Network Working Group P. Psenak
Internet-Draft S. Mirtorabi
Expires: September 27, 2005 A. Roy
L. Nguyen
P. Pillay-Esnault
Cisco Systems
March 29, 2005
Multi-Topology (MT) Routing in OSPF
draft-ietf-ospf-mt-03.txt
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of
which he or she is aware have been or will be disclosed, and any of
which he or she become aware will be disclosed, in accordance with
RFC 3668.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as
Internet-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on September 27, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This draft describes an extension to OSPF in order to define
independent IP topologies called Multi-Topologies (MTs). The MT
extension can be used for computing different paths for unicast
traffic, multicast traffic, different classes of service, or in-band
Psenak, et al. Expires September 27, 2005 [Page 1]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
network management. [M-ISIS] describes a similar mechanism for ISIS.
An optional extension to exclude selected links from the default
topology is also described.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Requirements notation . . . . . . . . . . . . . . . . . . 4
2.2 Terms . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Base MT Functional Specifications . . . . . . . . . . . . . . 5
3.1 MT Area Boundary . . . . . . . . . . . . . . . . . . . . . 5
3.2 Adjacency for MTs . . . . . . . . . . . . . . . . . . . . 5
3.3 Sending OSPF control packets . . . . . . . . . . . . . . . 5
3.4 Advertising MT Adjacencies and the Corresponding IP
Prefixes . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.4.1 Advertising MT Adjacencies and the Corresponding
IP Prefixes . . . . . . . . . . . . . . . . . . . . . 5
3.4.2 Inter-Area and External Routing . . . . . . . . . . . 6
3.5 Flushing MT Information . . . . . . . . . . . . . . . . . 6
3.6 MT SPF Computation . . . . . . . . . . . . . . . . . . . . 6
3.7 MT-ID Values . . . . . . . . . . . . . . . . . . . . . . . 7
3.8 Forwarding in MT . . . . . . . . . . . . . . . . . . . . . 7
4. Default Topology Link Exclusion Functional Specifications . . 8
4.1 Exclusion of Links in the Default Topology . . . . . . . . 8
4.2 New Area Data Structure Parameter . . . . . . . . . . . . 8
4.3 Adjacency Formation with Link Exclusion Capability . . . . 9
4.4 OSPF Control Packets Transmission Over Excluded Links . . 9
4.5 OSPF LSA Advertisement and SPF Computation for
Excluded Links . . . . . . . . . . . . . . . . . . . . . . 9
5. Interoperability between MT Capable and Non-MT Capable
Routers . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
6. Migration from non-MT-Area to MT-area . . . . . . . . . . . . 12
7. Security Considerations . . . . . . . . . . . . . . . . . . . 13
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
9.1 Normative References . . . . . . . . . . . . . . . . . . . . 15
9.2 Informative References . . . . . . . . . . . . . . . . . . . 15
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . 15
A. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
B. OSPF data formats . . . . . . . . . . . . . . . . . . . . . . 18
B.1 Router-LSAs . . . . . . . . . . . . . . . . . . . . . . . 18
B.2 Network-LSAs . . . . . . . . . . . . . . . . . . . . . . . 19
B.3 Summary-LSAs . . . . . . . . . . . . . . . . . . . . . . . 19
B.4 AS-External-LSAs . . . . . . . . . . . . . . . . . . . . . 20
B.5 NSSA-LSAs . . . . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . . 22
Psenak, et al. Expires September 27, 2005 [Page 2]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
1. Introduction
OSPF uses a fixed packet format, therefore it is not easy to
introduce any backward compatible extensions. However, the OSPF
specification [OSPF] introduced TOS metric in an earlier
specification [RFC1583] in order to announce a different link cost
based on TOS. TOS based routing as described in [RFC1583] was never
deployed and was subsequently deprecated.
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
different topologies by advertising separate metrics for each of
them.
Psenak, et al. Expires September 27, 2005 [Page 3]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
2. Terminology
2.1 Requirements notation
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC2119 [RFC2119].
2.2 Terms
We define the following terminology in this document:
Non-MT router
Routers that do not have the MT capability
MT router
Routers that have MT capability as described in this document
MT-ID
Renamed TOS field in LSAs to represent multitopology ID.
Default topology
Topology that is built using the TOS 0 metric (default metric)
MT topology
Topology that is built using the corresponding MT-ID metric
MT
Shorthand notation for MT topology
MT#0 topology
Representation of TOS 0 metric in MT-ID format
Non-MT-Area
An area that contains only non-MT routers
MT-Area
An area that contains both non-MT routers and MT routers or only
MT routers
Psenak, et al. Expires September 27, 2005 [Page 4]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
3. Base MT Functional Specifications
3.1 MT Area Boundary
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
for all MTs are the same but each MT's attachment to the area is
independent.
