Network Working Group A. Azimov
Internet-Draft E. Bogomazov
Intended status: Standards Track Qrator Labs
Expires: December 30, 2018 R. Bush
Internet Initiative Japan
K. Patel
Arrcus, Inc.
K. Sriram
US NIST
June 28, 2018
Route Leak Prevention using Roles in Update and Open messages
draft-ietf-idr-bgp-open-policy-03
Abstract
Route Leaks are the propagation of BGP prefixes which violate
assumptions of BGP topology relationships; e.g. passing a route
learned from one peer to another peer or to a transit provider,
passing a route learned from one transit provider to another transit
provider or to a peer. Today, approaches to leak prevention rely on
marking routes according to operator configuration options without
any check that the configuration corresponds to that of the BGP
neighbor, or enforcement that the two BGP speakers agree on the
relationship. This document enhances BGP Open to establish agreement
of the (peer, customer, provider, internal) relationship of two
neighboring BGP speakers to enforce appropriate configuration on both
sides. Propagated routes are then marked with an iOTC attribute
according to agreed relationship allowing prevention of route leaks.
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.
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 http://datatracker.ietf.org/drafts/current/.
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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 December 30, 2018.
Copyright Notice
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Table of Contents
1. Preamble . . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Peering Relationships . . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Role Definitions . . . . . . . . . . . . . . . . . . . . . . 3
4. BGP Role . . . . . . . . . . . . . . . . . . . . . . . . . . 4
5. Role capability . . . . . . . . . . . . . . . . . . . . . . . 4
6. Role correctness . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Strict mode . . . . . . . . . . . . . . . . . . . . . . . 5
7. BGP Internal Only To Customer attribute . . . . . . . . . . . 6
8. Attribute or Community . . . . . . . . . . . . . . . . . . . 6
9. Compatibility with BGPsec . . . . . . . . . . . . . . . . . . 7
10. Additional Considerations . . . . . . . . . . . . . . . . . . 7
11. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
12. Security Considerations . . . . . . . . . . . . . . . . . . . 8
13. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
14. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
14.1. Normative References . . . . . . . . . . . . . . . . . . 8
14.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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1. Preamble
1.1. Peering Relationships
Despite uses of words such as "Customer," "Peer." etc. the intent is
not business relationships, who pays whom, etc. These are common
terms to represent restrictions on BGP route propagation, sometimes
known as Gao-Rexford model. E.g. if A is a "peer" of B and C, A does
not propagate B's prefixes to C. If D is a "customer" of E and F, D
does not propagate prefixes learned from E to F.
As the whole point of route leak detection and prevention is to
prevent vioation of these relationships, they are inescapable.
2. Introduction
This document specifies a new BGP Capability Code, [RFC5492] Sec 4,
which two BGP speakers MAY use to ensure that they MUST agree on
their relationship; i.e. customer and provider or peers. Either or
both may optionally be configured to require that this option be
exchanged for the BGP Open to succeed.
Also this document specifies a way to mark routes according to BGP
Roles established in OPEN message and a way to create double-boundary
filters for prevention of route leaks via new BGP Path Attribute.
For the purpose of this document, BGP route leaks are when a BGP
route was learned from transit provider or peer and is announced to
another provider or peer. See
[I-D.ietf-grow-route-leak-problem-definition]. These are usually the
result of misconfigured or absent BGP route filtering or lack of
coordination between two BGP speakers.
[I-D.ietf-idr-route-leak-detection-mitigation] The mechanism proposed
in that draft provides the opportunity to detect route leaks made by
third parties but provides no support to strongly prevent route leak
creation.
Also, route tagging which relies on operator maintained policy
configuration is too easily and too often misconfigured.
3. Role Definitions
As many of these terms are used differently in various contexts, it
is worth being explicit.
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A Provider: sends their own routes and (possibly) a subset of routes
learned from their other customers, peers, and transit providers
to their customer.
A Customer: accepts 'transit routes' from its provider(s) and
announces their own routes and the routes they have learned from
the transitive closure of their customers (AKA their 'customer
cone') to their provider(s).
A Peer: announces their routes and the routes from their customer
cone to other Peers.
