draft-ietf-ospf-mt-03.txt   draft-ietf-ospf-mt-04.txt 
Network Working Group P. Psenak Network Working Group P. Psenak
Internet-Draft S. Mirtorabi Internet-Draft S. Mirtorabi
Expires: September 27, 2005 A. Roy Expires: October 22, 2005 A. Roy
L. Nguyen L. Nguyen
P. Pillay-Esnault P. Pillay-Esnault
Cisco Systems Cisco Systems
March 29, 2005 April 20, 2005
Multi-Topology (MT) Routing in OSPF Multi-Topology (MT) Routing in OSPF
draft-ietf-ospf-mt-03.txt draft-ietf-ospf-mt-04.txt
Status of this Memo Status of this Memo
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Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2005). Copyright (C) The Internet Society (2005).
Abstract Abstract
This draft describes an extension to OSPF in order to define This draft describes an extension to OSPF in order to define
independent IP topologies called Multi-Topologies (MTs). The MT independent IP topologies called Multi-Topologies (MTs). The MT
extension can be used for computing different paths for unicast extension can be used for computing different paths for unicast
traffic, multicast traffic, different classes of service, or in-band traffic, multicast traffic, different classes of service based on
network management. [M-ISIS] describes a similar mechanism for ISIS. flexible criteria, or an in-band network management topology.
[M-ISIS] describes a similar mechanism for ISIS.
An optional extension to exclude selected links from the default An optional extension to exclude selected links from the default
topology is also described. topology is also described.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 Differences with RFC 1583 TOS Based Routing . . . . . . . 4
2.1 Requirements notation . . . . . . . . . . . . . . . . . . 4 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.2 Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 4 2.1 Requirements notation . . . . . . . . . . . . . . . . . . 5
3. Base MT Functional Specifications . . . . . . . . . . . . . . 5 2.2 Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1 MT Area Boundary . . . . . . . . . . . . . . . . . . . . . 5 3. Base MT Functional Specifications . . . . . . . . . . . . . . 6
3.2 Adjacency for MTs . . . . . . . . . . . . . . . . . . . . 5 3.1 MT Area Boundary . . . . . . . . . . . . . . . . . . . . . 6
3.3 Sending OSPF control packets . . . . . . . . . . . . . . . 5 3.2 Adjacency for MTs . . . . . . . . . . . . . . . . . . . . 6
3.3 Sending OSPF control packets . . . . . . . . . . . . . . . 6
3.4 Advertising MT Adjacencies and the Corresponding IP 3.4 Advertising MT Adjacencies and the Corresponding IP
Prefixes . . . . . . . . . . . . . . . . . . . . . . . . . 5 Prefixes . . . . . . . . . . . . . . . . . . . . . . . . . 6
3.4.1 Advertising MT Adjacencies and the Corresponding 3.4.1 Advertising MT Adjacencies and the Corresponding
IP Prefixes . . . . . . . . . . . . . . . . . . . . . 5 IP Prefixes . . . . . . . . . . . . . . . . . . . . . 6
3.4.2 Inter-Area and External Routing . . . . . . . . . . . 6 3.4.2 Inter-Area and External Routing . . . . . . . . . . . 7
3.5 Flushing MT Information . . . . . . . . . . . . . . . . . 6 3.5 Flushing MT Information . . . . . . . . . . . . . . . . . 7
3.6 MT SPF Computation . . . . . . . . . . . . . . . . . . . . 6 3.6 MT SPF Computation . . . . . . . . . . . . . . . . . . . . 7
3.7 MT-ID Values . . . . . . . . . . . . . . . . . . . . . . . 7 3.7 MT-ID Values . . . . . . . . . . . . . . . . . . . . . . . 8
3.8 Forwarding in MT . . . . . . . . . . . . . . . . . . . . . 7 3.8 Forwarding in MT . . . . . . . . . . . . . . . . . . . . . 8
4. Default Topology Link Exclusion Functional Specifications . . 8 4. Default Topology Link Exclusion Functional Specifications . . 9
4.1 Exclusion of Links in the Default Topology . . . . . . . . 8 4.1 Exclusion of Links in the Default Topology . . . . . . . . 9
4.2 New Area Data Structure Parameter . . . . . . . . . . . . 8 4.2 New Area Data Structure Parameter . . . . . . . . . . . . 9
4.3 Adjacency Formation with Link Exclusion Capability . . . . 9 4.3 Adjacency Formation with Link Exclusion Capability . . . . 10
4.4 OSPF Control Packets Transmission Over Excluded Links . . 9 4.4 OSPF Control Packets Transmission Over Excluded Links . . 10
4.5 OSPF LSA Advertisement and SPF Computation for 4.5 OSPF LSA Advertisement and SPF Computation for
