BGP-LS Extension for Inter-AS Topology Retrieval
draft-ietf-idr-bgpls-inter-as-topology-ext-14
| Document | Type | Active Internet-Draft (idr WG) | |
|---|---|---|---|
| Authors | Aijun Wang , Huaimo Chen , Ketan Talaulikar , Shunwan Zhuang | ||
| Last updated | 2024-04-18 | ||
| Replaces | draft-wang-idr-bgpls-inter-as-topology-ext | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Intended RFC status | (None) | ||
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draft-ietf-idr-bgpls-inter-as-topology-ext-14
IDR Working Group A. Wang
Internet-Draft China Telecom
Intended status: Standards Track H. Chen
Expires: 20 October 2024 Futurewei
K. Talaulikar
Cisco Systems
S. Zhuang
Huawei Technologies
18 April 2024
BGP-LS Extension for Inter-AS Topology Retrieval
draft-ietf-idr-bgpls-inter-as-topology-ext-14
Abstract
This document describes the process to build Border Gateway Protocol-
Link State (BGP-LS) key parameters in inter-domain scenario, defines
one new BGP-LS Network Layer Reachability Information (NLRI) type
(Stub Link NLRI) and some new Type-Length-Values (TLVs) for BGP-LS to
let Software Definition Network (SDN) controller retrieve the network
topology automatically under various inter-AS environments.
Such extension and process can enable the network operator to collect
the interconnect information between different domains and then
calculate the overall network topology automatically based on the
information provided by BGP-LS protocol.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 20 October 2024.
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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
and restrictions with respect to this document. Code Components
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Inter-AS Domain Scenarios . . . . . . . . . . . . . . . . . . 3
5. Stub Link NLRI . . . . . . . . . . . . . . . . . . . . . . . 4
6. IGP Information for Inter-AS Link . . . . . . . . . . . . . . 5
7. BGP-LS Extensions for Inter-AS Link . . . . . . . . . . . . . 5
7.1. Remote AS Number TLV . . . . . . . . . . . . . . . . . . 6
7.2. IPv4 Remote ASBR ID . . . . . . . . . . . . . . . . . . . 7
7.3. IPv6 Remote ASBR ID . . . . . . . . . . . . . . . . . . . 7
8. Topology Reconstruction. . . . . . . . . . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 8
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
10.1. New BGP-LS NLRI type . . . . . . . . . . . . . . . . . . 9
10.2. New Stub Link Descriptors . . . . . . . . . . . . . . . 9
11. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 9
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
12.1. Normative References . . . . . . . . . . . . . . . . . . 9
12.2. Informative References . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
BGP-LS [RFC9552] describes the methodology that using BGP protocol to
transfer the Link-State information. Such method can enable SDN
controller to collect the underlay network topology automatically,
but normally it can only get the information within one Interior
Gateway Protocol (IGP) domain. If the operator has more than one IGP
domain, and these domains interconnect with each other, there is no
mechanic within current BGP- LS to transfer the interconnect topology
information.
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Draft [RFC9086] defines some extensions for exporting BGP peering
node topology information (including its peers, interfaces and
peering ASs) in a way that is exploitable in order to compute
efficient BGP Peering Engineering policies and strategies. Such
information can also be used to calculate the interconnection
topology among different IGP domains, but it requires every border
router to run BGP-LS protocol and report the information to SDN
controller. Considering there will be plenty of border routers on
the network boundary, such solution restricts its deployment
flexibility.
This draft analysis the situations that the SDN controller needs to
get the interconnected topology information between different AS
domains, defines the new Stub Link NLRI and some new TLVs within the
BGP-LS protocol to transfer the key information related to them.
After that, the SDN controller can then deduce the multi-domain
topology automatically based on the information from BGP-LS protocol.
2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119] .
3. Terminology
The following terms are defined in this document:
* IDCs: Internet Data Centers
* MAN: Metrio-Area-Network
* SDN: Software Definition Network
4. Inter-AS Domain Scenarios
Figure 1 illustrates the multi-domain scenarios that this draft
discusses. Normally, SDN Controller can get the topology of IGP A
and IGP B individually via the BGP-LS protocol, but it can't get the
topology connection information between these two IGP domains because
there is generally no IGP protocol run on the connected links.
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+-----------------+
+----+IP SDN Controller+----+
| +-----------------+ |
| |
|BGP-LS |BGP-LS
| |
+---------------+-----+ +-----+--------------+
| +--+ +-++ ++-+ +-++ +|-+ +--+|
| |S1+--------+S2+---+B1+-----------+B2+---+T1+--------+T2||
| +-++ N1 +-++ ++-+ +-++ ++++ N2 +-++|
| | | | | || | |
| | | | | || | |
| +-++ +-++ ++-+ +-++ ++++ +-++|
| |S4+--------+S3+---+B3+-----------+B4+---+T3+--------+T4||
| +--+ +--+ ++-+ +-++ ++-+ +--+|
| | | |
| | | |
| IGP A | | IGP B |
+---------------------+ +--------------------+
Figure 1: Inter-AS Domain Scenarios
5. Stub Link NLRI
[RFC9552] defines four NLRI types(Node NLRI, Link NLRI, IPv4 Topology
Prefix NLRI, IPv6 Topology Prefix NLRI) to transfer the topology and
prefix information. For inter-as link, the two ends of the link
locates in different IGP domains, then it is not appropriate to
transfer their information within the current defined NLRI types.
