draft-ietf-lsr-ospf-prefix-originator-01.txt   draft-ietf-lsr-ospf-prefix-originator-02.txt 
LSR Working Group A. Wang LSR Working Group A. Wang
Internet-Draft China Telecom Internet-Draft China Telecom
Intended status: Standards Track A. Lindem Intended status: Standards Track A. Lindem
Expires: January 2, 2020 Cisco Systems Expires: February 26, 2020 Cisco Systems
J. Dong J. Dong
Huawei Technologies Huawei Technologies
K. Talaulikar K. Talaulikar
P. Psenak P. Psenak
Cisco Systems Cisco Systems
July 1, 2019 August 25, 2019
OSPF Extension for Prefix Originator OSPF Extension for Prefix Originator
draft-ietf-lsr-ospf-prefix-originator-01 draft-ietf-lsr-ospf-prefix-originator-02
Abstract Abstract
This document describes OSPFv2 and OSPFv3 encodings to advertise the This document describes Open Shortest Path First (OSPF) v2 and OSPFv3
router-id of the originator of inter-area prefixes for OSPFv2 and encodings to advertise the router-id of the originator of inter-area
OSPFv3 LSAs, which are needed in several use cases in multi-area OSPF prefixes for OSPFv2 and OSPFv3 Link-State Advertisement (LSA), which
use cases. are needed in several use cases in multi-area OSPF use cases.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
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Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3 2. Conventions used in this document . . . . . . . . . . . . . . 3
3. Scenario Description . . . . . . . . . . . . . . . . . . . . 3 3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Prefix Source Router-ID sub-TLV . . . . . . . . . . . . . . . 4 4. Conventions used in this document . . . . . . . . . . . . . . 4
5. Extended LSA Elements of Procedure . . . . . . . . . . . . . 5 5. Scenario Description . . . . . . . . . . . . . . . . . . . . 4
6. Security Considerations . . . . . . . . . . . . . . . . . . . 5 6. Prefix Source Router-ID sub-TLV . . . . . . . . . . . . . . . 5
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Extended LSA Elements of Procedure . . . . . . . . . . . . . 6
8. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 6 8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 6 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
9.1. Normative References . . . . . . . . . . . . . . . . . . 6 10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7 11. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
Appendix A. Inter-Area Topology Retrieval Process . . . . . . . 7 11.1. Normative References . . . . . . . . . . . . . . . . . . 7
11.2. Informative References . . . . . . . . . . . . . . . . . 8
Appendix A. Inter-Area Topology Retrieval Process . . . . . . . 8
Appendix B. Special Considerations on Inter-Area Topology Appendix B. Special Considerations on Inter-Area Topology
Retrieval . . . . . . . . . . . . . . . . . . . . . 8 Retrieval . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
[I-D.ietf-ospf-mpls-elc] defines mechanisms to signal Entropy Label [I-D.ietf-ospf-mpls-elc] defines mechanisms to Entropy Readable Label
Capability (ELC) and Entropy Readable Label Depth (ERLD) for ingress Depth (ERLD) for ingress Label Switching Router (LSR) to discover
LSR to discover each LSR's capability of reading the maximum label each LSR's capability of performing Entropy Label (EL) -based load-
stack depth and performing EL-based load-balancing in MPLS networks. balancing in Multi Protocol Label Switch (MPLS) networks. The
The ingress LSR can use this information to push the appropriate ingress LSR can use this information to push the appropriate label
label stack for specific FEC trafffic, especially in segment routing stack for specific traffic, especially in segment routing
environments and other stacked LSPs scenarios. environments and other stacked LSPs scenarios.
However, in inter-area scenarios, the Area Border Router (ABR) does However, in inter-area scenarios, the Area Border Router (ABR) does
not advertise the originating OSPF router-id for inter-area prefixes. not advertise the originating OSPF router-id for inter-area prefixes.
An OSPF router in one area doesn't know where the prefixes really An OSPF router in one area doesn't know where the prefixes really
came from and can't determine the router that originated inter-area came from and can't determine the router that originated inter-area
prefixes and then can't judge the ELC and ERLD capabilities of the prefixes and then can't judge the ERLD capabilities of the
destination. It is necessary to transfer the originator information destination. It is necessary to transfer the originator information
of these inter-area prefixes to ensure the ingress LSR constructs the of these inter-area prefixes to ensure the ingress LSR constructs the
right Label stack. right Label stack.