An Internal: announces all routes, accepts all routes.
Of course, any BGP speaker may apply policy to reduce what is
announced, and a recipient may apply policy to reduce the set of
routes they accept.
4. BGP Role
BGP Role is new configuration option that SHOULD be configured at
each BGP session. It reflects the real-world agreement between two
BGP speakers about their peering relationship.
Allowed Role values for eBGP sessions are:
o Provider - sender is a transit provider to neighbor;
o Customer - sender is customer of neighbor;
o Peer - sender and neighbor are peers;
o Internal - sender and neighbor is part of same organization.
For iBGP sessions only Internal role MAY be configured.
Since BGP Role reflects the relationship between two BGP speakers, it
could also be used for more than route leak mitigation.
5. Role capability
The TLV (type, length, value) of the BGP Role capability are:
o Type - <TBD1>;
o Length - 1 (octet);
o Value - integer corresponding to speaker' BGP Role.
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+--------+----------------------+
| Value | Role name |
+--------+----------------------+
| 0 | Sender is Peer |
| 1 | Sender is Provider |
| 2 | Sender is Customer |
| 3 | Sender is Internal |
+--------+----------------------+
Table 1: Predefined BGP Role Values
6. Role correctness
Section 4 described how BGP Role is a reflection of the relationship
between two BGP speakers. But the mere presence of BGP Role doesn't
automatically guarantee role agreement between two BGP peers.
To enforce correctness, the BGP Role check is used with a set of
constrains on how speakers' BGP Roles MUST corresponded. Of course,
each speaker MUST announce and accept the BGP Role capability in the
BGP OPEN message exchange.
If a speaker receives a BGP Role capability, it MUST check value of
the received capability with its own BGP Role (if it is set). The
allowed pairings are (first a sender's Role, second the receiver's
Role):
+--------------+----------------+
| Sender Role | Receiver Role |
+--------------+----------------+
| Peer | Peer |
| Provider | Customer |
| Customer | Provider |
| Internal | Internal |
+--------------+----------------+
Table 2: Allowed Role Capabilities
In case of any other pair of roles, speaker MUST send a Role Mismatch
Notification (code 2, sub-code <TBD2>).
6.1. Strict mode
A new BGP configuration option "strict mode" is defined with values
of true or false. If set to true, then the speaker MUST refuse to
establish a BGP session with peers which do not announce the BGP Role
capability in their OPEN message. If a speaker rejects a connection,
it MUST send a Connection Rejected Notification [RFC4486]
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(Notification with error code 6, subcode 5). By default strict mode
SHOULD be set to false for backward compatibility with BGP speakers,
that do not yet support this mechanism.
7. BGP Internal Only To Customer attribute
The Internal Only To Customer (iOTC) attribute is a new optional,
non-transitive BGP Path attribute with the Type Code <TBD3>. This
attribute has zero length as it is used only as a flag.
There are three rules of iOTC attribute usage:
1. The iOTC attribute MUST be added to all incoming routes if the
receiver's Role is Customer or Peer;
2. Routes with the iOTC attribute set MUST NOT be announced by a
sender whose Role is Customer or Peer;
3. A sender MUST NOT include this attribute in UPDATE messages if
its Role is Customer, Provider or Peer. If it is contained in an
UPDATE message from eBGP speaker and receiver's Role is Customer,
Provider, Peer or unspecified, then this attribute MUST be
removed.
These three rules provide mechanism that strongly prevents route leak
creation by an AS.
8. Attribute or Community
Having the relationship hard set by agreement between the two peers
in BGP OPEN is critical; the routers enforce the relationship
irrespective of operator configuration errors.
Similarly, it is critical that the application of that relationship
on prefix propagation using iOTC is enforced by the router(s), and
minimally exposed to user misconfiguration. There is a question
whether the iOTC marking should be an attribute or a well-known
community.
There is a long and sordid history of mis-configurations inserting
incorrect communities, deleting communities, ignoring well-known
community markings etc. In this mechanism's case, an operator could,
for example, accidentally strip the well-known community on receipt.
As opposed to communities, BGP attributes may not be generally
modified or filtered by the operator. The router(s) enforce them.
