Internet DRAFT - draft-ietf-grow-route-leak-detection-mitigation
draft-ietf-grow-route-leak-detection-mitigation
Internet Engineering Task Force (IETF) K. Sriram, Ed.
Internet-Draft USA NIST
Intended status: Standards Track A. Azimov, Ed.
Expires: 11 July 2024 Yandex
8 January 2024
Methods for Detection and Mitigation of BGP Route Leaks
draft-ietf-grow-route-leak-detection-mitigation-10
Abstract
Problem definition for route leaks and enumeration of types of route
leaks are provided in RFC 7908. This document describes a new well-
known Large Community that provides a way for route-leak prevention,
detection, and mitigation. The configuration process for this
Community can be automated with the methodology for setting BGP roles
that is described in RFC 9234.
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
working documents as Internet-Drafts. The list of current Internet-
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 11 July 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
Sriram & Azimov Expires 11 July 2024 [Page 1]
Internet-Draft Route-Leak Detection and Mitigation January 2024
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
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Peering Relationships . . . . . . . . . . . . . . . . . . . . 3
3. Community vs Attribute . . . . . . . . . . . . . . . . . . . 4
4. Down Only Community . . . . . . . . . . . . . . . . . . . . . 4
4.1. Route-Leak Mitigation . . . . . . . . . . . . . . . . . . 5
4.2. Only Marking . . . . . . . . . . . . . . . . . . . . . . 6
5. Implementation Considerations . . . . . . . . . . . . . . . . 7
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
8.1. Normative References . . . . . . . . . . . . . . . . . . 8
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 9
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
RFC 7908 [RFC7908] provides a definition of the route-leak problem
and enumerates several types of route leaks. For this document, the
definition that is applied is that a route leak occurs when a route
received from a transit provider or a lateral peer is forwarded
(against commonly used policy) to another transit provider or a
lateral peer. The commonly used policy is that a route received from
a transit provider or a lateral peer MAY be forwarded only to
customers.
This document describes a solution for prevention, detection and
mitigation of route leaks which is based on conveying route-leak
detection information in a transitive well-known BGP Large Community
[RFC8092]. The configuration process for the Large Community MUST be
defined according to peering relations between ISPs. This process
can be automated with the methodology for setting BGP roles that is
described in [RFC9234].
Sriram & Azimov Expires 11 July 2024 [Page 2]
Internet-Draft Route-Leak Detection and Mitigation January 2024
The techniques described in this document can be incrementally
deployed. If a pair of ISPs and/or Internet Exchanges (IXes) deploy
the proposed techniques, then they would detect and mitigate any
route leaks that occur in an AS path between them even when other
ASes in the path are not upgraded.
1.1. 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.
2. Peering Relationships
As described in [RFC9234], there are several common peering relations
between eBGP neighbors:
* Provider - sender is a transit provider of the neighbor;
* Customer - sender is a customer of the neighbor;
* Route Server (RS) - sender is route server at an internet exchange
(IX)
* RS-client - sender is client of an RS at an IX
* Peer - sender and neighbor are lateral (non-transit) peers;
If a route is received from a provider, peer, or RS-client, it MUST
follow the 'down only' rule, i.e., it MAY be advertised only to
customers. If a route is sent to a customer, peer, or RS-client, it
also MUST follow the 'down only' rule at each subsequent AS in the AS
path.
A standardized transitive route-leak detection signal is needed that
will prevent Autonomous Systems (ASes) from leaking and also inform a
remote ISP (or AS) in the AS path that a received route violates the
'down only' policy. This signal would facilitate a way to stop the
propagation of leaked prefixes.
To improve reliability and cover for non-participating preceding
neighbor, the signal should be set on both receiver and sender sides.
Sriram & Azimov Expires 11 July 2024 [Page 3]
Internet-Draft Route-Leak Detection and Mitigation January 2024
3. Community vs Attribute
This section presents a brief discussion of the advantages and
disadvantages of communities and BGP path attributes for the purpose
of route-leak detection.
A transitive path attribute is a native way to implement the route-
leak detection signal. Based on the way BGP protocol works, the use
of a transitive attribute makes it more certain that the route-leak
detection signal would pass unaltered through non-participating
(i.e., not upgraded) BGP routers. The main disadvantage of this
approach is that the deployment of a new BGP attribute requires a
software upgrade in the router OS which may delay wide adoption for
years.
On the other hand, BGP Communities do not require a router OS update.
The potential disadvantage of using a Community for the route-leak
detection signal is that it is more likely to be dropped somewhere
along the way in the AS path. Currently, the use of BGP Communities
is somewhat overloaded. BGP Communities are already used for
numerous applications: different types of route marking, route policy
control, blackholing, etc. It is observed that some ASes seem to
purposefully or accidentally remove BGP Communities on receipt,
sometimes well-known ones. Perhaps this issue may be mitigated with
strong policy guidance related to the handling of Communities.