More generally, draft [I-D.ietf-ospf-segment-routing-msd] defines a More generally, draft [RFC8476] defines a mechanism to advertise
mechanism to advertise multiple types of supported Maximum SID Depths multiple types of supported Maximum SID Depths (MSD) at node and/or
(MSD) at node and/or link granularity. This information will be link granularity. This information will be referred when the head-
referred when the head-end router starts to send traffic to end router starts to send traffic to destination prefixes. In inter-
destination prefixes. In inter-area scenario, it is also necessary area scenario, it is also necessary for the sender to learn the
for the sender to learn the capabilities of the receivers associated capabilities of the receivers associated with the inter-area
with the inter-area prefixes. prefixes.
There is also another scenario where knowing the originator of inter- There is also another scenario where knowing the originator of inter-
area prefixes is useful. For example, BGP-LS [RFC7752] describes area prefixes is useful. For example, Border Gateway Protocol Link-
mechanisms using the BGP protocol to advertise Link-State State (BGP-LS) [RFC7752] describes mechanisms using the BGP protocol
information. This can enable an SDN controller to collect the to advertise Link-State information. This can enable an Soft
underlay network topology automatically. Definition Network (SDN) controller to collect the underlay network
topology automatically.
But if the underlay network is divided into multiple areas and But if the underlay network is divided into multiple areas and
running the OSPF protocol, it is not easy for the SDN controller to running the OSPF protocol, it is not easy for the SDN controller to
rebuild the multi-area topology, because normally an Area Border rebuild the multi-area topology, because normally an ABR that
Router (ABR) that connects multiple areas will hide the detailed connects multiple areas will hide the detailed topology information
topology information for these non-backbone areas, and the router in for these non-backbone areas. If only the router in backbone area
backbone area that runs the BGP-LS protocol can only learn and report runs the BGP-LS protocol, it just learn and report the summary
the summary network information from the non-backbone areas. If the network information from the non-backbone areas. If the SDN
SDN controller can learn the originator of the inter-area prefixes, controller can learn the originator of the inter-area prefixes, it is
it is possible for them to rebuild the inter-area topology possible for them to rebuild the inter-area topology automatically.
automatically.
[RFC7794] introduces the IS-IS "IPv4/IPv6 Source Router IDs" TLV to [RFC7794] introduces the Intermediate System to Intermediate System
(IS-IS) "IPv4/IPv6 Source Router IDs" Type-Length-Value (TLV) to
advertise the source of the prefixes redistributed from a different advertise the source of the prefixes redistributed from a different
IS-IS level. This TLV can be used in the above scenarios. Such IS-IS level. This TLV can be used in the above scenarios. Such
solution can also be applied in networks that run the OSPF protocol, solution can also be applied in networks that run the OSPF protocol,
but the related Link state Advertisements (LSAs) must be extended. but the related LSAs TLV must be extended.
This draft provides such solution for the OSPFv2 and OSPFv3 This draft provides such solution for the OSPFv2 and OSPFv3
protocols. protocols.
2. Conventions used in this document 2. Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119] . document are to be interpreted as described in [RFC2119] .
3. Scenario Description 3. Terminology
Fig.1 illustrates the topology scenario when OSPF is running in The following terms are used in this document:
o ABR: Area Border Router
o ERLD: Entropy Readable Label Depth
o EL: Entropy Label
o IS-IS: Intermediate System to Intermediate System
o LSA: Link-State Advertisement
o MSD: Maximum SID Depths
o OSPF: Open Shortest Path First
o SID: Segment IDentifier
4. 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 [RFC2119] .
5. Scenario Description
Figure 1 illustrates the topology scenario when OSPF is running in
multi-area. R0-R4 are routers in backbone area, S1-S4,T1-T4 are multi-area. R0-R4 are routers in backbone area, S1-S4,T1-T4 are
internal routers in area 1 and area 2 respectively. R1 and R3 are internal routers in area 1 and area 2 respectively. R1 and R3 are
area border routers between area 0 and area 1. R2 and R4 are area area border routers between area 0 and area 1. R2 and R4 are area
border routers between area 0 and area 2. N1 is the network between border routers between area 0 and area 2. N1 is the network between
router S1 and S2 and N2 is the network between router T1 and T2. Ls1 router S1 and S2 and N2 is the network between router T1 and T2. Ls1
is the loopback address of Node S1 and Lt1 is the loopback address of is the loopback address of Node S1 and Lt1 is the loopback address of
Node T1. Node T1.
