draft-ietf-ospf-ospfv2-hbit-05.txt   rfc8770.txt 
OSPF K. Patel Internet Engineering Task Force (IETF) K. Patel
Internet-Draft Arrcus Request for Comments: 8770 Arrcus
Intended status: Standards Track P. Pillay-Esnault Updates: 6987 P. Pillay-Esnault
Expires: February 2, 2019 Huawei Technologies Category: Standards Track PPE Consulting
M. Bhardwaj ISSN: 2070-1721 M. Bhardwaj
S. Bayraktar S. Bayraktar
Cisco Systems Cisco Systems
August 1, 2018 April 2020
H-bit Support for OSPFv2 Host Router Support for OSPFv2
draft-ietf-ospf-ospfv2-hbit-05
Abstract Abstract
OSPFv3 defines an option bit for router-LSAs known as the R-bit in The Open Shortest Path First Version 2 (OSPFv2) protocol does not
RFC5340. If the R-bit is clear, an OSPFv3 router can participate in have a mechanism for a node to repel transit traffic if it is on the
OSPF topology flooding, however it will not used as a transit router. shortest path. This document defines a bit called the Host-bit
In such cases, other routers in the OSPFv3 routing domain only (H-bit). This bit enables a router to advertise that it is a non-
install routes to allow local traffic delivery. This draft defines transit router. This document also describes the changes needed to
the H-bit functionality to prevent other OSPFv2 routers from using support the H-bit in the domain. In addition, this document updates
the router for transit traffic in OSPFv2 routing domains as described RFC 6987 to advertise Type 2 External and Not-So-Stubby Area (NSSA)
in RFC 2328. Link State Advertisements (LSAs) (RFC 3101) with a high cost in order
to repel traffic effectively.
Status of This Memo Status of This Memo
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provisions of BCP 78 and BCP 79.
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Internet Standards is available in Section 2 of RFC 7841.
This Internet-Draft will expire on February 2, 2019. Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc8770.
Copyright Notice Copyright Notice
Copyright (c) 2018 IETF Trust and the persons identified as the Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language
3. H-bit Support . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Host-Bit Support
4. SPF Modifications . . . . . . . . . . . . . . . . . . . . . . 5 4. SPF Modifications
5. Auto Discovery and Backward Compatibility . . . . . . . . . . 5 5. Autodiscovery and Backward Compatibility
6. OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics . . . . . 6 6. OSPF AS-External-LSAs / NSSA-LSAs with Type 2 Metrics
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. Security Considerations
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 9. References
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 9.1. Normative References
10.1. Normative References . . . . . . . . . . . . . . . . . . 7 9.2. Informative References
10.2. Informative References . . . . . . . . . . . . . . . . . 7 Acknowledgements
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses
1. Introduction 1. Introduction
OSPFv3 [RFC5340] defines an option bit for router-LSAs known as the The OSPFv2 protocol specifies a Shortest Path First (SPF) algorithm
R-bit. If the R-bit is clear, an OSPFv3 router can participate in that identifies transit vertices based on their adjacencies.
OSPFv3 topology flooding without acting as a transit router. In such Therefore, OSPFv2 does not have a mechanism to prevent traffic
cases, other routers in the OSPFv3 routing domain only install routes transiting a participating node if it is a transit vertex in the only
used for local traffic. existing or shortest path to the destination. The use of metrics to
make the node undesirable can help to repel traffic only if an
alternative better route exists.
This functionality is particularly useful for BGP Route Reflectors, A mechanism to move traffic away from the shortest path is
known as virtual Route Reflectors (vRRs), that are not in the particularly useful for a number of use cases:
forwarding path but are in central locations such as data centers.
Such Route Reflectors typically are used for route distribution and
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 1. Graceful isolation of a router, to avoid blackhole scenarios when
defined in [I-D.ietf-idr-bgp-optimal-route-reflection] there is a reload and possible long reconvergence times.
