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Versions: (draft-keyupate-ospf-ospfv2-hbit)
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OSPF K. Patel
Internet-Draft Arrcus
Updates: 2328 (if approved) P. Pillay-Esnault
Intended status: Standards Track Huawei Technologies
Expires: February 28, 2019 M. Bhardwaj
S. Bayraktar
Cisco Systems
August 27, 2018
H-bit Support for OSPFv2
draft-ietf-ospf-ospfv2-hbit-06
Abstract
OSPFv3 defines an option bit for router-LSAs known as the R-bit in
RFC5340. If the R-bit is clear, an OSPFv3 router can participate in
OSPF topology flooding, however it will not be used as a transit
router. In such cases, other routers in the OSPFv3 routing domain
only install routes to allow local traffic delivery. This document
defines the H-bit functionality to prevent other OSPFv2 routers from
using the router for transit traffic in OSPFv2 routing domains as
described in RFC 2328. This document updates RFC 2328.
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 February 28, 2019.
Copyright Notice
Copyright (c) 2018 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. H-bit Support . . . . . . . . . . . . . . . . . . . . . . . . 3
4. SPF Modifications . . . . . . . . . . . . . . . . . . . . . . 5
5. Auto Discovery and Backward Compatibility . . . . . . . . . . 5
6. OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
OSPFv3 [RFC5340] defines an option bit for router-LSAs known as the
R-bit. If the R-bit is clear, an OSPFv3 router can participate in
OSPFv3 topology flooding without acting as a transit router. In such
cases, other routers in the OSPFv3 routing domain only install routes
used for local traffic.
This functionality is particularly useful for BGP Route Reflectors,
known as virtual Route Reflectors (vRRs), that are not in the
forwarding path but are in central locations such as data centers.
Such Route Reflectors typically are used for route distribution and
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are not capable of forwarding transit traffic. However, they need to
learn the OSPF topology for:
1. SPF computation for Optimal Route Reflection functionality as
defined in [I-D.ietf-idr-bgp-optimal-route-reflection]
2. Reachability resolution for its Route Reflector Clients.
This document defines the R-bit functionality equivalent for OSPFv2
defined in [RFC2328] by introducing a new router-LSA bit known as the
"H-bit". This document updates appendix A.4.2 of RFC 2328.
2. Requirements Language
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. H-bit Support
This document defines a new router-LSA bit known as the Host Bit or
the H-bit. An OSPFv2 router advertising a router-LSA with the H-bit
set indicates to other OSPFv2 routers in the area supporting the
functionality that it MUST NOT be used as a transit router. The bit
value usage of the H-bit is reversed from the R-bit defined in OSPFv3
[RFC5340] to support backward compatibility. The modified OSPFv2
router-LSA format is:
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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 | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|H|0|0|N|W|V|E|B| 0 | # links |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | # TOS | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TOS | 0 | TOS metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
bit H
When set, an OSPFv2 router is a non-transit router and is
incapable of forwarding transit traffic.
When the H-bit is set, an OSPFv2 router is a non-transit router and
should not be used to forward transit traffic. In this mode, the
other OSPFv2 routers in the area SHOULD NOT use the originating
OSPFv2 router for transit traffic, but MAY use the OSPFv2 router for
local traffic destined to that OSPFv2 router.
An OSPFv2 router originating a router-LSA with the H-bit set SHOULD
advertise all its non-local router links with a link cost of
MaxLinkMetric as defined in Section 3 of [RFC6987]. This is to
increase the applicability of the H-bit to partial deployments where
it is the responsibility of the operator to ensure that OSPFv2
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routers not supporting the H-bit do not install routes causing
routing loops.
When the H-bit is set, IPv4 prefixes associated with local interfaces
in other areas MAY be advertised in summary LSAs. Non-local IPv4
prefixes, e.g., those advertised by other routers and installed
during the SPF computation, MAY be advertised in summary-LSAs if
configured by policy. Likewise, when the H-bit is set, only IPv4
prefixes associated with local interfaces MAY be advertised in AS-
external LSAs. Non-local IPv4 prefixes, e.g., those exported from
other routing protocols, MUST NOT be advertised in AS-external-LSAs.
Finally, when the H-bit is set, an Area Border Router (ABR) MUST
advertise a consistent H-bit setting in its self-originated router-
LSAs for all attached areas.