+-----------------+ +-----------------+
|IP SDN Controller| |IP SDN Controller|
skipping to change at page 4, line 25 skipping to change at page 4, line 51
| | | | | || | | | | | | | || | |
| | | | | || | | | | | | | || | |
| +-++ +-++ ++-+ +-++ ++++ +-++| | +-++ +-++ ++-+ +-++ ++++ +-++|
| |S4+--------+S3+---+R3+-----------+R4+---+T3+--------+T4|| | |S4+--------+S3+---+R3+-----------+R4+---+T3+--------+T4||
| +--+ +--+ ++-+ +-++ ++-+ +--+| | +--+ +--+ ++-+ +-++ ++-+ +--+|
| | | | | | | |
| | | | | | | |
| Area 1 | Area 0 | Area 2 | | Area 1 | Area 0 | Area 2 |
+---------------------+---------------+--------------------+ +---------------------+---------------+--------------------+
Fig.1 OSPF Inter-Area Prefix Originator Scenario Figure 1: OSPF Inter-Area Prefix Originator Scenario
If S1 wants to send traffic to prefix Lt1 that is connected T1 in If S1 wants to send traffic to prefix Lt1 that is connected T1 in
another area, it should know the ELC, ERLD, and MSD values that are another area, it should know the ERLD, and MSD values that are
associated with the node T1, and then construct the right label stack associated with the node T1, and then construct the right label stack
at the ingress node for the target traffic. at the ingress node for the target traffic.
In another scenario, If R0 has some method to learn the originator of In another scenario, If R0 has some method to learn the originator of
network N1 and reports such information to IP SDN controller, then it network N1 and reports such information to IP SDN controller, then it
is possible for the controller to retrieval the topology in non- is possible for the controller to retrieval the topology in non-
backbone area. The topology retrieval process and its usage backbone area. The topology retrieval process and its usage
limitation are described in the Appendix A and Appendix B. limitation are described in the Appendix A and Appendix B.
From the above scenarios, we can conclude it is useful to introduce From the above scenarios, we can conclude it is useful to introduce
and define the prefix originator sub TLV within OSPF. and define the prefix originator sub TLV within OSPF.
4. Prefix Source Router-ID sub-TLV 6. Prefix Source Router-ID sub-TLV
[RFC7684] and [RFC8362] define the TLV extensions for OSPFv2 and [RFC7684] and [RFC8362] define the TLV extensions for OSPFv2 and
OSPFv3 respectively. These documents facilitate addition of new OSPFv3 respectively. These documents facilitate addition of new
attributes for prefixes and links. Based on these formats, we can attributes for prefixes. Based on these formats, we can define new
define new sub-TLV to advertise the "Prefix Source Router ID", as sub-TLV to advertise the "Prefix Source Router ID", as that defined
that defined in [RFC7794]. in [RFC7794].
The "Prefix Source Router-ID" sub-TLV has the following format: The "Prefix Source Router-ID" sub-TLV has the following format:
0 1 2 3 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 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 | | Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Source Router-ID | | Prefix Source Router-ID |
+---------------------------------------------------------------+ +---------------------------------------------------------------+
Fig. 2 Prefix Source Router-ID sub-TLV Format Figure 2: Prefix Source Router-ID sub-TLV Format
o Source Router-ID Sub-TLV Type: TBD1[RFC7684] or TBD2 [RFC8362] o Source Router-ID Sub-TLV Type: TBD1[RFC7684] or TBD2 [RFC8362]
o Length: 4 o Length: 4
o Value: Router-ID of OSPFv2/OSPFv3 source router o Value: Router-ID of OSPFv2/OSPFv3 source router
This sub-TLV can be included in the "OSPFv2 Extended Prefix Opaque For OSPFv2, this sub-TLV is a sub-TLV of OSPFv2 Extended Prefix TLV,
LSA" [RFC7684] or the "E-Inter-Area-Prefix-LSA" [RFC8362]. which is included in the "OSPFv2 Extended Prefix Opaque LSA"
[RFC7684].
5. Extended LSA Elements of Procedure For OSPFv3, this sub-TLV is a sub-TLV of "Inter-Area-Prefix TLV",
which is included in the "E-Inter-Area-Prefix-LSA".