Excluded Links . . . . . . . . . . . . . . . . . . . . . . 9 Excluded Links . . . . . . . . . . . . . . . . . . . . . . 11
5. Interoperability between MT Capable and Non-MT Capable 5. Interoperability between MT Capable and Non-MT Capable
Routers . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Routers . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
6. Migration from non-MT-Area to MT-area . . . . . . . . . . . . 12 6. Migration from non-MT-Area to MT-area . . . . . . . . . . . . 13
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13 7. Security Considerations . . . . . . . . . . . . . . . . . . . 14
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16
9.1 Normative References . . . . . . . . . . . . . . . . . . . . 15 9.1 Normative References . . . . . . . . . . . . . . . . . . . 16
9.2 Informative References . . . . . . . . . . . . . . . . . . . 15 9.2 Informative References . . . . . . . . . . . . . . . . . . 16
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 16
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17 A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 18
B. OSPF data formats . . . . . . . . . . . . . . . . . . . . . . 18 B. OSPF data formats . . . . . . . . . . . . . . . . . . . . . . 19
B.1 Router-LSAs . . . . . . . . . . . . . . . . . . . . . . . 18 B.1 Router-LSAs . . . . . . . . . . . . . . . . . . . . . . . 19
B.2 Network-LSAs . . . . . . . . . . . . . . . . . . . . . . . 19 B.2 Network-LSAs . . . . . . . . . . . . . . . . . . . . . . . 20
B.3 Summary-LSAs . . . . . . . . . . . . . . . . . . . . . . . 19 B.3 Summary-LSAs . . . . . . . . . . . . . . . . . . . . . . . 20
B.4 AS-External-LSAs . . . . . . . . . . . . . . . . . . . . . 20 B.4 AS-External-LSAs . . . . . . . . . . . . . . . . . . . . . 21
B.5 NSSA-LSAs . . . . . . . . . . . . . . . . . . . . . . . . 21 B.5 NSSA-LSAs . . . . . . . . . . . . . . . . . . . . . . . . 22
Intellectual Property and Copyright Statements . . . . . . . . 22 Intellectual Property and Copyright Statements . . . . . . . . 23
1. Introduction 1. Introduction
OSPF uses a fixed packet format, therefore it is not easy to OSPF uses a fixed packet format, therefore it is not easy to
introduce any backward compatible extensions. However, the OSPF introduce any backward compatible extensions. However, the OSPF
specification [OSPF] introduced TOS metric in an earlier specification [OSPF] introduced TOS metric in an earlier
specification [RFC1583] in order to announce a different link cost specification [RFC1583] in order to announce a different link cost
based on TOS. TOS based routing as described in [RFC1583] was never based on TOS. TOS based routing as described in [RFC1583] was never
deployed and was subsequently deprecated. deployed and was subsequently deprecated.
We propose to reuse the TOS based metric fields. They have been We propose to reuse the TOS based metric fields. They have been
redefined as MT-ID and MT-ID Metric and are used to advertise redefined as MT-ID and MT-ID Metric and are used to advertise
different topologies by advertising separate metrics for each of different topologies by advertising separate metrics for each of
them. them.
1.1 Differences with RFC 1583 TOS Based Routing
Multi-topology routing differs from RFC 1583 TOS based routing in the
following ways:
1. With RFC 1583 TOS routing, the TOS or DSCP in the IP header is
mapped directly to the the corresponding OSPF SPF calculation and
routing table. This limits the number and definition of the
topologies to the 16 TOS values specified is section 12.3 of RFC
1583 [RFC1583]. With multi-topology routing, the classification
of what type of traffic maps to which topology is not within the
scope of the document.
2. With RFC 1583 TOS routing, traffic which is unreachable in the
routing table associated with the corresponding TOS will revert
to the TOS 0 routing table. With multi-topology routing, this is
optional.
3. With RFC 1583 TOS routing, individual links or prefixes could not
be excluded from a topology. If the LSA options T-bit was set,
all links or prefixes were either advertised explicitly or
defaulted to the TOS 0 metric. With multi-topology routing,
links or prefixes that are not advertised for a specific topology
do not exist in that topology.