2. Reachability resolution for its Route Reflector Clients. 2. Closet switches that are not usually used for transit traffic but
need to participate in the topology.
This draft defines the R-bit functionality equivalent for OSPFv2 3. Overloaded routers that could use such a capability to
defined in [RFC2328] by introducing a new router-LSA bit known as the temporarily repel traffic until they stabilize.
"H-bit".
4. BGP route reflectors, known as virtual Route Reflectors, that are
not in the forwarding path but are in central locations such as
data centers. Such route reflectors are typically used for route
distribution and are not capable of forwarding transit traffic.
However, they need to learn the OSPF topology to perform SPF
computation for optimal routes and reachability resolution for
their clients [BGP-ORR].
This document describes the functionality provided by the Host-bit
(H-bit); this functionality prevents other OSPFv2 routers from using
the host router by excluding it in path calculations for transit
traffic in OSPFv2 routing domains. If the H-bit is set, then the
calculation of the shortest-path tree for an area, as described in
Section 16.1 of [RFC2328], is modified by including a check to verify
that transit vertices DO NOT have the H-bit set (see Section 4).
Furthermore, in order to repel traffic effectively, this document
updates [RFC6987] so that Type 2 External and Not-So-Stubby Area
(NSSA) Link State Advertisements (LSAs) [RFC3101] are advertised with
a high cost (see Section 6). OSPFv3 [RFC5340] defines an option bit,
known as the R-bit, for router-LSAs; the H-bit supports similar
functionality.
2. Requirements Language 2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP "OPTIONAL" in this document are to be interpreted as described in
14 [RFC2119] [RFC8174] when, and only when, they appear in all BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. H-bit Support 3. Host-Bit Support
This document defines a new router-LSA bit known as the Host Bit or 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 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 set indicates that it MUST NOT be used as a transit router (see
functionality that it MUST NOT be used as a transit router. The bit Section 4) by other OSPFv2 routers in the area that support the H-bit
value usage of the H-bit is reversed from the R-bit defined in OSPFv3 functionality.
[RFC5340] to support backward compatibility. The modified OSPFv2
router-LSA format is:
0 1 2 3 If the H-bit is not set, then backward compatibility is achieved, as
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 the behavior will be the same as in [RFC2328].
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 0 1 2 3
When set, an OSPFv2 router is a non-transit router and is 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
incapable of forwarding transit traffic. +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
When the H-bit is set, an OSPFv2 router is a non-transit router and Figure 1: OSPF Router-LSA
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 Bit H is the high-order bit of the OSPF flags, as shown below.
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
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 0 1 2 3 4 5 6 7
in other areas MAY be advertised in summary LSAs. Non-local IPv4 +-+-+-+-+-+-+-+-+
prefixes, e.g., those advertised by other routers and installed |H|0|0|N|W|V|E|B|
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- Figure 2: OSPF Router-LSA Option Bits
external LSAs. Non-local IPv4 prefixes, e.g., those exported from
other routing protocols, MUST NOT be advertised in AS-external-LSAs. When the H-bit is set, the OSPFv2 router is a host (non-transit)
Finally, when the H-bit is set, an Area Border Router (ABR) MUST router and is incapable of forwarding transit traffic. In this mode,
advertise a consistent H-bit setting in its self-originated router- the other OSPFv2 routers in the area MUST NOT use the host router for
LSAs for all attached areas. transit traffic but may send traffic to its local destinations.
An OSPFv2 router originating a router-LSA with the H-bit set MUST
advertise all its non-stub links with a link cost of MaxLinkMetric
[RFC6987].
When the H-bit is set, an Area Border Router (ABR) MUST advertise the
same H-bit setting in its self-originated router-LSAs for all
attached areas. The consistency of the setting will prevent
inter-area traffic transiting through the router by suppressing
advertisements of prefixes from other routers in the area in its
summary-LSAs. Only IPv4 prefixes associated with its local
interfaces MUST be advertised in summary-LSAs to provide reachability
to end hosts attached to a router with the H-bit set.
