draft-ietf-ospf-ospfv2-hbit-09.txt   draft-ietf-ospf-ospfv2-hbit-10.txt 
OSPF K. Patel OSPF K. Patel
Internet-Draft Arrcus Internet-Draft Arrcus
Updates: 6987 (if approved) P. Pillay-Esnault Updates: 6987 (if approved) P. Pillay-Esnault
Intended status: Standards Track PPE Consulting Intended status: Standards Track PPE Consulting
Expires: March 16, 2020 M. Bhardwaj Expires: April 26, 2020 M. Bhardwaj
S. Bayraktar S. Bayraktar
Cisco Systems Cisco Systems
September 13, 2019 October 24, 2019
Host Router Support for OSPFv2 Host Router Support for OSPFv2
draft-ietf-ospf-ospfv2-hbit-09 draft-ietf-ospf-ospfv2-hbit-10
Abstract Abstract
The Open Shortest Path First Version 2 (OSPFv2) does not have a The Open Shortest Path First Version 2 (OSPFv2) does not have a
mechanism for a node to repel transit traffic if it is on the mechanism for a node to repel transit traffic if it is on the
shortest path. This document assigns a new bit (Host-bit) in the shortest path. This document defines a bit (Host-bit) that enables a
OSPF Router-LSA bit registry and in the OSPF Router Informational router to advertise that it is a non-transit router." It also
Capability Bits Registry that enables a host router to advertise that describes the changes needed to support the H-bit in the domain. In
it is a non-transit router. It also describes the changes needed to addition, this document updates RFC 6987 to advertise type-2 External
support the Host-bit in the domain. In addition, this document and NSSA LSAs with a high cost in order to repel traffic effectively.
updates OSPF Stub Router Advertisement (RFC6987) to advertise for
type-2 External and NSSA LSAs with a high cost in order to repel
traffic effectively.
Status of This Memo Status of This Memo
This Internet-Draft is submitted in full conformance with the This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/. Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on March 16, 2020. This Internet-Draft will expire on April 26, 2020.
Copyright Notice Copyright Notice
Copyright (c) 2019 IETF Trust and the persons identified as the Copyright (c) 2019 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents Provisions Relating to IETF Documents
(https://trustee.ietf.org/license-info) in effect on the date of (https://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents publication of this document. Please review these documents
skipping to change at page 2, line 27 skipping to change at page 2, line 23
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Host-bit Support . . . . . . . . . . . . . . . . . . . . . . 3 3. Host-bit Support . . . . . . . . . . . . . . . . . . . . . . 3
4. SPF Modifications . . . . . . . . . . . . . . . . . . . . . . 5 4. SPF Modifications . . . . . . . . . . . . . . . . . . . . . . 5
5. Auto Discovery and Backward Compatibility . . . . . . . . . . 6 5. Auto Discovery and Backward Compatibility . . . . . . . . . . 6
6. OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics . . . . . 7 6. OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics . . . . . 7
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 8 8. Security Considerations . . . . . . . . . . . . . . . . . . . 8
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 8
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
10.1. Normative References . . . . . . . . . . . . . . . . . . 9 10.1. Normative References . . . . . . . . . . . . . . . . . . 8
10.2. Informative References . . . . . . . . . . . . . . . . . 9 10.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction 1. Introduction
The OSPFv2 specifies a Shortest Path First (SPF) algorithm that The OSPFv2 specifies a Shortest Path First (SPF) algorithm that
identifies transit vertices based on their adjacencies. Therefore, identifies transit vertices based on their adjacencies. Therefore,
OSPFv2 does not have a mechanism to prevent traffic transiting a OSPFv2 does not have a mechanism to prevent traffic transiting a
participating node if it is a transit vertex in the only existing or participating node if it is a transit vertex in the only existing or
shortest path to the destination. The use of metrics to make the shortest path to the destination. The use of metrics to make the
skipping to change at page 3, line 14 skipping to change at page 3, line 9
4. BGP Route reflectors known as virtual Route Reflectors (vRRs), 4. BGP Route reflectors known as virtual Route Reflectors (vRRs),
that are not in the forwarding path but are in central locations that are not in the forwarding path but are in central locations
such as data centers. Such Route Reflectors typically are used such as data centers. Such Route Reflectors typically are used
for route distribution and are not capable of forwarding transit for route distribution and are not capable of forwarding transit
traffic. However, they need to learn the OSPF topology to traffic. However, they need to learn the OSPF topology to
perform SPF computation for optimal routes and reachability perform SPF computation for optimal routes and reachability
resolution for its clients resolution for its clients
[I-D.ietf-idr-bgp-optimal-route-reflection]. [I-D.ietf-idr-bgp-optimal-route-reflection].