2. Terminology 2. Terminology
2.1 Requirements notation 2.1 Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119]. document are to be interpreted as described in RFC2119 [RFC2119].
2.2 Terms 2.2 Terms
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Each interface can be configured to belong to a set of topologies. A Each interface can be configured to belong to a set of topologies. A
single adjacency will be formed with neighbors on the interface even single adjacency will be formed with neighbors on the interface even
if the interface is configured to participate in multiple topologies. if the interface is configured to participate in multiple topologies.
Furthermore, adjacency formation will be independent of the Furthermore, adjacency formation will be independent of the
topologies configured for the interface or neighbors on that topologies configured for the interface or neighbors on that
interface. interface.
3.3 Sending OSPF control packets 3.3 Sending OSPF control packets
OSPF control packets MUST be sent over the default topology. Sending OSPF control packets is unchanged from RFC2328. For OSPF
control packets sent to the remote end of a virtual link, the transit
OSPF control packets sent to the remote end-point of a virtual link area path MUST be composed solely of links in the default topology
may need to traverse multiple hops. These control packets MUST be and the OSPF control packets MUST be forwarded using the default
correctly classified by the virtual link end-point routers as packets
belonging to the default topology. Even though the VL may belong to
one or more non-default topologies, OSPF control packets sent to the
remote end of a virtual link MUST be forwarded using the default
topology. topology.
3.4 Advertising MT Adjacencies and the Corresponding IP Prefixes 3.4 Advertising MT Adjacencies and the Corresponding IP Prefixes
We will reuse the TOS metric field in order to advertise a topology We will reuse the TOS metric field in order to advertise a topology
and prefixes belonging to that topology. The TOS field is redefined and prefixes belonging to that topology. The TOS field is redefined
as MT-ID in the payload of Router-LSAs, Summary-LSAs, NSSA-LSAs, and as MT-ID in the payload of Router-LSAs, Summary-LSAs, NSSA-LSAs, and
AS-External-LSAs (see Appendix A). AS-External-LSAs (see Appendix A).
MT-ID metrics in LSAs SHOULD be in ascending order of MT-ID. If an MT-ID metrics in LSAs SHOULD be in ascending order of MT-ID. If an
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0 - Reserved for advertising the metric associated with the 0 - Reserved for advertising the metric associated with the
default topology (see Section 4.2) default topology (see Section 4.2)
1 - Reserved for advertising the metric associated with the 1 - Reserved for advertising the metric associated with the
default multicast topology default multicast topology
MT-IDs [128-255] SHOULD be ignored. MT-IDs [128-255] SHOULD be ignored.
3.8 Forwarding in MT 3.8 Forwarding in MT
Forwarding assures that only routes belonging to a single topology It's outside of the scope of this document to specify how the
are used to forward a packet along its way from source to information in various topology specific forwarding structures are
destination. Therefore, user configuration MUST be consistently used during packet forwarding or how incoming packets are associated
applied throughout the network so that an incoming packet is with the corresponding topology. For correct operation, both
associated with the same topology through each hop end to end. It is forwarding behavior and methods of associating incoming packets to a
outside of the scope of this document to consider different methods corresponding topology must be consistently applied in the network.
of associating an incoming packet to a corresponding topology.
4. Default Topology Link Exclusion Functional Specifications 4. Default Topology Link Exclusion Functional Specifications
The multi-topologies imply that all the routers participate in the The multi-topologies imply that all the routers participate in the
default topology. However, it can be useful to exclude some links default topology. However, it can be useful to exclude some links
from the default topology and reserve them for some specific classes from the default topology and reserve them for some specific classes
of traffic. of traffic.
The multi-topologies extension for default topology link or prefix The multi-topologies extension for default topology link or prefix
exclusion is described in the following subsections. exclusion is described in the following subsections.
4.1 Exclusion of Links in the Default Topology 4.1 Exclusion of Links in the Default Topology
OSPF does not have the notion of an unreachable link. All links can OSPF does not have the notion of an unreachable link. All links can
have a maximum metric of 0xFFFF advertised in the Router-LSA. The have a maximum metric of 0xFFFF advertised in the Router-LSA. The
link exclusion capability requires routers to ignore TOS0 metrics in link exclusion capability requires routers to ignore TOS0 metrics in
Router-LSAs in the default topology and to alternately use the Router-LSAs in the default topology and to alternately use the MT-
MT-ID#0 metric to advertise the metric associated with the default ID#0 metric to advertise the metric associated with the default
topology. Hence, all routers within an area MUST agree on how the topology. Hence, all routers within an area MUST agree on how the
metric for default topology will be advertised. metric for default topology will be advertised.
