draft-ietf-ospf-mt-00.txt   draft-ietf-ospf-mt-01.txt 
Network Working Group Peter Psenak Network Working Group Peter Psenak
Internet Draft Sina Mirtorabi Internet Draft Sina Mirtorabi
Expiration Date: April 2005 Abhay Roy Expiration Date: February 2005 Abhay Roy
File name: draft-ietf-ospf-mt-00.txt Liem Nguyen File name: draft-ietf-ospf-mt-01.txt Liem Nguyen
Cisco Systems
Padma Pillay-Esnault Padma Pillay-Esnault
Juniper Networks Cisco Systems
October 2004 February 2005
MT-OSPF: Multi Topology (MT) Routing in OSPF Multi-Topology (MT) Routing in OSPF
Status of This Memo Status of This Memo
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Copyright (C) The Internet Society (2005).
Abstract Abstract
This draft describes the 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 different extension can be used for computing different paths for unicast
classes of service, in-band management network or incongruent traffic, multicast traffic, different classes of service, or
topologies for unicast and multicast. M-ISIS describes a similar in-band network management. [M-ISIS] describes a similar
mechanism for ISIS. mechanism for ISIS. An optional extension to exclude
This draft also describes an optional extension of selected links from the default topology is also described.
Multi-topologies whereby some links might be excluded from the
default topology.
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 [2] introduced TOS metric in an earlier specification specification [OSPF] introduced TOS metric in an earlier
[3] in order to announce a different link's cost based on TOS. The specification [RFC1583] in order to announce a different link cost
TOS based routing as described in [3] was never deployed in the field based on TOS. TOS based routing as described in [RFC1583] was never
and later was removed from the spec. 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, to announce different topologies redefined as MT-ID and MT-ID Metric and are used to advertise
by advertising separate metrics for each of them. different topologies by advertising separate metrics for each
of them.
2. Terminology 2. Terminology
We define the following terminology in this document: We define the following terminology in this document:
Non-MT router : Routers that do not have the MT capability Non-MT router : Routers that do not have the MT capability
MT router : Routers that have MT capability as described in MT router : Routers that have MT capability as described in
this document this document
MT-ID : Renamed TOS field in LSAs to represent multi MT-ID : Renamed TOS field in LSAs to represent multi
topology ID. topology ID.
Default topology : Topology that is built using the TOS 0 metric Default topology : Topology that is built using the TOS 0 metric
(default metric) (default metric)
MT topology : Topology that is built using the corresponding MT topology : Topology that is built using the corresponding
MT-ID metric MT-ID metric
MT : Shorthand notation for MT topology
MT#0 topology : Representation of TOS 0 metric in MT-ID format MT#0 topology : Representation of TOS 0 metric in MT-ID format
Non-MT-Area : An area that contains only non-MT routers Non-MT-Area : An area that contains only non-MT routers
MT-Area : An area that contains both non-MT routers and MT MT-Area : An area that contains both non-MT routers and MT
routers or only MT routers routers or only MT routers
3. MT area boundary 3. MT area boundary
Each OSPF interface belongs to a single area and all MTs sharing that Each OSPF interface belongs to a single area and all MTs sharing that
link need to belong to the same area. Therefore the area boundaries link need to belong to the same area. Therefore the area boundaries
for all MTs are the same but each MT's attachment to the area is for all MTs are the same but each MT's attachment to the area is
independent. independent.
4. Adjacency for MTs 4. Adjacency for MTs
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 the remote neighbor even if the single adjacency will be formed with neighbors on the interface
interface is configured to participate in multiple topologies and even if the interface is configured to participate in multiple
independently of the MT-IDs. topologies. Furthermore, adjacency formation will be independent
of the topologies configured for the interface or neighbors on that
interface.
5. Sending OSPF control packets 5. Sending OSPF control packets
OSPF control packets should be sent over the default topology. OSPF control packets MUST be sent over the default topology.
