OSPF Prefix Originator Extension
draft-ietf-lsr-ospf-prefix-originator-04
The information below is for an old version of the document.
| Document | Type |
This is an older version of an Internet-Draft that was ultimately published as RFC 9084.
|
|
|---|---|---|---|
| Authors | Aijun Wang , Acee Lindem , Jie Dong , Peter Psenak , Ketan Talaulikar | ||
| Last updated | 2019-09-12 (Latest revision 2019-08-26) | ||
| Replaces | draft-wang-lsr-ospf-prefix-originator-ext | ||
| RFC stream | Internet Engineering Task Force (IETF) | ||
| Formats | |||
| Reviews | |||
| Additional resources | Mailing list discussion | ||
| Stream | WG state | WG Document | |
| Document shepherd | Christian Hopps | ||
| IESG | IESG state | Became RFC 9084 (Proposed Standard) | |
| Consensus boilerplate | Yes | ||
| Telechat date | (None) | ||
| Responsible AD | (None) | ||
| Send notices to | Christian Hopps <chopps@chopps.org> |
draft-ietf-lsr-ospf-prefix-originator-04
LSR Working Group A. Wang
Internet-Draft China Telecom
Intended status: Standards Track A. Lindem
Expires: March 15, 2020 Cisco Systems
J. Dong
Huawei Technologies
P. Psenak
K. Talaulikar
Cisco Systems
September 12, 2019
OSPF Prefix Originator Extension
draft-ietf-lsr-ospf-prefix-originator-04
Abstract
This document defines Open Shortest Path First (OSPF) encodings to
advertise the router-id of the originator of inter-area prefixes for
OSPFv2 and OSPFv3 Link-State Advertisements (LSAs). The source
originator is needed in several 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
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Internet-Drafts are draft documents valid for a maximum of six months
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 15, 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. Inter-Area Prefix Source Advertisement Use Cases . . . . . . 4
5. Prefix Source Router-ID sub-TLV . . . . . . . . . . . . . . . 5
6. Elements of Procedure . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 9
Appendix A. Inter-Area Topology Retrieval Process . . . . . . . 9
Appendix B. Special Considerations on Inter-Area Topology
Retrieval . . . . . . . . . . . . . . . . . . . . . 10
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 10
1. Introduction
[I-D.ietf-ospf-mpls-elc] defines mechanisms to advertise Entropy
Readable Label Depth (ERLD) for ingress Label Switching Routers (LSR)
to discover other LSR's capability of performing Entropy Label based
load-balancing in MPLS networks. The ingress LSR can use this
information to construct the appropriate label stack for specific
traffic requirements, especially in segment routed networks and other
deployments requiring stacked LSPs.
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 the origin area of inter-area
prefixes and can't determine the router that originated these
prefixes or the ERLD capabilities of the destination. Therefore, it
is necessary to advertise the originator of these inter-area prefixes
to ensure the ingress LSR can construct the appropriate label stack.
More generally, [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-end
router starts to send traffic to destination prefixes. In inter-area
scenario, it is also necessary for the sender to learn the
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capabilities of the receivers associated with the inter-area
prefixes.
There is 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 information can enable a
Software Definition Network (SDN) controller to automatically
determine the underlay network topology.
However, if the underlay network is partitioned into multiple areas
and running the OSPF protocol, it is not easy for the SDN controller
to rebuild the multi-area topology since ABR that connects multiple
areas will normally hide the detailed topology for these non-backbone
areas. If only the internal routers within backbone area run the
BGP-LS protocol, they 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 to
rebuild the inter-area topology.
[RFC7794] introduces the Intermediate System to Intermediate System
(IS-IS) "IPv4/IPv6 Source Router IDs" Type-Length-Value (TLV) to
advertise the source of prefixes leaked 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 existing OSPF
LSAs TLVs must be extended to include the router originating the
prefix.
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", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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 NLRI: Network Layer Reachability Information
o OSPF: Open Shortest Path First
o SID: Segment IDentifier
o SDN: Software Definition Network
4. Inter-Area Prefix Source Advertisement Use Cases
Figure 1 illustrates a topology where OSPF is running in multiple
areas. R0-R4 are routers in the backbone area, S1-S4 are internal
routers in area 1, and T1-T4 are internal routers in area 2. R1 and
R3 are ABRs between area 0 and area 1. R2 and R4 are ABRs 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
If S1 wants to send traffic to prefix Lt1 that is connected to T1 in
another area, it should know the ERLD and MSD values associated with
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the node T1, and then construct the right label stack at the ingress
node for traffic destined to prefix Lt1.
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 reconstruct the topology in the
non-backbone areas. The topology reconstruction process and its
limitations are described in the Appendix A and Appendix B.
From the above scenarios, we can conclude it is useful to define the
OSPF prefix originator sub TLV .
5. Prefix Source Router-ID sub-TLV
[RFC7684] and [RFC8362] respectively define TLV-based LSAs for OSPFv2
and OSPFv3. These documents facilitate addition of new attributes
for prefixes and provide the basis for a sub-TLV to advertise the
"Prefix Source Router ID". For OSPFv2, this sub-TLV is a sub-TLV of
OSPFv2 Extended Prefix TLV which SHOULD be included in the "OSPFv2
Extended Prefix Opaque LSA" [RFC7684] for inter-area prefixes. For
OSPFv3, this sub-TLV is a sub-TLV of "Inter-Area-Prefix TLV", which
SHOULD be included in the "E-Inter-Area-Prefix-LSA" [RFC8362].
