wdiff draft-ietf-idr-bgp-open-policy-05.txt draft-ietf-idr-bgp-open-policy-06.txt

Network Working Group A. Azimov
Internet-Draft E. Bogomazov
Intended status: Standards Track Qrator Labs
Expires: August 19, 2019 January 9, 2020 R. Bush
Internet Initiative Japan & Arrcus
K. Patel
Arrcus, Inc.
K. Sriram
US NIST
February 15,
July 8, 2019

Route Leak Prevention using Roles in Update and Open messages
draft-ietf-idr-bgp-open-policy-05
draft-ietf-idr-bgp-open-policy-06

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 by operator configuration options, configuration, 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 OPEN to establish agreement of the (peer, customer,
provider, RS, RS-client, internal) Route Server, Route Server client) relationship of two
neighboring BGP speakers to enforce appropriate configuration on both
sides. Propagated routes are then marked with an iOTC OTC attribute
according to the agreed relationship relationship, allowing both prevention and
detection of route leaks.

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 RFC 2119
BCP 14 [RFC2119] [RFC8174] when, and only when when, they appear in all upper case. They may also appear in lower or mixed
case
capitals, as English words, without normative meaning. shown here.

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 August 19, 2019. January 9, 2020.

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 Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 3
2. Peering Relationships . . . . . . . . . . . . . . . . . . . . 3
3. BGP Role . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Role capability . . . . . . . . . . . . . . . . . . . . . . . 4
5. Role correctness . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Strict mode . . . . . . . . . . . . . . . . . . . . . . . 6 5
6. BGP Internal Only To Customer attribute . . . . . . . . . . . 6
7. Attribute or Community . . . . . . . . . . . . 6
7. Enforcement . . . . . . . 6
8. Compatibility with BGPsec . . . . . . . . . . . . . . . . . . 7
9. 6
8. Additional Considerations . . . . . . . . . . . . . . . . . . 7
10.
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
11.
10. Security Considerations . . . . . . . . . . . . . . . . . . . 8
12.
11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 8
13.
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
13.1.
12.1. Normative References . . . . . . . . . . . . . . . . . . 8
13.2.
12.2. 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
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 route(s) which were learned from transit
provider or peer and is then announced to another provider or peer. See[RFC7908]. 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
[I-D.ietf-idr-route-leak-detection-mitigation] uses large-communities
to detect attempt detection of route leaks made by
third parties but provides no mechanism leaks. While signaling using
communities is easy to strongly prevent route
leak creation.

Also, route tagging which implement, ut relies on operator maintained
policy configuration which is too easily, and too often,
misconfigured. Another problem may occur if the community signal is
stripped, accidentally or maliciously.

This document provides configuration automation using 'BGP roles',
which are negotiated using a new BGP Capability Code in OPEN message,
[RFC5492] Sec 4. Either or both BGP speakers MAY be configured to
require that this capability be agreed for the BGP OPEN to succeed.

A new BGP Path Attribute is specified that SHOULD be automatically
configured using BGP roles. This attribute prevents networks from
creating leaks, and detects leaks created by third-parties.

2. Peering Relationships

Despite uses of words such as "Customer," "Peer." etc. described
above etc.; these 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. model [cite].

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 its peers, from other providers,
or RS. from Route Servers.

A Route Server (RS) MAY send to a RS client 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, from its providers, or
from other RS. RS(s).

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, from its providers, or RS.

An Internal: MAY send all available prefixes through internal link. from RS(s).

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 Violation of the above rules marked MUST NOT may result in route leaks.
leaks so MUST not be allowed. Automatic enforment of these rules
should significantly reduce configuration mistakes. While these
enforcing the above rules will address most BGP peering relations cover 99% of
possible scenarios,
their configuration isn't part of the BGP itself,
thus itself; therefore requiring
configuration of communities ingress and corresponding egress prefix filters. The automation of this process may significantly
decrease number of configuration mistakes. filters is still strongly
advised.

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 transit customer of neighbor;

o RS - sender is route server a Route Server, usually at internet exchange point
(IX)

o RS-client 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.

