draft-ietf-idr-bgp-open-policy-15.txt   draft-ietf-idr-bgp-open-policy-16.txt 
Network Working Group A. Azimov Network Working Group A. Azimov
Internet-Draft Qrator Labs & Yandex Internet-Draft Qrator Labs & Yandex
Intended status: Standards Track E. Bogomazov Intended status: Standards Track E. Bogomazov
Expires: July 20, 2021 Qrator Labs Expires: February 11, 2022 Qrator Labs
R. Bush R. Bush
Internet Initiative Japan & Arrcus, Inc. Internet Initiative Japan & Arrcus, Inc.
K. Patel K. Patel
Arrcus Arrcus
K. Sriram K. Sriram
USA NIST USA NIST
January 16, 2021 August 10, 2021
Route Leak Prevention using Roles in Update and Open messages Route Leak Prevention and Detection using Roles in UPDATE and OPEN
draft-ietf-idr-bgp-open-policy-15 Messages
draft-ietf-idr-bgp-open-policy-16
Abstract Abstract
Route leaks are the propagation of BGP prefixes which violate Route leaks are the propagation of BGP prefixes that violate
assumptions of BGP topology relationships; e.g. passing a route assumptions of BGP topology relationships, e.g., passing a route
learned from one lateral peer to another lateral peer or a transit learned from one lateral peer to another lateral peer or a transit
provider, passing a route learned from one transit provider to provider and passing a route learned from one transit provider to
another transit provider or a lateral peer. Existing approaches to another transit provider or a lateral peer. Existing approaches to
leak prevention rely on marking routes by operator configuration, leak prevention rely on marking routes by operator configuration,
with no check that the configuration corresponds to that of the eBGP with no check that the configuration corresponds to that of the eBGP
neighbor, or enforcement that the two eBGP speakers agree on the neighbor, or enforcement that the two eBGP speakers agree on the
relationship. This document enhances BGP OPEN to establish agreement relationship. This document enhances the BGP OPEN message to
of the (peer, customer, provider, Route Server, Route Server client) establish an agreement of the relationship on each eBGP session
relationship of two neighboring eBGP speakers to enforce appropriate between autonomous systems in order to enforce appropriate
configuration on both sides. Propagated routes are then marked with configuration on both sides. Propagated routes are then marked
an Only to Customer (OTC) attribute according to the agreed according to the agreed relationship, allowing both prevention and
relationship, allowing both prevention and detection of route leaks. detection of route leaks.
Requirements Language Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in "OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
Status of This Memo Status of This Memo
skipping to change at page 2, line 12 skipping to change at page 2, line 15
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
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This Internet-Draft will expire on July 20, 2021. This Internet-Draft will expire on February 11, 2022.
Copyright Notice Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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described in the Simplified BSD License. described in the Simplified BSD License.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Peering Relationships . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Peering Relationships . . . . . . . . . . . . . . . . . . . . 4
3. BGP Role . . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. BGP Role . . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. BGP Role Capability . . . . . . . . . . . . . . . . . . . . . 5 3.1. BGP Role Capability . . . . . . . . . . . . . . . . . . . 5
5. Role correctness . . . . . . . . . . . . . . . . . . . . . . 5 3.2. Role Correctness . . . . . . . . . . . . . . . . . . . . 5
5.1. Strict mode . . . . . . . . . . . . . . . . . . . . . . . 6 4. BGP Only to Customer (OTC) Attribute . . . . . . . . . . . . 6
6. BGP Only to Customer (OTC) Attribute . . . . . . . . . . . . 6 5. Additional Considerations . . . . . . . . . . . . . . . . . . 8
7. Enforcement . . . . . . . . . . . . . . . . . . . . . . . . . 7 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
8. Additional Considerations . . . . . . . . . . . . . . . . . . 7 7. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
10. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8.1. Normative References . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9 8.2. Informative References . . . . . . . . . . . . . . . . . 11
11.1. Normative References . . . . . . . . . . . . . . . . . . 9 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 11
11.2. Informative References . . . . . . . . . . . . . . . . . 9 Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 10 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction 1. Introduction
A BGP route leak occurs when a route is learned from a transit A BGP route leak occurs when a route is learned from a transit
provider or lateral peer and then announced to another provider or provider or lateral peer and then announced to another provider or
lateral peer. See [RFC7908]. These are usually the result of lateral peer [RFC7908]. These are usually the result of
misconfigured or absent BGP route filtering or lack of coordination misconfigured or absent BGP route filtering or lack of coordination
between two eBGP speakers. between autonomous systems (ASes).