This document describes the Host-bit (H-Bit)functionality that This document describes the Host-bit (H-bit) functionality that
prevents other OSPFv2 routers from using the router for transit prevents other OSPFv2 routers from using the host router for transit
traffic in OSPFv2 routing domains. This document defines the Host- traffic in OSPFv2 routing domains. If the H-bit is set then the
bit in the OSPFv2 Router Properties Registry and if the host-bit is calculation of the shortest-path tree for an area, as described in
set then the calculation of the shortest-path tree for an area, as section 16.1 of [RFC2328], is modified by including a check to verify
described in section 16.1 of [RFC2328], is modified by including a that transit vertices DO NOT have the H-bit set (see Section 4).
new check to verify that transit vertices DO NOT have the host-bit Furthermore, in order to repel traffic effectively, [RFC6987] is
set. updated so that type-2 External and NSSA LSAs are advertised with a
high cost (see Section 6).
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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here. capitals, as shown here.
3. Host-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 that it MUST NOT be used as a transit router (see set indicates that it MUST NOT be used as a transit router (see
section 4) by other OSPFv2 routers in the area supporting the Section 4) by other OSPFv2 routers in the area supporting the
functionality. functionality.
If the host-bit is NOT set routers MUST act transit routers as If the H-bit is not set then backwards compatibility is achieved as
described in [RFC2328] ensuring backward compatibility. the behavior will be the same as in [RFC2328].
0 1 2 3 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 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 | | LS age | Options | 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID | | Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router | | Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TOS | 0 | TOS metric | | TOS | 0 | TOS metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID | | Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data | | Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | | ... |
Figure 1 Figure 1: OSPF Router-LSA
Host Bit in Router-LSA Bit H is the high-order bit of the OSPF flags as shown below.
0 1 2 3 4 5 6 7 0 1 2 3 4 5 6 7
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
|H|0|0|N|W|V|E|B| |H|0|0|N|W|V|E|B|
+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+
Host Bit Figure 2: OSPF Router-LSA Option bits
Bit H is the high-order bit of the OSPF as shown above. When set, an When the H-bit is set, the OSPFv2 router is a Host (non-transit)
OSPFv2 router is a Host (non-transit) router and is incapable of router and is incapable of forwarding transit traffic. In this mode,
forwarding transit traffic. In this mode, the other OSPFv2 routers the other OSPFv2 routers in the area MUST NOT use the host router for
in the area MUST NOT use the host router for transit traffic, but use transit traffic, but may send traffic to its local destinations.
the host router only for its local destinations.
An OSPFv2 router originating a router-LSA with the H-bit set MUST An OSPFv2 router originating a router-LSA with the H-bit set MUST
advertise all its router links with a link cost of MaxLinkMetric advertise all its non-stub links with a link cost of MaxLinkMetric
[RFC6987]. This is to increase the applicability of the H-bit to [RFC6987].
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, an Area Border Router (ABR) MUST advertise the 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 same H-bit setting in its self-originated router-LSAs for all
attached areas. The consistency of the setting will prevent inter- attached areas. The consistency of the setting will prevent inter-
area traffic transiting through the router by suppressing area traffic transiting through the router by suppressing
advertisement of prefixes from other routers in the area in its advertisement of prefixes from other routers in the area in its
summary LSAs. Only IPv4 prefixes associated with its local summary LSAs. Only IPv4 prefixes associated with its local
interfaces MUST be advertised in summary LSAs to provide reachability interfaces MUST be advertised in summary-LSAs to provide reachability
to end hosts attached behind a router with the H-bit set. 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 AS Boundary When the H-bit is set the host router cannot act as an AS Boundary
Router (ASBR). Indeed, ASBR are transit routers to prefixes that are Router (ASBR). Indeed, ASBR are transit routers to prefixes that are
typically imported through redistribution of prefixes of other typically imported through redistribution of prefixes from other
routing protocols. Therefore, non-local IPv4 prefixes, e.g., those routing protocols. Therefore, non-local IPv4 prefixes, e.g., those
exported from other routing protocols, MUST NOT be advertised in AS- imported from other routing protocols, SHOULD NOT be advertised in
external-LSAs for routers acting permanently as a host. However, in AS-external-LSAs if the H-bit is set. Some use cases, such as an
use cases such as an overloaded router or a router being gracefully overloaded router or a router being gracefully isolated, may benefit
isolated, these routers are only temporarily acting as host routers from continued advertisement of non-local prefixes. In these cases,
and therefore SHOULD continue to advertise their External LSAs but the type 2-metric in AS-external-LSAs MUST be set to LSInfinity to
ensure that they do not attract traffic. In addition to the repel traffic.(see Section 6 of this document).
