Internet DRAFT - draft-uttaro-idr-bgp-oad
draft-uttaro-idr-bgp-oad
Inter-Domain Routing J. Uttaro
Internet-Draft Individual Contributor
Intended status: Standards Track A. Retana
Expires: 13 July 2024 Futurewei Technologies, Inc.
P. Mohapatra
Google
K. Patel
Arrcus, Inc.
B. Wen
Comcast
10 January 2024
One Administrative Domain using BGP
draft-uttaro-idr-bgp-oad-03
Abstract
This document defines a new External BGP (EBGP) peering type known as
EBGP-OAD, which is used between two EBGP peers that belong to One
Administrative Domain (OAD).
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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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 13 July 2024.
Copyright Notice
Copyright (c) 2024 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
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
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and restrictions with respect to this document. Code Components
extracted from this document must include Revised BSD License text as
described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. ORIGIN . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.2. AS_PATH . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. NEXT_HOP . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4. MULTI_EXIT_DISC . . . . . . . . . . . . . . . . . . . . . 5
3.5. LOCAL_PREF . . . . . . . . . . . . . . . . . . . . . . . 6
3.6. ATOMIC_AGGREGATE . . . . . . . . . . . . . . . . . . . . 6
3.7. AGGREGATOR . . . . . . . . . . . . . . . . . . . . . . . 6
3.8. COMMUNITIES . . . . . . . . . . . . . . . . . . . . . . . 6
3.9. ORIGINATOR_ID . . . . . . . . . . . . . . . . . . . . . . 6
3.10. CLUSTER_LIST . . . . . . . . . . . . . . . . . . . . . . 7
3.11. MP_REACH_NLRI . . . . . . . . . . . . . . . . . . . . . . 7
3.12. MP_UNREACH_NLRI . . . . . . . . . . . . . . . . . . . . . 7
3.13. EXTENDED COMMUNITIES . . . . . . . . . . . . . . . . . . 7
3.14. AS4_PATH . . . . . . . . . . . . . . . . . . . . . . . . 7
3.15. AS4_AGGREGATOR . . . . . . . . . . . . . . . . . . . . . 8
3.16. PMSI_TUNNEL . . . . . . . . . . . . . . . . . . . . . . . 8
3.17. Tunnel Encapsulation . . . . . . . . . . . . . . . . . . 8
3.18. Traffic Engineering . . . . . . . . . . . . . . . . . . . 8
3.19. IPv6 Address Specific Extended Community . . . . . . . . 8
3.20. AIGP . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.21. PE Distinguisher Labels . . . . . . . . . . . . . . . . . 9
3.22. BGP-LS Attribute . . . . . . . . . . . . . . . . . . . . 9
3.23. LARGE_COMMUNITY . . . . . . . . . . . . . . . . . . . . . 9
3.24. BGPsec_PATH . . . . . . . . . . . . . . . . . . . . . . . 9
3.25. BGP Community Container . . . . . . . . . . . . . . . . . 9
3.26. Only to Customer . . . . . . . . . . . . . . . . . . . . 10
3.27. D-PATH . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.28. SFP . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
3.29. BFD Discriminator . . . . . . . . . . . . . . . . . . . . 10
3.30. BGP Router Capabilities . . . . . . . . . . . . . . . . . 10
3.31. BGP Prefix-SID . . . . . . . . . . . . . . . . . . . . . 10
3.32. ATTR_SET . . . . . . . . . . . . . . . . . . . . . . . . 11
3.33. Summary Table . . . . . . . . . . . . . . . . . . . . . . 11
4. Changes to the Decision Process . . . . . . . . . . . . . . . 13
5. Deployment and Operational Considerations . . . . . . . . . . 13
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
7. Security Considerations . . . . . . . . . . . . . . . . . . . 16
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8. References . . . . . . . . . . . . . . . . . . . . . . . . . 16
8.1. Normative References . . . . . . . . . . . . . . . . . . 16
8.2. Informative References . . . . . . . . . . . . . . . . . 19
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 20
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
At each EBGP boundary, BGP path attributes are modified as per
[RFC4271], which includes stripping any attributes not allowed over
an EBGP session. An example is the LOCAL_PREF attribute.
Some networks span more than one autonomous system and require more
flexibility in the propagation of path attributes. It is worth
noting that these multi-AS networks have a common or single
administrative entity. These networks are said to belong to One
Administrative Domain (OAD). It is desirable to have the ability to
carry any attribute across EBGP peerings when the peers belong to an
OAD.
This document defines a new EBGP peering type known as EBGP-OAD,
which is used between two EBGP peers that belong to an OAD. This
document also defines rules for route announcement and processing for
EBGP-OAD peers.
1.1. 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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2. Discussion
Networks have traditionally been demarcated by an autonomous system/
BGP border, which correlates to an administrative boundary. This
paradigm no longer serves the needs of network designers or customers
due to the decoupling of the Interior Gateway Protocol (IGP) from
BGP, BGP-free core in the underlay (e.g., using BGP labeled unicast
[RFC8277]), the use of BGP to facilitate multiple service overlays
(e.g., L2VPN, L3VPN, etc.) spanning multiple regions and AS domains,
and the instantiation of customer sites on multiple content service
providers (CSPs).