The unused T-bit is defined as the MT-bit in the option field in The unused T-bit is defined as the MT-bit in the option field in
order to assure that a multi-topology link-excluding capable router order to assure that a multi-topology link-excluding capable router
will only form an adjacency with another similarly configured router. will only form an adjacency with another similarly configured router.
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
|DN |O |DC |EA |NP |MC |E |MT | |DN |O |DC |EA |NP |MC |E |MT |
+---+---+---+---+---+---+---+---+ +---+---+---+---+---+---+---+---+
MT-bit: This bit MUST be set in the Hello packet only if MT-bit: This bit MUST be set in the Hello packet only if
MTRoutingExclusionCapability is enabled (see Section 4.2) DefaultExclusionCapability is enabled (see Section 4.2)
4.2 New Area Data Structure Parameter 4.2 New Area Data Structure Parameter
We define a new parameter in the Area Data Structure: We define a new parameter in the Area Data Structure:
MTRoutingExclusionCapability DefaultExclusionCapability
This is a configurable parameter that will be used to facilitate This configurable parameter ensures that all routers in an area
the introduction of MT routers in an area and ensure backward have this capability enabled before the default topology can be
compatibility. disabled on a router link in the area without causing backward
compatibility problems.
When an area data structure is created the When an area data structure is created the DefaultExclusionCapability
MTRoutingExclusionCapability is disabled by default. is disabled by default.
If MTRoutingExclusionCapability is disabled: If DefaultExclusionCapability is disabled:
o The MT-bit MUST be cleared in Hello packets. o The MT-bit MUST be cleared in Hello packets.
o If a link participates in a non-default topology, it is o If a link participates in a non-default topology, it is
automatically included in the default topology to support backward automatically included in the default topology to support backward
compatibility between MT and non-MT routers. This is accomplished compatibility between MT and non-MT routers. This is accomplished
through advertisement via the TOS0 metric field the same as in through advertisement via the TOS0 metric field the same as in
standard OSPF [OSPF]. standard OSPF [OSPF].
If MTRoutingExclusionCapability is enabled: If DefaultExclusionCapability is enabled:
o The MT-bit MUST be set in Hello packets o The MT-bit MUST be set in Hello packets
o The router will only accept a Hello if the MT-bit is set (see o The router will only accept a Hello if the MT-bit is set (see
Section 4.3) Section 4.3)
When MTRoutingExclusionCapability is set to enabled a router is said When DefaultExclusionCapability is set to enabled a router is said to
to be operating in MTRoutingExclusionCapability mode. be operating in DefaultExclusionCapability mode.
4.3 Adjacency Formation with Link Exclusion Capability 4.3 Adjacency Formation with Link Exclusion Capability
In order to have a smooth transition from a non-MT area to an In order to have a smooth transition from a non-MT area to an MT-
MT-area, an MT router with MTRoutingExclusionCapability disabled will area, an MT router with DefaultExclusionCapability disabled will form
form adjacencies with non-MT routers and will include all links as adjacencies with non-MT routers and will include all links as part of
part of default topology. default topology.
A link may cease participating in default topology if A link may cease participating in default topology if
MTRoutingExclusionCapability is set to enabled. In this state, a DefaultExclusionCapability is set to enabled. In this state, a
router will only form adjacency with routers that set the MT-bit in router will only form adjacency with routers that set the MT-bit in
their Hello packets. This will ensure that all routers have their Hello packets. This will ensure that all routers have
MTRoutingExclusionCapability enabled before the default topology can DefaultExclusionCapability enabled before the default topology can be
be disabled on a link. disabled on a link.
Receiving OSPF Hello packets as defined in section 10.5 of [OSPF] is Receiving OSPF Hello packets as defined in section 10.5 of [OSPF] is
modified as follows: modified as follows:
o If the MTRoutingExclusionCapability of the Area Data structure is o If the DefaultExclusionCapability of the Area Data structure is
set to enabled, the Hello packets are discarded if the the set to enabled, the Hello packets are discarded if the the
received Hello packet does not have the MT-bit in the hello received Hello packet does not have the MT-bit in the hello
options set. options set.
