Internet DRAFT - draft-uttaro-idr-bgp-oad
draft-uttaro-idr-bgp-oad
Inter-Domain Routing J. Uttaro
Internet-Draft A. Lingala
Intended status: Standards Track AT&T
Expires: 11 September 2023 K. Patel
Arrcus, Inc.
D. Rao
Cisco Systems
B. Wen
Comcast
A. Retana
Futurewei Technologies, Inc.
S. Sangli
Juniper Networks
P. Mohapatra
Sproute Networks
10 March 2023
One Administrative Domain using BGP
draft-uttaro-idr-bgp-oad-00
Abstract
This document defines a new External BGP (EBGP) peering type known as
EBGP-OAD. EBGP-OAD peering is used between two EBGP peers that
belong to One Administrative Domain (OAD).
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on 11 September 2023.
Copyright Notice
Copyright (c) 2023 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2. Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. Next Hop Handling . . . . . . . . . . . . . . . . . . . . 4
3.2. MULTI_EXIT_DISC (MED) Handling . . . . . . . . . . . . . 4
3.3. Route Reflection . . . . . . . . . . . . . . . . . . . . 4
4. Deployment and Operational Considerations . . . . . . . . . . 4
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 7
Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
At each EBGP boundary, BGP path attributes are modified as per
standard BGP rules [RFC4271]. This includes prepending the AS_PATH
attribute with the autonomous-system number of the BGP speaker and
stripping any IBGP-only attributes.
Some networks span more than one autonomous system and require more
flexibility in the propagation of path attributes. These networks
are said to belong to One Administrative Domain (OAD). It is
desirable to carry IBGP-only attributes across EBGP peering when the
peers belong to OAD. This document defines a new EBGP peering type
known as EBGP-OAD. EBGP-OAD peering is used between two EBGP peers
that belong to OAD. This document also defines rules for route
announcement and processing for EBGP-OAD peers.
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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 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).
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. An example could be
LOCAL_PREF which is ignored if received on an EBGP session [RFC4271].
3. Operation
[RFC4271] defines two types of BGP peerings used during a BGP
protocol session. As part of the extensions defined in this
document, the 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 two external peers
in different Autonomous Systems that belong to OAD. In general, the
EBGP-OAD speakers follow the EBGP route advertisement, route
processing, path attribute announcement and processing rules as
defined in [RFC4271]. However, EBGP-OAD speakers are also allowed to
announce and receive any IBGP-only or non-transitive attributes that
were restricted to remain within an Autonomous System [RFC4271].
Unless explicitly specified, all path attributes MAY be advertised
over an EBGP-OAD session. The reception of any path attribute over
an EBGP-OAD session MUST NOT result in an error, unless it is
malformed. Received path attributes SHOULD NOT be ignored by the
receiver, unless directed to by local policy.
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Unless explicitly specified, the current processes for the
advertisement of path attributes remains unchanged when advertised
through an EBGP-OAD peering. The process for EBGP advertisement MUST
take priority over the process for IBGP advertisement. For example,
the AS_PATH attribute is modified as specified in Section 5.1.2 of
[RFC4271], bullet b ("BGP speaker advertises the route to an external
peer").
An EBGP-OAD speaker MUST support four-octet AS numbers and avertize
the "support for four-octet AS number capability" [RFC6793] .
The following sections describe modifications to route advertisements
and path attribute announcements that are specific to the EBGP-OAD
peering.
3.1. Next Hop Handling
It is reasonable for EBGP-OAD peers to share a common Interior
Gateway Protocol (IGP). In such a case, NEXT_HOP attribute and the
Next Hop in the MP_REACH_NLRI attribute [RFC4760] MAY be left
unchanged.
3.2. MULTI_EXIT_DISC (MED) Handling
The determination of the neighboring AS for the purpose of BGP Route
Selection [RFC4271] MAY also consider the ASN of the EBGP-OAD peer.
If so, all the peers in the receiving ASN MUST be configured to use
the same criteria.
3.3. Route Reflection
BGP Route Reflection [RFC4456] is an alternative to full-mesh IBGP.
The ORIGINATOR_ID and CLUSTER_LIST attributes MUST NOT be advertised
over an EBGP-OAD session. If received, the procedures in [RFC7606]
apply.
4. Deployment and Operational Considerations
For the EBGP-OAD session to operate as expected, both BGP 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, but the BGP session will remain operational.
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The default BGP peering type for a session that is across autonomous
systems SHOULD be EBGP. BGP implementation SHOULD provide a
configuration-time option to enable the EBGP-OAD session type. If
the session type is changed once the BGP connection has been
established, the BGP speaker MUST readvertise its entire Adj-RIB-Out
to its peer. Requesting a route refresh [RFC7313] is RECOMMENDED.
The requirement that Import and Export Policies exist [RFC8212]
SHOULD be disabled if both peers are configured with the EBGP-OAD
session type.
If multiple peerings exist between two autonomous systems that belong
to 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.
The consideration of the ASN of the EBGP-OAD peer to determine the
neighboring AS for MED comparison Section 3.2 may result in the
creation persistent route oscillations, similar to the Type II Churn
described in [RFC3345]. [RFC7964] provides solutions and
recommendations to address this issue.
5. IANA Considerations
This memo includes no request to IANA.
6. Security Considerations
This extension to BGP does not change the underlying security issues
inherent in the existing BGP protocol, such as those described in
[RFC4271] and [RFC4272].
This document defines a new BGP session type which combines the path
attribute propagation rules for EBGP and IBGP peering. Any existing
security considerations related to existing path attributes apply to
the new EBGP-OAD session type.
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By combining the path attribute propagation rules, IBGP information
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 OAD. If misconfigured, the impact
is minimal due to the fact that both [RFC4271] and [RFC7606] define
mechanisms to deal with unexpected path attributes.
7. References
7.1. 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>.
[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>.
[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>.
[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>.
[RFC7313] Patel, K., Chen, E., and B. Venkatachalapathy, "Enhanced
Route Refresh Capability for BGP-4", RFC 7313,
DOI 10.17487/RFC7313, July 2014,
<https://www.rfc-editor.org/info/rfc7313>.
[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>.
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[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>.
7.2. 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>.
[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>.
[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>.
Acknowledgements
TBD
Authors' Addresses
Jim Uttaro
AT&T
Email: ju1738@att.com
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Avinash Lingala
AT&T
Email: ar977m@att.com
Keyur Patel
Arrcus, Inc.
Email: keyur@arrcus.com
Dhananjaya Rao
Cisco Systems
Email: dhrao@cisco.com
Bin Wen
Comcast
Email: bin_wen@comcast.com
Alvaro Retana
Futurewei Technologies, Inc.
Email: alvaro.retana@futurewei.com
Srihari Sangli
Juniper Networks
Email: ssangli@juniper.net
Pradosh Mohapatra
Sproute Networks
Email: pradosh@sproute.com
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