This draft defines one new NLRI type, called Stub Link NLRI, which is
coded as the following format:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+
| Protocol-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier |
| (64 bits) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Local Node Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Stub Link Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Stub Link NLRI Format
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The "Protocol-ID" should be set to the value that indicates "Direct"
protocol.
The semantics of "Local Node Descriptors" and "Stub Link Descriptors"
are same as that defined in [RFC9552] for "Node Descriptors" and
"Link Descriptor".
This newly defined NLRI can be used to describe the link that has
only one end located within the IGP domain, as described in the
following sections.
6. IGP Information for Inter-AS Link
[RFC5316] and [RFC5392] define IS-IS and OSPF extensions respectively
to deal with the situation for inter-AS link. Three sub-TLVs(Remote
AS Number、IPv4 Remote ASBR ID、IPv6 Remote ASBR ID) which are
associated with the inter-AS link are defined.
These TLVs are flooded within the IGP domain automatically. They
should be carried within the newly defined Stub Link NLRI within the
BGP-LS protocol, as the descriptors for the inter-AS stub link.
The "Local Node Descriptors" should describe the the characteristics
of ASBRs that are connected these inter-AS links.
If the SDN controller knows these information via one of the interior
router that runs BGP-LS protocol, the SDN controller can rebuild the
inter-AS topology correctly according to the procedure described in
Section 8
7. BGP-LS Extensions for Inter-AS Link
This section proposes to add three new TLVs that is included within
the Stub Link NLRI to transfer the information via BGP-LS, which are
required to build the inter-AS related topology by the SDN
controller.
The following Link Descriptor TLVs are added into the BGP-LS protocol
:
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+-----------+---------------------+--------------+----------------+
| TLV Code | Description |IS-IS/OSPF TLV| Reference |
| Point | | /Sub-TLV | (RFC/Section) |
+-----------+---------------------+--------------+----------------+
| TBD |Remote AS Number | 24/21 | [RFC5316]/3.3.1|
| | | | [RFC5392]/3.3.1|
| TBD |IPv4 Remote ASBR ID | 25/22 | [RFC5316]/3.3.2|
| | | | [RFC5392]/3.3.2|
| TBD |IPv6 Remote ASBR ID | 26/24 | [RFC5316]/3.3.3|
| | | | [RFC5392]/3.3.3|
+-----------+---------------------+--------------+----------------+
Figure 3: Stub Link Descriptor TLVs
Detail encoding of these TLVs are synchronized with the corresponding
parts in [RFC5316] and [RFC5392], which keeps the BGP-LS protocol
agnostic to the underly protocol.
7.1. Remote AS Number TLV
A new TLV, the remote AS number TLV, is defined for inclusion in the
link descriptor when advertising inter-AS links. The remote AS
number TLV specifies the AS number of the neighboring AS to which the
advertised link connects.
The remote AS number TLV is TLV type TBD (see Section 10 ) and is 4
octets in length. The format is as follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote AS Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Remote AS Number TLV Format
The Remote AS number field has 4 octets. When only 2 octets are used
for the AS number, as in current deployments, the left (high-order) 2
octets MUST be set to 0. The remote AS number TLV MUST be included
when a router advertises an inter-AS link.
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7.2. IPv4 Remote ASBR ID
A new TLV, which is referred to as the IPv4 remote ASBR ID TLV, is
defined for inclusion in the link descriptor when advertising inter-
AS links. The IPv4 remote ASBR ID TLV specifies the IPv4 identifier
of the remote ASBR to which the advertised inter-AS link connects.
This could be any stable and routable IPv4 address of the remote
ASBR. Use of the TE Router ID as specified in the Traffic
Engineering router ID TLV [RFC5316] is RECOMMENDED.
The IPv4 remote ASBR ID TLV is TLV type TBD (see Section 10) and is 4
octets in length. The format of the IPv4 remote ASBR ID TLV is as
follows:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote ASBR ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: IPv4 Remote ASBR ID TLV Format
The IPv4 remote ASBR ID TLV MUST be included if the neighboring ASBR
has an IPv4 address. If the neighboring ASBR does not have an IPv4
address (not even an IPv4 TE Router ID), the IPv6 remote ASBR ID TLV
MUST be included instead. An IPv4 remote ASBR ID TLV and IPv6 remote
ASBR ID TLV MAY both be present in an inter-AS stub link NLRI.