4.4 OSPF Control Packets Transmission Over Excluded Links 4.4 OSPF Control Packets Transmission Over Excluded Links
If MTRoutingExclusionCapability is enabled and the default topology If DefaultExclusionCapability is enabled, the default topology can be
is not configured on an interface, connected routes MUST exist for disabled on an interface. Disabling the default topology on an
the default topology so that OSPF control packets can be sent and interface does not impact the installation of connected routes for
received on that interface. the interface in the default topology. It only affects what a router
advertises in its Router-LSA.
This allows OSPF control packets to be sent and received over an
interface even if the default topology is disabled on the interface.
4.5 OSPF LSA Advertisement and SPF Computation for Excluded Links 4.5 OSPF LSA Advertisement and SPF Computation for Excluded Links
When MTRoutingExclusionCapability is enabled and the link does not When DefaultExclusionCapability is enabled and the link does not
participate in the default topology, the MT-ID#0 metric is not participate in the default topology, the MT-ID#0 metric is not
advertised. The link's TOS0 metric is ignored during the default advertised. The link's TOS0 metric is ignored during the default
topology SPF computation. topology SPF computation.
When MTRoutingExclusionCapability is enabled and a link participates When DefaultExclusionCapability is enabled and a link participates in
in the default topology, MT-ID#0 metric is used to advertise the the default topology, MT-ID#0 metric is used to advertise the metric
metric associated with the default topology. The link's TOS0 metric associated with the default topology. The link's TOS0 metric is
is ignored during the default topology SPF computation. ignored during the default topology SPF computation.
Independent of the MTRoutingExclusionCapability setting, the TOS0 Independent of the DefaultExclusionCapability setting, the TOS0
metric is used for Summary-LSAs, NSSA-LSAs, and AS-External-LSAs. metric is used for Summary-LSAs, NSSA-LSAs, and AS-External-LSAs.
o If the prefix or router does not exist in the default topology, o If the prefix or router does not exist in the default topology,
the TOS0 metric is set to infinity (0xFFFFFF). the TOS0 metric is set to infinity (0xFFFFFF).
o If the prefix or router exists in default the topology, the TOS0 o If the prefix or router exists in default the topology, the TOS0
metric is used to advertise the metric in the default topology. metric is used to advertise the metric in the default topology.
During the summary and external prefix calculation for the default During the summary and external prefix calculation for the default
topology the TOS0 metric is used for Summary-LSAs, NSSA-LSAs, and topology the TOS0 metric is used for Summary-LSAs, NSSA-LSAs, and AS-
AS-External-LSAs. External-LSAs.
5. Interoperability between MT Capable and Non-MT Capable Routers 5. Interoperability between MT Capable and Non-MT Capable Routers
The default metric field is mandatory in all LSAs (even when metric The default metric field is mandatory in all LSAs (even when metric
value is 0). Even when a link or prefix does not exist in the value is 0). Even when a link or prefix does not exist in the
default topology, a non-MT router can consider the zero value in the default topology, a non-MT router can consider the zero value in the
metric field as a valid metric and consider the link or prefix as metric field as a valid metric and consider the link or prefix as
part of the default topology. part of the default topology.
In order to prevent the above problem, an MT capable router will In order to prevent the above problem, an MT capable router will
include all links as part of the default topology. If links need to include all links as part of the default topology. If links need to
be removed from the default topology, an MT capable router MUST be be removed from the default topology, an MT capable router MUST be
configured in MTRoutingExclusionCapability mode. In this mode, configured in DefaultExclusionCapability mode. In this mode,
routers will assure that all other routers in the area are in the routers will assure that all other routers in the area are in the
MTRoutingExclusionCapability mode before considering the MT-ID#0 DefaultExclusionCapability mode before considering the MT-ID#0 metric
metric in the SPF calculation. Only then can the TOS0 metric field in the SPF calculation. Only then can the TOS0 metric field in
in Router LSAs be safely ignored during the default topology SPF Router LSAs be safely ignored during the default topology SPF
computation. computation.
Note that for any prefix or router to become reachable in a certain Note that for any prefix or router to become reachable in a certain
topology, a contiguous path inside that topology must exist between topology, a contiguous path inside that topology must exist between
the calculating router and the destination prefix or router. the calculating router and the destination prefix or router.