OSPF control packets sent to the remote end-point of the virtual OSPF control packets sent to the remote end-point of a virtual
link may need to traverse multiple hops. These control packets link may need to traverse multiple hops. These control packets
should be correctly classified by the routers as packets belonging MUST be correctly classified by the virtual link end-point
to the default topology. Event though the VL may belong to other than routers as packets belonging to the default topology. Even though
default topology (or multiple of them), OSPF control packets sent to the VL may belong to one or more non-default topologies, OSPF control
the remote end of the virtual link should be forwarded using the packets sent to the remote end of a virtual link MUST be forwarded
default topology. using the default topology.
6. Advertising MT adjacencies and corresponding IP prefixes 6. Advertising MT adjacencies and corresponding IP prefixes
We will reuse the TOS metric field in order to announce a topology or We will reuse the TOS metric field in order to advertise a topology
prefixes that belongs to a given MT. The TOS field is renamed to and prefixes belonging to that topology. The TOS field is redefined
MT-ID in the LSAs payload (see Appendix A). as MT-ID in the payload of Router-LSAs, Summary-LSAs, NSSA-LSAs,
and AS-External-LSAs (see Appendix A).
MT-ID metrics in LSAs SHOULD be in ascending order of MT-ID. If
an MT-ID exists in an LSA or router link multiple times, the metric
in the first MT-ID instance MUST be used.
6.1 Intra-area routing 6.1 Intra-area routing
When a router establishes a FULL adjacency over a link that belongs When a router establishes a FULL adjacency over a link that belongs
to a set of MTs, it will advertise the corresponding cost for each to a set of MTs, it will advertise the corresponding cost for each
MT-ID. MT-ID.
All links are by default included in default topology, all By default, all links are included in default topology and all
advertised adjacency belonging to the default topology will use advertised prefixes belonging to the default topology will use
the TOS0 metric as in standard OSPF. the TOS0 metric the same as in standard OSPF [OSPF].
Each MT has its own MT-ID metric field and when a link is not part of Each MT has its own MT-ID metric field. When a link is not
a given MT, the corresponding MT-ID metric will not appear in the LSA. part of a given MT, the corresponding MT-ID metric is excluded from
the LSA.
The Network LSA does not contain any MT information as the DR is The Network-LSA does not contain any MT information since the DR is
shared by all MTs and thus there is no change to the Network LSA. shared by all MTs. Hence, there is no change to the Network-LSA.
6.2 Inter-area and external routing 6.2 Inter-area and External Routing
In Summary and External LSAs, the TOS metric fields are renamed to In Summary-LSAs, NSSA-LSAs, and AS-External-LSAs, the TOS metric
MT-ID metric fields and are used in order to announce prefix/router field are defined as MT-ID metric fields and are used in order to
reachability in the corresponding topology. advertise prefix and router reachability in the corresponding
topology.
When a router originates a type 3/4/5/7 LSA that belongs to a set of MTs, When a router originates a Summary-LSA, NSSA-LSA, or AS-External-LSA
it will include the corresponding cost for each MT-ID. The router that belongs to a set of MTs, it will include the corresponding cost
by default participate in default topology and use the TOS0 metric for each MT-ID. By default, the router participates in the default
for default topology as in standard OSPF. topology and uses the TOS0 metric for the default topology the same
as in standard OSPF [OSPF].
Setting the P-bit in NSSA-LSAs is topology independent and pertains
to all MT-ID advertised in the body of the LSA.
7. Flushing MT information 7. Flushing MT information
When a certain link/prefix that existed or was reachable in a certain When a certain link or prefix that existed or was reachable in a
topology is no longer part of this topology or the reachability of certain topology is no longer part of that topology or is unreachable
the link/prefix in this topology was lost, a new version of the LSA in that topology, a new version of the LSA must be originated
that advertised the link/prefix must be originated. This new version excluding metric information representing the link or prefix in that
of the LSA must not include any metric information representing the topology.
link/prefix in this topology.
The MT metric in the Router-LSA can also be set to the maximum The MT metric in the Router-LSA can also be set to the maximum
possible metric to enable the router to become a stub in a certain possible metric to enable the router to become a stub in a certain
topology [4]. topology [STUB].