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For example, sites in a BGP/MPLS VPN [RFC4364] may be distributed
across different AS domains. In some cases, the administrator of the
VPN may prefer that some attributes are propagated to all their sites
to influence the BGP decision process.
3. Operation
[RFC4271] defines two types of BGP peerings used during a BGP
protocol session. As part of the extensions defined in this
document, EBGP peering is divided into two types:
1. EBGP as defined in [RFC4271].
2. EBGP-OAD as defined below.
The EBGP-OAD session is a BGP connection between peers in different
Autonomous Systems that belong to an OAD. By default, the EBGP-OAD
speakers follow the EBGP route advertisement, route processing, path
attribute announcement, and processing rules as defined in [RFC4271].
EBGP-OAD peers handle receiving optional transitive attributes as
specified in [RFC4271]. Unrecognized non-transitive optional
attributes MUST be quietly ignored and not passed along to other BGP
peers.
Unless explicitly specifed, EBGP-OAD speakers are allowed to announce
and receive any attribute over an EBGP-OAD session. Receiving any
attribute over an EBGP-OAD session MUST NOT result in an error. For
example, the ORIGINATOR_ID (Section 3.9) and the CLUSTER_LIST
(Section 3.10) are not allowed over EBGP-OAD sessions.
EBGP-OAD sessions MUST comply with the behavior specified in
[RFC8212]. Furthermore, the propagation of attributes not allowed
over EBGP sessions (see Table 1) MUST be explicitly allowed by an
Export Policy, and their reception SHOULD be explicitly allowed by an
Import Policy.
An EBGP-OAD speaker MUST support four-octet AS numbers and advertise
the "support for four-octet AS number capability" [RFC6793].
This section addresses all path attributes defined at the time of
this writing that are not marked as "deprecated" in the "BGP Path
Attributes" registry [IANA-BGP-ATTRS]. The following subsections
specify the behavior for each path attribute as related to an EBGP-
OAD session. Table 1 summarizes the behavior for all session types.
Documents specifying new path attributes MUST indicate whether they
are allowed for each session type: IBGP, EBGP, and EBGP-OAD.
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3.1. ORIGIN
The ORIGIN attribute is a well-known mandatory BGP path attribute
[RFC4271] that MUST be present in UPDATE messages sent over EBGP-OAD
sessions. Its origination and value MUST comply with the
specification in [RFC4271].
3.2. AS_PATH
The AS_PATH attribute is a well-known mandatory BGP path attribute
[RFC4271]. It SHOULD be present in UPDATE messages sent over EBGP-
OAD sessions unless it has been replaced by the BGPsec_PATH attribute
[RFC8205]. The origination and modification of the AS_PATH attribute
MUST comply with the EBGP-related specification in [RFC4271].
3.3. NEXT_HOP
The NEXT_HOP attribute is a well-known mandatory BGP path attribute
[RFC4271] that SHOULD be present in UPDATE messages sent over EBGP-
OAD sessions [RFC4760]. The origination and modification of the
NEXT_HOP attribute MUST comply with the EBGP-related specification in
[RFC4271].
It is reasonable for members of an OAD to share a common reachability
domain. In such a case, the NEXT_HOP attribute MAY be left
unchanged.
3.4. MULTI_EXIT_DISC
The MULTI_EXIT_DISC attribute is an optional non-transitive BGP path
attribute [RFC4271] that MAY be present in UPDATE messages sent over
EBGP-OAD sessions, even if it has been received from a neighboring
AS. Otherwise, the use of the MULTI_EXIT_DISC attribute MUST comply
with the specification in [RFC4271].
The determination of the neighboring AS for the purpose of BGP Route
Selection [RFC4271] MAY ignore the ASNs of other members of the OAD.
If so, all the members of the OAD SHOULD be configured to use the
same criteria. Failure to do so may result in inconsistent
forwarding between members of the OAD. Care should also be taken to
avoid the creation of persistent route oscillations, similar to the
Type II Churn described in [RFC3345]. [RFC7964] provides solutions
and recommendations to address this issue.
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3.5. LOCAL_PREF
The LOCAL_PREF attribute is a well-known BGP path attribute [RFC4271]
that MAY be present in UPDATE messages sent over EBGP-OAD sessions.
The use of the LOCAL_PREF attribute MUST comply with the
specification in [RFC4271].
3.6. ATOMIC_AGGREGATE
The ATOMIC_AGGREGATE attribute is a well-known discretionary BGP path
attribute [RFC4271] that MAY be present in UPDATE messages sent over
EBGP-OAD sessions. The use of the ATOMIC_AGGREGATE attribute MUST
comply with the specification in [RFC4271].
3.7. AGGREGATOR
The AGGREGATOR attribute is an optional transitive BGP path attribute
[RFC4271] that MAY be present in UPDATE messages sent over EBGP-OAD
sessions. The use of the AGGREGATOR attribute MUST comply with the
specification in [RFC4271].
3.8. COMMUNITIES
The COMMUNITIES attribute is an optional transitive BGP path
attribute [RFC1997] that MAY be present in UPDATE messages sent over
EBGP-OAD sessions. The advertisement semantics MUST comply with the
specification in [RFC1997].