6. Migration from non-MT-Area to MT-area 6. Migration from non-MT-Area to MT-area
Introducing MT-OSPF into a network can be done gradually to allow MT Introducing MT-OSPF into a network can be done gradually to allow MT
routers and non-MT routers to participate in the default topology routers and non-MT routers to participate in the default topology
while MT routers participate in other topologies. while MT routers participate in other topologies.
If there is a requirement to exclude some links from the default If there is a requirement to exclude some links from the default
topology in an area, all routers in the area MUST be in topology in an area, all routers in the area MUST be in
MTRoutingExclusionCapability mode. In this section we describe the DefaultExclusionCapability mode. In this section we describe the
migration steps to consider while transitioning from a non-MT network migration steps to consider while transitioning from a non-MT network
to an MT network. to an MT network.
Consider a network with a backbone area and a set of non-backbone Consider a network with a backbone area and a set of non-backbone
areas functioning in standard OSPF mode. We would like to migrate to areas functioning in standard OSPF mode. We would like to migrate to
an MT network either partially or completely. an MT network either partially or completely.
1. As required, part of an area is upgrade to be MT capable. The MT 1. As required, part of an area is upgrade to be MT capable. The MT
routers will interact with non-MT routers in the default topology routers will interact with non-MT routers in the default topology
and participate in other topologies as required. and participate in other topologies as required.
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migration steps to consider while transitioning from a non-MT network migration steps to consider while transitioning from a non-MT network
to an MT network. to an MT network.
Consider a network with a backbone area and a set of non-backbone Consider a network with a backbone area and a set of non-backbone
areas functioning in standard OSPF mode. We would like to migrate to areas functioning in standard OSPF mode. We would like to migrate to
an MT network either partially or completely. an MT network either partially or completely.
1. As required, part of an area is upgrade to be MT capable. The MT 1. As required, part of an area is upgrade to be MT capable. The MT
routers will interact with non-MT routers in the default topology routers will interact with non-MT routers in the default topology
and participate in other topologies as required. and participate in other topologies as required.
2. If a new non-backbone area is created for MT routers, it may be 2. If a new non-backbone area is created for MT routers, it may be
configured in MTRoutingExclusionCapability mode since there is no configured in DefaultExclusionCapability mode since there is no
interaction required with non-MT routers. In this mode, the interaction required with non-MT routers. In this mode, the
default topology can be excluded on links as required. default topology can be excluded on links as required.
3. If there is more than one non-backbone areas where MT is being 3. If there is more than one non-backbone areas where MT is being
used, it is desirable that the backbone area first be upgraded to used, it is desirable that the backbone area first be upgraded to
be MT capable so that inter-area routing is assured for MT be MT capable so that inter-area routing is assured for MT
destinations in different areas. destinations in different areas.
4. Gradually the whole network can be made MT capable. 4. Gradually the whole network can be made MT capable.
Note that inter-area routing for the MT-area still depends on the Note that inter-area routing for the MT-area still depends on the
backbone area. Therefore, if different areas configured for a given backbone area. Therefore, if different areas configured for a given
topology need to communicate, the backbone area also needs to be topology need to communicate, the backbone area also needs to be
configured for this topology. configured for this topology.
7. Security Considerations 7. Security Considerations
This document does not raise any security issues that are not already This document does not raise any security issues that are not already
skipping to change at page 15, line 21 skipping to change at page 16, line 21
[OSPF] Moy, J., "OSPF Version 2", RFC 2328, April 1998. [OSPF] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994. [RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994.
[RFC2119] Bradner, S., "Key words for use in RFC's to Indicate [RFC2119] Bradner, S., "Key words for use in RFC's to Indicate
Requirement Levels", RFC 2119, March 1997. Requirement Levels", RFC 2119, March 1997.
9.2 Informative References 9.2 Informative References
[M-ISIS] Przygienda, T., Shen, N. and N. Sheth, "M-ISIS: Multi [M-ISIS] Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in IS-IS", Topology (MT) Routing in IS-IS",
draft-ietf-isis-wg-multi-topology-07.txt (work in draft-ietf-isis-wg-multi-topology-07.txt (work in
progress). progress).
[STUB] Retana, A., Nguyen, L., White, R., Zinin, A. and D. [STUB] Retana, A., Nguyen, L., White, R., Zinin, A., and D.