When the H-bit is set, the host router cannot act as an Autonomous
System Border Router (ASBR). Indeed, ASBRs are transit routers to
prefixes that are typically imported through redistribution of
prefixes from other routing protocols. Therefore, non-local IPv4
prefixes, e.g., those imported from other routing protocols, SHOULD
NOT be advertised in AS-external-LSAs if the H-bit is set. Some use
cases, such as an overloaded router or a router being gracefully
isolated, may benefit from continued advertisements of non-local
prefixes. In these cases, the Type 2 metric in AS-external-LSAs MUST
be set to LSInfinity [RFC2328] to repel traffic (see Section 6 of
this document).
4. SPF Modifications 4. SPF Modifications
The SPF calculation described in section 16.1 [RFC2328] will be The SPF calculation described in Section 16.1 of [RFC2328] is
modified to ensure that the routers originating router-LSAs with the 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 H-bit set will not be used for transit traffic. Step (2) is modified
as follows: to include a check on the H-bit, as shown below. (Please note that
all of the sub-procedures of Step (2) remain unchanged and are not
included in the excerpt below.)
2) Call the vertex just added to the (2) Call the vertex just added to the tree "vertex V". Examine
tree vertex V. Examine the LSA the LSA associated with vertex V. This is a lookup in
associated with vertex V. This is Area A's link state database based on the Vertex ID. If this
a lookup in the Area A's link state is a router-LSA, and the H-bit of the router-LSA is set, and
database based on the Vertex ID. If vertex V is not the root, then the router should not be used
this is a router-LSA, and the H-bit for transit and Step (3) should be executed immediately. If
of the router-LSA is set, and this is a router-LSA and bit V of the router-LSA (see
vertex V is not the root, then the Appendix A.4.2) is set, set Area A's TransitCapability to
router should not be used for transit TRUE. In any case, each link described by the LSA gives the
and step (3) should be executed cost to an adjacent vertex. For each described link (say it
immediately. If this is a router-LSA, joins vertex V to vertex W):
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 5. Autodiscovery and Backward Compatibility
To avoid the possibility of any routing loops due to partial To reduce the possibility of any routing loops due to partial
deployment, this document defines a OSPF Router-Information LSA deployment, this document defines an OSPF Router Information (RI) LSA
functional capability bit known as the Host Support capability. capability bit [RFC7770]. See Section 7 (Table 2).
Auto Discovery via announcement of the Host Support Functional The RI LSA MUST be area-scoped.
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 Autodiscovery via announcement of the OSPF Host Router capability
to manually override enforcement of the H-bit functionality in (Section 7) ensures that the H-bit functionality and its associated
partial deployments where the topology guarantees that OSPFv2 routers SPF changes MUST only take effect if all the routers in a given OSPF
not supporting the H-bit do not compute routes resulting in routing area support this functionality.
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 In normal operation, it is possible that the RI LSA will fail to
reach all routers in an area in a timely manner. For example, if a
new router without H-bit support joins an area that previously had
only H-bit-capable routers with the H-bit set, then it may take some
time for the RI LSA to propagate to all routers. While it is
propagating, the routers in the area will gradually detect the
presence of a router that does not support the capability and will
revert back to the normal SPF calculation. During the propagation
time, the area as a whole is unsure of the status of the new router;
this type of situation can cause temporary transient loops.
When calculating the path to an OSPF AS-External-LSA or NSSA-LSA with The following recommendations will mitigate transient routing loops:
a Type-2 metric, the advertised Type-2 metric is taken as more
significant than the OSPF intra-area or inter-area path. Hence, * Implementations are RECOMMENDED to provide a configuration
advertising the links with MaxLinkMetric as specified in [RFC6987] parameter to manually override enforcement of the H-bit
does not discourage transit traffic when calculating AS external or functionality in partial deployments where the topology guarantees
NSSA routes. Consequently, OSPF routers implementing [RFC6987] or that OSPFv2 routers not supporting the H-bit do not compute routes
this specification should advertise a Type-2 metric of LSInfinity for resulting in routing loops.
any self-originated AS-External-LSAs or NSSA-LSAs in situations when
the OSPF router is acting as a stub router [RFC6987] or implementing * All routers with the H-bit set MUST advertise all of the router's
this specification. non-stub links with a metric equal to MaxLinkMetric [RFC6987] in
its LSAs in order to prevent OSPFv2 routers (unless a last-resort
path) that do not support the H-bit from attempting to use the
non-stub links for transit traffic.
