Network Working Group A. Azimov
Internet-Draft E. Bogomazov
Intended status: Standards Track Qrator Labs
Expires: August 19, 2019 R. Bush
Internet Initiative Japan
K. Patel
Arrcus, Inc.
K. Sriram
US NIST
February 15, 2019
Route Leak Prevention using Roles in Update and Open messages
draft-ietf-idr-bgp-open-policy-05
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, with no
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, RS, RS-client, 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 https://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 August 19, 2019.
Copyright Notice
Copyright (c) 2019 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
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Peering Relationships . . . . . . . . . . . . . . . . . . . . 3
3. BGP Role . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Role capability . . . . . . . . . . . . . . . . . . . . . . . 4
5. Role correctness . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Strict mode . . . . . . . . . . . . . . . . . . . . . . . 6
6. BGP Internal Only To Customer attribute . . . . . . . . . . . 6
7. Attribute or Community . . . . . . . . . . . . . . . . . . . 6
8. Compatibility with BGPsec . . . . . . . . . . . . . . . . . . 7
9. Additional Considerations . . . . . . . . . . . . . . . . . . 7
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
11. Security Considerations . . . . . . . . . . . . . . . . . . . 8
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
13.1. Normative References . . . . . . . . . . . . . . . . . . 8
13.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. 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
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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 using the 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[RFC7908]. 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 mechanism to strongly prevent route
leak creation.
Also, route tagging which relies on operator maintained policy
configuration is too easily, and too often, misconfigured.
2. Peering Relationships
Despite uses of words such as "Customer," "Peer." etc. described
above are not business relationships, who pays whom, etc. These are
common terms to represent restrictions on BGP route propagation,
sometimes known as the Gao-Rexford model.
A Provider: MAY send to a customer all available prefixes.
A Customer: MAY send to a provider their own prefixes and prefixes
learned from any of their customers. A customer MUST NOT send to
a provider prefixes learned from peers, other providers, or RS.
A Route Server (RS) MAY send to a RS client all available prefixes.
A Route Server Client (RS-client) MAY send to an RS its own prefixes
and prefixes learned from its customers. A RS-client MUST NOT
send to an RS prefixes learned from peers, providers, or other RS.
A Peer: MAY send to a peer its own prefixes and prefixes learned
from its customers. A peer MUST NOT send to a peer prefixes
learned from other peers, providers, or RS.
An Internal: MAY send all available prefixes through internal link.
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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. But violation of rules marked MUST NOT may
result in route leaks. While these peering relations cover 99% of
possible scenarios, their configuration isn't part of the BGP itself,
thus requiring configuration of communities and corresponding egress
prefix filters. The automation of this process may significantly
decrease number of configuration mistakes.
3. BGP Role
BGP Role is new configuration option that SHOULD be configured on
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 RS - sender is route server at internet exchange point (IX)
o RS-client - sender is client of RS at internet exchange point (IX)
o Peer - sender and neighbor are peers;
o Internal - sender and neighbor are part of the same organization.
For iBGP sessions, only the 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.
4. 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 Internal |
| 1 | Sender is Provider |
| 2 | Sender is RS |
| 3 | Sender is RS-Client |
| 4 | Sender is Customer |
| 5 | Sender is Peer |
+-------+---------------------+
Table 1: Predefined BGP Role Values
5. Role correctness
Section 3 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 correspond. 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 the 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 |
+-------------+---------------+
| Internal | Internal |
| Provider | Customer |
| Customer | Provider |
| RS | RS-Client |
| RS-Client | RS |
| Peer | Peer |
+-------------+---------------+
Table 2: Allowed Role Capabilities
In case of any other pairs of roles, a speaker MUST send a Role
Mismatch Notification (code 2, sub-code <TBD2>).
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5.1. 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 a neighbor which does not announce the
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.
6. 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 four rules of iOTC attribute usage:
1. The iOTC attribute MUST be added to all incoming routes if the
receiver's Role is Customer, Peer, or RS-client;
2. Routes with the iOTC attribute set MUST NOT be announced by a
sender whose Role is Customer, Peer, or RS-client;
3. A sender MUST NOT include iOTC in UPDATE messages advertised to
eBGP neighbor if its Role isn't Internal.
4. If iOTC is contained in an UPDATE message from eBGP speaker and
receiver's Role isn't Internal then this attribute MUST be
removed.
These rules provide mechanism to strongly prevent route leak creation
by an AS.
7. 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 policy 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 mis-configuration. There is a question
whether the iOTC marking should be an attribute or a well-known
community.
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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.
8. Compatibility with BGPsec
As the iOTC attribute is non-transitive, it is not seen by or signed
by BGPsec [RFC8205].
9. Additional Considerations
As the BGP Role reflects the peering 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 ASs.
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. [RFC8212]
This document doesn't provide any security measures to check
correctness of iOTC usage if role isn't configured.
10. 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
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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.
11. Security Considerations
This document proposes a mechanism for prevention of route leaks that
are the result of BGP policy mis-configuration.
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.
12. Acknowledgments
The authors wish to thank Douglas Montgomery, Brian Dickson, Andrei
Robachevsky and Daniel Ginsburg for their contributions to a variant
of this work.
13. References
13.1. 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>.
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13.2. Informative References
[I-D.ietf-idr-route-leak-detection-mitigation]
Sriram, K. and A. Azimov, "Methods for Detection and
Mitigation of BGP Route Leaks", draft-ietf-idr-route-leak-
detection-mitigation-10 (work in progress), October 2018.
[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>.
[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>.
[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>.
[RFC8212] Mauch, J., Snijders, J., and G. Hankins, "Default External
BGP (EBGP) Route Propagation Behavior without Policies",
RFC 8212, DOI 10.17487/RFC8212, July 2017,
<https://www.rfc-editor.org/info/rfc8212>.
Authors' Addresses
Alexander Azimov
Qrator Labs
Email: a.e.azimov@gmail.com
Eugene Bogomazov
Qrator Labs
Email: eb@qrator.net
Randy Bush
Internet Initiative Japan
Email: randy@psg.com
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Keyur Patel
Arrcus, Inc.
Email: keyur@arrcus.com
Kotikalapudi Sriram
US NIST
Email: ksriram@nist.gov
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