Large Communities have much higher capacity, and therefore they are
likely to be less overloaded. Hence, Large Community is proposed to
be used for route-leak detection. This document suggests reserving
<TBD1> class for the purpose of transitive well-known Large
Communities that MUST NOT be stripped on ingress or egress.
While it is not a part of this document, the route-leak detection
signal described here can also be carried in a transitive BGP Path
Attribute, and similar prevention and mitigation techniques as
described here would apply (see [RFC9234]).
Due to frequently occurring regional and global disruptions in
Internet connectivity, it is critical to move forward with a solution
that is viable in the near term. That solution would be route-leak
detection using a well-known Large Community.
4. Down Only Community
This section specifies the semantics of route-leak detection
Community and its usage. This Community is given the specific name
Down Only (DO) Community. The DO Community is carried in a BGP Large
Community with a format as shown in Figure 1.
Sriram & Azimov Expires 11 July 2024 [Page 4]
Internet-Draft Route-Leak Detection and Mitigation January 2024
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD1 (class for transitive well-known Large Communities) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD2 (subclass for DO) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ASN |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Format of the DO Community using a BGP Large Community.
The authors studied different options for route-leak mitigation. The
main options considered are (1) drop detected route leaks and (2)
deprioritize detected route leaks. It can be demonstrated that the
loose mode that uses deprioritization is not safe. Traffic
Engineering (TE) techniques which limit prefix visibility are quite
common. It may happen that a more specific TE prefix is sent only to
downstream ASes or to IX(es)/selected peers, and a control Community
is used to restrict its propagation. If such a more specific prefix
is leaked, deprioritization will not stop such a route leak from
propagating. In addition, propagation of leaked prefixes based on
deprioritization may result in priority loops leading to BGP wedgies
[RFC4264] or even persistent route oscillations.
So, the only truly safe way to implement route-leak mitigation is to
drop detected route leaks. The ingress and egress policies
corresponding to 'drop detected route leaks' is described in
Section 4.1. This policy SHOULD be used as a default behavior.
Nevertheless, early adopters might want to deploy only the signaling
and perhaps use it only for diagnostics before applying any route-
leak mitigation policy. They are also encouraged to use slightly
limited marking, which is described in Section 4.2.
4.1. Route-Leak Mitigation
This section describes the eBGP ingress and egress policies that MUST
be used to perform route-leak prevention, detection and mitigation
using the DO Community. It should be noted that a route may carry
more than one DO Communities. Hence, in the rest of this document,
"a route with DO Community" means "a route with one or more DO
Communities".
The ingress policy MUST use the following procedure:
Sriram & Azimov Expires 11 July 2024 [Page 5]
Internet-Draft Route-Leak Detection and Mitigation January 2024
1. If a route with DO Community is received from a Customer or RS-
client, then it is a route leak and MUST be dropped. The
procedure halts.
2. If a route with DO Community is received from a Peer (non-
transit) and at least one DO value is not equal to the sending
neighbor's ASN, then it is a route leak and MUST be dropped. The
procedure halts.
3. If a route is received from a Provider, Peer, or RS, then a DO
Community MUST be added with a value equal to the sending
neighbor's ASN.
The egress policy MUST use the following procedure:
1. A route with DO Community (i.e., DO Community was present or
added at ingress) MUST NOT be sent to a Provider, Peer, or RS.
2. If a route is sent to a Customer or Peer, then a DO Community
MUST be added with value equal to the ASN of the sender.
The above procedures comprehensively provide route-leak prevention,
detection and mitigation. Policy consisting of these procedures
SHOULD be used as a default behavior.
4.2. Only Marking
This section describes eBGP ingress and egress marking policies that
MUST be used if an AS is not performing route-leak mitigation (i.e.,
not dropping detected route leaks) as described in Section 4.1, but
wants to use the DO Community only for marking. The slightly limited
DO marking (compared to that in Section 4.1) described below
guarantees that this DO marking will not limit the leak detection
opportunities for subsequent ASes in the AS path.
The ingress policy MUST use the following procedure:
1. If a route with DO Community is received from a Customer or RS-
client, then it is a route leak. The procedure halts.
2. If a route with DO Community is received from a Peer (non-
transit) and at least one DO value is not equal to the sending
neighbor's ASN, then it is a route leak. The procedure halts.
3. If a route is received from a Provider, Peer, or RS, then a DO
Community MUST be added with value equal to the sending
neighbor's ASN.
Sriram & Azimov Expires 11 July 2024 [Page 6]
Internet-Draft Route-Leak Detection and Mitigation January 2024
The egress policy MUST use the following procedure:
1. If a route is sent to a Customer or RS-client, then a DO
Community MUST be added with value equal to the ASN of the
sender.
2. If a route without DO Community is sent to a Peer, then a DO
Community MUST be added with value equal to the ASN of the
sender. Conversely, if a route with DO Community (i.e., DO
Community was present or added at ingress) is sent to a Peer,
then an additional DO Community MUST NOT be added.)
