LSR Working Group A. Wang
Internet-Draft China Telecom
Intended status: Standards Track June 28, 2018
Expires: December 30, 2018
OSPF Extend for Inter-Area Topology Retrieval
draft-wang-lsr-ospf-inter-area-topology-ext-00
Abstract
This document describes method to transfer the source router id of
inter-area prefixes for OSPFv2 [RFC2328] and OSPFv3 [RFC5340], which
is needed in topology retrieval processing for inter-area scenario.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
3. Inter-Area Topology Retrieval Scenario . . . . . . . . . . . 3
3.1. OSPFv2 Extend Solution (IPv4 Source Router ID) . . . . . 4
3.2. OSPFv3 Extend Solution (IPv6 Source Router ID) . . . . . 5
3.3. Prefix Source Router ID sub TLV . . . . . . . . . . . . . 7
3.4. Extend LSA generate process . . . . . . . . . . . . . . . 8
3.5. Inter-Area Topology Retrieval Process . . . . . . . . . . 8
4. Security Considerations . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
6.1. Normative References . . . . . . . . . . . . . . . . . . 9
6.2. Informative References . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 10
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 if the underlay network is divided into multi area and running
OSPF protocol, it is not easy for the SDN controller to rebuild the
multi-area topology, because normally the ABR that locates on the
boundary of different area will hide the detail topology information
in non-backbone area, and the router in backbone area that runs BGP-
LS protocol can only get and report the summary network information
in non-backbone area.
[RFC7794] introduces "IPv4/IPv6 Source Router IDs" TLV to label the
source of the prefixes redistributed from different Level, this TLV
can be used to reconstruct the detail overall topology within level 1
and level 2. Such solution can also be applied into network that run
OSPF protocol, but the related LSP message must be redefined.
This draft gives such solution for the OSPF v2 and OSPF v3 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 [RFC2119] .
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3. Inter-Area Topology Retrieval Scenario
Fig.1 illustrates the topology retrieval scenario when OSPF is
running in multi-area. R0-R4 are routers in backbone area,
S1-S4,T1-T4 are interal router in area 1 and area 2 respectively. R1
and R3 are border routers between area 0 and area 1; R2 and R4 are
border routers between area 0 and area 2. N1 is the network between
router S1 and S2, N2 is the network between router T1 and T2.
Normally, ABR router R1 or R3 will send the summary LSA(for OSPFv2)
or Inter-Area-Prefix-LSAs(for OSPFv3) for network N1. When R0
receives such LSA, it can only know network N1 locates behind R1, and
does not know where it is originated. When R0 reports the summary
LSA information via BGP-LS protocol, the IP SDN controller can't
certainly deduce the detail network topology within area 1. The
situation is same as that in Area 2.
+-----------------+
|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 |
+---------------------+---------------+--------------------+
Fig.1 OSPF Inter-Area Topology Retrieval Scenario
If R0 has some methods to know the originator of network N1 and
reports such information to IP SDN controller, then it is easy for
the controller to retrieval the detail topology in non-backbone area.
Because traditional OSPFv2/v3 packet is not in the TLV format, we
need to find some solutions to reuse or redefine the existing fields
in summary LSA (OSPFv2) and Inter-Area-Prefix-LSAs(for OSPFv3)to
transfer the additional information. The extend methods should not
conflict with the usage of existing semantics.
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Section 3.1 and section 3.2 give the proposed solutions for OSPFv2
and OSPFv3 respectively.
3.1. OSPFv2 Extend Solution (IPv4 Source Router ID)
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 3 or 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TOS | TOS metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
Fig.2 Summary LSA Format
Fig.2 illustrates the format of summary LSA. There is one byte that
originately defined for the number of TOS types but in actually this
feature does not applied in real network or implemented in the main
stream router.
To transfer the additional information, this draft proposes to reuse/
redefine this field. In order to prevent possible conflict, even it
is in very rare event, we can start the usage of this field from the
upper limit, for example, 0xFE. Then the proposed extend summary LSA
format is the followings:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS age | Options | 3 or 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0xFE | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPv4 Source Router ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fig.3 Extended Summary LSA Format
That is to say, if the field of "Numbers of TOS" equal "0xFE", then
the "IPv4 Source Router ID"(4 bytes) of the inter-area network
reported in summary LSA and its associated area id(4 bytes) are
included in the field that follows the "metric" field.