The mechanism proposed in Existing approaches to leak prevention rely on marking routes by
[I-D.ietf-grow-route-leak-detection-mitigation] uses large- operator configuration, with no check that the configuration
communities to perform detection and mitigation of route leaks. corresponds to that of the eBGP neighbor, or enforcement that the two
While signaling using communities is easy to implement and deploy eBGP speakers agree on the relationship. This document enhances the
quickly, it normally relies on operator-maintained policy BGP OPEN message to establish an agreement of the relationship on
configuration, which is vulnerable to misconfiguration [Streibelt]. each eBGP session between autonomous systems in order to enforce
The community signal can also be stripped at the ISP boundaries. appropriate configuration on both sides. Propagated routes are then
marked according to the agreed relationship, allowing both prevention
and detection of route leaks.
This document provides configuration automation using 'BGP roles', This document provides configuration automation using BGP Roles,
which are negotiated using a new BGP Capability Code in OPEN message which are negotiated using a BGP Role Capability in the OPEN message
(see Section 4 in [RFC5492]). Either or both BGP speakers MAY be [RFC5492]. An eBGP speaker may require the use of this capability
configured to require that this capability be agreed for the BGP OPEN and confirmation of BGP Role with a neighbor for the BGP OPEN to
to succeed. succeed.
A new optional, transitive BGP Path Attribute Only to Customer (OTC) An optional, transitive BGP Path Attribute, called Only to Customer
is specified that SHOULD be automatically configured using BGP roles. (OTC), is specified in Section 4. It prevents ASes from creating
This attribute prevents networks from creating leaks, and detects leaks, and detects leaks created by the ASes in the middle of an AS
leaks created by third parties. path. The main focus/applicability is the Internet (IPv4 and IPv6
unicast route advertisements).
In the rest of this document, we use the term "peer" to refer to 1.1. Terminology
"lateral peer" for simplicity.
2. Peering Relationships In the rest of this document, the term "Peer" is used to refer to a
"lateral peer" for simplicity. Also, the terms Provider and Customer
are used to refer to a transit provider and a transit customer,
respectively. Further, the terms RS and RS-Client are used to refer
to a Route Server and its client, respectively.
Despite the use of terms such as "customer", "peer", etc. in this The terms "local AS" and "remote AS" are used to refer to the two
document, these are not necessarily business relationships based on ends of an eBGP session. The "local AS" is the AS where the protocol
payment agreements. These terms are used to represent restrictions action being described is to be performed, and "remote AS" is the AS
on BGP route propagation, sometimes known as the Gao-Rexford model at the other end of the eBGP session in consideration.
[Gao]. The following is a list of various roles in eBGP peering and
the corresponding rules for route propagation:
Provider: MAY send to a customer all available prefixes. The use of the term "route is ineligible" in this document has the
same meaning as in [RFC4271], i.e., "route is ineligible to be
installed in Loc-RIB and will be excluded from the next phase of
route selection."
Customer: MAY send to a provider prefixes which the sender 2. Peering Relationships
originates 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 from Route Servers.
Route Server (RS): MAY send to an Route Server client (RS-client) The terms defined and used in this document (see below) do not
all available prefixes. necessarily represent business relationships based on payment
agreements. These terms are used to represent restrictions on BGP
route propagation, sometimes known as the Gao-Rexford model [Gao].
The following is a list of BGP Roles for eBGP peering and the
corresponding rules for route propagation:
RS-client: MAY send to an RS prefixes which the sender originates Provider: MAY propagate any available route to a Customer.
and prefixes learned from its customers. An RS-client MUST NOT
send to an RS prefixes learned from its peers or providers, or
from another RS.