These above procedures specify setting the DO signals in a way that
can be used to evaluate the potential impact of route-leak mitigation
policy before deploying strict dropping of detected route leaks.
5. Implementation Considerations
It was observed that the majority of BGP implementations do not
support negative match for communities like a:b:!c. Further, it is
observed that a route received from a compliant Peer (non-transit)
adhering to procedures from either Section 4.1 or Section 4.2 will
always have a single DO Community with value equal to the peer's ASN.
Hence, it is suggested to replace the second rule from the ingress
policies (in Section 4.1 and Section 4.2) with the following:
In Section 4.1: If a route with DO Community is received from a
Peer and a DO value is equal to the sending neighbor's ASN, then
it is a valid route, otherwise it is a route leak and MUST be
dropped. The procedure halts.
In Section 4.2: If a route with DO Community is received from a
Peer and a DO value is equal to the sending neighbor's ASN, then
it is a valid route, otherwise it is a route leak. The procedure
halts.
This rule is based on a weaker assumption that a peer that is doing
marking is also doing filtering (i.e., dropping detected leaks).
That is why networks that do not follow the route-leak mitigation
policy in Section 4.1 MUST carefully follow marking rules described
in Section 4.2.
6. IANA Considerations
IANA is requested to reserve a Global Administrator ID <TBD1> for
transitive well-known Large Community registry. IANA is also
requested to register a subclass <TBD2> for DO Community in this
registry.
Sriram & Azimov Expires 11 July 2024 [Page 7]
Internet-Draft Route-Leak Detection and Mitigation January 2024
7. Security Considerations
In specific circumstances in a state of partial adoption, route-leak
mitigation mechanism can result in Denial of Service (DoS) for the
victim prefix. Such a scenario may happen only for a prefix that has
a single path from the originator to a Tier-1 ISP and only when the
prefix is not covered with a less specific prefix with multiple paths
to the Tier-1 ISP. If, in such unreliable topology, a route leak is
injected somewhere inside this single path, then it may be dropped by
upper tier providers in the path, thus limiting prefix visibility.
While such anomaly is unlikely to happen, such an issue should be
easy to debug, since it directly affects the sequence of originator's
providers.
With the use of BGP Community, there is often a concern that the
Community propagates beyond its intended perimeter and causes harm
[streibelt]. However, that concern does not apply to the DO
Community because it is a transitive Community that must propagate as
far as the update goes.
8. References
8.1. 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>.
[RFC8092] Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas,
I., and N. Hilliard, "BGP Large Communities Attribute",
RFC 8092, DOI 10.17487/RFC8092, February 2017,
<https://www.rfc-editor.org/info/rfc8092>.
[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>.
8.2. Informative References
[RFC4264] Griffin, T. and G. Huston, "BGP Wedgies", RFC 4264,
DOI 10.17487/RFC4264, November 2005,
<https://www.rfc-editor.org/info/rfc4264>.
[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>.
Sriram & Azimov Expires 11 July 2024 [Page 8]
Internet-Draft Route-Leak Detection and Mitigation January 2024
[RFC9234] Azimov, A., Bogomazov, E., Bush, R., Patel, K., and K.
Sriram, "Route Leak Prevention and Detection Using Roles
in UPDATE and OPEN Messages", RFC 9234,
DOI 10.17487/RFC9234, May 2022,
<https://www.rfc-editor.org/info/rfc9234>.
[streibelt]
Streibelt et al., F., "BGP Communities: Even more Worms in
the Routing Can", ACM IMC, October 2018,
<https://archive.psg.com//181101.imc-communities.pdf>.
Acknowledgements
The authors wish to thank John Scudder, Susan Hares, Ruediger Volk,
Jeffrey Haas, Mat Ford, Greg Skinner for their review and comments.
Contributors
The following people made significant contributions to this document
and should be considered co-authors:
Brian Dickson
Independent
Email: brian.peter.dickson@gmail.com
Doug Montgomery
USA National Institute of Standards and Technology
Email: dougm@nist.gov
Keyur Patel
Arrcus
Email: keyur@arrcus.com
Andrei Robachevsky
Internet Society
Email: robachevsky@isoc.org
Eugene Bogomazov
Qrator Labs
Email: eb@qrator.net
Randy Bush
Internet Initiative Japan
Email: randy@psg.com
Authors' Addresses
Sriram & Azimov Expires 11 July 2024 [Page 9]
Internet-Draft Route-Leak Detection and Mitigation January 2024
Kotikalapudi Sriram (editor)
USA National Institute of Standards and Technology
100 Bureau Drive
Gaithersburg, MD 20899
United States of America
Email: ksriram@nist.gov
Alexander Azimov (editor)
Yandex
Ulitsa Lva Tolstogo 16
Moscow
Email: a.e.azimov@gmail.com
Sriram & Azimov Expires 11 July 2024 [Page 10]