3.2 Adjacency for MTs
Each interface can be configured to belong to a set of topologies. A
single adjacency will be formed with neighbors on the interface even
if the interface is configured to participate in multiple topologies.
Furthermore, adjacency formation will be independent of the
topologies configured for the interface or neighbors on that
interface.
3.3 Sending OSPF control packets
OSPF control packets MUST be sent over the default topology.
OSPF control packets sent to the remote end-point of a virtual link
may need to traverse multiple hops. These control packets MUST be
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.
3.4 Advertising MT Adjacencies and the Corresponding IP Prefixes
We will reuse the TOS metric field in order to advertise a topology
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-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.
3.4.1 Advertising MT Adjacencies and the Corresponding IP Prefixes
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
MT-ID.
By default, all links are included in default topology and all
Psenak, et al. Expires September 27, 2005 [Page 5]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
advertised prefixes belonging to the default topology will use the
TOS0 metric the same as in standard OSPF [OSPF].
Each MT has its own MT-ID metric field. When a link is not part of a
given MT, the corresponding MT-ID metric is excluded from the LSA.
The Network-LSA does not contain any MT information since the DR is
shared by all MTs. Hence, there is no change to the Network-LSA.
3.4.2 Inter-Area and External Routing
In Summary-LSAs, NSSA-LSAs, and AS-External-LSAs, the TOS metric
fields are defined as MT-ID metric fields and are used in order to
advertise prefix and router reachability in the corresponding
topology.
When a router originates a Summary-LSA, NSSA-LSA, or AS-External-LSA
that belongs to a set of MTs, it will include the corresponding cost
for each MT-ID. By default, the router participates in the default
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.
3.5 Flushing MT Information
When a certain link or prefix that existed or was reachable in a
certain topology is no longer part of that topology or is unreachable
in that topology, a new version of the LSA must be originated
excluding metric information representing the link or prefix in that
topology.
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
topology [STUB].
3.6 MT SPF Computation
By considering MT-ID metrics in the LSAs, OSPF will be able to
compute multiple topologies and find paths to IP prefixes for each MT
independently. A separate SPF will be computed for each MT-ID to
find independent paths to IP prefixes. Each nexthop computed during
the MT SPF MUST belong to the same MT.
Network-LSAs are used by all topologies during the SPF computation.
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
Psenak, et al. Expires September 27, 2005 [Page 6]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
be MT-ID specific.
During the SPF computation for the default topology only the TOS0
metric is considered during the SPF computation.
3.7 MT-ID Values
Since AS-External-LSAs use the high order bit in the MT-ID field (E
bit) for the external metric-type, only MT-IDs in the range [0-127]
are valid. The following MT-ID values are reserved:
0 - Reserved for advertising the metric associated with the
default topology (see Section 4.2)
1 - Reserved for advertising the metric associated with the
default multicast topology
MT-IDs [128-255] SHOULD be ignored.
3.8 Forwarding in MT
Forwarding assures that only routes belonging to a single topology
are used to forward a packet along its way from source to
destination. Therefore, user configuration MUST be consistently
applied throughout the network so that an incoming packet is
associated with the same topology through each hop end to end. It is
outside of the scope of this document to consider different methods
of associating an incoming packet to a corresponding topology.
Psenak, et al. Expires September 27, 2005 [Page 7]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
4. Default Topology Link Exclusion Functional Specifications
The multi-topologies imply that all the routers participate in the
default topology. However, it can be useful to exclude some links
from the default topology and reserve them for some specific classes
of traffic.
The multi-topologies extension for default topology link or prefix
exclusion is described in the following subsections.
4.1 Exclusion of Links in the Default Topology
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
link exclusion capability requires routers to ignore TOS0 metrics in
Router-LSAs in the default topology and to alternately use the
MT-ID#0 metric to advertise the metric associated with the default
topology. Hence, all routers within an area MUST agree on how the
metric for default topology will be advertised.
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
will only form an adjacency with another similarly configured router.
+---+---+---+---+---+---+---+---+
|DN |O |DC |EA |NP |MC |E |MT |
+---+---+---+---+---+---+---+---+
MT-bit: This bit MUST be set in the Hello packet only if
MTRoutingExclusionCapability is enabled (see Section 4.2)
4.2 New Area Data Structure Parameter
We define a new parameter in the Area Data Structure:
MTRoutingExclusionCapability
This is a configurable parameter that will be used to facilitate
the introduction of MT routers in an area and ensure backward
compatibility.