Peer: MAY send to a peer prefixes which the sender originates and Customer: MAY propagate any route learned from a Customer, or
prefixes learned from its customers. A peer MUST NOT send to a locally originated, to a Provider. All other routes MUST NOT be
peer prefixes learned from other peers, from its providers, or propagated.
from RS(s).
Of course, any BGP speaker may apply policy to reduce what is Route Server (RS): MAY propagate any available route to a Route
announced, and a recipient may apply policy to reduce the set of Server Client (RS-Client).
routes they accept. Violation of the above rules may result in route
leaks and MUST NOT be allowed. Automatic enforcement of these rules
should significantly reduce route leaks that may otherwise occur due
to manual configuration mistakes. While enforcing the above rules
will address most BGP peering scenarios, their configuration is not
part of BGP itself; therefore, configuration of ingress and egress
prefix filters is still strongly advised.
3. BGP Role RS-Client: MAY propagate any route learned from a Customer, or
locally originated, to an RS. All other routes MUST NOT be
propagated.
BGP Role is a new configuration option that is configured on a per- Peer: MAY propagate any route learned from a Customer, or locally
session basis. BGP Roles reflect the agreement between two BGP originated, to a Peer. All other routes MUST NOT be propagated.
speakers about their relationship. One of the Roles described below
SHOULD be configured on each eBGP session between ISPs that carry
IPv4 and(or) IPv6 unicast prefixes.
Allowed Role values for eBGP sessions between ISPs are: A BGP speaker may apply policy to reduce what is announced, and a
recipient may apply policy to reduce the set of routes they accept.
Violation of the above rules may result in route leaks. Automatic
enforcement of these rules should significantly reduce route leaks
that may otherwise occur due to manual configuration mistakes.
o Provider - sender is a transit provider to neighbor; 3. BGP Role
o Customer - sender is a transit customer of neighbor; The BGP Role characterizes the relationship between the eBGP speakers
forming a session. BGP Role is configured on a per-session basis.
An eBGP speaker SHOULD configure the BGP Role locally based on the
local AS's knowledge of its Role. The only exception is when the
eBGP connection is complex (see Section 5). BGP Roles are mutually
confirmed using the BGP Role Capability (described in Section 3.1) on
each eBGP session between autonomous systems (ASes). One of the
Roles described below SHOULD be configured at the local AS for each
eBGP session with a neighbor (remote AS) (see definitions in
Section 1.1).
o RS - sender is a Route Server, usually at an Internet exchange Allowed Roles for eBGP sessions are:
point (IX);
o RS-client - sender is client of an RS; o Provider - the local AS is a transit Provider of the remote AS;
o Customer - the local AS is a transit Customer of the remote AS;
o Peer - sender and neighbor are peers. o RS - the local AS is a Route Server (usually at an Internet
exchange point) and the remote AS is its RS-Client;
Since BGP Role reflects the relationship between two BGP speakers, it o RS-Client - the local AS is a client of an RS and the RS is the
could also be used for other purposes besides route leak mitigation. remote AS;
4. BGP Role Capability o Peer - the local and remote ASes are Peers (i.e., have a lateral
peering relationship).
The TLV (type, length, value) of the BGP Role capability are: 3.1. BGP Role Capability
o Type - <TBD1>; The BGP Role Capability is defined as follows:
o Length - 1 (byte); o Code - 9
o Length - 1 (octet)
o Value - integer corresponding to speaker's BGP Role (see Table 1). o Value - integer corresponding to speaker's BGP Role (see Table 1).