* All routers supporting the H-bit MUST check the RI LSAs of all
nodes in the area to verify that all nodes support the H-bit
before actively using the H-bit feature. If any router does not
advertise the OSPF Host Router capability (Section 7), then the
SPF modifications described in Section 4 MUST NOT be used in the
area.
6. OSPF AS-External-LSAs / NSSA-LSAs with Type 2 Metrics
When calculating the path to a prefix in an OSPF AS-external-LSA or
NSSA-LSA [RFC3101] 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 with Type 2 metrics.
Consequently, this document updates [RFC6987] so that the Type 2
metric in any self-originated AS-external-LSAs or NSSA-LSAs is
advertised as LSInfinity-1 [RFC2328]. If the H-bit is set, then the
Type 2 metric MUST be set to LSInfinity.
7. IANA Considerations 7. IANA Considerations
IANA is requested to create the OSPF Router-LSA bit registry with the IANA has registered the following value in the "OSPFv2 Router
following assignments: Properties Registry".
Value Description Reference +-------+--------------+-----------+
0x01 Area Border Router (B-bit) [RFC2328] | Value | Description | Reference |
0x02 AS Boundary Router (E-bit) [RFC2328] +=======+==============+===========+
0x04 Virtual Link Endpoint (V-bit) [RFC2328] | 0x80 | Host (H-bit) | RFC 8770 |
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 Table 1: H-Bit
[RFC7770] known as the Host Support Functional Capability. This
document requests IANA to allocate the value of this capability from IANA has registered the following in the "OSPF Router Informational
the Router Functional Capability Bits TLV. Capability Bits" registry.
+------------+------------------+-----------+
| Bit Number | Capability Name | Reference |
+============+==================+===========+
| 7 | OSPF Host Router | RFC 8770 |
+------------+------------------+-----------+
Table 2: OSPF Host Router Capability Bit
8. Security Considerations 8. Security Considerations
This document introduces no new security considerations beyond those This document introduces the H-bit, which is a capability feature
already specified in [RFC6987], [RFC2328], and [RFC5340]. that restricts the use of a router for transit, while only its local
destinations are reachable. This is a subset of the operations of a
normal router and therefore should not introduce new security
considerations beyond those already known in OSPFv2 [RFC2328]. The
feature introduces the advertisement of host router capability
information to all OSPFv2 routers in an area. This information can
be leveraged for discovery and verification that all routers in the
area support the capability before the feature is turned on. In the
event that a rogue or buggy router incorrectly advertises its
capability, possible scenarios are as follows:
9. Acknowledgements * The router does not have the capability but sends the H-bit set in
its LSAs. In this case, a routing loop is possible. However,
this is mitigated by the fact that this router should be avoided
anyway. Moreover, the link metrics cost (MaxLinkMetric) of this
router will mitigate this situation. In any case, a router
advertising the H-bit capability without its link metrics cost
equal to MaxLinkMetric could be a rogue router and should be
avoided.
The authors would like to acknowledge Hasmit Grover for discovery of * The router has the capability but sends the H-bit clear in its
the limitation in [RFC6987], Acee Lindem, Abhay Roy, David Ward, LSAs. In this case, the router merely prevents the support of
Burjiz Pithawala and Michael Barnes for their comments. other H-bit routers in the area and prevents all the routers from
running the modified SPF. Any impacts are also mitigated in this
scenario, as other H-bit routers in the area also advertise the
MaxLinkMetric cost, so they will still be avoided unless they are
the last-resort path.
