pursue solutions to the route-leak problem, it is important to first provide a clear, technical definition of the problem and enumerate its most common forms.
The document therefore provides a working definition of route leaks, keeping in view many recent incidents that received significant attention, and then enumerates, though not exhaustively, different types of route leak based on observed events on the Internet. It builds on and extends earlier work in the IETF.
The reason the matter needs care is that the same label was applied to events with different causes and different effects. A definition has to be loose enough to cover the incidents that have happened and tight enough to be useful for building detection and mitigation tools.
Operators had been calling several different kinds of mistake a route leak. Before anyone could build a tool to spot them or prevent them, the community needed to agree on what the words meant.
§2The Working Definition of a Route Leak
The proposed working definition is that a route leak is the propagation of routing announcements beyond their intended scope. That is, an announcement from an Autonomous System (AS) of a learned BGP route to another AS is in violation of the intended policies of the receiver, the sender, and/or one of the ASes along the preceding AS path.
The intended scope is usually defined by a set of local redistribution and filtering policies distributed among the ASes involved. Often these intended policies are defined in terms of the pair-wise peering business relationship between ASes, for example customer, transit provider or peer. A multihomed AS, one connected to more than one upstream provider, has rules about which routes it may pass to which neighbour: routes learned from a transit provider are normally sent to customers and peers, and not to other transit providers.
The result of a route leak can be redirection of traffic through an unintended path, which may enable eavesdropping or traffic analysis, and may or may not result in an overload or a black hole. Route leaks can be accidental or malicious, but most often they arise from accidental misconfigurations.
The definition is not intended to be all-encompassing. The stated aim is a working definition that fits enough observed incidents so that the IETF community has a basis for developing solutions for route-leak detection and mitigation.
A route leak is a network passing on a route it should have kept to itself. Each network has rules about which routes it shares with which neighbour, and a leak breaks one of those rules. The traffic then takes a path nobody planned, which can break connections, slow the network down, or let someone read the traffic.
- Traffic is redirectedThe result can be redirection of traffic through an unintended path.
- Eavesdropping becomes possibleThe unintended path may enable eavesdropping or traffic analysis.
- Overload or black holeThe result may or may not result in an overload or a black hole.
- Usually a mistakeRoute leaks can be accidental or malicious, but most often arise from accidental misconfigurations.
§3The Common Shape of a Leak
The common form of a route leak occurs when a multihomed customer AS learns a prefix update from one transit provider and leaks the update to another transit provider in violation of intended routing policies. The second transit provider does not detect the leak, and propagates the leaked update to its customers, peers and transit ISPs.
In the figure that illustrates this, ISP1 (AS1) and ISP2 (AS2) are peers of each other, and both are upstream providers for a customer network, AS3. The customer learns the prefix from ISP1 and passes it on to ISP2, and ISP2 spreads it further out. The network that announces a route in violation of the intended policies is referred to in this document as the offending AS.
Once the leak has happened, the damage depends on what the receiving networks do with the announcement. Some will drop it, some will accept it and pass it on, and in the worst case the traffic for the affected prefixes is drawn towards a network that cannot carry it.
The typical case is a customer with two providers. It learns a route from one, passes it to the other, and the second provider treats it as a real route and spreads it further. The customer is the network that made the mistake, and the document calls it the offending network.
- prefix(P) updateThe customer learns the route from one transit provider.
- route leak(P)The customer passes the route to its other transit provider, against its routing policies.
- route leak(P) propagatedThe second provider does not detect the leak and spreads the update onwards.
§3.1The Six Types of Route Leak
Type 1, hairpin turn with full prefix. A multihomed AS learns a route from one upstream ISP and simply propagates it to another upstream ISP, with the turn resembling a hairpin. Neither the prefix nor the AS path in the update is altered. This is similar to a straightforward path-poisoning attack, but with the full prefix, and leaks of this type are often accidental. The leak often succeeds because the second ISP prefers a customer announcement over a peer announcement of the same prefix. Data packets would reach the legitimate destination, albeit via the offending AS, unless they are dropped there because it cannot handle the resulting large volume of traffic. Examples are the Dodo-Telstra incident of March 2012, the VolumeDrive-Atrato incident of September 2014, and the Telekom Malaysia route leak of about 179,000 prefixes, which Level3 accepted and propagated.
Type 2, lateral ISP-ISP-ISP leak. The word lateral here is synonymous with non-transit or peer-to-peer. This type typically occurs when three sequential ISP peers are involved: ISP-B receives a route from ISP-A and in turn leaks it to ISP-C. The typical routing policy between laterally peering ISPs is that they should only propagate to each other their respective customer prefixes. Such leaks are reported by monitoring updates in the global BGP system and finding three or more very large ISPs' AS numbers in sequence in a BGP update's AS path, on the grounds that very large ISPs do not in general buy transit from each other. The detection method also notes exceptions, when one very large ISP does buy transit from another, and makes exceptions for known cases.