+-------+---------------------+ +-------+------------------------------+
| Value | Role name | | Value | Role name (for the local AS) |
+-------+---------------------+ +-------+------------------------------+
| 0 | Sender is Provider | | 0 | Provider |
| 1 | Sender is RS | | 1 | RS |
| 2 | Sender is RS-client | | 2 | RS-Client |
| 3 | Sender is Customer | | 3 | Customer |
| 4 | Sender is Peer | | 4 | Peer (Lateral Peer) |
+-------+---------------------+ | 5-255 | Unassigned |
+-------+------------------------------+
Table 1: Predefined BGP Role Values Table 1: Predefined BGP Role Values
5. Role correctness If BGP Role is locally configured, the eBGP speaker MUST advertise
BGP Role Capability in the BGP OPEN message. An eBGP speaker MUST
NOT advertise multiple versions of the BGP Role Capability.
Section 3 described how BGP Role encodes the relationship between two 3.2. Role Correctness
eBGP 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 applied with a set of Section 3.1 described how BGP Role encodes the relationship on each
constraints on how speakers' BGP Roles MUST correspond. Of course, eBGP session between autonomous systems (ASes).
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 The mere receipt of BGP Role Capability does not automatically
of the received capability (i.e., the sender's role) with its own BGP guarantee the Role agreement between two eBGP neighbors. If the BGP
Role. The allowed pairings are as follows: Role Capability is advertised, and one is also received from the
peer, the roles MUST correspond to the relationships in Table 2. If
the roles do not correspond, the BGP speaker MUST reject the
connection using the Role Mismatch Notification (code 2, subcode 8).
+---------------+-----------------+ +---------------+----------------+
| Sender's Role | Receiver's Role | | Local AS Role | Remote AS Role |
+---------------+-----------------+ +---------------+----------------+
| Provider | Customer | | Provider | Customer |
| Customer | Provider | | Customer | Provider |
| RS | RS-client | | RS | RS-Client |
| RS-client | RS | | RS-Client | RS |
| Peer | Peer | | Peer | Peer |
+---------------+-----------------+ +---------------+----------------+
Table 2: Allowed Pairs of Role Capabilities Table 2: Allowed Pairs of Role Capabilities
If the role of the receiving speaker for the eBGP session in If the BGP Role Capability is sent, but one is not received, then the
consideration is included in Table 1 and the observed Role pair is connection MAY be rejected using the Role Mismatch Notification (code
not in the above table, then the receiving speaker MUST reject the 2, subcode 8); this mode of operation is called the "strict mode".
eBGP connection, send a Role Mismatch Notification (code 2, subcode For backward compatibility, if the BGP speaker does not receive the
<TBD2>), and also send a Connection Rejected Notification [RFC4486] capability from its peer, it SHOULD ignore the absence of BGP Role
(Notification with error code 6, subcode 5). Capability and proceed with session establishment; this SHOULD be the
default non-strict mode of operation. In this case, the locally
configured BGP Role is used for the procedures described in
Section 4.
5.1. Strict mode If an eBGP speaker receives multiple but identical BGP Role
Capabilities with the same value in each, then the speaker MUST
consider it to be a single BGP Role Capability and proceed [RFC5492].
If multiple BGP Role Capabilities are received and not all of them
have the same value, then the BGP speaker MUST reject the connection
using the Role Mismatch Notification (code 2, subcode 8).
A new BGP configuration option "strict mode" is defined with values The BGP Role value for the local AS is used in the route leak
of true or false. If set to true, then the speaker MUST refuse to prevention and detection procedures described in Section 4.
establish a BGP session with a neighbor which does not announce the
BGP Role capability in the OPEN message. If a speaker rejects a
connection, it MUST send a send a Role Mismatch Notification (code 2,
subcode <TBD2>), and also 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 Only to Customer (OTC) Attribute 4. BGP Only to Customer (OTC) Attribute
Newly defined here, the Only to Customer (OTC) is an optional, 4 The Only to Customer (OTC) Attribute is an optional transitive path
bytes long, transitive BGP Path attribute with the Type Code <TBD3>. attribute with Attribute Type Code 35 and a length of 4 octets. The
The purpose of this attribute is to guarantee that once a route is purpose of this attribute is to guarantee that once a route is sent
sent to customer, peer, or RS-client, it will subsequently go only to to a Customer, Peer, or RS-Client, it will subsequently go only to
customers. The value of OTC is an AS number determined by policy as Customers. The attribute value is an AS number determined by the
described below. The semantics and usage of the OTC attribute are policy described below.
made clear by the ingress and egress policies described below.