Routes with a COMMUNITIES attribute containing the well-known
NO_EXPORT community [RFC1997] SHOULD NOT be advertised across an
EBGP-OAD session unless allowed by explicit policy configuration. If
allowed, all the members of the OAD SHOULD be configured to use the
same criteria. Failure to do so may result in inconsistent
forwarding between members of the OAD.
Routes with a COMMUNITIES attribute containing the well-known
NO_EXPORT_SUBCONFED community [RFC1997] MUST NOT be advertised across
an EBGP-OAD session.
3.9. ORIGINATOR_ID
The ORIGINATOR_ID attribute is an optional non-transitive BGP path
attribute [RFC4456] that MUST NOT be advertised over an EBGP-OAD
session. If received from an EBGP-OAD neighbor, it SHALL be
discarded using the "attribute discard" approach [RFC7606]. An
implementation MAY log an error message for further analysis.
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3.10. CLUSTER_LIST
The CLUSTER_LIST attribute is an optional non-transitive BGP path
attribute [RFC4456] that MUST NOT be advertised over an EBGP-OAD
session. If received from an EBGP-OAD neighbor, it SHALL be
discarded using the "attribute discard" approach [RFC7606]. An
implementation MAY log an error message for further analysis.
3.11. MP_REACH_NLRI
The MP_REACH_NLRI attribute is an optional non-transitive BGP path
attribute [RFC4760] that MAY be advertised over an EBGP-OAD session.
The use of the MP_REACH_NLRI attribute MUST comply with the EBGP-
related specification in [RFC4760].
It is reasonable for members of an OAD to share a common reachability
domain. In such a case, the Next Hop in the MP_REACH_NLRI attribute
MAY be left unchanged.
3.12. MP_UNREACH_NLRI
The MP_UNREACH_NLRI attribute is an optional non-transitive BGP path
attribute [RFC4760] that MAY be advertised over an EBGP-OAD session.
The use of the MP_UNREACH_NLRI attribute MUST comply with the
specification in [RFC4760].
3.13. EXTENDED COMMUNITIES
The EXTENDED COMMUNITIES attribute is a transitive optional BGP path
attribute [RFC4360] that MAY be advertised over an EBGP-OAD session.
Extended communities which are non-transitive across an AS boundary
MAY be advertised over an EBGP-OAD session if allowed by explicit
policy configuration. If allowed, all the members of the OAD SHOULD
be configured to use the same criteria. For example, the Origin
Validation State Extended Community, defined as non-transitive in
[RFC8097], can be advertised to peers in the same OAD.
3.14. AS4_PATH
The AS4_PATH attribute is an optional transitive BGP path attribute
[RFC6793] that MAY be advertised over an EBGP-OAD session. The use
of the AS4_PATH attribute MUST comply with the specification in
[RFC6793].
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3.15. AS4_AGGREGATOR
The AS4_AGGREGATOR attribute is an optional transitive BGP path
attribute [RFC6793] that MAY be advertised over an EBGP-OAD session.
The use of the AS4_AGGREGATOR attribute MUST comply with the
specification in [RFC6793].
3.16. PMSI_TUNNEL
The PMSI_TUNNEL attribute is an optional transitive BGP path
attribute [RFC6514] that MAY be advertised over an EBGP-OAD session.
The use of the PMSI_TUNNEL attribute MUST comply with the EBGP-
related specification in [RFC6514].
3.17. Tunnel Encapsulation
The Tunnel Encapsulation attribute is an optional transitive BGP path
attribute [RFC9012] that MAY be advertised over an EBGP-OAD session.
The use of the Tunnel Encapsulation attribute MUST comply with the
EBGP-related specification in [RFC9012].
3.18. Traffic Engineering
The Traffic Engineering attribute is an optional non-transitive BGP
path attribute [RFC5543] that MAY be advertised over an EBGP-OAD
session. The use of the Traffic Engineering attribute MUST comply
with the specification in [RFC5543].
3.19. IPv6 Address Specific Extended Community
The IPv6 Address Specific Extended Community attribute is an optional
transitive BGP path attribute [RFC5701] that MAY be advertised over
an EBGP-OAD session.
Extended communities which are non-transitive across Autonomous
Systems MAY be advertised over an EBGP-OAD session if allowed by
explicit policy configuration. If allowed, all the members of the
OAD SHOULD be configured to use the same criteria.
3.20. AIGP
The AIGP attribute is an optional non-transitive BGP path attribute
[RFC7311] that MAY be advertised over an EBGP-OAD session. The
default value of AIGP_SESSION [RFC7311] MUST be "disabled" and it MAY
be "enabled" by explicit policy configuration. The use of the AIGP
attribute MUST comply with the specification in [RFC7311].
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3.21. PE Distinguisher Labels
The PE Distinguisher Labels attribute is an optional transitive BGP
path attribute [RFC6514] that MAY be advertised over an EBGP-OAD
session. The use of the PE Distinguisher Labels attribute MUST
comply with the specification in [RFC6513] and [RFC6514].
3.22. BGP-LS Attribute
The BGP Link-State (BGP-LS) attribute is an optional non-transitive
BGP path attribute [RFC9552] that MAY be advertised over an EBGP-OAD
session. The use of the BGP-LS Attribute MUST comply with the
specification in [RFC9552].