Type 3, leak of transit-provider prefixes to peer. The offending AS leaks routes learned from its transit provider to a lateral peer.
Type 4, leak of peer prefixes to transit provider. The offending AS leaks routes learned from a lateral peer to its own transit provider. These leaked routes typically originate from the customer cone of the lateral peer. Examples are the Axcelx-Hibernia leak of Amazon Web Services prefixes, the Hathway-Airtel leak of 336 Google prefixes causing widespread interruption of Google services in Europe and Asia, the Moratel-PCCW leak of Google prefixes, and, in the Dodo-Telstra incident, leaked routes that included routes learned from transit providers as well as lateral peers.
Type 5, prefix re-origination with data path to legitimate origin. A multihomed AS learns a route from one upstream ISP and announces the prefix to another upstream ISP as if it were originating it, stripping the received AS path. This can be called re-origination or mis-origination. Somehow a reverse path to the legitimate origination AS may be present, and data packets reach the legitimate destination albeit via the offending AS; the presence of a reverse path is not attributable to a path-poisoning trick. Sometimes the reverse path is not present, and data packets for the leaked prefix are simply discarded at the offending AS. Examples are the China Telecom incident of April 2010, the GlobalOneBel route leaks of February to March 2013 and May 2013, the Opin Kerfi-Simmin route leaks of July to August 2013, and the Indosat route leak of April 2014. The reverse paths were present in the first three of those and not in the fourth, where the misrouted packets were dropped at Indosat's AS.
Type 6, accidental leak of internal prefixes and more-specific prefixes. An offending AS simply leaks its internal prefixes to one or more of its transit-provider ASes and/or ISP peers. The leaked internal prefixes are often more-specific prefixes subsumed by an already announced, less-specific prefix, and were not intended to be routed in External BGP. The AS receiving those leaks fails to filter them. Such announcements are typically due to transient failures within the AS, so they are short-lived and usually withdrawn quickly. While they last, the more-specific prefixes may be preferred over other aggregate route announcements, redirecting traffic from its normal best path. Leaks of internal routes occur frequently, multiple times in a week, with numbers of prefixes ranging from hundreds to thousands per incident; one conspicuous and widely disruptive leak happened in August 2014, when AS701 and AS705 leaked about 22,000 more-specific prefixes of already-announced aggregates.
The six types differ in who leaked what to whom. A customer can pass a route from one provider straight to another, or pass a provider's route to a peer, or a peer's route to its provider. A peer-to-peer chain of three networks counts as its own type. One type is worse than the others: the network claims the prefix as its own and hides the path it came by, and then either the traffic still finds its way to the right place or it is dropped.
- 1Hairpin turn with full prefix — A multihomed AS learns a route from one upstream ISP and propagates it to another, with neither the prefix nor the AS path altered.
- 2Lateral ISP-ISP-ISP leak — Three sequential ISP peers are involved: ISP-B receives a route from ISP-A and leaks it to ISP-C.
- 3Transit-provider prefixes to a peer — The offending AS leaks routes learned from its transit provider to a lateral peer.
- 4Peer prefixes to a transit provider — The offending AS leaks routes learned from a lateral peer to its own transit provider.
- 5Prefix re-origination — The AS announces the prefix as its own, stripping the received AS path, but a reverse path to the real origin may still exist.
- 6Internal and more-specific prefixes — Internal prefixes, often more-specifics, are leaked to transit providers or peers and are not filtered on receipt.
§4What the Classification Leaves Out
Types 1 through 4 are similar in that a route is leaked in violation of policy in each case, but what varies is the context of the source and destination roles of the leaked route. The document notes that a Type 5 route leak can also happen in conjunction with the relationship contexts of Types 2, 3 and 4. While those possibilities are acknowledged, simply enumerating more types to cover every such special case does not add value as far as solution development is concerned, so those special cases are not included in the enumeration.
The list of types is not meant to be exhaustive either. The taxonomy is meant to cover the forms that have been observed and that concern the Internet user community as well as the network operator community.
The list covers the common cases rather than every combination. A network that hides the path it learned a route by can also be doing any of the other tricks at the same time, and the document says it is not worth adding a new type for each combination.
§5Security Considerations
The document states that no security considerations apply, since it is a problem definition document.
The security content that does exist sits in the definition and the taxonomy rather than in a separate section. The definition notes that the result of a route leak can be redirection of traffic through an unintended path that may enable eavesdropping or traffic analysis, and that leaks can be accidental or malicious but most often arise from accidental misconfigurations. The Type 1 description compares the shape of the update to a straightforward path-poisoning attack, with the full prefix.
The document adds no security section of its own, because it is only defining the problem. The security points are in the definition itself: a leaked route can send traffic past someone who can read it, and a leak can be deliberate or a mistake.