IDR Working Group A. Wang
Internet-Draft China Telecom
Intended status: Standards Track H. Chen
Expires: October 10, 2019 Huawei Technologies
S. Ma
Mellanox Technologies
April 8, 2019
BGP-LS Extension for Inter-AS Topology Retrieval
draft-ietf-idr-bgpls-inter-as-topology-ext-02
Abstract
This document describes the process to build BGP-LS key parameters in
multi-domain scenario, defines one new BGP-LS NLRI type(Stub Link
NLRI) and some new inter-AS TE related TLVs for BGP-LS to let SDN
controller retrieve the network topology automatically under various
environments.
Such process and extension 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 October 10, 2019.
Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved.
Wang, et al. Expires October 10, 2019 [Page 1]
Internet-Draft BGP-LS-Inter-AS-Ext April 2019
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 extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Inter-AS Domain Scenarios. . . . . . . . . . . . . . . . . . 3
4. Stub Link NLRI . . . . . . . . . . . . . . . . . . . . . . . 3
4.1. Inter-AS Native IP Scenario . . . . . . . . . . . . . . . 4
4.2. Inter-AS TE Scenario . . . . . . . . . . . . . . . . . . 4
5. Inter-AS TE NLRI related TLVs . . . . . . . . . . . . . . . . 5
5.1. Remote AS Number TLV . . . . . . . . . . . . . . . . . . 5
5.2. IPv4 Remote ASBR ID . . . . . . . . . . . . . . . . . . . 6
5.3. IPv6 Remote ASBR ID . . . . . . . . . . . . . . . . . . . 7
6. Topology Reconstruction. . . . . . . . . . . . . . . . . . . 7
7. Security Considerations . . . . . . . . . . . . . . . . . . . 8
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 8
10. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
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 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.
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 the border routers to run BGP-LS protocol and report
the information to the PCE/SDN controller, which restricts the
solution deployment flexibility.
Wang, et al. Expires October 10, 2019 [Page 2]
Internet-Draft BGP-LS-Inter-AS-Ext April 2019
This draft analysis the situations that the PCE/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. Inter-AS Domain Scenarios.
Fig.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.
+-----------------+
+----+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
4. 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
Wang, et al. Expires October 10, 2019 [Page 3]
Internet-Draft BGP-LS-Inter-AS-Ext April 2019
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) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
// Inter-AS TE Link Descriptors (variable) //
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: The Inter-AS TE Link NLRI Format
The semantics of "Stub Link Descriptors" is same as that defined in
[RFC7752] for "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.
4.1. Inter-AS Native IP Scenario
When IGP A or IGP B 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 to be reported via the
BGP-LS protocol to the SDN controller.
The "Local Node Descriptors" should describe the the characteristics
of ASBRs that are connected these stub links.
When such information is reported via the BGP-LS protocol, the PCE/
SDN controller can construct the underlay inter-domain topology
according to procedure described in section 6.
4.2. Inter-AS TE Scenario
When IGP A or IGP B run IS-IS TE/OSPF-TE protocol, [RFC5316] and
[RFC5392] define the IS-IS and OSPF extensions respectively to deal
with the situation for inter-AS traffic engineering. Three new sub-
Wang, et al. Expires October 10, 2019 [Page 4]
Internet-Draft BGP-LS-Inter-AS-Ext April 2019
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 can
also 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 PCE/SDN controller know these information via one of the
interior router that runs BGP-LS protocol, the PCE/SDN controller can
rebuild the inter-AS TE topology correctly according to the procedure
described in section 6
5. 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 PCE/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 is
agnostic to the underly protocol.
5.1. 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.
Wang, et al. Expires October 10, 2019 [Page 5]
Internet-Draft BGP-LS-Inter-AS-Ext April 2019
The remote AS number TLV is TLV type TBD (see Section 8) 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.
5.2. 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 [RFC5305] is RECOMMENDED.
The IPv4 remote ASBR ID TLV is TLV type TBD (see Section 8) 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
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.
Wang, et al. Expires October 10, 2019 [Page 6]
Internet-Draft BGP-LS-Inter-AS-Ext April 2019
5.3. IPv6 Remote ASBR ID
A new TLV, which is referred to as the IPv6 remote ASBR ID TLV, is
defined for inclusion in the inter-AS reachability TLV 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 [RFC6119] is RECOMMENDED.
The IPv6 remote ASBR ID TLV is TLV type TBD (see Section 8) 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.
6. 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, then 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.
Wang, et al. Expires October 10, 2019 [Page 7]
Internet-Draft BGP-LS-Inter-AS-Ext April 2019
7. 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/IDCs. When they do traffic engineering which spans MAN-
backbone-IDC, they need to know the inter-as topology via the process
described in this draft. Using the passive interface features or
configuring the TE parameters on the interconnect links will not
spread the topology fluctuation across each other domain.
8. IANA Considerations
TBD.
9. Acknowledgement
The author would like to thank Acee Lindem, Ketan Talaulikar, Jie
Dong, Jeff Tantsura and Dhruv Dhody for their valuable comments and
suggestions.
10. Normative References
[I-D.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "BGP Link-State extensions for Segment
Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-12
(work in progress), March 2019.
[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-18 (work in progress), March 2019.
[I-D.ietf-ospf-ospfv3-lsa-extend]
Lindem, A., Roy, A., Goethals, D., Vallem, V., and F.
Baker, "OSPFv3 LSA Extendibility", draft-ietf-ospf-ospfv3-
lsa-extend-23 (work in progress), January 2018.
[I-D.ietf-teas-native-ip-scenarios]
Wang, A., Huang, X., Qou, C., Li, Z., and P. Mi,
"Scenario, Simulation and Suggestion of PCE in Native IP
Network", draft-ietf-teas-native-ip-scenarios-02 (work in
progress), October 2018.
[RFC1195] Callon, R., "Use of OSI IS-IS for routing in TCP/IP and
dual environments", RFC 1195, DOI 10.17487/RFC1195,
December 1990, <https://www.rfc-editor.org/info/rfc1195>.
Wang, et al. Expires October 10, 2019 [Page 8]
Internet-Draft BGP-LS-Inter-AS-Ext April 2019
[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>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[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>.
[RFC6119] Harrison, J., Berger, J., and M. Bartlett, "IPv6 Traffic
Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119,
February 2011, <https://www.rfc-editor.org/info/rfc6119>.
[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>.
[RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
March 2016, <https://www.rfc-editor.org/info/rfc7794>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>.
Authors' Addresses
Wang, et al. Expires October 10, 2019 [Page 9]
Internet-Draft BGP-LS-Inter-AS-Ext April 2019
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing, Beijing 102209
China
Email: wangaj.bri@chinatelecom.cn
Huaimo Chen
Huawei Technologies
Boston, MA
USA
Email: Huaimo.chen@huawei.com
Shaowen Ma
Mellanox Technologies
Email: mashaowen@gmail.com
Wang, et al. Expires October 10, 2019 [Page 10]