8. MT SPF Computation 8. MT SPF Computation
By considering MT-ID metrics in the LSAs, OSPF will be able to By considering MT-ID metrics in the LSAs, OSPF will be able to
compute multiple topologies, one for each MT the router is part of compute multiple topologies and find paths to IP prefixes for each MT
and find paths to IP prefixes for each MT independently. A separate independently. A separate SPF will be computed for each MT-ID to find
SPF will be computed for each MT-ID to find independent paths to IP independent paths to IP prefixes. Each nexthop computed during the MT
prefixes. Each nexthop computed during the MT SPF MUST belong to the SPF MUST belong to the same MT.
same MT.
Network LSAs are used by all topologies during the SPF computation. Network-LSAs are used by all topologies during the SPF computation.
During SPF for a given MT-ID, only the link/metric for the given During the SPF for a given MT-ID, only the links and metrics for that
MT-ID will be considered. Entries in the Router Routing table will MT-ID will be considered. Entries in the Router Routing table will
be MT-ID specific. be MT-ID specific.
During the SPF computation for default topology the TOS0 metric is During the SPF computation for the default topology only the TOS0
considered during the SPF computation. metric is considered during the SPF computation.
9. MT ID Values 9. MT ID Values
Only MT-IDs in the range [0-127] are valid, because external LSAs use Since AS-External-LSAs use the high order bit in the MT-ID field
one bit in the MT-ID field (E bit) for the external metric-type. (E bit) for the external metric-type, only MT-IDs in the range
Following MT-ID values are reserved: [0-127] are valid. The following MT-ID values are reserved:
0 - reserved for routers in MTRoutingExclusionCapability mode 0 - Reserved for routers in MTRoutingExclusionCapability mode
to advertise the metric associated with default topology to advertise the metric associated with the default
(see section 11.2). topology (see section 11.2).
1 - reserved for default multicast topology. 1 - Reserved for the default multicast topology.
Any unknown MT-ID should be ignored. Unknown MT-IDs SHOULD be ignored.
10. Forwarding in MT 10. Forwarding in MT
Forwarding must make sure that only routes belonging to the single Forwarding assures that only routes belonging to a single
topology are used to forward the packet along its way from source to topology are used to forward a packet along its way from source to
destination, therefore user configuration MUST be consistently destination. Therefore, user configuration MUST be consistently
applied throughout the network so that an incoming packet is applied throughout the network so that an incoming packet is
associated with the same topology on each hop as it is being associated with the same topology through each hop end to end.
forwarded. It is outside of the scope of this document to consider It is outside of the scope of this document to consider
different methods of associating an incoming packet to the different methods of associating an incoming packet to a
corresponding MT. corresponding topology.
11. Exclusion of links in the default topology 11. Exclusion of links in the default topology
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 is useful in some circumstances default topology. However, it can be useful to exclude some links
to exclude some links from the default topology and reserve them from the default topology and reserve them for some specific
for some specific classes of traffic. classes of traffic.
The multi-topologies extension for default topology link exclusion The multi-topologies extension for default topology link or prefix
is described in the following sections. exclusion is described in the following subsections.
11.1 MT-bit in Hello packet 11.1 MT-bit in Hello packet
OSPF does not have the notion of unreachable link. All links can OSPF does not have the notion of an unreachable link. All links can
have a maximum metric of 0xFFFF carried in the Router LSA. The link have a maximum metric of 0xFFFF advertised in the Router-LSA. The
exclusion capability requires routers to ignore TOS 0 metric in link exclusion capability requires routers to ignore TOS0 metrics in
router-LSA in default topology and use MT-ID#0 metric instead to Router-LSAs in the default topology and to alternately use the
advertise the metric associated with the default topology. Hence, MT-ID#0 metric to advertise the metric associated with the default
all routers within an area MUST agree on how the metric for default topology. Hence, all routers within an area MUST agree on how the
topology will be advertised. metric for default topology will be advertised.
The unused T-bit is renamed (MT) in the option field in order to The unused T-bit is defined as the MT-bit in the option field
enforce that a multi-topology link-excluding capable router will in order to assure that a multi-topology link-excluding capable
only interact with another similarly configured router. 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 11.2). MTRoutingExclusionCapability is enabled (see section 11.2).