procedure described above, temporary host routers advertising type
2-metric External LSAs MUST set the metrics to LSInfinity 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 [RFC2328] will be
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: as follows:
2) Call the vertex just added to the 2) Call the vertex just added to the
tree vertex V. Examine the LSA tree vertex V. Examine the LSA
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and bit V of the router-LSA (see and bit V of the router-LSA (see
Section A.4.2) is set, set Area A's Section A.4.2) is set, set Area A's
TransitCapability to TRUE. In any case, TransitCapability to TRUE. In any case,
each link described by the LSA gives each link described by the LSA gives
the cost to an adjacent vertex. For the cost to an adjacent vertex. For
each described link, (say it joins each described link, (say it joins
vertex V to vertex W): vertex V to vertex W):
5. Auto Discovery and Backward Compatibility 5. Auto Discovery 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 (RI) LSA deployment, this document defines an OSPF Router Information (RI) LSA
[RFC7770] with and an area flooding scope and a new bit assigned in [RFC7770] capability. The RI LSA MUST be area-scoped. Bit:
the OSPF Router Informational Capability Bits Registry. Bit:
Bit Capabilities Bit Capabilities
7 Host Router Support capability 7 Host Router Support capability
Auto Discovery via announcement of the Host Support Functional Table 1: OSPF Router Information LSA Capabilities
Capability ensures that the H-bit functionality and its associated
SPF changes MUST only take effect if all the routers in a given OSPF
area support this functionality.
In normal operations, there is no guarantee that the RI LSA will Auto Discovery via announcement of the Host Router Support Capability
reach all routers in an area in a timely manner that may result in ensures that the H-bit functionality and its associated SPF changes
rooting loops in partial deployments. For example, in a new router MUST only take effect if all the routers in a given OSPF area support
joins an area which previous had only H-bit capable routers with this functionality.
H-bit set then it may take some time for the RI to propagate to all
routers. In normal operation, there is no guarantee that the RI LSA will reach
all routers in an area in a timely manner, which may result in
forwarding loops in partial deployments. For example, if a new
router joins an area, which previously had only H-bit capable routers
with H-bit set then it may take some time for the RI to propagate to
all routers.
The following recommendations will mitigate transient routing loops: The following recommendations will mitigate transient routing loops:
o Implementations are RECOMMENDED to provide a configuration o Implementations are RECOMMENDED to provide a configuration
parameter to manually override enforcement of the H-bit parameter to manually override enforcement of the H-bit
functionality in partial deployments where the topology guarantees functionality in partial deployments where the topology guarantees
that OSPFv2 routers not supporting the H-bit do not compute routes that OSPFv2 routers not supporting the H-bit do not compute routes
resulting in routing loops. resulting in routing loops.
o All routers, with the H-bit set, MUST advertise all of the o All routers, with the H-bit set, MUST advertise all of the
router's non-local links with a metric equal to MaxLinkMetric in router's non-stub links with a metric equal to MaxLinkMetric
its LSAs in order to avoid OSPFv2 (unless last resort) routers not [RFC6987] in its LSAs in order to avoid OSPFv2 (unless last
supporting the H-bit from attempting to use it for transit resort) routers not supporting the H-bit from attempting to use it
traffic. for transit traffic.
o All routers supporting H-Bit MUST check all the RI LSAs of nodes o All routers supporting H-Bit MUST check all the RI LSAs of nodes
in the area before actively running the modified SPF to account in the area before actively running the modified SPF to account
for the H-bit in order to verify that all routers are in routing for the H-bit in order to verify that all routers are in routing
capability. If any router does not have the H-Bit support then capability. If any router does not advertise the Host Router
all routers in the areas MUST run the normal SPF. Support capability then the SPF Modifications (Section 4) MUST NOT
be used in the area.
o Any router not supporting the H-bit capability is detected (by
examination of RI- LSA or RTR LSA in the area database) then all
routers in the area MUST revert back to normal operations.
6. OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics 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 When calculating the path to an OSPF AS-External-LSA or NSSA-LSA
a Type-2 metric, the advertised Type-2 metric is taken as more [RFC3101] with a Type-2 metric, the advertised Type-2 metric is taken
significant than the OSPF intra-area or inter-area path. Hence, as more significant than the OSPF intra-area or inter-area path.
advertising the links with MaxLinkMetric as specified in [RFC6987] Hence, advertising the links with MaxLinkMetric as specified in
does not discourage transit traffic when calculating AS external or [RFC6987] does not discourage transit traffic when calculating AS
NSSA routes with Type-2 metrics. external or NSSA routes with Type-2 metrics.