The following ingress policy applies to the OTC attribute: The following ingress policy applies to the processing of the OTC
Attribute:
1. If a route with OTC attribute is received from a Customer or RS- 1. If a route with the OTC Attribute is received from a Customer or
client, then it is a route leak and MUST be rejected. RS-Client, then it is a route leak and MUST be considered
ineligible (see Section 1.1).
2. If a route with OTC attribute is received from a Peer and its 2. If a route with the OTC Attribute is received from a Peer and at
value is not equal to the sending neighbor's Autonomous System least one of the OTC Attributes has a value that is not equal to
(AS) number, then it is a route leak and MUST be rejected. the remote (i.e., Peer's) AS number, then it is a route leak and
MUST be considered ineligible.
3. If a route is received from a Provider, Peer, or RS and the OTC 3. If a route is received from a Provider, Peer, or RS, and the OTC
attribute is not present, then it MUST be added with value equal Attribute is not present, then it MUST be added with a value
to the sending neighbor's AS number. equal to the AS number of the remote AS.
The egress policy MUST be: The following egress policy applies to the processing of the OTC
Attribute:
1. A route with the OTC attribute set MUST NOT be sent to Providers, 1. If a route is to be advertised to a Customer, Peer, or RS-Client
Peers, or RS(s). (when the sender is an RS), and the OTC Attribute is not present,
then an OTC Attribute MUST be added with a value equal to the AS
number of the local AS.
2. If route is sent to a Customer or Peer, or an RS-client (when the 2. If a route already contains the OTC Attribute, it MUST NOT be
sender is an RS) and the OTC attribute is not present, then it propagated to Providers, Peers, or RS(s).
MUST be added with value equal to AS number of the sender.
Once the OTC attribute has been set, it MUST be preserved unchanged. The described policies provide both leak prevention for the local AS
and leak detection and mitigation multiple hops away. In the case of
prevention at the local AS, the presence of an OTC Attribute
indicates to the egress router that the route was learned from a
Peer, Provider, or RS, and it can be advertised only to the
customers. The same OTC Attribute which is set locally also provides
a way to detect route leaks by an AS multiple hops away if a route is
received from a Customer, Peer, or RS-Client.
7. Enforcement The OTC Attribute may be set by the egress policy of remote AS or by
the ingress policy of local AS. In both scenarios, the OTC value
will be the same. This makes the scheme more robust and benefits
early adopters.
Having the relationship unequivocally agreed between the two peers in If an eBGP speaker receives an UPDATE with an OTC Attribute with a
BGP OPEN is critical; BGP implementations MUST enforce the length different from 4 octets, then the UPDATE SHALL be considered
relationship/role establishment rules (see Section 5) in order to malformed. If malformed, the UPDATE message SHALL be handled using
ameliorate operator policy configuration errors (if any). the approach of "treat-as-withdraw" [RFC7606].
Similarly, the application of that relationship on prefix propagation Once the OTC Attribute has been set, it MUST be preserved unchanged.
using OTC MUST be enforced by the BGP implementations, and not
exposed to user misconfiguration.
As opposed to communities, BGP attributes may not be generally Correct implementation of the procedures specified in this document
modified or stripped by the operator; BGP router implementations is not expected to result in the presence of multiple OTC Attributes
enforce such treatment. This is the desired property for the OTC in an UPDATE. However, if an eBGP speaker receives multiple OTC
marking. Hence, this document specifies OTC as an attribute. Attributes with a route, then the only difference in the processing
is in Step 2 of the ingress policy.
8. Additional Considerations The described ingress and egress policies are applicable only for
unicast IPv4 and IPv6 address families and MUST not affect other
address families by default. The operator MUST NOT have the ability
to modify the policies defined in this section.
