Network Working Group A. Azimov
Internet-Draft E. Bogomazov
Intended status: Standards Track Qrator Labs
Expires: September 22, 2016 R. Bush
Internet Initiative Japan
March 21, 2016
Route Leak Detection and Filtering using Roles in Update and Open
messages
draft-ymbk-idr-bgp-open-policy-00
Abstract
Route Leaks are 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 some configuration options without any check of 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 BGP neighboring speakers to
enforce appropriate configuration on both sides. Propagated routes
are then marked with a flag according to agreed relationship allowing
detection and mitigation 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
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Drafts is at http://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
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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 September 22, 2016.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. BGP Role . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Role capability . . . . . . . . . . . . . . . . . . . . . . . 4
4. Role correctness . . . . . . . . . . . . . . . . . . . . . . 4
4.1. Strict mode . . . . . . . . . . . . . . . . . . . . . . . 5
5. BGP Only To Customer attribute . . . . . . . . . . . . . . . 5
5.1. Attribute usage . . . . . . . . . . . . . . . . . . . . . 5
6. Additional Considerations . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
For the purposes 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] describes a method of
marking and detecting leaks which relies on operator maintained
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markings. Unfortunately, in most cases, a leaking router will likely
also be misconfigured to mark incorrectly. The proposed mechanism
provides an opportunity to detect route leaks made by third parties
but provides no support to avoid route leak creation. The leak
avoidance still relies on communities which are optional and often
missed due to mistakes or misunderstanding of the BGP configuration
process.
It has been suggested to use white list filtering, relying on knowing
the prefixes in the customer cone as import filtering, in order to
detect route leaks. Unfortunately, a large number of incidents is
created by leaking routes defined in customer cone; a lot of medium
size transit operators use a single prefix list as only the ACL for
export filtering, without community tagging and and paying attention
to the source of a learned route. So, if they learn a customer's
route from their provider or peer - they will announce it in all
directions, including other providers or peers. This
misconfiguration affects a limited number of prefixes; but such route
leaks will obviously bypass customer cone import filtering made by
upper level upstream providers.
Also, route tagging which relies on operator maintained policy
configuration is too easily and too often misconfigured.
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 and a way to create double-boundary filters for detection and
preventing propagation of route leaks via a new BGP Path Attribute.
2. BGP Role
BGP Role is new mandatory configuration option. It reflects the
real-world agreement between two BGP speakers about their business
relationship.
Allowed Role values are:
o Provider - sender is a transit provider to neighbor;
o Customer - sender is customer of neighbor;
o Peer - sender and neighbor are peers;
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o Internal - sender is part of an internal AS of an organization
which has multiple ASs, is a confederation, ...
Since BGP Role reflects the relationship between two BGP speakers, it
could also be used for more than route leak mitigation.
3. 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.
+--------+----------------------+
| Value | Role name |
+--------+----------------------+
| 0 | Undefined |
| 1 | Sender is Peer |
| 2 | Sender is Provider |
| 3 | Sender is Customer |
| 4 | Sender is Internal |
+--------+----------------------+
Table 1: Predefined BGP Role Values
4. Role correctness
Section 2 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, use the BGP Role check 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 SHOULD check value of
the received capability with its own BGP Role. The allowed pairings
are (first a sender's Role, second the receiver's Role):
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+--------------+----------------+
| Sender Role | Receiver Role |
+--------------+----------------+
| Peer | Peer |
| Provider | Customer |
| Customer | Provider |
| Internal | Internal |
+--------------+----------------+
Table 2: Allowed Role Capabilities
In all other cases speaker MUST send a Role Mismatch Notification
(code 2, sub-code <TBD2>).
4.1. 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 BGP Role
capability in their OPEN message. If a speaker rejects a connection,
it MUST send a Connection Rejected Notification [RFC4486]
(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.
5. BGP Only To Customer attribute
The Only To Customer (OTC) attribute is a new optional, transitive
BGP Path attribute with the Type Code <TBD3>. This attribute has
zero length as it used only as a flag.
5.1. Attribute usage
There are four rules for setting the OTC attribute:
1. The OTC attribute SHOULD be added to all incoming routes if the
receiver's Role is Customer or Peer;
2. Routes with the OTC attribute set MUST NOT be announced to a
neighbor which is a Provider or a Peer;
3. The OTC attribute SHOULD be added to all outgoing routes if the
neighbor has not sent the Role capability in the OPEN message and
sender's Role is Provider or Peer;
4. If the receiver's Role is Provider or Peer, incoming routes with
the OTC attribute set SHOULD be given a lower local preference,
or they MAY be dropped.
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The first two rules avoid creation of route leaks by an AS. The last
two rules provide the data to allow detection of route leaks made by
some other AS in the AS Path.
The OTC attribute will be added automatically if at least one of the
speakers correctly sets its role. Additionally, the OTC attribute
will be checked if at least one of the speakers set its role
correctly. In other words, this double-checks at borders to prevent
route leaks.
6. Additional Considerations
As 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.
7. 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, transitive BGP Path Attributes
option, named "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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8. Security Considerations
This document proposes a mechanism for avoiding route leaks, that are
the result of BGP policy misconfiguration. That includes preventing
route leaks created inside an AS (company), and route leak detection,
if a route was leaked by third party.
Deliberate sending of a known conflicting BGP Role could be used to
sabotage a BGP connection. This is easily detectable.
Deliberate mis-marking of the OTC flag could be used to sabotage a
route's propagation.
BGP Role is disclosed only to an immediate BGP speaker, so it will
not itself reveal any sensitive information to third parties.
On the other hand, OTC is a transitive BGP AS_PATH attribute which
reveals a bit about a BGP speaker's business relationship. It will
give a strong hint that some link isn't customer to provider, but
will not help to distinguish if it is provider to customer or peer to
peer. If OTC is BGPsec signed, it can not be removed for business
confidentiality.
9. References
9.1. 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,
<http://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,
<http://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, <http://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, <http://www.rfc-editor.org/info/rfc5492>.
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9.2. Informative References
[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-03 (work in progress), October 2015.
[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-01 (work in progress), October 2015.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://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
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