11.2 New parameter in the Area Data Structure 11.2 New parameter in the Area Data Structure
We define a new parameters in the Area Data Structure: We define a new parameter in the Area Data Structure:
MTRoutingExclusionCapability MTRoutingExclusionCapability
This is a configurable parameter that will be used to facilitate This is a configurable parameter that will be used to facilitate
the introduction of MT routers in an area and ensure the backward the introduction of MT routers in an area and ensure backward
compatibility. compatibility.
By default, when an area data structure is created the By default, when an area data structure is created the
MTRoutingExclusionCapabilty is disabled. MTRoutingExclusionCapability is disabled.
If MTRoutingExclusionCapability is disabled: If MTRoutingExclusionCapability is disabled:
o MT-bit MUST be cleared in the Hello packet o The MT-bit MUST be cleared in Hello packets.
o If a link participates in a non-default topology, o If a link participates in a non-default topology,
it is automatically included in default topology (by using it is automatically included in the default topology
the default metric field as it is done in standard OSPF [2]) to support backward compatibility between MT and
so that MT routers interact correctly with non-MT routers. non-MT routers. This is accomplished through advertisement
via the TOS0 metric field the same as in standard OSPF [OSPF].
If MTRoutingExclusionCapability is set to Enabled: If MTRoutingExclusionCapability is enabled:
o MT-bit MUST be set in the Hello packet 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 11.3) section 11.3)
We call MTRoutingExclusionCapability "mode", when When MTRoutingExclusionCapability is set to enabled a router is
MTRoutingExclusionCapability is set to Enabled. said to be operating in MTRoutingExclusionCapability mode.
11.3. Forming adjacency with link exclusion capability. 11.3 Adjacency Formation with Link Exclusion Capability
In order to have a smooth transition from a non-MT area to MT-area, a In order to have a smooth transition from a non-MT area to an
MT router with MTRoutingExclusionCapability set to disable will form MT-area, an MT router with MTRoutingExclusionCapability disabled will
adjacency with non-MT routers and it will include all links as part form adjacencies with non-MT routers and will include all links
of default topology. as part of default topology.
A link can cease participating in default topology if A link may cease participating in default topology if
MTRoutingExclusionCapability is set to Enabled. In this state, a MTRoutingExclusionCapability is set to enabled. In this state, a
router will only form adjacency with routers that set the MT-bit router will only form adjacency with routers that set the MT-bit
in their Hello packets. This will ensure that all routers are in in their Hello packets. This will ensure that all routers have
Enabled mode before default topology can be disabled on a link. MTRoutingExclusionCapability enabled before the default topology
can be disabled on a link.
Receiving OSPF Hello packets defined in section 8.2 of [2] are Receiving OSPF Hello packets as defined in section 10.5 of [OSPF] is
modified as follows: modified as follows:
If the MTRoutingExclusionCapability of the Area Data structure o If the MTRoutingExclusionCapability of the Area Data structure
is set to Enabled, the Hello packets are discarded if: is set to enabled, the Hello packets are discarded if the
the received Hello packet does not have the MT-bit in the hello
o the received Hello packet does not have the MT-bit set options set.
11.4. Sending OSPF control packets over an excluded link. 11.4 OSPF Control Packets Transmission Over Excluded Links
If MTRoutingExclusionCapability is set to Enabled and default If MTRoutingExclusionCapability is enabled and the default
topology is not configured on the interface, connected route should topology is not configured on an interface, connected routes MUST
still exist for a default topology that would enable the OSPF still exist for the default topology and should enable OSPF control
control packets to be sent and received. packets to be sent and received over that interface.
11.5. Modified MT SPF Computation with link exclusion capability. 11.5 OSPF LSA Advertisement and SPF Computation for Excluded Links
When MTRoutingExclusionCapability is set to Enabled, MT#0 can be When MTRoutingExclusionCapability is enabled and the link does
removed if a link does not participate in default topology. In that not participate in the default topology, the MT-ID#0 metric is not
case the TOS0 metric is set to infinity (0xFFFF) and ignored during advertised. The TOS0 metric is set to infinity (0xFFFF) but is
the MT#0 SPF computation. ignored during the default topology SPF computation.