+-------+---------------------+
| Value | Role name |
+-------+---------------------+
| 0 | Sender is Internal |
| 1 | Sender is Provider |
| 2 1 | Sender is RS |
| 3 2 | Sender is RS-Client |
| 4 3 | Sender is Customer |
| 5 4 | Sender is Peer |
+-------+---------------------+

Table 1: Predefined BGP Role Values

5. Role correctness

Section 3 described how BGP Role is a reflection of encodes 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):

Table 2: Allowed Role Capabilities

In case of any other pairs of roles,

If the Role pair is not in the above table, a speaker MUST send a
Role Mismatch Notification (code 2, sub-code <TBD2>).

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 the 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 (OTC) BGP Attribute is a new optional,
non-transitive
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 byte attribute usage: MUST apply the following policy:

1. The iOTC If a route with OTC attribute is received from Customer or RS-
client - it's a route leak and MUST be added rejected.

2. If a route with OTC attribute is received from Peer and its value
isn't equal to all incoming routes if the
receiver's Role neighbor's ASN - it's a route leak and MUST be
rejected.

3. If a route is Customer, Peer, received from a Provider, Peer or RS-client;

2. Routes with RS and the iOTC OTC
attribute has not been set it MUST NOT be announced by a
sender whose Role is Customer, Peer, or RS-client;

3. added with value equal to
AS number of the neighbor (sender).

The egress policy MUST be:

1. A sender route with the OTC attribute set MUST NOT include iOTC in UPDATE messages advertised be sent to
eBGP neighbor if its Role isn't Internal.

4. providers,
peers, or RS(s).

2. If iOTC route is contained in an UPDATE message from eBGP speaker sent to customer or peer and
receiver's Role isn't Internal then this the OTC attribute is not
set it MUST be
removed.

These rules provide mechanism added with value equal to strongly prevent route leak creation
by an AS. AS number of the sender.

Once the OTC attribute has been set, it MUST be preserved unchanged.

7. Attribute or Community Enforcement

Having the relationship hard set by agreement unequivocally agreed between the two peers in
BGP OPEN is critical; the routers BGP implementations 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 OTC MUST BE enforced by the router(s), BGP implementations, and
minimally not
exposed to user mis-configuration. 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 OTC marking. Hence, this
document specifies iOTC OTC 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 might have other uses. As an For 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

There are peering relationships which are 'complex'; e.g. when both
parties are intentionally sending prefixes received from each other
to their peers and/or upstreams. If multiple BGP peerings can
segregate the 'complex' parts of the relationship, the complex
peering roles can be segregated into different BGP sessions, and
normal BGP Roles MUST be used on the non-complex sessions. No Roles
SHOULD be configured on 'complex' BGP sessions, and OTC MUST be set
by configuration on a per-prefix basis. There can be no measures to
check correctness of iOTC usage OTC use if role isn't Role is not configured.

10.

9. 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 transitive BGP Path Attributes
option, named "Internal Only "Only To Customer", assigned value <TBD3> [To be
removed upon publication:
http://www.iana.org/assignments/bgp-parameters/bgp-
parameters.xhtml#bgp-parameters-2] http://www.iana.org/assignments/bgp-
parameters/bgp-parameters.xhtml#bgp-parameters-2] [RFC4271]. The
length of this attribute is 0.

11.

10. 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

A misconfiguration in OTC setup may affect prefix propagation. But
the automation that is disclosed only to an immediate provided by BGP neighbor, so it will
not itself reveal any sensitive information to third parties.

12. roles should make such
misconfiguration unlikely.

11. Acknowledgments

The authors wish to thank Douglas Montgomery, Brian Dickson, Andrei
Robachevsky
Robachevsky, and Daniel Ginsburg for their contributions to a variant
of this work.

13.

12. References

13.1.

12.1. 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>.

13.2.

[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>.

12.2. 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 & Arrcus

Email: randy@psg.com

Keyur Patel
Arrcus, Inc.

Email: keyur@arrcus.com
Kotikalapudi Sriram
US NIST

Email: ksriram@nist.gov