4. SPF Modifications
The SPF calculation described in section 16.1 [RFC2328] will be
modified to ensure that the routers originating router-LSAs with the
H-bit set will not be used for transit traffic. Step 2 is modified
as follows:
2) Call the vertex just added to the
tree vertex V. Examine the LSA
associated with vertex V. This is
a lookup in the Area A's link state
database based on the Vertex ID. If
this is a router-LSA, and the H-bit
of the router-LSA is set, and
vertex V is not the root, then the
router should not be used for transit
and step (3) should be executed
immediately. If this is a router-LSA,
and bit V of the router-LSA (see
Section A.4.2) is set, set Area A's
TransitCapability to TRUE. In any case,
each link described by the LSA gives
the cost to an adjacent vertex. For
each described link, (say it joins
vertex V to vertex W):
5. Auto Discovery and Backward Compatibility
To avoid the possibility of any routing loops due to partial
deployment, this document defines a OSPF Router-Information LSA
functional capability bit known as the Host Support capability.
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Auto Discovery via announcement of the Host Support Functional
Capability ensures that the H-bit functionality and its associated
SPF changes SHOULD only take effect if all the routers in a given
OSPF area support this functionality.
Implementations are encouraged to provide a configuration parameter
to manually override enforcement of the H-bit functionality in
partial deployments where the topology guarantees that OSPFv2 routers
not supporting the H-bit do not compute routes resulting in routing
loops. More precisely, the advertisement of MaxLinkMetric for the
router's non-local links will prevent OSPFv2 routers not supporting
the H-bit from attempting to use it for transit traffic.
6. OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics
When calculating the path to an OSPF AS-External-LSA or NSSA-LSA with
a Type-2 metric, the advertised Type-2 metric is taken as more
significant than the OSPF intra-area or inter-area path. Hence,
advertising the links with MaxLinkMetric as specified in [RFC6987]
does not discourage transit traffic when calculating AS external or
NSSA routes. Consequently, OSPF routers implementing [RFC6987] or
this specification should advertise a Type-2 metric of LSInfinity for
any self-originated AS-External-LSAs or NSSA-LSAs in situations when
the OSPF router is acting as a stub router [RFC6987] or implementing
this specification.
7. IANA Considerations
IANA is requested to create the OSPF Router-LSA bit registry with the
following assignments:
Value Description Reference
0x01 Area Border Router (B-bit) [RFC2328]
0x02 AS Boundary Router (E-bit) [RFC2328]
0x04 Virtual Link Endpoint (V-bit) [RFC2328]
0x08 Historic (W-bit) [RFC1584]
0x10 Unconditional NSSA Translator (Nt-bit) [RFC3101]
0x20 Unassigned
0x40 Unassigned
0x80 Host (H-bit) This Document
This document also defines a new Router Functional Capability
[RFC7770] known as the Host Support Functional Capability. This
document requests IANA to allocate the value of this capability from
the Router Functional Capability Bits TLV.
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8. Security Considerations
This document introduces no new security considerations beyond those
already specified in [RFC6987], [RFC2328], and [RFC5340].
9. Acknowledgements
The authors would like to acknowledge Hasmit Grover for discovery of
the limitation in [RFC6987], Acee Lindem, Abhay Roy, David Ward,
Burjiz Pithawala and Michael Barnes for their 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>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>.
[RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
RFC 3101, DOI 10.17487/RFC3101, January 2003,
<https://www.rfc-editor.org/info/rfc3101>.
[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>.
[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>.
[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>.
10.2. Informative References
[I-D.ietf-idr-bgp-optimal-route-reflection]
Raszuk, R., Cassar, C., Aman, E., Decraene, B., and K.
Wang, "BGP Optimal Route Reflection (BGP-ORR)", draft-
ietf-idr-bgp-optimal-route-reflection-16 (work in
progress), April 2018.
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[RFC1584] Moy, J., "Multicast Extensions to OSPF", RFC 1584,
DOI 10.17487/RFC1584, March 1994,
<https://www.rfc-editor.org/info/rfc1584>.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013,
<https://www.rfc-editor.org/info/rfc6987>.
Authors' Addresses
Keyur Patel
Arrcus
Email: keyur@arrcus.com
Padma Pillay-Esnault
Huawei Technologies
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: padma@huawei.com
Manish Bhardwaj
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: manbhard@cisco.com
Serpil Bayraktar
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95134
USA
Email: serpil@cisco.com
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