This is the desired property for the iOTC marking. Hence, this
document specifies iOTC as an attribute.
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9. Compatibility with BGPsec
As the iOTC field is non-transitive, it is not seen by or signed by
BGPsec [I-D.ietf-sidr-bgpsec-protocol].
10. Additional Considerations
As the BGP Role reflects the relationship between neighbors, it can
also have other uses. As an example, BGP Role might affect route
priority, or be used to distinguish borders of a network if a network
consists of multiple AS.
Though such uses may be worthwhile, they are not the goal of this
document. Note that such uses would require local policy control.
As BGP role configuration results in automatic creation of inbound/
outbound filters, existence of roles should be treated as existence
of Import and Export policy. [I-D.ietf-grow-bgp-reject]
This document doesn't provide any security measures to check
correctness of iOTC usage if role isn't configured.
11. IANA Considerations
This document defines a new Capability Codes option [to be removed
upon publication: http://www.iana.org/assignments/capability-codes/
capability-codes.xhtml] [RFC5492], named "BGP Role", assigned value
<TBD1> . The length of this capability is 1.
The BGP Role capability includes a Value field, for which IANA is
requested to create and maintain a new sub-registry called "BGP Role
Value". Assignments consist of Value and corresponding Role name.
Initially this registry is to be populated with the data in Table 1.
Future assignments may be made by a standard action procedure
[RFC5226].
This document defines new subcode, "Role Mismatch", assigned value
<TBD2> in the OPEN Message Error subcodes registry [to be removed
upon publication: http://www.iana.org/assignments/bgp-parameters/bgp-
parameters.xhtml#bgp-parameters-6] [RFC4271].
This document defines a new optional, non-transitive BGP Path
Attributes option, named "Internal Only To Customer", assigned value
<TBD3> [To be removed upon publication:
http://www.iana.org/assignments/bgp-parameters/bgp-
parameters.xhtml#bgp-parameters-2] [RFC4271]. The length of this
attribute is 0.
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12. Security Considerations
This document proposes a mechanism for prevention of route leaks that
are the result of BGP policy misconfiguration.
Deliberate sending of a known conflicting BGP Role could be used to
sabotage a BGP connection. This is easily detectable.
BGP Role is disclosed only to an immediate BGP neighbor, so it will
not itself reveal any sensitive information to third parties.
13. Acknowledgments
The authors wish to thank Douglas Montgomery, Brian Dickson, Andrei
Robachevsky and Daniel Ginsburg for their contributions to a variant
of this work.
14. References
14.1. 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>.
[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>.
[RFC4486] Chen, E. and V. Gillet, "Subcodes for BGP Cease
Notification Message", RFC 4486, DOI 10.17487/RFC4486,
April 2006, <https://www.rfc-editor.org/info/rfc4486>.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <https://www.rfc-editor.org/info/rfc5492>.
14.2. Informative References
[I-D.ietf-grow-bgp-reject]
Mauch, J., Snijders, J., and G. Hankins, "Default EBGP
Route Propagation Behavior Without Policies", draft-ietf-
grow-bgp-reject-08 (work in progress), May 2017.
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[I-D.ietf-grow-route-leak-problem-definition]
Sriram, K., Montgomery, D., McPherson, D., Osterweil, E.,
and B. Dickson, "Problem Definition and Classification of
BGP Route Leaks", draft-ietf-grow-route-leak-problem-
definition-06 (work in progress), May 2016.
[I-D.ietf-idr-route-leak-detection-mitigation]
Sriram, K., Montgomery, D., Dickson, B., Patel, K., and A.
Robachevsky, "Methods for Detection and Mitigation of BGP
Route Leaks", draft-ietf-idr-route-leak-detection-
mitigation-03 (work in progress), May 2016.
[I-D.ietf-sidr-bgpsec-protocol]
Lepinski, M. and K. Sriram, "BGPsec Protocol
Specification", draft-ietf-sidr-bgpsec-protocol-15 (work
in progress), March 2016.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008, <https://www.rfc-
editor.org/info/rfc5226>.
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
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Kotikalapudi Sriram
US NIST
Email: ksriram@nist.gov
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