Internet DRAFT - draft-keyupate-ospf-ospfv2-hbit
draft-keyupate-ospf-ospfv2-hbit
OSPF K. Patel
Internet-Draft P. Pillay-Esnault
Intended status: Standards Track M. Bhardwaj
Expires: November 22, 2015 S. Bayraktar
Cisco Systems
May 21, 2015
H-bit Support for OSPFv2
draft-keyupate-ospf-ospfv2-hbit-01
Abstract
OSPFv3 [RFC5340] defines an option field for router-LSAs known as a
R-bit. If the R-bit is clear, an OSPFv3 router can participate in
OSPF topology distribution without acting as a forwarder to forward
the transit traffic. In such cases, an OSPF router would only accept
traffic intended for local delivery. This draft defines R-bit
functionality for OSPFv2 defined in [RFC2328].
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 November 22, 2015.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
3. H-bit Support . . . . . . . . . . . . . . . . . . . . . . . . 3
4. SPF Modifications . . . . . . . . . . . . . . . . . . . . . . 4
5. Auto Discovery and Backwards Compatibility . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
9. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . 6
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
10.1. Normative References . . . . . . . . . . . . . . . . . . 6
10.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
OSPFv3 [RFC5340] defines an option field for router-LSAs known as a
R-bit. If the R-bit is clear, an OSPF router can participate in
OSPFv3 topology distribution without acting as a forwarder to forward
the transit traffic. In such cases, an OSPF router would only accept
traffic intended for local delivery.
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 location such as data centers.
Such Route Reflectors typically are used for route distribution and
are not capable of forwarding data traffic. However, they need to
participate in the IGP routing for: 1) computing SPFs for Optimal
Route Reflection functionality defined in [I-D.ietf-idr-bgp-orr], and
2) resolving reachability for its Route Reflector Clients.
This draft defines R-bit functionality for OSPFv2 defined in
[RFC2328] by introducing a new Router LSA bit known as a "H-bit".
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to
be interpreted as described in [RFC2119] only when they appear in all
upper case. They may also appear in lower or mixed case as English
words, without any normative meaning.
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3. H-bit Support
This draft defines a new Router-LSA bit known as a Host Bit or a
H-bit. The H-bit indicates the OSPFv2's capability of acting as a
forwarder router. When set, the OSPFv2 router indicates that the
forwarding capability is disabled. The bit value usage of the H-bit
is reversed as opposed to the R-bit value defined in OSPFv3 [RFC5340]
to support backward compatibility. The OSPFv2 Router LSA format is
defined as:
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 acting as a forwarder.
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When H-bit is set, an OSPFv2 router is a non-transit router and is
incapable of acting as a forwarder. In this mode, the other OSPFv2
routers MUST not use the originating OSPFv2 router for the transit
traffic, but they will use the OSPFv2 router for data traffic
destined to that OSPFv2 router. An OSPFv2 router originating a
Router LSA with the H-bit set SHOULD advertise its LINKS with MAX
Link cost as defined in Section 3 of [RFC6987]. This is to increase
the applicability of the H-bit in partial deployments where it is the
responsibility of the operator to ensure that the H-bit does not
result in routing loops.
When H-bit is set, only IPv4 prefixes associated with local
interfaces MAY be advertised in summary LSAs. Non-local IPv4
prefixes, e.g., those advertised by other routers and installed
during the SPF computation, MUST NOT be adverised in summary-LSAs.
Likewise, when 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 H-bit is set, an
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 assure that the routers originating router-LSAs with the
H-bit set will not be used for transit traffic. Step 2 is modified
as follows:
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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
immediatately. 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 Backwards Compatibility
To avoid the possibility of any routing loops due to partial
deployments, this draft defines a new OSPF Router Functional
Capability known as a Host Support Capability. The value of this
capability is a bit value to be assigned by IANA from OSPF Router
Functional Capability Bits registry [I-D.ietf-ospf-rfc4970bis].
The 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 knob to manually override
enforcement of the H-bit functionality in partial deployment
scenarios for cases where the topology gurantees that the router
supporting the H-bit will not cause routing loops.
6. IANA Considerations
This draft defines a new Router LSA bit known as a H-bit. This draft
requests IANA to 1) Create a new OSPF Router LSA bits registry and 2)
assign a H-bit code type from the newly allocated OSPF Router LSA bit
registry.
This draft defines a new Router Fucntional Capability known as a Host
Support Functional Capability. This draft requests IANA to allocate
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the value of this capability from the Router Functional Capability
Bits TLV.
7. Security Considerations
This document introduces no new security considerations above and
beyond those already specified in [RFC2328] and [RFC5340].
8. Acknowledgements
The authors would like to acknowledge Acee Lindem, Abhay Roy, David
Ward, Burjiz Pithawala and Michael Barnes for their comments.
9. Change Log
Initial Version: April 23 2015
10. References
10.1. Normative References
[I-D.ietf-ospf-rfc4970bis]
Lindem, A., Shen, N., Vasseur, J., Aggarwal, R., and S.
Shaffer, "Extensions to OSPF for Advertising Optional
Router Capabilities", draft-ietf-ospf-rfc4970bis-00 (work
in progress), January 2015.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC5340] Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
for IPv6", RFC 5340, July 2008.
[RFC6987] Retana, A., Nguyen, L., Zinin, A., White, R., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 6987,
September 2013.
10.2. Informative References
[I-D.ietf-idr-bgp-optimal-route-reflection]
Raszuk, R., Cassar, C., Aman, E., Decraene, B., and S.
Litkowski, "BGP Optimal Route Reflection (BGP-ORR)",
draft-ietf-idr-bgp-optimal-route-reflection-09 (work in
progress), April 2015.
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Authors' Addresses
Keyur Patel
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95124 95134
USA
Email: keyupate@cisco.com
Padma Pillay-Esnault
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95124 95134
USA
Email: ppe@cisco.com
Manish Bhardwaj
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95124 95134
USA
Email: manbhard@cisco.com
Serpil Bayraktar
Cisco Systems
170 W. Tasman Drive
San Jose, CA 95124 95134
USA
Email: serpil@cisco.com
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