When MTRoutingExclusionCapability is set to Enabled and a link When MTRoutingExclusionCapability is enabled and a link participates
participates in default topology, MT-ID#0 metric is used to advertise in the default topology, MT-ID#0 metric is used to advertise the
metric associated with the default topology. Further TOS0 metric is metric associated with the default topology. The TOS0 metric is set
set to the same value as MT-ID#0 metric. However TOS 0 metric is to the same value as the MT-ID#0 metric but is ignored during the
ignored during SPF for default topology and only MT-ID#0 metric default topology SPF computation.
is used for SPF in default topology.
When originating Summary and External LSAs, if Independent of the MTRoutingExclusionCapability setting, the TOS0
MTRoutingExclusionCapability is set to Enabled: metric is used for Summary-LSAs, NSSA-LSAs, and AS-External-LSAs.
o if the prefix / router does not exist in default topology, TOS0 o If the prefix or router does not exist in the default topology,
metric is set to infinity (0xFFFFFF). the TOS0 metric is set to infinity (0xFFFFFF).
o if the prefix / router exist in default topology, TOS0 metric o If the prefix or router exists in default the topology, the
is used to announce a prefix / router in default topology. TOS0 metric is used to advertise the metric in the default
topology.
During the Summary and External prefix calculation for default topology During the summary and external prefix calculation for the default
TOS0 metric is used in LSA Type-3/4/5/7. topology the TOS0 metric is used for Summary-LSAs, NSSA-LSAs, and
AS-External-LSAs.
12. Interoperability between MT capable and non-MT capable routers 12. 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 the link or a 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 capable router can consider the zero value default topology, a non-MT router can consider the zero value
in the metric field as a valid metric and consider the link/prefix as in the metric field as a valid metric and consider the link or
part of the default topology. prefix as part of the default topology.
In order to prevent the above problem, a MT capable router will In order to prevent the above problem, an MT capable router will
by default include all links as part of the default topology. If links include all links as part of the default topology. If links need
need to be removed from the default topology, a MT capable router to be removed from the default topology, an MT capable router
MUST be configured in MTRoutingExclusionCapability mode. In this mode MUST be configured in MTRoutingExclusionCapability mode. In this
the router will make sure that all routers in the area are in the mode, routers will assure that all other routers in the area are
MTRoutingExclusionCapability mode before forming any adjacency so that in the MTRoutingExclusionCapability mode before considering the
TOS0 metric field can be safely ignored during the MT#0 SPF computation. MT-ID#0 metric in the SPF calculation. Only then can the TOS0 metric
field be safely ignored during the default topology SPF 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 the topology, a contiguous path inside that topology must exist between
calculating router and the destination prefix or router. the calculating router and the destination prefix or router.
13. Migration from non-MT-Area to MT-area 13. Migration from non-MT-Area to MT-area
Introducing MT-OSPF in a network can be gradually done since MT Introducing MT-OSPF into a network can be done gradually to allow
routers will interact in default topology with non-MT routers, MT routers and non-MT routers to participate in the default topology
yet exchanging information about other topologies with other MT while MT routers participate in other topologies.
capable routers.
If there is a requirement to exclude some links from default topology If there is a requirement to exclude some links from the default
in an area, all routers MUST be in MTRoutingExclusionCapability mode. topology in an area, all routers in the area MUST be in
In this section we describe migrations steps to consider while MTRoutingExclusionCapability mode. In this section we describe the
transitioning from a non-MT network to a MT network. migration steps to consider while transitioning from a non-MT network
to an MT network.
Migration Steps Consider a network with a backbone area and a set of non-backbone
---------------
Consider a network with a backbone area and a sets 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
a MT network either partially or completely. an MT network either partially or completely.
1) Part of an area is upgraded as needed to have MT capability, the 1) As required, part of an area is upgrade to be MT capable. The
MT routers will interact with non-MT routers in default topology, MT routers will interact with non-MT routers in the default
further MT routers will participate in MT topology as needed. topology 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
set in MTRoutingExclusionCapability mode as there is no interaction configured in MTRoutingExclusionCapability mode since there is no
required with non-MT routers, in this mode default topology interaction required with non-MT routers. In this mode, the
can be excluded if 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 area 0 be first upgraded to MT capable used, it is desirable that the backbone area first be upgraded to
routers so that inter-area routing is assured for MT destinations be MT capable so that inter-area routing is assured for MT
in different areas. destinations in different areas.
