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Versions: (draft-wang-lsr-ospf-prefix-originator-ext)
00 01 02 03 04 05
LSR Working Group A. Wang
Internet-Draft China Telecom
Intended status: Standards Track A. Lindem
Expires: February 26, 2020 Cisco Systems
J. Dong
Huawei Technologies
K. Talaulikar
P. Psenak
Cisco Systems
August 25, 2019
OSPF Extension for Prefix Originator
draft-ietf-lsr-ospf-prefix-originator-02
Abstract
This document describes Open Shortest Path First (OSPF) v2 and OSPFv3
encodings to advertise the router-id of the originator of inter-area
prefixes for OSPFv2 and OSPFv3 Link-State Advertisement (LSA), which
are needed in several use cases in multi-area OSPF use cases.
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 February 26, 2020.
Copyright Notice
Copyright (c) 2019 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
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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. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Conventions used in this document . . . . . . . . . . . . . . 4
5. Scenario Description . . . . . . . . . . . . . . . . . . . . 4
6. Prefix Source Router-ID sub-TLV . . . . . . . . . . . . . . . 5
7. Extended LSA Elements of Procedure . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 6
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
10. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 7
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 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
Retrieval . . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
[I-D.ietf-ospf-mpls-elc] defines mechanisms to Entropy Readable Label
Depth (ERLD) for ingress Label Switching Router (LSR) to discover
each LSR's capability of performing Entropy Label (EL) -based load-
balancing in Multi Protocol Label Switch (MPLS) networks. The
ingress LSR can use this information to push the appropriate label
stack for specific traffic, especially in segment routing
environments and other stacked LSPs scenarios.
However, in inter-area scenarios, the Area Border Router (ABR) does
not advertise the originating OSPF router-id for inter-area prefixes.
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
prefixes and then can't judge the ERLD capabilities of the
destination. It is necessary to transfer the originator information
of these inter-area prefixes to ensure the ingress LSR constructs the
right Label stack.
More generally, draft [RFC8476] defines a mechanism to advertise
multiple types of supported Maximum SID Depths (MSD) at node and/or
link granularity. This information will be referred when the head-
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end router starts to send traffic to destination prefixes. In inter-
area scenario, it is also necessary for the sender to learn the
capabilities of the receivers associated with the inter-area
prefixes.
There is also another scenario where knowing the originator of inter-
area prefixes is useful. For example, Border Gateway Protocol Link-
State (BGP-LS) [RFC7752] describes mechanisms using the BGP protocol
to advertise Link-State information. This can enable an Soft
Definition Network (SDN) controller to collect the underlay network
topology automatically.
But if the underlay network is divided into multiple areas and
running the OSPF protocol, it is not easy for the SDN controller to
rebuild the multi-area topology, because normally an ABR that
connects multiple areas will hide the detailed topology information
for these non-backbone areas. If only the router in backbone area
runs the BGP-LS protocol, it just learn and report the summary
network information from the non-backbone areas. If the SDN
controller can learn the originator of the inter-area prefixes, it is
possible for them to rebuild the inter-area topology automatically.
[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
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,
but the related LSAs TLV must be extended.
This draft provides such solution for the OSPFv2 and OSPFv3
protocols.
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 [RFC2119] .
3. Terminology
The following terms are used in this document:
o ABR: Area Border Router
o ERLD: Entropy Readable Label Depth
o EL: Entropy Label
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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
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
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
is the loopback address of Node S1 and Lt1 is the loopback address of
Node T1.
+-----------------+
|IP SDN Controller|
+--------+--------+
|
| BGP-LS
|
+---------------------+------+--------+-----+--------------+
| +--+ +--+ ++-+ ++-+ +-++ + -+ +--+|
| |S1+--------+S2+---+R1+---|R0+----+R2+---+T1+--------+T2||
| +-++ N1 +-++ ++-+ +--+ +-++ ++++ N2 +-++|
| | | | | || | |
| | | | | || | |
| +-++ +-++ ++-+ +-++ ++++ +-++|
| |S4+--------+S3+---+R3+-----------+R4+---+T3+--------+T4||
| +--+ +--+ ++-+ +-++ ++-+ +--+|
| | | |
| | | |
| Area 1 | Area 0 | Area 2 |
+---------------------+---------------+--------------------+
Figure 1: OSPF Inter-Area Prefix Originator Scenario
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If S1 wants to send traffic to prefix Lt1 that is connected T1 in
another area, it should know the ERLD, and MSD values that are
associated with the node T1, and then construct the right label stack
at the ingress node for the target traffic.
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
is possible for the controller to retrieval the topology in non-
backbone area. The topology retrieval process and its usage
limitation are described in the Appendix A and Appendix B.
From the above scenarios, we can conclude it is useful to introduce
and define the prefix originator sub TLV within OSPF.
6. Prefix Source Router-ID sub-TLV
[RFC7684] and [RFC8362] define the TLV extensions for OSPFv2 and
OSPFv3 respectively. These documents facilitate addition of new
attributes for prefixes. Based on these formats, we can define new
sub-TLV to advertise the "Prefix Source Router ID", as that defined
in [RFC7794].