3.2. OSPFv3 Extend Solution (IPv6 Source Router ID)
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Age |0|0|1| 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | PrefixOptions | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fig.4 Inter-Area-Prefix-LSA Format
For OSPFv3, this draft proposes the similar method, because the
semantic of the Inter-Area-Prefix-LSA format is almost same as the
summary LSA format.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Age |0|0|1| 3 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS Checksum | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0xFE | Metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Prefix Source Router ID |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PrefixLength | PrefixOptions | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Address Prefix |
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Fig.5 Extended Inter-Area-Prefix-LSA Format
If the value of "Numbers of TOS" equal "0xFE", then the "IPv6 source
router ID" (16 bytes) and its corresponding area ID (4 bytes)
information are inserted in the "Inter-Area-Prefix-LSA" after the
field "Metric". After this, the normal Prefix information is
followed as shown in Fig.5
3.3. Prefix Source Router ID sub TLV
[RFC7684] and [RFC8362] define the TLV format extension for OSPFv2
and OSPFv3 respectively. These documents give the flexibility to add
new attributes for the prefixes and links. Based on these formats,
we can define new sub TLV to transfer the "Prefix Source Router ID",
as that defined in [RFC7794].
The proposed "Prefix Source Router ID" format is the following:
For IPv4 network, it is the following:
o Pv4 Source Router ID Type: TBD
o Length: 4
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o Value: IPv4 Router ID of the source of the advertisement
This sub TLV should be included in the "OSPFv2 Extended Prefix Opaque
LSA" that defined in [RFC7684]
For IPv6 network, it is the following:
o IPv6 Source Router ID Type: TBD
o Length: 16
o Value: IPv6 Router ID of the source of the advertisement
This sub TLV should be included in "E-Inter-Area-Prefix-LSA" that
defined in [RFC8362]
3.4. Extend LSA generate process
When ABR(for example R1 in Fig.1)receives the "Router LSA"
announcement in area 1, it should generate the corresponding extend
"Summary LSA" or "Inter-Area-Prefix-LSA" that includes the "Source
Router ID" of the network prefixes, which labels the corresponding
link and the "area ID" that the source router belongs to.
When R0 receives such extend LSA, it then strips this additional
information, put it into the corresponding part that in BGP-LS
protocol as described in[I-D.wang-idr-bgpls-inter-as-topology-ext]
and reports them to the IP SDN Controller.
3.5. Inter-Area Topology Retrieval Process
When 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 router in non-backbone area.
Iterating the above process continuously, the IP SDN controller can
then retrieve the detail topology that span multi-area.
4. Security Considerations
TBD.
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5. IANA Considerations
TBD.
6. References
6.1. Normative References
[I-D.ietf-pce-pcep-extension-native-ip]
Wang, A., Khasanov, B., Cheruathur, S., and C. Zhu, "PCEP
Extension for Native IP Network", draft-ietf-pce-pcep-
extension-native-ip-00 (work in progress), June 2018.
[I-D.ietf-teas-native-ip-scenarios]
Wang, A., Huang, X., Qou, C., Huang, L., and K. Mi, "CCDR
Scenario, Simulation and Suggestion", draft-ietf-teas-
native-ip-scenarios-00 (work in progress), February 2018.
[I-D.ietf-teas-pcecc-use-cases]
Zhao, Q., Li, Z., Khasanov, B., Ke, Z., Fang, L., Zhou,
C., Communications, T., and A. Rachitskiy, "The Use Cases
for Using PCE as the Central Controller(PCECC) of LSPs",
draft-ietf-teas-pcecc-use-cases-01 (work in progress), May
2017.
[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>.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
<https://www.rfc-editor.org/info/rfc5340>.
[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>.
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[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>.
6.2. Informative References
[I-D.wang-idr-bgpls-inter-as-topology-ext]
Wang, A., "BGP-LS extend for inter-AS topology retrieval",
draft-wang-idr-bgpls-inter-as-topology-ext-00 (work in
progress), March 2018.
Author's Address
Aijun Wang
China Telecom
Beiqijia Town, Changping District
Beijing, Beijing 102209
China
Email: wangaj.bri@chinatelecom.cn
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