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 router that is the source of the
prefix.
This sub-TLV provides the same functionality as the IS-IS "IPv4/IPv6
Source Router" TLV defined in [RFC7794].
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6. Elements of Procedure
When an ABR, for example R2 in Figure 1, receives a Router-LSA
advertisement 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. For example, to identify the source router
prefix Lt1 and other inter-area prefixes in Figure 1.
When a router in another area, e.g., S1, receives such LSA, it then
can ascertain that prefix Lt1 is associated with node T1 and obtain
the ERLD or MSD value from T1's Router-Information LSA [RFC7770] and
construct the right label stack at the ingress node S1 for traffic
destined to prefix Lt1.
When a router in another area, e.g., 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.
7. Security Considerations
Since this document extends the "OSPFv2 Extended Prefix LSA" and
"OSPFv3 E-Inter-Area-Prefix LSA", the security considerations for
[RFC7684] and [RFC8362] are applicable.
Modification of the "Prefix Source Sub-TLV" could be used for a
Denial-of-Service attack and could inhibit the use cases described in
Section 4. If the OSPF domain is vulnerable to such attacks, OSPF
authentication should be used as defined for OSPFv2 in [RFC5709] and
[RFC7474] and for OSPFv3 in [RFC7166].
Additionally, advertisement of the prefix source for inter-area
prefixes facilitates reconstruction of the OSPF topology for other
areas. Network operators may consider their topologies to be
sensitive confidential data. For OSPFv3, IPsec can be used to
provide confidentiality [RFC4552]. Since there is no standard
defined for native OSPFv2 IPsec, some form of secure tunnel is
required to provide confidentiality.
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8. IANA Considerations
This specification defines the Prefix Source Router-ID sub-TLV as
described in Section 5. This value should be added to the both
existing "OSPFv2 Extended Prefix TLV Sub-TLVs" and "OSPFv3 Extended-
LSA Sub-TLVs" registries.
The following sub-TLV is added to the "OSPFv2 Extended Prefix TLV
Sub-TLVs" registry. The allocation policy is IETF Review as defined
in [RFC7684]
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code Point | Description | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD | Prefix Source Sub-TLV | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Code Point in "OSPFv2 Extended Prefix TLV Sub-TLVs"
The following sub-TLV is added to the "OSPFv3 Extended-LSA Sub-TLVs"
registry. The allocation policy is IETF Review as defined in
[RFC8362]
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Code Point | Description | Status |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TBD | Prefix Source Sub-TLV | Allocation from IANA |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Code Point in "OSPFv3 Extended-LSA Sub-TLVs"
9. Acknowledgement
Many thanks to Les Ginsberg for his suggestions on this draft. Also
thanks to Jeff Tantsura, Rob Shakir, Gunter Van De Velde, Goethals
Dirk, Shaofu Peng, and John E Drake for their valuable comments.
10. References
10.1. 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>.
[RFC4552] Gupta, M. and N. Melam, "Authentication/Confidentiality
for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
<https://www.rfc-editor.org/info/rfc4552>.
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[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>.
[RFC7166] Bhatia, M., Manral, V., and A. Lindem, "Supporting
Authentication Trailer for OSPFv3", RFC 7166,
DOI 10.17487/RFC7166, March 2014,
<https://www.rfc-editor.org/info/rfc7166>.
[RFC7474] Bhatia, M., Hartman, S., Zhang, D., and A. Lindem, Ed.,
"Security Extension for OSPFv2 When Using Manual Key
Management", RFC 7474, DOI 10.17487/RFC7474, April 2015,
<https://www.rfc-editor.org/info/rfc7474>.
[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>.
[RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
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10.2. 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-09 (work in progress), September 2019.
[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>.
Appendix A. Inter-Area Topology Retrieval Process
When an IP SDN Controller receives BGP-LS [RFC7752] information, it
should compare the prefix Network Layer Reachability Information
(NLRI) that is included in the BGP-LS NLRI. 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 source
routers in the non-backbone area. Below is one example that based on
the Figure 1:
Assuming we want to rebuild the connection between router S1 and
router S2 located 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 using
the BGP-LS protocol with IP SDN Controller. The controller then
knows the prefix for N1 is from S1.
d. Router S2 will perform a similar process, and the controller will
also learn that prefix N1 is also from S2.
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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, the 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 point-to-point or multi-access link connecting 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.
The Appendix A heuristic to rebuild the topology can normally be used
if all links are numbered. For anycast prefixes, if it corresponds
to the loopback interface and has a host prefix length, i.e., 32 for
IPv4 prefixes and 128 for IPv6 prefixes, Appendix A can also applied
since these anycast prefixes are not required to reconstruct the
topology.
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
Peter Psenak
Cisco Systems
Pribinova Street 10
Bratislava, Eurovea Centre, Central 3 81109
Slovakia
Email: ppsenak@cisco.com
Ketan Talaulikar
Cisco Systems
S.No. 154/6, Phase I, Hinjawadi
Pune 411 057
India
Email: ketant@cisco.com
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