The "Prefix Source Router-ID" sub-TLV has 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Source Router-ID |
+---------------------------------------------------------------+
Figure 2: Prefix Source Router-ID sub-TLV Format
o Source Router-ID Sub-TLV Type: TBD1[RFC7684] or TBD2 [RFC8362]
o Length: 4
o Value: Router-ID of OSPFv2/OSPFv3 source router
For OSPFv2, this sub-TLV is a sub-TLV of OSPFv2 Extended Prefix TLV,
which is included in the "OSPFv2 Extended Prefix Opaque LSA"
[RFC7684].
For OSPFv3, this sub-TLV is a sub-TLV of "Inter-Area-Prefix TLV",
which is included in the "E-Inter-Area-Prefix-LSA".
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7. Extended LSA Elements of Procedure
When an ABR, for example R2 in Fig.1, receives the Router-LSA
announcement in area 2, it should originate the corresponding "OSPFv2
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
prefixes, e.g., for prefix Lt1, N2. etc., which identifies the source
router that advertised the prefix.
When S1 in another area receives such LSA, it then can learn that
prefix Lt1 is associated with node T1, check the ERLD, or MSD value
according to its necessity, and construct the right label stack at
the ingress node S1 for the traffic destined to Lt1.
When R0 receives such LSA, it learns the Prefix Source Router-id and
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
controller can then use such information to build the inter-area
topology according to the process described in the Appendix A. The
topology retrieval process may not suitable for some environments as
stated in Appendix B.
8. Security Considerations
Security concerns for OSPF are addressed in [RFC5709]
Advertisement of the additional information defined in this document
introduces no new security concerns
9. IANA Considerations
This specification defines one Prefix Source Router-ID sub-TLV as
described in Section 6. This value should be added to the existing
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++
| TBD | Prefix Source Sub-TLV | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++
Figure 3: Prefix Source sub-TLV CodePoint from OSPFv2 Extended Prefix TLV Sub-TLVs
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The following sub-TLV is added to the registry of "OSPFv3 Extended-
LSA Sub-TLVs". The allocation is IETF Review that defined in
[RFC8362]
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++
| Code Point | Description | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++
| TBD | Prefix Source Sub-TLV | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++++++++
Figure 4: Prefix Source sub-TLV CodePoint from OSPFv3 Extended-LSA Sub-TLVs
10. Acknowledgement
Many thanks to Les Ginsberg for his valuable suggestions on this
draft. And also thanks Jeff Tantsura,Rob Shakir, Van De Velde
Gunter, Goethals Dirk, Shaofu Peng, John E Drake for their valuable
comments on this draft.
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>.
[RFC5709] Bhatia, M., Manral, V., Fanto, M., White, R., Barnes, M.,
Li, T., and R. Atkinson, "OSPFv2 HMAC-SHA Cryptographic
Authentication", RFC 5709, DOI 10.17487/RFC5709, October
2009, <https://www.rfc-editor.org/info/rfc5709>.
[RFC7684] Psenak, P., Gredler, H., Shakir, R., Henderickx, W.,
Tantsura, J., and A. Lindem, "OSPFv2 Prefix/Link Attribute
Advertisement", RFC 7684, DOI 10.17487/RFC7684, November
2015, <https://www.rfc-editor.org/info/rfc7684>.
[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>.
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[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>.
[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]
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-16
(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
When an IP SDN Controller receives this information, it should
compare the prefix NLRI that included in the BGP-LS packet. When it
encounters the same prefix but with different source router ID, it
should extract the corresponding area-ID, rebuild the link between
these two different source routers in non-backbone area. Belows is
one example that based on the Fig.1:
Assuming we want to rebuild the connection between router S1 and
router S2 that locates in area 1:
a. Normally, router S1 will advertise prefix N1 within its router-
LSA.
b. When this router-LSA reaches the ABR router R1, it will convert
it into summary-LSA, add the Prefix Source Router-ID sub-TLV,
which is router id of S1 in this example.
c. R1 then floods this extension summary-LSA to R0, which is running
BGP-LS protocol with IP SDN Controller. The controller then
knows the prefixes of N1 is from S1.
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d. Router S2 will do the similar process, and the controller will
also learn that prefixes N1 is also from S2.
e. Then it can reconstruct the link between S1 and S2, using the
prefix N1. The topology within Area 1 can then be reconstructed
accordingly.
Iterating the above process continuously, an IP SDN controller can
retrieve a detailed topology that spans multiple areas.
Appendix B. Special Considerations on Inter-Area Topology Retrieval
The above topology retrieval process can be applied in the case where
each link between routers is assigned a unique prefix. However,
there are some situations where this heuristic cannot be applied.
Specifically, the cases where the link is unnumbered or the prefix
corresponding to the link is an anycast prefix and is not unique.
The Appendix A heuristic to rebuild the topology can normally be used
if all links are numbered and the anycast prefixes correspond to
loopbacks and have a host prefix length, i.e., 32 for IPv4 prefixes
and 128 for IPv6 prefixes.
Authors' Addresses
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing 102209
China
Email: wangaj3@chinatelecom.cn
Acee Lindem
Cisco Systems
301 Midenhall Way
Cary, NC 27513
USA
Email: acee@cisco.com
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Jie Dong
Huawei Technologies
Beijing
China
Email: jie.dong@huawei.com
Ketan Talaulikar
Cisco Systems
S.No. 154/6, Phase I, Hinjawadi
Pune 411 057
India
Email: ketant@cisco.com
Peter Psenak
Cisco Systems
Pribinova Street 10
Bratislava, Eurovea Centre, Central 3 81109
Slovakia
Email: ppsenak@cisco.com
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