3.23. LARGE_COMMUNITY
The LARGE_COMMUNITY attribute is an optional transitive BGP path
attribute [RFC8092] that MAY be advertised over an EBGP-OAD session.
The use of the LARGE_COMMUNITY attribute MUST comply with the
specification in [RFC8092].
3.24. BGPsec_PATH
The BGPsec_PATH attribute is an optional non-transitive BGP path
attribute [RFC8205] that MAY be advertised over an EBGP-OAD session.
The use of the BGPsec_PATH attribute MUST comply with the
specification in [RFC8205].
3.25. BGP Community Container
The BGP Community Container attribute is an optional transitive BGP
path attribute [WIDE] that MAY be advertised over an EBGP-OAD
session.
In particular, communities with the T bit [WIDE] not set MAY be
advertised over an EBGP-OAD session if allowed by explicit policy
configuration. Communities with the T bit set MUST be advertised
over an EBGP-OAD session. Communities with the C bit [WIDE] not set
MUST NOT be advertised over an EBGP-OAD session. Communities with
the C bit set MAY be advertised over an EBGP-OAD session if allowed
by explicit policy configuration. In all cases, all the members of
the OAD SHOULD be configured to use the same criteria.
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3.26. Only to Customer
The Only to Customer (OTC) attribute is an optional transitive BGP
path attribute [RFC9234] that MAY be advertised over an EBGP-OAD
session. However, the BGP Role negotiation and OTC Attribute-based
procedures specified in [RFC9234] are NOT RECOMMENDED to be used
between peers using an EBGP-OAD session. If received, the OTC
attribute MUST be preserved unchanged. The use and negotiation of
BGP Roles between EBGP-OAD peers is outside the scope of this
document.
3.27. D-PATH
The Domain Path (D-PATH) attribute is an optional transitive BGP path
attribute [IPVPN] that MAY be advertised over an EBGP-OAD session.
The use of the D-PATH attribute MUST comply with the specification in
[IPVPN].
3.28. SFP
The Service Function Path (SFP) attribute is an optional transitive
BGP path attribute [RFC9015] that MAY be advertised over an EBGP-OAD
session. The use of the SFP attribute MUST comply with the
specification in [RFC9015].
3.29. BFD Discriminator
The BFD Discriminator attribute is an optional transitive BGP path
attribute [RFC9026] that MAY be advertised over an EBGP-OAD session.
The use of the BFD Discriminator attribute MUST comply with the
specification in [RFC9026].
3.30. BGP Router Capabilities
The BGP Router Capabilities attribute (RCA) is an optional transitive
BGP path attribute [ENTROPY] that MAY be advertised over an EBGP-OAD
session. The use of the RCA attribute MUST comply with the
specification in [ENTROPY].
3.31. BGP Prefix-SID
The BGP Prefix-SID attribute is an optional transitive BGP path
attribute [RFC8669] that MAY be advertised over an EBGP-OAD session.
The use of the BGP Prefix-SID attribute MUST comply with the
specification in [RFC8669].
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3.32. ATTR_SET
The ATTR_SET attribute is an optional transitive BGP path attribute
[RFC6368] that MAY be advertised over an EBGP-OAD session. The use
of the ATTR_SET attribute MUST comply with the specification in
[RFC6368].
3.33. Summary Table
+===================+===========+===========+===========+===========+
| Path Attribute | EBGP | IBGP | EBGP-OAD | Reference |
+===================+===========+===========+===========+===========+
| ORIGIN | Mandatory | Mandatory | Mandatory | Section |
| | | | | 3.1 |
+-------------------+-----------+-----------+-----------+-----------+
| AS_PATH | Optional | Optional | Optional | Section |
| | | | | 3.2 |
+-------------------+-----------+-----------+-----------+-----------+
| NEXT_HOP | Optional | Optional | Optional | Section |
| | | | | 3.3 |
+-------------------+-----------+-----------+-----------+-----------+
| MULTI_EXIT_DISC | Optional | Optional | Optional | Section |
| | | | | 3.4 |
+-------------------+-----------+-----------+-----------+-----------+
| LOCAL_PREF | Not | Mandatory | Optional | Section |
| | allowed | | | 3.5 |
+-------------------+-----------+-----------+-----------+-----------+
| ATOMIC_AGGREGATE | Optional | Optional | Optional | Section |
| | | | | 3.6 |
+-------------------+-----------+-----------+-----------+-----------+
| AGGREGATOR | Optional | Optional | Optional | Section |
| | | | | 3.7 |
+-------------------+-----------+-----------+-----------+-----------+
| COMMUNITIES | Optional | Optional | Optional | Section |
| | | | | 3.8 |
+-------------------+-----------+-----------+-----------+-----------+
| ORIGINATOR_ID | Not | Optional | Not | Section |
| | Allowed | | allowed | 3.9 |
+-------------------+-----------+-----------+-----------+-----------+
| CLUSTER_LIST | Not | Optional | Not | Section |
| | Allowed | | allowed | 3.10 |
+-------------------+-----------+-----------+-----------+-----------+
| MP_REACH_NLRI | Optional | Optional | Optional | Section |
| | | | | 3.11 |
+-------------------+-----------+-----------+-----------+-----------+
| MP_UNREACH_NLRI | Optional | Optional | Optional | Section |
| | | | | 3.12 |
+-------------------+-----------+-----------+-----------+-----------+