5. Additional Considerations
There are peering relationships that are 'complex', i.e., both There are peering relationships that are 'complex', i.e., both
parties are intentionally sending prefixes received from each other parties intentionally advertise prefixes received from each other to
to their non-transit peers and/or transit providers. If multiple BGP their Peers and/or transit Providers. If multiple eBGP sessions can
peerings can segregate the 'complex' parts of the relationship, the segregate the 'complex' parts of the relationship, then the complex
complex peering roles can be segregated into different normal BGP peering roles can be segregated into different normal eBGP sessions,
sessions, and BGP Roles MUST be used on each of the resulting normal and BGP Roles MUST be used on each of the resulting normal (non-
(non-complex) BGP sessions. complex) eBGP sessions.
No Roles SHOULD be configured on a 'complex' BGP session (assuming it No Roles SHOULD be configured on a 'complex' eBGP session (assuming
is not segregated) and in that case, OTC MUST be set by configuration it is not segregated) and in that case, the OTC Attribute processing
on a per-prefix basis. However, there are no built-in measures to MUST be done relying on configuration on a per-prefix basis. Also,
check correctness of OTC use if BGP Role is not configured. in this case, the per-prefix peering configuration MUST follow the
same definitions of peering relations as described in Section 2.
However, in this case, there are no built-in measures to check
correctness of the per-prefix peering configuration.
The incorrect setting of BGP Roles and/or OTC attributes may affect The incorrect setting of BGP Roles and/or OTC Attributes may affect
prefix propagation. Further, this document doesn't specify any prefix propagation. Further, this document does not specify any
special handling of incorrect/private ASNs in OTC attribute; such special handling of incorrect AS numbers in the OTC Attribute. Such
errors should not happen with proper configuration. errors should not happen with proper configuration.
As the BGP Role reflects the peering relationship between neighbors, 6. IANA Considerations
it might have other uses beyond the route leak solution discussed so
far. 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.
The use of BGP Roles are specified for unicast IPv4 and IPv6 address IANA has registered a new BGP Capability described in Section 3.1 in
families. While BGP roles can be configured on other address the "Capability Codes" registry's "IETF Review" range [RFC5492]. The
families its applicability for these cases is out of scope of this description for the new capability is "BGP Role". IANA has assigned
document. the value 9 [to be removed upon publication:
https://www.iana.org/assignments/capability-codes/capability-
codes.xhtml]. This document is the reference for the new capability.
As BGP role configuration results in automatic creation of inbound/ The BGP Role capability includes a Value field, for which IANA is
outbound filters, existence of roles should be treated as existence requested to create and maintain a new sub-registry called "BGP Role
of Import and Export policy [RFC8212]. Value" in the Capability Codes registry. Assignments consist of a
Value and a corresponding Role name. Initially, this registry is to
be populated with the data contained in Table 1 found in Section 3.1.
Future assignments may be made by the "IETF Review" policy as defined
in [RFC8126]. The registry is as shown in Table 3.
9. IANA Considerations +-------+--------------------------------+---------------+
| Value | Role name (for the local AS) | Reference |
+-------+--------------------------------+---------------+
| 0 | Provider | This document |
| 1 | RS | This document |
| 2 | RS-Client | This document |
| 3 | Customer | This document |
| 4 | Peer (i.e., Lateral Peer) | This document |
| 5-255 | To be assigned by IETF Review |
+-------+--------------------------------+---------------+
This document defines a new Capability Codes option [to be removed Table 3: IANA Registry for BGP Role
upon publication: https://www.iana.org/assignments/capability-codes/
capability-codes.xhtml ] [RFC5492], named "BGP Role" with an assigned
value <TBD1>. The length of this capability is 1.
The BGP Role capability includes a Value field, for which IANA is IANA has registered a new OPEN Message Error subcode named the "Role
requested to create and maintain a new sub-registry called "BGP Role Mismatch" (see Section 3.2) in the OPEN Message Error subcodes
Value". Assignments consist of Value and corresponding Role name. registry. IANA has assigned the value 8 [to be removed upon
Initially this registry is to be populated with the data contained in publication: https://www.iana.org/assignments/bgp-parameters/bgp-
Table 1 found in Section 4. Future assignments may be made by a parameters.xhtml#bgp-parameters-6]. This document is the reference
Standard Action procedure [RFC8126]. The allocation policy for new for the new subcode.
entries up to and including value 127 is "Expert Review" [RFC8126].
