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.

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This Internet-Draft will expire on October 10, 2019.

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Table of Contents

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.

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.

                      +-----------------+
                 +----+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

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.

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 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, and [RFC5392] define the 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 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.

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

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.

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.

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", Internet-Draft draft-ietf-idr-bgp-ls-segment-routing-ext-12, 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", Internet-Draft draft-ietf-idr-bgpls-segment-routing-epe-18, March 2019.
[I-D.ietf-ospf-ospfv3-lsa-extend] Lindem, A., Roy, A., Goethals, D., Vallem, V. and F. Baker, "OSPFv3 LSA Extendibility", Internet-Draft draft-ietf-ospf-ospfv3-lsa-extend-23, 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", Internet-Draft draft-ietf-teas-native-ip-scenarios-02, 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.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, DOI 10.17487/RFC2328, April 1998.
[RFC5305] Li, T. and H. Smit, "IS-IS Extensions for Traffic Engineering", RFC 5305, DOI 10.17487/RFC5305, October 2008.
[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.
[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.
[RFC6119] Harrison, J., Berger, J. and M. Bartlett, "IPv6 Traffic Engineering in IS-IS", RFC 6119, DOI 10.17487/RFC6119, February 2011.
[RFC7752] Gredler, H., 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.
[RFC7794] Ginsberg, L., 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.
[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.

Authors' Addresses

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