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| EXTENDED | Optional | Optional | Optional | Section |
| COMMUNITIES | | | | 3.13 |
+-------------------+-----------+-----------+-----------+-----------+
| AS4_PATH | Optional | Optional | Optional | Section |
| | | | | 3.14 |
+-------------------+-----------+-----------+-----------+-----------+
| AS4_AGGREGATOR | Optional | Optional | Optional | Section |
| | | | | 3.15 |
+-------------------+-----------+-----------+-----------+-----------+
| PMSI_TUNNEL | Optional | Optional | Optional | Section |
| | | | | 3.16 |
+-------------------+-----------+-----------+-----------+-----------+
| Tunnel | Optional | Optional | Optional | Section |
| Encapsulation | | | | 3.17 |
+-------------------+-----------+-----------+-----------+-----------+
| Traffic | Not | Optional | Optional | Section |
| Engineering | Allowed | | | 3.18 |
+-------------------+-----------+-----------+-----------+-----------+
| IPv6 Address | Optional | Optional | Optional | Section |
| Specific | | | | 3.19 |
| Extended | | | | |
| Community | | | | |
+-------------------+-----------+-----------+-----------+-----------+
| AIGP | Optional | Optional | Optional | Section |
| | | | | 3.20 |
+-------------------+-----------+-----------+-----------+-----------+
| PE Distinguisher | Optional | Optional | Optional | Section |
| Labels | | | | 3.21 |
+-------------------+-----------+-----------+-----------+-----------+
| BGP-LS Attribute | Not | Optional | Optional | Section |
| | Allowed | | | 3.22 |
+-------------------+-----------+-----------+-----------+-----------+
| LARGE_COMMUNITY | Optional | Optional | Optional | Section |
| | | | | 3.23 |
+-------------------+-----------+-----------+-----------+-----------+
| BGPsec_PATH | Optional | Optional | Optional | Section |
| | | | | 3.24 |
+-------------------+-----------+-----------+-----------+-----------+
| BGP Community | Optional | Optional | Optional | Section |
| Container | | | | 3.25 |
+-------------------+-----------+-----------+-----------+-----------+
| Only to Customer | Optional | Optional | Optional | Section |
| | | | | 3.26 |
+-------------------+-----------+-----------+-----------+-----------+
| D-PATH | Optional | Optional | Optional | Section |
| | | | | 3.27 |
+-------------------+-----------+-----------+-----------+-----------+
| SFP | Optional | Optional | Optional | Section |
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| | | | | 3.28 |
+-------------------+-----------+-----------+-----------+-----------+
| BFD | Optional | Optional | Optional | Section |
| Discriminator | | | | 3.29 |
+-------------------+-----------+-----------+-----------+-----------+
| BGP Router | Optional | Optional | Optional | Section |
| Capabilities | | | | 3.30 |
+-------------------+-----------+-----------+-----------+-----------+
| BGP Prefix-SID | Optional | Optional | Optional | Section |
| | | | | 3.31 |
+-------------------+-----------+-----------+-----------+-----------+
| ATTR_SET | Optional | Optional | Optional | Section |
| | | | | 3.32 |
+-------------------+-----------+-----------+-----------+-----------+
Table 1: Path Attribute Behavior
4. Changes to the Decision Process
Section 9 of [RFC4271] describes the BGP Decision Process to select
routes for local forwarding and subsequent advertisement.
Section 9.1.2.2 of [RFC4271] describes tie breaking procedures in
cases where a BGP speaker has several routes to the same destination.
This document modifies step d) as follows:
d) If at least one of the candidate routes was received via EBGP,
remove from consideration all routes that were received via EBGP-
OAD and IBGP. If at least one of the candidate routes was
received via EBGP-OAD, remove from consideration all routes that
were received via IBGP.
The algorithm defined in [RFC5004] to avoid unnecessary path
transitions between external paths MUST be used when the routes
considered were received via EBGP-OAD.
5. Deployment and Operational Considerations
For the Import and Export Policies to behave as expected, both EBGP-
OADGP speakers must be configured with the same session type. If
only one BGP speaker is configured that way, and the other uses an
EBGP session, the result is that some path attributes may be ignored
and others will be discarded.
The default BGP peering type for a session that is across autonomous
systems SHOULD be EBGP. A BGP implementation SHOULD provide a
configuration-time option to enable the EBGP-OAD session type. The
session type may be changed once the BGP connection has been
established.
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If multiple peerings exist between autonomous systems that belong to
an OAD, all SHOULD be configured consistently. Improper
configuration may result in inconsistent or unexpected forwarding.
The inconsistent use of EBGP-OAD sessions is out of scope of this
document.
BGP Confederations [RFC5065] provide similar behavior, on a session
by session basis, as what is specified in this document. The use of
confederations with an EBGP-OAD peering is out of scope of this
document.
6. IANA Considerations
IANA is requested to update the BGP Path Attributes registry as shown
in Table 2. Also, IANA is requested to add [this document] as a
reference in the registry.