7.3. IPv6 Remote ASBR ID
A new TLV, which is referred to as the IPv6 remote ASBR ID TLV, is
defined for inclusion in the link descriptor when advertising inter-
AS links. The IPv6 remote ASBR ID TLV specifies the IPv6 identifier
of the remote ASBR to which the advertised inter-AS link connects.
This could be any stable and routable IPv6 address of the remote
ASBR. Use of the TE Router ID as specified in the IPv6 Traffic
Engineering router ID TLV [RFC5316] is RECOMMENDED.
The IPv6 remote ASBR ID TLV is TLV type TBD (see Section 10) and is
16 octets in length. The format of the IPv6 remote ASBR ID TLV is as
follows:
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0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote ASBR ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote ASBR ID (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote ASBR ID (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Remote ASBR ID (continued) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: IPv6 Remote ASBR ID TLV Format
The IPv6 remote ASBR ID TLV MUST be included if the neighboring ASBR
has an IPv6 address. If the neighboring ASBR does not have an IPv6
address, the IPv4 remote ASBR ID TLV MUST be included instead. An
IPv4 remote ASBR ID TLV and IPv6 remote ASBR ID TLV MAY both be
present in an inter-AS stub link NLRI.
8. Topology Reconstruction.
When SDN controller gets such information from BGP-LS protocol, it
should find the corresponding associated router information, build
the link between these two border routers. After iterating the above
procedures for all of the stub links, the SDN controller can then
retrieve the connection topology between different domains
automatically.
9. Security Considerations
It is common for one operator to occupy several IGP domains that are
composited by its backbone network and several MAN(Metrio-Area-
Network)s/Internet Data Centers (IDCs). When they do traffic
engineering which spans MAN, Backbone and IDC, they need to know the
inter-as topology via the process described in this draft. Using the
passive interface features or configuring the Traffic Engineering
(TE) parameters on the interconnect links will not spread the
topology fluctuation across each other domain.
10. IANA Considerations
This document defines:
* A new BGP NLRI Type: Stub Link NLRI. The codepoint is from the
"BGP-LS NLRI Types"
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* Three new Link Descriptors TLV: Remote AS Number TLV, IPv4 Remote
ASBR ID, IPv6 Remote ASBR ID. The codepoint are from "BGP-LS Node
Descriptor, Link Descriptor, Prefix Descriptor, and Attribute
TLVs" registry.
10.1. New BGP-LS NLRI type
This document defines a new value in the registry "BGP-LS NLRI
Types":
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code Point | Description | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|TBD(suggestion 7)| Stub Link NLRI | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Stub Link NLRI Codepoint
10.2. New Stub Link Descriptors
This document defines three new values in the registry "BGP-LS NLRI
and Attribute TLVs":
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code Point | Description | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|TBD(suggestion 270)| Remote AS Number | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|TBD(suggestion 271)| IPv4 Remote ASBR ID | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|TBD(suggestion 272)| IPv6 Remote ASBR ID | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: BGP-LS Link Descriptors TLV
11. Acknowledgement
The author would like to thank Acee Lindem, Jie Dong, Shaowen Ma,
Jeff Tantsura and Dhruv Dhody for their valuable comments and
suggestions.
12. References
12.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC5316] Chen, M., Zhang, R., and X. Duan, "ISIS Extensions in
Support of Inter-Autonomous System (AS) MPLS and GMPLS
Traffic Engineering", RFC 5316, DOI 10.17487/RFC5316,
December 2008, <https://www.rfc-editor.org/info/rfc5316>.
[RFC5392] Chen, M., Zhang, R., and X. Duan, "OSPF Extensions in
Support of Inter-Autonomous System (AS) MPLS and GMPLS
Traffic Engineering", RFC 5392, DOI 10.17487/RFC5392,
January 2009, <https://www.rfc-editor.org/info/rfc5392>.
[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>.
12.2. Informative References
[RFC9086] Previdi, S., Talaulikar, K., Ed., Filsfils, C., Patel, K.,
Ray, S., and J. Dong, "Border Gateway Protocol - Link
State (BGP-LS) Extensions for Segment Routing BGP Egress
Peer Engineering", RFC 9086, DOI 10.17487/RFC9086, August
2021, <https://www.rfc-editor.org/info/rfc9086>.
Authors' Addresses
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing
Beijing, 102209
China
Email: wangaj3@chinatelecom.cn
Huaimo Chen
Futurewei
Boston, MA
United States of America
Email: hchen.ietf@gmail.com
Ketan Talaulikar
Cisco Systems
India
Email: ketant.ietf@gmail.com
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Shunwan Zhuang
Huawei Technologies
Huawei Building, No.156 Beiqing Rd.
Beijing
100095
China
Email: zhuangshunwan@huawei.com
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