The allocation policy for values 128 through 251 is "First Come First
Served". The values from 252 through 255 are for "Experimental Use".
This document defines a new subcode, "Role Mismatch" with an assigned IANA has also registered a new path attribute named "Only to Customer
value <TBD2> in the OPEN Message Error subcodes registry [to be (OTC)" (see Section 4) in the "BGP Path Attributes" registry. IANA
removed upon publication: http://www.iana.org/assignments/bgp- has assigned code value 35 [To be removed upon publication:
parameters/bgp-parameters.xhtml#bgp-parameters-6] [RFC4271]. http://www.iana.org/assignments/bgp-parameters/bgp-
parameters.xhtml#bgp-parameters-2]. This document is the reference
for the new attribute.
This document defines a new optional, transitive BGP Path Attributes 7. Security Considerations
option, named "Only to Customer (OTC)" with an 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 four bytes.
10. Security Considerations The security considerations of BGP (as specified in [RFC4271] and
[RFC4272]) apply.
This document proposes a mechanism for prevention of route leaks that This document proposes a mechanism using BGP Role for the prevention
are the result of BGP policy misconfiguration. and detection of route leaks that are the result of BGP policy
misconfiguration. A misconfiguration of the BGP Role may affect
prefix propagation. For example, if a downstream (i.e., towards a
Customer) peering link were misconfigured with a Provider or Peer
role, this will limit the number of prefixes that can be advertised
in this direction. On the other hand if an upstream provider were
misconfigured (by a local AS) with the Customer role, this may result
in propagating routes that are received from other Providers or
Peers. But the BGP Role negotiation and the resulting confirmation
of Roles make such misconfigurations unlikely.
A misconfiguration in OTC setup may affect prefix propagation. But Setting the strict mode of operation for BGP Role negotiation as the
the automation that is provided by BGP roles should make such default may result in a situation where the eBGP session will not
misconfiguration unlikely. come up after a software update. Such an implementation of this
document is strongly discouraged.
11. References Removing the OTC Attribute or changing its value can limit the
opportunity of route leak detection. Such activity can be done on
purpose as part of a Man in the Middle (MITM) attack. For example,
an AS can remove the OTC Attribute on a received route and then leak
the route to its transit provider. Such malicious activity cannot be
prevented without cryptographically signing the BGP UPDATE [RFC8205]
or out of band detection [I-D.ietf-sidrops-aspa-verification], but
such schemes are beyond the scope of this document.
11.1. Normative References Adding an OTC Attribute when the route is advertised from Customer to
Provider will limit the propagation of the route. Such a route may
be considered as ineligible by the immediate Provider or its Peers or
upper layer Providers. This kind of OTC Attribute addition is
unlikely to happen on the Provider side because it will limit the
traffic volume towards its Customer. On the Customer side, adding an
OTC Attribute for traffic engineering purposes is also discouraged
because it will limit route propagation in an unpredictable way.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A [RFC4271] Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A
Border Gateway Protocol 4 (BGP-4)", RFC 4271, Border Gateway Protocol 4 (BGP-4)", RFC 4271,
DOI 10.17487/RFC4271, January 2006, DOI 10.17487/RFC4271, January 2006,
<https://www.rfc-editor.org/info/rfc4271>. <https://www.rfc-editor.org/info/rfc4271>.
[RFC4486] Chen, E. and V. Gillet, "Subcodes for BGP Cease [RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
Notification Message", RFC 4486, DOI 10.17487/RFC4486, RFC 4272, DOI 10.17487/RFC4272, January 2006,
April 2006, <https://www.rfc-editor.org/info/rfc4486>. <https://www.rfc-editor.org/info/rfc4272>.
[RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement [RFC5492] Scudder, J. and R. Chandra, "Capabilities Advertisement
with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February with BGP-4", RFC 5492, DOI 10.17487/RFC5492, February
2009, <https://www.rfc-editor.org/info/rfc5492>. 2009, <https://www.rfc-editor.org/info/rfc5492>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, Patel, "Revised Error Handling for BGP UPDATE Messages",
May 2017, <https://www.rfc-editor.org/info/rfc8174>. RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
11.2. Informative References
[Gao] Gao, L. and J. Rexford, "Stable Internet routing without
global coordination", IEEE/ACM Transactions on
Networking, Volume 9, Issue 6, pp 689-692, DOI
10.1109/90.974523, December 2001,
<https://ieeexplore.ieee.org/document/974523>.
[I-D.ietf-grow-route-leak-detection-mitigation]
Sriram, K. and A. Azimov, "Methods for Detection and
Mitigation of BGP Route Leaks", draft-ietf-grow-route-
leak-detection-mitigation-04 (work in progress), October
2020.
[RFC7908] Sriram, K., Montgomery, D., McPherson, D., Osterweil, E., [RFC7908] Sriram, K., Montgomery, D., McPherson, D., Osterweil, E.,
and B. Dickson, "Problem Definition and Classification of and B. Dickson, "Problem Definition and Classification of
BGP Route Leaks", RFC 7908, DOI 10.17487/RFC7908, June BGP Route Leaks", RFC 7908, DOI 10.17487/RFC7908, June
2016, <https://www.rfc-editor.org/info/rfc7908>. 2016, <https://www.rfc-editor.org/info/rfc7908>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26, Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017, RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>. <https://www.rfc-editor.org/info/rfc8126>.
[RFC8212] Mauch, J., Snijders, J., and G. Hankins, "Default External [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
BGP (EBGP) Route Propagation Behavior without Policies", 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
RFC 8212, DOI 10.17487/RFC8212, July 2017, May 2017, <https://www.rfc-editor.org/info/rfc8174>.
<https://www.rfc-editor.org/info/rfc8212>.
[Streibelt] 8.2. Informative References
Streibelt, F., Lichtblau, F., Beverly, R., Feldmann, A.,
Cristel, C., Smaragdakis, G., and R. Bush, "BGP [Gao] Gao, L. and J. Rexford, "Stable Internet routing without
Communities: Even more Worms in the Routing Can", global coordination", IEEE/ACM Transactions on
<https://people.mpi-inf.mpg.de/~fstreibelt/preprint/ Networking, Volume 9, Issue 6, pp 689-692, DOI
communities-imc2018.pdf>. 10.1109/90.974523, December 2001,
<https://ieeexplore.ieee.org/document/974523>.
[I-D.ietf-sidrops-aspa-verification]
Azimov, A., Bogomazov, E., Bush, R., Patel, K., and J.
Snijders, "Verification of AS_PATH Using the Resource
Certificate Public Key Infrastructure and Autonomous
System Provider Authorization", draft-ietf-sidrops-aspa-
verification-07 (work in progress), February 2021.
[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>.
Acknowledgements Acknowledgements
The authors wish to thank Andrei Robachevsky, Daniel Ginsburg, Jeff The authors wish to thank Alvaro Retana, Andrei Robachevsky, Daniel
Haas, Ruediger Volk, Pavel Lunin, Gyan Mishra, Ignas Bagdonas, Sue Ginsburg, Jeff Haas, Ruediger Volk, Pavel Lunin, Gyan Mishra, Ignas
Hares, and John Scudder for comments, suggestions, and critique. Bagdonas, Sue Hares, and John Scudder for comments, suggestions, and
critique.
Contributors Contributors
Brian Dickson Brian Dickson
Independent Independent
Email: brian.peter.dickson@gmail.com Email: brian.peter.dickson@gmail.com
Doug Montgomery Doug Montgomery
USA National Institute of Standards and Technology USA National Institute of Standards and Technology
Email: dougm@nist.gov Email: dougm@nist.gov
Authors' Addresses Authors' Addresses
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