10. References * The rogue router is on the only transit path for some destinations
and sends the H-bit set (for no good/valid reason) in its LSAs,
and effectively partitions the network. This case is
indistinguishable from the normal case where an operator may
consciously decide to set the H-bit to perform maintenance on a
router that is on the only transit path. The OSPF protocol will
continue to function within the partitioned domains.
10.1. Normative References 9. References
9.1. Normative References
[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>.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, [RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328,
DOI 10.17487/RFC2328, April 1998, DOI 10.17487/RFC2328, April 1998,
<https://www.rfc-editor.org/info/rfc2328>. <https://www.rfc-editor.org/info/rfc2328>.
[RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option", [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
RFC 3101, DOI 10.17487/RFC3101, January 2003, McPherson, "OSPF Stub Router Advertisement", RFC 6987,
<https://www.rfc-editor.org/info/rfc3101>. DOI 10.17487/RFC6987, September 2013,
<https://www.rfc-editor.org/info/rfc6987>.
[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 [RFC7770] Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
S. Shaffer, "Extensions to OSPF for Advertising Optional S. Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", RFC 7770, DOI 10.17487/RFC7770, Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
February 2016, <https://www.rfc-editor.org/info/rfc7770>. February 2016, <https://www.rfc-editor.org/info/rfc7770>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References 9.2. Informative References
[I-D.ietf-idr-bgp-optimal-route-reflection] [BGP-ORR] Raszuk, R., Ed., Cassar, C., Aman, E., Decraene, B., and
Raszuk, R., Cassar, C., Aman, E., Decraene, B., and K. K. Wang, "BGP Optimal Route Reflection (BGP-ORR)", Work in
Wang, "BGP Optimal Route Reflection (BGP-ORR)", draft- Progress, Internet-Draft, draft-ietf-idr-bgp-optimal-
ietf-idr-bgp-optimal-route-reflection-16 (work in route-reflection-20, 8 January 2020,
progress), April 2018. <https://tools.ietf.org/html/draft-ietf-idr-bgp-optimal-
route-reflection-20>.
[RFC1584] Moy, J., "Multicast Extensions to OSPF", RFC 1584, [RFC3101] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
DOI 10.17487/RFC1584, March 1994, RFC 3101, DOI 10.17487/RFC3101, January 2003,
<https://www.rfc-editor.org/info/rfc1584>. <https://www.rfc-editor.org/info/rfc3101>.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. [RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
McPherson, "OSPF Stub Router Advertisement", RFC 6987, for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
DOI 10.17487/RFC6987, September 2013, <https://www.rfc-editor.org/info/rfc5340>.
<https://www.rfc-editor.org/info/rfc6987>.
Acknowledgements
The authors would like to acknowledge Hasmit Grover for discovering
the limitation in [RFC6987], and Acee Lindem, Abhay Roy, David Ward,
Burjiz Pithawala, and Michael Barnes for their comments.
Authors' Addresses Authors' Addresses
Keyur Patel Keyur Patel
Arrcus Arrcus
Email: keyur@arrcus.com Email: keyur@arrcus.com
Padma Pillay-Esnault Padma Pillay-Esnault
Huawei Technologies PPE Consulting
2330 Central Expressway
Santa Clara, CA 95050
USA
Email: padma@huawei.com Email: padma.ietf@gmail.com
Manish Bhardwaj Manish Bhardwaj
Cisco Systems Cisco Systems
170 W. Tasman Drive 170 W. Tasman Drive
San Jose, CA 95134 San Jose, CA 95134
USA United States of America
Email: manbhard@cisco.com Email: manbhard@cisco.com
Serpil Bayraktar Serpil Bayraktar
Cisco Systems Cisco Systems
170 W. Tasman Drive 170 W. Tasman Drive
San Jose, CA 95134 San Jose, CA 95134
USA United States of America
Email: serpil@cisco.com Email: serpil@cisco.com
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