4) Gradually the whole network can be made MT aware 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 in a given MT-ID need to backbone area. Therefore, if different areas configured for a given
communicate, the backbone area also needs to be configured for this topology need to communicate, the backbone area also needs to be
MT-ID. configured for this topology.
14. Acknowledgments 14. Acknowledgments
The authors would like to thank Scott Sturgess and Alvaro Retana for The authors would like to thank Scott Sturgess and Alvaro Retana for
their comments on the document. their comments on the document. Thanks to Acee Lindem for review and
extensive editing.
15. Security Consideration 15. Security Consideration
No specific security issues with the proposed solutions are known. The described protocol extension does not introduce any new security
issues into the OSPF protocol.
16. IANA Considerations 16. IANA Considerations
T-bit defined in [3] for router's TOS capability is reclaimed as The T-bit as defined in [RFC1583] for a router's TOS capability is
MT-bit in this document. Likewise, TOS field in type 1,3,4,5,7 LSAs redefined as the MT-bit in this document. Similarly, the TOS field
defined in [2] is reclaimed as MT-ID in this document. for Router-LSAs, Summary-LSAs, NSSA-LSAs, and AS-External LSAs as
defined in [OSPF] is redefined as MT-ID in this document.
17. References 17. Normative References
[1] Przygienda, Shen, Sheth, "Multi Topology (MT) Routing in IS-IS", [M-ISIS] Przygienda, T., Shen, N., Sheth, N.,
draft-ietf-isis-wg-multi-topology-06.txt, Work in progress. "Multi Topology (MT) Routing in IS-IS",
draft-ietf-isis-wg-multi-topology-06.txt,
Work in progress.
[2] Moy, J., "OSPF Version 2", RFC 2328, April 1998. [OSPF] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[3] Moy, J., "OSPF Version 2", RFC 1583, Proteon, Inc., March 1994. [RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994.
[4] Retana, Nguyen, White, "OSPF Stub Router Advertisement", [NSSA] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
RFC 3137, June 2001. RFC 3101, January 2003.
[RFC2119] Bradner, S., "Key words for use in RFC's to Indicate
Requirement Levels", RFC 2328, March 1977.
18. Informative References
[STUB] Retana, A., Nguyen, L., White, R., Zinin, A. and D.
McPherson, "OSPF Stub Router Advertisement", RFC 3137, June
2001.
Appendix A. Appendix A.
LSAs content defined in [2] are modified to introduce MT-ID. LSA content defined in [OSPF] is modified to introduce the MT-ID.
A.1 Router-LSAs A.1 Router-LSAs
Router-LSAs are the Type 1 LSAs. Each router in an area originates 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 a 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
the area must be described in a single router-LSA. For details the area must be described in a single router-LSA. For details
concerning the construction of router-LSAs, see Section 12.4.1. [2] concerning the construction of router-LSAs, see Section
12.4.1 [OSPF].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 10, line 18 skipping to change at page 12, line 18
each broadcast and NBMA network in the area which supports two or each broadcast and NBMA network in the area which supports two or
more routers. The network-LSA is originated by the network's more routers. The network-LSA is originated by the network's
Designated Router. The LSA describes all routers attached to the Designated Router. The LSA describes all routers attached to the
network, including the Designated Router itself. The LSA's Link network, including the Designated Router itself. The LSA's Link
State ID field lists the IP interface address of the Designated State ID field lists the IP interface address of the Designated
Router. Router.
The distance from the network to all attached routers is zero. This The distance from the network to all attached routers is zero. This
is why metric fields need not be specified in the network-LSA. For is why metric fields need not be specified in the network-LSA. For
details concerning the construction of network-LSAs, see Section details concerning the construction of network-LSAs, see Section
12.4.2. [2] 12.4.2 [OSPF].
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 | 2 | | LS age | Options | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID | | Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router | | Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number | | LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length | | LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask | | Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attached Router | | Attached Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | | ... |
Note that network LSA does not contain any MT-ID field as the cost of Note that network LSA does not contain any MT-ID fields as the cost
the network to the attached routers is 0 and DR is shared by all MT. of the network to the attached routers is 0 and DR is shared by
all topologies.
