IDR Working Group A. Wang
Internet-Draft China Telecom
Intended status: Standards Track H. Chen
Expires: April 1, 2021 Futurewei
K. Talaulikar
Cisco Systems
S. Zhuang
Huawei Technologies
September 28, 2020
BGP-LS Extension for Inter-AS Topology Retrieval
draft-ietf-idr-bgpls-inter-as-topology-ext-09
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 inter Autonomous (inter-AS) Traffic
Engineering (TE) related 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
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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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 1, 2021.
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Copyright Notice
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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
5.1. Inter-AS Native IP Scenario . . . . . . . . . . . . . . . 5
5.2. Inter-AS TE Scenario . . . . . . . . . . . . . . . . . . 6
6. Inter-AS TE NLRI related TLVs . . . . . . . . . . . . . . . . 6
6.1. Remote AS Number TLV . . . . . . . . . . . . . . . . . . 7
6.2. IPv4 Remote ASBR ID . . . . . . . . . . . . . . . . . . . 7
6.3. IPv6 Remote ASBR ID . . . . . . . . . . . . . . . . . . . 8
7. Topology Reconstruction. . . . . . . . . . . . . . . . . . . 8
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
9.1. New BGP-LS NLRI type . . . . . . . . . . . . . . . . . . 9
9.2. New Link Descriptors . . . . . . . . . . . . . . . . . . 10
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 10
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 10
11.1. Normative References . . . . . . . . . . . . . . . . . . 10
11.2. Informative References . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 11
1. Introduction
BGP-LS [RFC7752] 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
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mechanic within current BGP- LS to transfer the interconnect topology
information.
Draft [I-D.ietf-idr-bgpls-segment-routing-epe] 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 several
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:
o IDCs: Internet Data Centers
o MAN: Metrio-Area-Network
o 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
[RFC7752] 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 [RFC7752] 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.
5.1. Inter-AS Native IP Scenario
Draft [RFC8735] describes the situation that operator needs some
traffic engineering solution for the inter-as native IP environment.
In such situation, different domain may run different IGP protocol.
The operator needs to know the inter-as topology first to calculate
the end to end optimal path centrally.
When IGP A or IGP B in Figure 1 runs native IS-IS/OSPF protocol, the
operator can use passive feature for the inter-domain links to let
the routers within the IGP domain know these links. Such stub links
information can then be carried within the Stub Link NLRI reported
via the BGP-LS protocol to the SDN controller.
For OSPFv2, when the interface is configured as passive, the
"Linktype" field in corresponding Router LSA will be set to 3, to
indicate it connects with stub network. Other routers in the IGP
domain can identify such interfaces via this characteristics, and
report them via the newly defined "Stub Link NLRI".
For OSPFv3 and ISIS, [I-D.wang-lsr-passive-interface-attribute]
describes the method to label the passive interfaces within the
network. The router that runs BGP-LS can extract these passive
interfaces from other interfaces that participate in the IGP protocol
and report them via the newly defined "Stub Link NLRI".
The "Local Node Descriptors" should describe the characteristics of
ASBRs that are connected these stub links.
When such information is reported via the BGP-LS protocol, the SDN
controller can construct the underlay inter-domain topology according
to procedure described in Section 7
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5.2. Inter-AS TE Scenario
When IGP A or IGP B in Figure 1 runs IS-IS TE/OSPF-TE protocol,
[RFC5316] and [RFC5392] define IS-IS and OSPF extensions respectively
to deal with the situation for inter-AS traffic engineering. Three
new sub-TLVs(Remote AS Number、IPv4 Remote ASBR ID、IPv6
Remote ASBR ID) which are associated with the inter-AS TE 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 TE 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 TE topology correctly according to the procedure described
in Section 7
6. Inter-AS TE NLRI related TLVs
This draft 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 TE related topology by the SDN
controller.
The following Link Descriptor TLVs are added into the BGP-LS protocol
:
+-----------+---------------------+--------------+----------------+
| 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: 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.
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6.1. Remote AS Number TLV
A new TLV, the remote AS number TLV, is defined for inclusion in the
link descriptor when advertising inter-AS TE 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 9 ) 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 TE link.
6.2. 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 TE 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 9) and is 4
octets in length. The format of the IPv4 remote ASBR ID sub-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
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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 TE link NLRI.
6.3. 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 9) and is 16
octets in length. The format of the IPv6 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 TE link NLRI.
7. Topology Reconstruction.
When SDN controller gets such information from BGP-LS protocol, it
should compares the proximity of these stub links. If they are under
the same network scope and in different AS, then it should find the
corresponding associated router information, build the link between
these two border routers.
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If the prefixes reported via the "Stub Link" NLRI are under the same
network scope, and in the same AS, the SDN controller can then
determine there is some IGP adjacency irregular. The usage of such
information is out of scope of this draft.
After iterating the above procedures for all of the stub links, the
SDN controller can then retrieve the connection topology between
different domains automatically.
8. 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.
9. IANA Considerations
This document defines:
o A new BGP NLRI Type: Stub Link NLRI. The codepoint is from the
"BGP-LS NLRI Types"
o 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.
9.1. New BGP-LS NLRI type
This document defines a new value in the registry "BGP-LS NLRI
Types":
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code Point | Description | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD | Stub Link NLRI | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Stub Link NLRI Codepoint
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9.2. New Link Descriptors
This document defines three new values in the registry "BGP-LS Node
Descriptor, Link Descriptor, Prefix Descriptor, and Attribute TLVs":
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code Point | Description | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD | Remote AS Number | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD |IPv4 Remote ASBR ID| Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD |IPv6 Remote ASBR ID| Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: BGP-LS Link Descriptors TLV
10. Acknowledgement
The author would like to thank Acee Lindem, Jie Dong, Shaowen Ma,
Jeff Tantsura and Dhruv Dhody for their valuable comments and
suggestions.
11. References
11.1. 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>.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic
Engineering", RFC 5305, DOI 10.17487/RFC5305, October
2008, <https://www.rfc-editor.org/info/rfc5305>.
[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>.
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[RFC7752] Gredler, H., Ed., Medved, J., Previdi, S., Farrel, A., and
S. Ray, "North-Bound Distribution of Link-State and
Traffic Engineering (TE) Information Using BGP", RFC 7752,
DOI 10.17487/RFC7752, March 2016,
<https://www.rfc-editor.org/info/rfc7752>.
[RFC8735] Wang, A., Huang, X., Kou, C., Li, Z., and P. Mi,
"Scenarios and Simulation Results of PCE in a Native IP
Network", RFC 8735, DOI 10.17487/RFC8735, February 2020,
<https://www.rfc-editor.org/info/rfc8735>.
11.2. Informative References
[I-D.ietf-idr-bgpls-segment-routing-epe]
Previdi, S., Talaulikar, K., Filsfils, C., Patel, K., Ray,
S., and J. Dong, "BGP-LS extensions for Segment Routing
BGP Egress Peer Engineering", draft-ietf-idr-bgpls-
segment-routing-epe-19 (work in progress), May 2019.
[I-D.wang-lsr-passive-interface-attribute]
Wang, A., Hu, Z., and G. Mishra, "Passive Interface
Attribute", draft-wang-lsr-passive-interface-attribute-03
(work in progress), September 2020.
Authors' Addresses
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing, Beijing 102209
China
Email: wangaj3@chinatelecom.cn
Huaimo Chen
Futurewei
Boston, MA
USA
Email: hchen@futurewei.com
Ketan Talaulikar
Cisco Systems
Email: ketant@cisco.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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