draft-ietf-ospf-ospfv2-hbit-06.txt   draft-ietf-ospf-ospfv2-hbit-07.txt 
OSPF K. Patel OSPF K. Patel
Internet-Draft Arrcus Internet-Draft Arrcus
Updates: 2328 (if approved) P. Pillay-Esnault Updates: 2328 (if approved) P. Pillay-Esnault
Intended status: Standards Track Huawei Technologies Intended status: Standards Track Huawei Technologies
Expires: February 28, 2019 M. Bhardwaj Expires: November 20, 2019 M. Bhardwaj
S. Bayraktar S. Bayraktar
Cisco Systems Cisco Systems
August 27, 2018 May 19, 2019
H-bit Support for OSPFv2 Host Router Support for OSPFv2
draft-ietf-ospf-ospfv2-hbit-06 draft-ietf-ospf-ospfv2-hbit-07
Abstract Abstract
OSPFv3 defines an option bit for router-LSAs known as the R-bit in The OSPFv2 specifies an SPF algorithm that identifies transit
RFC5340. If the R-bit is clear, an OSPFv3 router can participate in vertices based on their adjacencies. Therefore, OSPFv2 does not have
OSPF topology flooding, however it will not be used as a transit a mechanism to prevent traffic transiting a participating node if it
router. In such cases, other routers in the OSPFv3 routing domain is a transit vertex in the only existing or shortest path to the
only install routes to allow local traffic delivery. This document destination. The use of metrics to make the node undesirable can
defines the H-bit functionality to prevent other OSPFv2 routers from only help to repel traffic if an alternative better route exists.
using the router for transit traffic in OSPFv2 routing domains as This document defines the Host-bit functionality to prevent other
described in RFC 2328. This document updates RFC 2328. OSPFv2 routers from using the router for transit traffic in OSPFv2
routing domains. This document updates the [RFC2328] by assigning a
new bit (Host-bit) in the OSPF Router-LSA bit registry. If the Host-
bit is set, the calculation of the shortest-path tree for an area, as
described in [RFC2328], is modified by including a new check to
verify that transit vertices have the Host-bit clear.
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
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This Internet-Draft will expire on February 28, 2019. This Internet-Draft will expire on November 20, 2019.
Copyright Notice Copyright Notice
Copyright (c) 2018 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.
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the copyright in such materials, this document may not be modified the copyright in such materials, this document may not be modified
outside the IETF Standards Process, and derivative works of it may outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other it for publication as an RFC or to translate it into languages other
than English. than English.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3 2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. H-bit Support . . . . . . . . . . . . . . . . . . . . . . . . 3 3. Host-bit Support . . . . . . . . . . . . . . . . . . . . . . 3
4. SPF Modifications . . . . . . . . . . . . . . . . . . . . . . 5 4. SPF Modifications . . . . . . . . . . . . . . . . . . . . . . 5
5. Auto Discovery and Backward Compatibility . . . . . . . . . . 5 5. Auto Discovery and Backward Compatibility . . . . . . . . . . 6
6. OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics . . . . . 6 6. OSPF AS-External-LSAs/NSSA LSAs with Type 2 Metrics . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7 8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7 9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7 10.1. Normative References . . . . . . . . . . . . . . . . . . 7
10.2. Informative References . . . . . . . . . . . . . . . . . 7 10.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction 1. Introduction
OSPFv3 [RFC5340] defines an option bit for router-LSAs known as the The OSPFv2 specifies an SPF algorithm that identifies transit
R-bit. If the R-bit is clear, an OSPFv3 router can participate in vertices based on their adjacencies. Therefore, OSPFv2 does not have
OSPFv3 topology flooding without acting as a transit router. In such a mechanism to prevent traffic transiting a participating node if it
cases, other routers in the OSPFv3 routing domain only install routes is a transit vertex in the only existing or shortest path to the
used for local traffic. destination. The use of metrics to make the node undesirable can
only help to repel traffic if an alternative better route exists.
This functionality is particularly useful for BGP Route Reflectors, This functionality is particularly useful for a number of use cases:
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
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. To isolate a router to avoid blackhole scenarios when there is a
defined in [I-D.ietf-idr-bgp-optimal-route-reflection] reload and possible long reconvergence times.
2. Reachability resolution for its Route Reflector Clients. 2. Closet Switches are usually not used for transit traffic but need
to participate in the topology.
This document defines the R-bit functionality equivalent for OSPFv2 3. Overloaded routers could use such a capability to repel traffic
defined in [RFC2328] by introducing a new router-LSA bit known as the until they stabilize.
"H-bit". This document updates appendix A.4.2 of RFC 2328.
4. 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 are not capable of forwarding transit
traffic. However, they need to learn the OSPF topology to
perform spf computation for optimal routes and reachbility
resolution for its clients
[I-D.ietf-idr-bgp-optimal-route-reflection].
This document defines the Host-bit (H-Bit)functionality to prevent
other OSPFv2 routers from using the router for transit traffic in
OSPFv2 routing domains. This document updates the [RFC2328] by -
assigning the Host-bit in the OSPF Router-LSA bit registry - if the
host-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 new check to verify that transit vertices DO NOT have the
host-bit set.
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. 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 to other OSPFv2 routers in the area supporting the
functionality that it MUST NOT be used as a transit router. The bit functionality that it MUST NOT be used as a transit router (see
value usage of the H-bit is reversed from the R-bit defined in OSPFv3 section 4).