A.3 Summary-LSAs A.3 Summary-LSAs
Summary-LSAs are the Type 3 and 4 LSAs. These LSAs are originated Summary-LSAs are the Type 3 and 4 LSAs. These LSAs are originated
by area border routers. Summary-LSAs describe inter-area by area border routers. Summary-LSAs describe inter-area
destinations. For details concerning the construction of summary- destinations. For details concerning the construction of summary-
LSAs, see Section 12.4.3. [2] LSAs, see Section 12.4.3 [OSPF].
Type 3 summary-LSAs are used when the destination is an IP network. Type 3 summary-LSAs are used when the destination is an IP network.
In this case the LSA's Link State ID field is an IP network number In this case the LSA's Link State ID field is 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 [2] for details). When the network's "host" bits set; see Appendix E [OSPF] for details). When
destination is an AS boundary router, a Type 4 summary-LSA is used, the destination is an AS boundary router, a Type 4 summary-LSA is
and the Link State ID field is the AS boundary router's OSPF Router used, and the Link State ID field is the AS boundary router's OSPF
ID. (To see why it is necessary to advertise the location of each Router ID. (To see why it is necessary to advertise the location of
ASBR, consult Section 16.4 of [2]). Other than the difference in the each ASBR, consult Section 16.4 of [OSPF]). Other than the difference
Link State ID field, the format of Type 3 and 4 summary-LSAs is in the Link State ID field, the format of Type 3 and 4 summary-LSAs
identical. is identical.
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 | 3 or 4 | | LS age | Options | 3 or 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID | | Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router | | Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 11, line 52 skipping to change at page 14, line 10
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID | MT-ID metric | | MT-ID | MT-ID metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A.4.5 AS-external-LSAs A.4.5 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. [2] 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 For these LSAs the Link State ID field specifies an IP network number
number (if necessary, the Link State ID can also have one or more of (if necessary, the Link State ID can also have one or more of the
the network's "host" bits set; see Appendix E [2] for details). AS- network's "host" bits set; see Appendix E [OSPF] for details).
external-LSAs are also used to describe a default route. Default AS-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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID | | Link State ID |
skipping to change at page 12, line 5 skipping to change at page 15, line 5
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... | | ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| MT-ID | MT-ID metric | |E| MT-ID | MT-ID metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding address | | Forwarding address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Route Tag | | External Route Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
A.4.6 NSSA-LSAs
NSSA-LSAs are the Type 7 LSAs. These LSAs are originated by
AS boundary routers local to an NSSA, and describe destinations
external to the AS. The changes to NSSA-LSAs are identical to those
for External-LSAs (Appendix A.4.5). For details concerning the
construction of NSSA-LSAs see Section 2.4 [NSSA].
Authors' address Authors' address
Peter Psenak Abhay Roy Peter Psenak Abhay Roy
Cisco Systems Cisco systems Cisco Systems Cisco systems
Parc Pegasus, 170 W. Tasman Dr. Parc Pegasus, 170 W. Tasman Dr.
De Kleetlaan 6A San Jose, CA 95134 De Kleetlaan 6A San Jose, CA 95134
1831 Diegem, Belgium USA 1831 Diegem, Belgium USA
E-mail: ppsenak@cisco.com E-mail: akr@cisco.com E-mail: ppsenak@cisco.com E-mail: akr@cisco.com
Sina Mirtorabi Liem Nguyen Sina Mirtorabi Liem Nguyen
Cisco Systems Cisco Systems Cisco Systems Cisco Systems
225 West Tasman drive 7025 Kit Creek Rd. 225 West Tasman drive 7025 Kit Creek Rd.
San Jose, CA 95134 Research Triangle Park, NC 27709 San Jose, CA 95134 Research Triangle Park, NC 27709
USA USA USA USA
E-mail: sina@cisco.com E-mail: lhnguyen@cisco.com E-mail: sina@cisco.com E-mail: lhnguyen@cisco.com
Padma PIllay-Esnault Padma Pillay-Esnault
Juniper Networks Cisco Systems
1194 N. Mathilda Avenue 3750 Cisco Way
Sunnyvale, CA 94089 San Jose, CA 95134
USA USA
E-mail: padma@juniper.net E-mail: ppe@cisco.com
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