+=====+===================+=========+=========+=========+===========+
|Value| Code | EBGP | IBGP | EBGP-OAD| Reference |
+=====+===================+=========+=========+=========+===========+
|1 | ORIGIN |Mandatory|Mandatory|Mandatory| [RFC4271] |
+-----+-------------------+---------+---------+---------+-----------+
|2 | AS_PATH |Optional |Optional |Optional | [RFC4271] |
| | | | | | [RFC8205] |
+-----+-------------------+---------+---------+---------+-----------+
|3 | NEXT_HOP |Optional |Optional |Optional | [RFC4271] |
| | | | | | [RFC4760] |
+-----+-------------------+---------+---------+---------+-----------+
|4 | MULTI_EXIT_DISC |Optional |Optional |Optional | [RFC4271] |
+-----+-------------------+---------+---------+---------+-----------+
|5 | LOCAL_PREF |Not |Mandatory|Optional | [RFC4271] |
| | |allowed | | | |
+-----+-------------------+---------+---------+---------+-----------+
|6 | ATOMIC_AGGREGATE |Optional |Optional |Optional | [RFC4271] |
+-----+-------------------+---------+---------+---------+-----------+
|7 | AGGREGATOR |Optional |Optional |Optional | [RFC4271] |
+-----+-------------------+---------+---------+---------+-----------+
|8 | COMMUNITIES |Optional |Optional |Optional | [RFC1997] |
+-----+-------------------+---------+---------+---------+-----------+
|9 | ORIGINATOR_ID |Not |Optional |Not | [RFC4456] |
| | |Allowed | |allowed | |
+-----+-------------------+---------+---------+---------+-----------+
|10 | CLUSTER_LIST |Not |Optional |Not | [RFC4456] |
| | |Allowed | |allowed | |
+-----+-------------------+---------+---------+---------+-----------+
|14 | MP_REACH_NLRI |Optional |Optional |Optional | [RFC4760] |
+-----+-------------------+---------+---------+---------+-----------+
|15 | MP_UNREACH_NLRI |Optional |Optional |Optional | [RFC4760] |
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+-----+-------------------+---------+---------+---------+-----------+
|16 | EXTENDED |Optional |Optional |Optional | [RFC4360] |
| | COMMUNITIES | | | | |
+-----+-------------------+---------+---------+---------+-----------+
|17 | AS4_PATH |Optional |Optional |Optional | [RFC6793] |
+-----+-------------------+---------+---------+---------+-----------+
|18 | AS4_AGGREGATOR |Optional |Optional |Optional | [RFC6793] |
+-----+-------------------+---------+---------+---------+-----------+
|22 | PMSI_TUNNEL |Optional |Optional |Optional | [RFC6514] |
+-----+-------------------+---------+---------+---------+-----------+
|23 | Tunnel |Optional |Optional |Optional | [RFC9012] |
| | Encapsulation | | | | |
+-----+-------------------+---------+---------+---------+-----------+
|24 | Traffic |Not |Optional |Optional | [RFC5543] |
| | Engineering |Allowed | | | |
+-----+-------------------+---------+---------+---------+-----------+
|25 | IPv6 Address |Optional |Optional |Optional | [RFC5701] |
| | Specific | | | | |
| | Extended | | | | |
| | Community | | | | |
+-----+-------------------+---------+---------+---------+-----------+
|26 | AIGP |Optional |Optional |Optional | [RFC7311] |
+-----+-------------------+---------+---------+---------+-----------+
|27 | PE Distinguisher |Optional |Optional |Optional | [RFC6514] |
| | Labels | | | | |
+-----+-------------------+---------+---------+---------+-----------+
|29 | BGP-LS Attribute |Not |Optional |Optional | [RFC9552] |
| | |Allowed | | | |
+-----+-------------------+---------+---------+---------+-----------+
|32 | LARGE_COMMUNITY |Optional |Optional |Optional | [RFC8092] |
+-----+-------------------+---------+---------+---------+-----------+
|33 | BGPsec_PATH |Optional |Optional |Optional | [RFC8205] |
+-----+-------------------+---------+---------+---------+-----------+
|34 | BGP Community |Optional |Optional |Optional | [WIDE] |
| | Container | | | | |
+-----+-------------------+---------+---------+---------+-----------+
|35 | Only to Customer |Optional |Optional |Optional | [RFC9234] |
+-----+-------------------+---------+---------+---------+-----------+
|36 | D-PATH |Optional |Optional |Optional | [IPVPN] |
+-----+-------------------+---------+---------+---------+-----------+
|37 | SFP |Optional |Optional |Optional | [RFC9015] |
+-----+-------------------+---------+---------+---------+-----------+
|38 | BFD |Optional |Optional |Optional | [RFC9026] |
| | Discriminator | | | | |
+-----+-------------------+---------+---------+---------+-----------+
|39 | BGP Router |Optional |Optional |Optional | [ENTROPY] |
| | Capabilities | | | | |
+-----+-------------------+---------+---------+---------+-----------+
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|40 | BGP Prefix-SID |Optional |Optional |Optional | [RFC8669] |
+-----+-------------------+---------+---------+---------+-----------+
|128 | ATTR_SET |Optional |Optional |Optional | [RFC6368] |
+-----+-------------------+---------+---------+---------+-----------+
Table 2: BGP Path Attributes
Table 2 only includes the path attributes referenced in this
document. Any Reserved, Deprecated, or Unassigned values should
contain empty IBGP, EBGP, and EBGP-OAD columns.