[RFC5340] to support backward compatibility. The modified OSPFv2
router-LSA format is: If the host-bit is NOT set routers MUST act transit routers as
described in [RFC2328] ensuring backward compatibility.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | | ... |
bit H Host Bit in router-LSA
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 0 1 2 3 4 5 6 7
should not be used to forward transit traffic. In this mode, the +-+-+-+-+-+-+-+-+
other OSPFv2 routers in the area SHOULD NOT use the originating |H|0|0|N|W|V|E|B|
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 Host Bit
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 Bit H is the high-order bit of the OSPF as shown above. When set, an
in other areas MAY be advertised in summary LSAs. Non-local IPv4 OSPFv2 router is a non-transit router and is incapable of forwarding
prefixes, e.g., those advertised by other routers and installed transit traffic.
during the SPF computation, MAY be advertised in summary-LSAs if
configured by policy. Likewise, when the H-bit is set, only IPv4 An OSPFv2 router originating a router-LSA with the H-bit set MUST
prefixes associated with local interfaces MAY be advertised in AS- advertise all its router links with a link cost of MaxLinkMetric
external LSAs. Non-local IPv4 prefixes, e.g., those exported from [RFC6987]. This is to increase the applicability of the H-bit to
other routing protocols, MUST NOT be advertised in AS-external-LSAs. partial deployments where it is the responsibility of the operator to
Finally, when the H-bit is set, an Area Border Router (ABR) MUST ensure that OSPFv2 routers not supporting the H-bit do not install
advertise a consistent H-bit setting in its self-originated router- routes causing routing loops.
LSAs for all attached areas.
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. ONLY IPv4 prefixes associated with its local
interfaces MAY be advertised in summary LSAs.
When the H-bit is set cannot act as an AS Boundary Router (ASBR), as
non-local IPv4 prefixes, e.g., those exported from other routing
protocols, MUST NOT be advertised in AS-external-LSAs.
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
skipping to change at page 5, line 48 skipping to change at page 6, line 8
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 avoid the possibility of any routing loops due to partial
deployment, this document defines a OSPF Router-Information LSA deployment, this document defines a OSPF Router Information (RI) LSA
functional capability bit known as the Host Support capability. with a Router Functional Capability TLV that includes the following
Router Functional Capability Bit:
Bit Capabilities
7 Host Router Support capability
Auto Discovery via announcement of the Host Support Functional Auto Discovery via announcement of the Host Support Functional
Capability ensures that the H-bit functionality and its associated Capability ensures that the H-bit functionality and its associated
SPF changes SHOULD only take effect if all the routers in a given SPF changes SHOULD only take effect if all the routers in a given
OSPF area support this functionality. OSPF area support this functionality.
Implementations are encouraged to provide a configuration parameter Implementations are encouraged to provide a configuration parameter
to manually override enforcement of the H-bit functionality in to manually override enforcement of the H-bit functionality in
partial deployments where the topology guarantees that OSPFv2 routers partial deployments where the topology guarantees that OSPFv2 routers
not supporting the H-bit do not compute routes resulting in routing not supporting the H-bit do not compute routes resulting in routing
skipping to change at page 6, line 47 skipping to change at page 7, line 16
0x01 Area Border Router (B-bit) [RFC2328] 0x01 Area Border Router (B-bit) [RFC2328]
0x02 AS Boundary Router (E-bit) [RFC2328] 0x02 AS Boundary Router (E-bit) [RFC2328]
0x04 Virtual Link Endpoint (V-bit) [RFC2328] 0x04 Virtual Link Endpoint (V-bit) [RFC2328]
0x08 Historic (W-bit) [RFC1584] 0x08 Historic (W-bit) [RFC1584]
0x10 Unconditional NSSA Translator (Nt-bit) [RFC3101] 0x10 Unconditional NSSA Translator (Nt-bit) [RFC3101]
0x20 Unassigned 0x20 Unassigned
0x40 Unassigned 0x40 Unassigned
0x80 Host (H-bit) This Document 0x80 Host (H-bit) This Document
This document also defines a new Router Functional Capability This document also defines a new Router Functional Capability
[RFC7770] known as the Host Support Functional Capability. This [RFC7770] known as the Host Router Support Functional Capability.
document requests IANA to allocate the value of this capability from This document requests IANA to allocate the value of this capability
the Router Functional Capability Bits TLV. from the Router Functional Capability Bits TLV.
8. Security Considerations 8. Security Considerations
This document introduces no new security considerations beyond those This document introduces no new security considerations beyond those
already specified in [RFC6987], [RFC2328], and [RFC5340]. already specified in [RFC6987], [RFC2328], and [RFC5340].
9. Acknowledgements 9. Acknowledgements
The authors would like to acknowledge Hasmit Grover for discovery of The authors would like to acknowledge Hasmit Grover for discovery of
the limitation in [RFC6987], Acee Lindem, Abhay Roy, David Ward, the limitation in [RFC6987], Acee Lindem, Abhay Roy, David Ward,
skipping to change at page 7, line 51 skipping to change at page 8, line 19
[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 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-16 (work in ietf-idr-bgp-optimal-route-reflection-18 (work in
progress), April 2018. progress), April 2019.
[RFC1584] Moy, J., "Multicast Extensions to OSPF", RFC 1584, [RFC1584] Moy, J., "Multicast Extensions to OSPF", RFC 1584,
DOI 10.17487/RFC1584, March 1994, DOI 10.17487/RFC1584, March 1994,
<https://www.rfc-editor.org/info/rfc1584>. <https://www.rfc-editor.org/info/rfc1584>.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D. [RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987, McPherson, "OSPF Stub Router Advertisement", RFC 6987,
DOI 10.17487/RFC6987, September 2013, DOI 10.17487/RFC6987, September 2013,
<https://www.rfc-editor.org/info/rfc6987>. <https://www.rfc-editor.org/info/rfc6987>.
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