7. Extended LSA Elements of Procedure
When an ABR, for example R2 in Fig.1, receives the Router-LSA When an ABR, for example R2 in Fig.1, receives the Router-LSA
announcement in area 2, it should originate the corresponding "OSPFv2 announcement in area 2, it should originate the corresponding "OSPFv2
Extended Prefix Opaque LSA" for OSPFv2 or "E-Inter-Area-Prefix-LSA" Extended Prefix Opaque LSA" for OSPFv2 or "E-Inter-Area-Prefix-LSA"
for OSPFv3 that includes the Source Router-ID sub-TLV for the network for OSPFv3 that includes the Source Router-ID sub-TLV for the network
prefixes, e.g., for prefix Lt1, N2. etc., which identifies the source prefixes, e.g., for prefix Lt1, N2. etc., which identifies the source
router that advertised the prefix. router that advertised the prefix.
When S1 in another area receives such LSA, it then can learn that When S1 in another area receives such LSA, it then can learn that
prefix Lt1 is associated with node T1, check the ELC, ERLD, or MSD prefix Lt1 is associated with node T1, check the ERLD, or MSD value
value according to its necessity, and construct the right label stack according to its necessity, and construct the right label stack at
at the ingress node S1 for the traffic destined to Lt1. the ingress node S1 for the traffic destined to Lt1.
When R0 receives such LSA, it learns the Prefix Source Router-id and When R0 receives such LSA, it learns the Prefix Source Router-id and
includes it in the prefix information advertised to an SDN controller includes it in the prefix information advertised to an SDN controller
as described in[I-D.ietf-idr-bgp-ls-segment-routing-ext]. The SDN as described in[I-D.ietf-idr-bgp-ls-segment-routing-ext]. The SDN
controller can then use such information to build the inter-area controller can then use such information to build the inter-area
topology according to the process described in the Appendix A. The topology according to the process described in the Appendix A. The
topology retrieval process may not suitable for some environments as topology retrieval process may not suitable for some environments as
stated in Appendix B. stated in Appendix B.
6. Security Considerations 8. Security Considerations
Security concerns for OSPF are addressed in [RFC5709] Security concerns for OSPF are addressed in [RFC5709]
Advertisement of the additional information defined in this document Advertisement of the additional information defined in this document
introduces no new security concerns introduces no new security concerns
7. IANA Considerations 9. IANA Considerations
This document adds the following new sub-TLV to the registry of This specification defines one Prefix Source Router-ID sub-TLV as
"OSPFv2 Extended Prefix TLV Sub-TLVs". The allocation policy is IETF described in Section 6. This value should be added to the existing
Review that defined in [RFC7684] OSPFv2 Extended Prefix TLV Sub-TLVs registry and OSPFv3 Extended-LSA
Sub-TLVs registry respectively.
Th following new sub-TLV is added to the registry of "OSPFv2 Extended
Prefix TLV Sub-TLVs". The allocation policy is IETF Review that
defined in [RFC7684]
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++
| Code Point | Description | Status | | Code Point | Description | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++
| TBD | Prefix Source Sub-TLV | Allocation from IANA | | TBD | Prefix Source Sub-TLV | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++
Fig.3: Prefix Source sub-TLV CodePoint from OSPFv2 Extended Prefix TLV Sub-TLVs Figure 3: Prefix Source sub-TLV CodePoint from OSPFv2 Extended Prefix TLV Sub-TLVs
The following sub-TLV is added to the registry of "OSPFv3 Extended-
This document adds the following sub-TLV to the registry of "OSPFv3 LSA Sub-TLVs". The allocation is IETF Review that defined in
Extended-LSA Sub-TLVs". The allocation is IETF Review that defined [RFC8362]
in [RFC8362]
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++
| Code Point | Description | Status | | Code Point | Description | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++
| TBD | Prefix Source Sub-TLV | Allocation from IANA | | TBD | Prefix Source Sub-TLV | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++
Fig.4: Prefix Source sub-TLV CodePoint from OSPFv3 Extended-LSA Sub-TLVs Figure 4: Prefix Source sub-TLV CodePoint from OSPFv3 Extended-LSA Sub-TLVs
8. Acknowledgement 10. Acknowledgement
Many thanks to Les Ginsberg for his valuable suggestions on this Many thanks to Les Ginsberg for his valuable suggestions on this
draft. And also thanks Jeff Tantsura,Rob Shakir, Van De Velde draft. And also thanks Jeff Tantsura,Rob Shakir, Van De Velde
Gunter, Goethals Dirk, Shaofu Peng, John E Drake for their valuable Gunter, Goethals Dirk, Shaofu Peng, John E Drake for their valuable
comments on this draft. comments on this draft.