7. Security Considerations
EBGP-OAD peering does not change the underlying security issues
inherent in the existing BGP protocol, such as those described in
[RFC4271] and [RFC4272]. Any security considerations related to
existing path attributes apply to EBGP-OAD sessions.
All BGP attributes may now be propagated to another autonomous
system. However, it is expected that the new session type will only
be enabled when peering with a router that also belongs to the OAD.
If misconfigured, the impact is minimal due to the fact that both
[RFC4271] and [RFC7606] define mechanisms to deal with unexpected
path attributes. Also, the use of the Import and Export Policy
mechanisms speficied in [RFC8212] are REQUIRED.
8. References
8.1. Normative References
[ENTROPY] Decraene, B., Scudder, J., Henderickx, W., Kompella, K.,
Mohanty, M., Uttaro, J., and B. Wen, "BGP Next Hop
Dependent Capabilities Attribute", Work in Progress,
Internet-Draft, draft-ietf-idr-entropy-label-13, 9 October
2023, <https://datatracker.ietf.org/doc/html/draft-ietf-
idr-entropy-label-13>.
[WIDE] Raszuk, R., Haas, J., Lange, A., Decraene, B., Amante, S.,
and P. Jakma, "BGP Community Container Attribute", Work in
Progress, Internet-Draft, draft-ietf-idr-wide-bgp-
communities-11, 9 March 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-idr-
wide-bgp-communities-11>.
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[IPVPN] Rabadan, J., Sajassi, A., Rosen, E. C., Drake, J., Lin,
W., Uttaro, J., and A. Simpson, "EVPN Interworking with
IPVPN", Work in Progress, Internet-Draft, draft-ietf-bess-
evpn-ipvpn-interworking-09, 9 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-bess-
evpn-ipvpn-interworking-09>.
[RFC1997] Chandra, R., Traina, P., and T. Li, "BGP Communities
Attribute", RFC 1997, DOI 10.17487/RFC1997, August 1996,
<https://www.rfc-editor.org/info/rfc1997>.
[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>.
[RFC4360] Sangli, S., Tappan, D., and Y. Rekhter, "BGP Extended
Communities Attribute", RFC 4360, DOI 10.17487/RFC4360,
February 2006, <https://www.rfc-editor.org/info/rfc4360>.
[RFC4456] Bates, T., Chen, E., and R. Chandra, "BGP Route
Reflection: An Alternative to Full Mesh Internal BGP
(IBGP)", RFC 4456, DOI 10.17487/RFC4456, April 2006,
<https://www.rfc-editor.org/info/rfc4456>.
[RFC5004] Chen, E. and S. Sangli, "Avoid BGP Best Path Transitions
from One External to Another", RFC 5004,
DOI 10.17487/RFC5004, September 2007,
<https://www.rfc-editor.org/info/rfc5004>.
[RFC5065] Traina, P., McPherson, D., and J. Scudder, "Autonomous
System Confederations for BGP", RFC 5065,
DOI 10.17487/RFC5065, August 2007,
<https://www.rfc-editor.org/info/rfc5065>.
[RFC5543] Ould-Brahim, H., Fedyk, D., and Y. Rekhter, "BGP Traffic
Engineering Attribute", RFC 5543, DOI 10.17487/RFC5543,
May 2009, <https://www.rfc-editor.org/info/rfc5543>.
[RFC5701] Rekhter, Y., "IPv6 Address Specific BGP Extended Community
Attribute", RFC 5701, DOI 10.17487/RFC5701, November 2009,
<https://www.rfc-editor.org/info/rfc5701>.
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[RFC6368] Marques, P., Raszuk, R., Patel, K., Kumaki, K., and T.
Yamagata, "Internal BGP as the Provider/Customer Edge
Protocol for BGP/MPLS IP Virtual Private Networks (VPNs)",
RFC 6368, DOI 10.17487/RFC6368, September 2011,
<https://www.rfc-editor.org/info/rfc6368>.
[RFC6513] Rosen, E., Ed. and R. Aggarwal, Ed., "Multicast in MPLS/
BGP IP VPNs", RFC 6513, DOI 10.17487/RFC6513, February
2012, <https://www.rfc-editor.org/info/rfc6513>.
[RFC6514] Aggarwal, R., Rosen, E., Morin, T., and Y. Rekhter, "BGP
Encodings and Procedures for Multicast in MPLS/BGP IP
VPNs", RFC 6514, DOI 10.17487/RFC6514, February 2012,
<https://www.rfc-editor.org/info/rfc6514>.
[RFC6793] Vohra, Q. and E. Chen, "BGP Support for Four-Octet
Autonomous System (AS) Number Space", RFC 6793,
DOI 10.17487/RFC6793, December 2012,
<https://www.rfc-editor.org/info/rfc6793>.
[RFC7311] Mohapatra, P., Fernando, R., Rosen, E., and J. Uttaro,
"The Accumulated IGP Metric Attribute for BGP", RFC 7311,
DOI 10.17487/RFC7311, August 2014,
<https://www.rfc-editor.org/info/rfc7311>.
[RFC7606] Chen, E., Ed., Scudder, J., Ed., Mohapatra, P., and K.