Consequently, OSPF routers implementing [RFC6987] and required to be Consequently, [RFC6987] is updated so that the Type-2 metric in any
the last resort transit then they MUST advertise a Type-2 metric of self-originated AS-External-LSAs or NSSA-LSAs is advertised as
LSInfinity-1 for any self-originated type 2 AS-External-LSAs or NSSA- LSInfinity-1 [RFC2328]. If the H-bit is set, then the Type-2 metric
LSAs. However, in situations, the router needs to repel traffic and MUST be set to LSInfinity.
acts as a host router then, in addition of the host bit procedure
described in this document they MUST advertise a Type-2 metric of
LSInfinity for any self-originated type 2 AS-External-LSAs or NSSA-
LSAs.
7. IANA Considerations 7. IANA Considerations
This document requests the IANA to assign the 0x80 value to the Host- This document requests the IANA to assign the 0x80 value to the Host-
Bit (H-bit)in the OSPFv2 Router Properties Registry Bit (H-bit)in the OSPFv2 Router Properties Registry
Value Description Reference Value Description Reference
0x80 Host (H-bit) This Document 0x80 Host (H-bit) This Document
This document requests the IANA to assign the Bit Number value of 7 This document requests the IANA to assign the Bit Number value of 7
to the Host Router Support Capability in the OSPF Router to the Host Router Support Capability in the OSPF Router
Informational Capability Bits Registry. [RFC7770] Informational Capability Bits Registry.
Bit Number Capability Name Reference Bit Number Capability Name Reference
7 OSPF Host Router This Document 7 OSPF Host Router This Document
8. Security Considerations 8. Security Considerations
This document introduces the H-bit which is a capability that This document introduces the H-bit which is a capability that
restricts the use of a router for transit except for its local restricts the use of a router for transit, while only its local
destinations. This is a subset of the operations of a normal router destinations are reachable. This is a subset of the operations of a
and therefore should not introduce new security considerations beyond normal router and therefore should not introduce new security
those already known in OSPF. The feature, however does introduce the considerations beyond those already known in OSPF [RFC2328]. The
flooding of a capability information that allows discovery and feature, however does introduce the flooding of a capability
verification that all routers in an area are capable before turning information that allows discovery and verification that all routers
on the feature. In the event that a rogue or buggy router advertises in an area are capable before turning on the feature. In the event
incorrectly its capability there are two possible cases: that a rogue or buggy router advertises incorrectly its capability
there are two possible cases:
o The router does not have the capability but sends H-Bit set in its o The router does not have the capability but sends the H-Bit set in
LSAs: In this case, there is a possibility of a routing loop. its LSAs: In this case, there is a possibility of a routing loop.
However this is mitigated by the fact that this router should be However this is mitigated by the fact that this router should be
avoided anyway. Moreover, the link metrics cost (MaxLinkMetric) avoided anyway. Moreover, the link metrics cost (MaxLinkMetric)
of this router will mitigate this situation. In any case, a of this router will mitigate this situation. In any case, a
router advertising the H-bit capability without its links cost router advertising the H-bit capability without its links cost
equal to MaxLinkMetric may be an indicator that this is a rogue equal to MaxLinkMetric may be an indicator that this is a rogue
router and to be avoided. router and should be avoided.
o The router has the capability but sends the H-Bit clear in its o The router has the capability but sends the H-Bit clear in its
LSAs: In this case, the router merely prevents support of other LSAs: In this case, the router merely prevents support of other
H-bit routers in the area and all the routers to run the modified H-bit routers in the area and all the routers to run the modified
SPF. The impact is also mitigated as other H-Bit routers in the SPF. The impact is also mitigated as other H-Bit routers in the
area also advertise MaxLinkMetric cost so they will still be area also advertise MaxLinkMetric cost so they will still be
avoided unless they are the last resort path. avoided unless they are the last resort path.
9. Acknowledgements 9. Acknowledgements
skipping to change at page 9, line 37 skipping to change at page 9, line 31
May 2017, <https://www.rfc-editor.org/info/rfc8174>. May 2017, <https://www.rfc-editor.org/info/rfc8174>.
10.2. Informative References 10.2. Informative References
[I-D.ietf-idr-bgp-optimal-route-reflection] [I-D.ietf-idr-bgp-optimal-route-reflection]
Raszuk, R., Cassar, C., Aman, E., Decraene, B., and K. Raszuk, R., Cassar, C., Aman, E., Decraene, B., and K.
Wang, "BGP Optimal Route Reflection (BGP-ORR)", draft- Wang, "BGP Optimal Route Reflection (BGP-ORR)", draft-
ietf-idr-bgp-optimal-route-reflection-19 (work in ietf-idr-bgp-optimal-route-reflection-19 (work in
progress), July 2019. progress), July 2019.
[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>.
Authors' Addresses Authors' Addresses
Keyur Patel Keyur Patel
Arrcus Arrcus
Email: keyur@arrcus.com Email: keyur@arrcus.com
Padma Pillay-Esnault Padma Pillay-Esnault
PPE Consulting PPE Consulting
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