McPherson, "OSPF Stub Router Advertisement", RFC 3137, June McPherson, "OSPF Stub Router Advertisement", RFC 3137,
2001. June 2001.
Authors' Addresses Authors' Addresses
Peter Psenak Peter Psenak
Cisco Systems Cisco Systems
Parc Pegasus, De Kleetlaan 6A Parc Pegasus, De Kleetlaan 6A
1831 Diegem 1831 Diegem
Belgium Belgium
EMail: ppsenak@cisco.com Email: ppsenak@cisco.com
Sina Mirtorabi Sina Mirtorabi
Cisco Systems Cisco Systems
225 West Tasman Drive 225 West Tasman Drive
San Jose, CA 95134 San Jose, CA 95134
USA USA
EMail: sina@cisco.com Email: sina@cisco.com
Abhay Roy Abhay Roy
Cisco Systems Cisco Systems
225 West Tasman Drive 225 West Tasman Drive
San Jose, CA 95134 San Jose, CA 95134
USA USA
EMail: akr@cisco.com Email: akr@cisco.com
Liem Nguyen Liem Nguyen
Cisco Systems Cisco Systems
7025 Kit Creek Road 7025 Kit Creek Road
Research Triangle Park, NC 27709 Research Triangle Park, NC 27709
USA USA
EMail: lhnguyen@cisco.com Email: lhnguyen@cisco.com
Padma Pillay-Esnault Padma Pillay-Esnault
Cisco Systems Cisco Systems
225 West Tasman Drive 225 West Tasman Drive
San Jose, CA 95134 San Jose, CA 95134
USA USA
EMail: ppe@cisco.com Email: ppe@cisco.com
Appendix A. Acknowledgments Appendix A. Acknowledgments
The authors would like to thank Scott Sturgess, Alvaro Retana, and The authors would like to thank Scott Sturgess, Alvaro Retana, David
David Kushi for their comments on the document. Thanks to Acee Kushi, Yakov Rekhter, Tony Przygienda, and Naiming Shen for their
Lindem for review and editing. comments on the document. Special thanks to Acee Lindem for editing
and to Tom Henderson for an extensive review during the OSPF Working
Group last call.
Appendix B. OSPF data formats Appendix B. OSPF data formats
LSA content defined in [OSPF] is modified to introduce the MT-ID. LSA content defined in [OSPF] is modified to introduce the MT-ID.
B.1 Router-LSAs B.1 Router-LSAs
Router-LSAs are the Type 1 LSAs. Each router in an area originates a Router-LSAs are the Type 1 LSAs. Each router in an area originates a
router-LSA. The LSA describes the state and cost of the router's router-LSA. The LSA describes the state and cost of the router's
links (i.e., interfaces) to the area. All of the router's links to links (i.e., interfaces) to the area. All of the router's links to
skipping to change at page 20, line 47 skipping to change at page 21, line 47
B.4 AS-External-LSAs B.4 AS-External-LSAs
AS-external-LSAs are the Type 5 LSAs. These LSAs are originated by AS-external-LSAs are the Type 5 LSAs. These LSAs are originated by
AS boundary routers, and describe destinations external to the AS. AS boundary routers, and describe destinations external to the AS.
For details concerning the construction of AS-external-LSAs, see For details concerning the construction of AS-external-LSAs, see
Section 12.4.3 [OSPF]. Section 12.4.3 [OSPF].
AS-external-LSAs usually describe a particular external destination. AS-external-LSAs usually describe a particular external destination.
For these LSAs the Link State ID field specifies an IP network number For these LSAs the Link State ID field specifies an IP network number
(if necessary, the Link State ID can also have one or more of the (if necessary, the Link State ID can also have one or more of the
network's "host" bits set; see Appendix E [OSPF] for details). network's "host" bits set; see Appendix E [OSPF] for details). AS-
AS-external-LSAs are also used to describe a default route. Default external-LSAs are also used to describe a default route. Default
routes are used when no specific route exists to the destination. routes are used when no specific route exists to the destination.
When describing a default route, the Link State ID is always set to When describing a default route, the Link State ID is always set to
DefaultDestination (0.0.0.0) and the Network Mask is set to 0.0.0.0. DefaultDestination (0.0.0.0) and the Network Mask is set to 0.0.0.0.
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 | 5 | | LS age | Options | 5 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 End of changes. 

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