Patel, "Revised Error Handling for BGP UPDATE Messages",
RFC 7606, DOI 10.17487/RFC7606, August 2015,
<https://www.rfc-editor.org/info/rfc7606>.
[RFC8092] Heitz, J., Ed., Snijders, J., Ed., Patel, K., Bagdonas,
I., and N. Hilliard, "BGP Large Communities Attribute",
RFC 8092, DOI 10.17487/RFC8092, February 2017,
<https://www.rfc-editor.org/info/rfc8092>.
[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>.
[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>.
[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>.
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[RFC8669] Previdi, S., Filsfils, C., Lindem, A., Ed., Sreekantiah,
A., and H. Gredler, "Segment Routing Prefix Segment
Identifier Extensions for BGP", RFC 8669,
DOI 10.17487/RFC8669, December 2019,
<https://www.rfc-editor.org/info/rfc8669>.
[RFC9012] Patel, K., Van de Velde, G., Sangli, S., and J. Scudder,
"The BGP Tunnel Encapsulation Attribute", RFC 9012,
DOI 10.17487/RFC9012, April 2021,
<https://www.rfc-editor.org/info/rfc9012>.
[RFC9015] Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L.
Jalil, "BGP Control Plane for the Network Service Header
in Service Function Chaining", RFC 9015,
DOI 10.17487/RFC9015, June 2021,
<https://www.rfc-editor.org/info/rfc9015>.
[RFC9026] Morin, T., Ed., Kebler, R., Ed., and G. Mirsky, Ed.,
"Multicast VPN Fast Upstream Failover", RFC 9026,
DOI 10.17487/RFC9026, April 2021,
<https://www.rfc-editor.org/info/rfc9026>.
[RFC9234] Azimov, A., Bogomazov, E., Bush, R., Patel, K., and K.
Sriram, "Route Leak Prevention and Detection Using Roles
in UPDATE and OPEN Messages", RFC 9234,
DOI 10.17487/RFC9234, May 2022,
<https://www.rfc-editor.org/info/rfc9234>.
[RFC9552] Talaulikar, K., Ed., "Distribution of Link-State and
Traffic Engineering Information Using BGP", RFC 9552,
DOI 10.17487/RFC9552, December 2023,
<https://www.rfc-editor.org/info/rfc9552>.
8.2. Informative References
[RFC3345] McPherson, D., Gill, V., Walton, D., and A. Retana,
"Border Gateway Protocol (BGP) Persistent Route
Oscillation Condition", RFC 3345, DOI 10.17487/RFC3345,
August 2002, <https://www.rfc-editor.org/info/rfc3345>.
[RFC4272] Murphy, S., "BGP Security Vulnerabilities Analysis",
RFC 4272, DOI 10.17487/RFC4272, January 2006,
<https://www.rfc-editor.org/info/rfc4272>.
[RFC4364] Rosen, E. and Y. Rekhter, "BGP/MPLS IP Virtual Private
Networks (VPNs)", RFC 4364, DOI 10.17487/RFC4364, February
2006, <https://www.rfc-editor.org/info/rfc4364>.
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[RFC4760] Bates, T., Chandra, R., Katz, D., and Y. Rekhter,
"Multiprotocol Extensions for BGP-4", RFC 4760,
DOI 10.17487/RFC4760, January 2007,
<https://www.rfc-editor.org/info/rfc4760>.
[RFC7964] Walton, D., Retana, A., Chen, E., and J. Scudder,
"Solutions for BGP Persistent Route Oscillation",
RFC 7964, DOI 10.17487/RFC7964, September 2016,
<https://www.rfc-editor.org/info/rfc7964>.
[RFC8097] Mohapatra, P., Patel, K., Scudder, J., Ward, D., and R.
Bush, "BGP Prefix Origin Validation State Extended
Community", RFC 8097, DOI 10.17487/RFC8097, March 2017,
<https://www.rfc-editor.org/info/rfc8097>.
[RFC8277] Rosen, E., "Using BGP to Bind MPLS Labels to Address
Prefixes", RFC 8277, DOI 10.17487/RFC8277, October 2017,
<https://www.rfc-editor.org/info/rfc8277>.
[IANA-BGP-ATTRS]
IANA, "BGP Path Attributes",
<http://www.iana.org/assignments/bgp-parameters>.
Acknowledgements
The authors would like to thank everyone who has commented on this
work, including (in alphabetical order) Donatas Abraitis, Randy Bush,
Gert Doering, Jeff Haas, Jakob Heitz, Nick Hilliard, Igor Malyushkin,
Gyan Mishra, Robert Raszuk, John Scudder, and Shyam Sethuram.
Contributors
The following people have made significant contributions to the
content of this document.
Avinash Lingala
AT&T
Email: ar977m@att.com
Dhananjaya Rao
Cisco Systems
Email: dhrao@cisco.com
Srihari Sangli
Juniper Networks
Email: ssangli@juniper.net
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Authors' Addresses
Jim Uttaro
Individual Contributor
Email: juttaro@ieee.org
Alvaro Retana
Futurewei Technologies, Inc.
Email: alvaro.retana@futurewei.com
Pradosh Mohapatra
Google
Email: pradosh@google.com
Keyur Patel
Arrcus, Inc.
Email: keyur@arrcus.com
Bin Wen
Comcast
Email: bin_wen@comcast.com
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