9. References 11. References
9.1. Normative References
[I-D.ietf-ospf-mpls-elc]
Xu, X., Kini, S., Psenak, P., Filsfils, C., and S.
Litkowski, "Signaling Entropy Label Capability and Entropy
Readable Label-stack Depth Using OSPF", draft-ietf-ospf-
mpls-elc-08 (work in progress), May 2019.
[I-D.ietf-ospf-segment-routing-msd] 11.1. Normative References
Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling MSD (Maximum SID Depth) using OSPF", draft-
ietf-ospf-segment-routing-msd-25 (work in progress),
October 2018.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997, DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>. <https://www.rfc-editor.org/info/rfc2119>.
[RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M., [RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
Authentication", RFC 5709, DOI 10.17487/RFC5709, October Authentication", RFC 5709, DOI 10.17487/RFC5709, October
2009, <https://www.rfc-editor.org/info/rfc5709>. 2009, <https://www.rfc-editor.org/info/rfc5709>.
skipping to change at page 7, line 36 skipping to change at page 8, line 10
[RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and [RFC7794] Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4 U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794, and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
March 2016, <https://www.rfc-editor.org/info/rfc7794>. March 2016, <https://www.rfc-editor.org/info/rfc7794>.
[RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and [RFC8362] Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
F. Baker, "OSPFv3 Link State Advertisement (LSA) F. Baker, "OSPFv3 Link State Advertisement (LSA)
Extensibility", RFC 8362, DOI 10.17487/RFC8362, April Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
2018, <https://www.rfc-editor.org/info/rfc8362>. 2018, <https://www.rfc-editor.org/info/rfc8362>.
9.2. Informative References [RFC8476] Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
"Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
DOI 10.17487/RFC8476, December 2018,
<https://www.rfc-editor.org/info/rfc8476>.
11.2. Informative References
[I-D.ietf-idr-bgp-ls-segment-routing-ext] [I-D.ietf-idr-bgp-ls-segment-routing-ext]
Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H., Previdi, S., Talaulikar, K., Filsfils, C., Gredler, H.,
and M. Chen, "BGP Link-State extensions for Segment and M. Chen, "BGP Link-State extensions for Segment
Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-15 Routing", draft-ietf-idr-bgp-ls-segment-routing-ext-16
(work in progress), May 2019. (work in progress), June 2019.
[I-D.ietf-ospf-mpls-elc]
Xu, X., Kini, S., Psenak, P., Filsfils, C., and S.
Litkowski, "Signaling Entropy Label Capability and Entropy
Readable Label-stack Depth Using OSPF", draft-ietf-ospf-
mpls-elc-08 (work in progress), May 2019.
Appendix A. Inter-Area Topology Retrieval Process Appendix A. Inter-Area Topology Retrieval Process
When an IP SDN Controller receives this information, it should When an IP SDN Controller receives this information, it should
compare the prefix NLRI that included in the BGP-LS packet. When it compare the prefix NLRI that included in the BGP-LS packet. When it
encounters the same prefix but with different source router ID, it encounters the same prefix but with different source router ID, it
should extract the corresponding area-ID, rebuild the link between should extract the corresponding area-ID, rebuild the link between
these two different source routers in non-backbone area. Belows is these two different source routers in non-backbone area. Belows is
one example that based on the Fig.1: one example that based on the Fig.1:
skipping to change at page 8, line 50 skipping to change at page 9, line 36
and 128 for IPv6 prefixes. and 128 for IPv6 prefixes.
Authors' Addresses Authors' Addresses
Aijun Wang Aijun Wang
China Telecom China Telecom
Beiqijia Town, Changping District Beiqijia Town, Changping District
Beijing 102209 Beijing 102209
China China
Email: wangaj.bri@chinatelecom.cn Email: wangaj3@chinatelecom.cn
Acee Lindem Acee Lindem
Cisco Systems Cisco Systems
301 Midenhall Way 301 Midenhall Way
Cary, NC 27513 Cary, NC 27513
USA USA
Email: acee@cisco.com Email: acee@cisco.com
Jie Dong Jie Dong
Huawei Technologies Huawei Technologies
Beijing Beijing
China China
Email: jie.dong@huawei.com Email: jie.dong@huawei.com
Ketan Talaulikar Ketan Talaulikar
Cisco Systems Cisco Systems
S.No. 154/6, Phase I, Hinjawadi S.No. 154/6, Phase I, Hinjawadi
 End of changes. 36 change blocks. 
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