When an area data structure is created the
MTRoutingExclusionCapability is disabled by default.
If MTRoutingExclusionCapability is disabled:
Psenak, et al. Expires September 27, 2005 [Page 8]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
o The MT-bit MUST be cleared in Hello packets.
o If a link participates in a non-default topology, it is
automatically included in the default topology to support backward
compatibility between MT and non-MT routers. This is accomplished
through advertisement via the TOS0 metric field the same as in
standard OSPF [OSPF].
If MTRoutingExclusionCapability is enabled:
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
Section 4.3)
When MTRoutingExclusionCapability is set to enabled a router is said
to be operating in MTRoutingExclusionCapability mode.
4.3 Adjacency Formation with Link Exclusion Capability
In order to have a smooth transition from a non-MT area to an
MT-area, an MT router with MTRoutingExclusionCapability disabled will
form adjacencies with non-MT routers and will include all links as
part of default topology.
A link may cease participating in default topology if
MTRoutingExclusionCapability is set to enabled. In this state, a
router will only form adjacency with routers that set the MT-bit in
their Hello packets. This will ensure that all routers have
MTRoutingExclusionCapability enabled before the default topology can
be disabled on a link.
Receiving OSPF Hello packets as defined in section 10.5 of [OSPF] is
modified as follows:
o If the MTRoutingExclusionCapability of the Area Data structure is
set to enabled, the Hello packets are discarded if the the
received Hello packet does not have the MT-bit in the hello
options set.
4.4 OSPF Control Packets Transmission Over Excluded Links
If MTRoutingExclusionCapability is enabled and the default topology
is not configured on an interface, connected routes MUST exist for
the default topology so that OSPF control packets can be sent and
received on that interface.
4.5 OSPF LSA Advertisement and SPF Computation for Excluded Links
When MTRoutingExclusionCapability is enabled and the link does not
Psenak, et al. Expires September 27, 2005 [Page 9]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
participate in the default topology, the MT-ID#0 metric is not
advertised. The link's TOS0 metric is ignored during the default
topology SPF computation.
When MTRoutingExclusionCapability is enabled and a link participates
in the default topology, MT-ID#0 metric is used to advertise the
metric associated with the default topology. The link's TOS0 metric
is ignored during the default topology SPF computation.
Independent of the MTRoutingExclusionCapability setting, the TOS0
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,
the TOS0 metric is set to infinity (0xFFFFFF).
o If the prefix or router exists in default the topology, the TOS0
metric is used to advertise the metric in the default topology.
During the summary and external prefix calculation for the default
topology the TOS0 metric is used for Summary-LSAs, NSSA-LSAs, and
AS-External-LSAs.
Psenak, et al. Expires September 27, 2005 [Page 10]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
5. Interoperability between MT Capable and Non-MT Capable Routers
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
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
part of the default topology.
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
be removed from the default topology, an MT capable router MUST be
configured in MTRoutingExclusionCapability mode. In this mode,
routers will assure that all other routers in the area are in the
MTRoutingExclusionCapability mode before considering the MT-ID#0
metric in the SPF calculation. Only then can the TOS0 metric field
in Router LSAs be safely ignored during the default topology SPF
computation.
Note that for any prefix or router to become reachable in a certain
topology, a contiguous path inside that topology must exist between
the calculating router and the destination prefix or router.
Psenak, et al. Expires September 27, 2005 [Page 11]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
6. Migration from non-MT-Area to MT-area
Introducing MT-OSPF into a network can be done gradually to allow MT
routers and non-MT routers to participate in the default topology
while MT routers participate in other topologies.
If there is a requirement to exclude some links from the default
topology in an area, all routers in the area MUST be in
MTRoutingExclusionCapability mode. In this section we describe the
migration steps to consider while transitioning from a non-MT network
to an MT network.
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
an MT network either partially or completely.
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
and participate in other topologies as required.
2. If a new non-backbone area is created for MT routers, it may be
configured in MTRoutingExclusionCapability mode since there is no
interaction required with non-MT routers. In this mode, the
default topology can be excluded on links as required.
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
be MT capable so that inter-area routing is assured for MT
destinations in different areas.
4. Gradually the whole network can be made MT capable.
Note that inter-area routing for the MT-area still depends on the
backbone area. Therefore, if different areas configured for a given
topology need to communicate, the backbone area also needs to be
configured for this topology.
Psenak, et al. Expires September 27, 2005 [Page 12]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
7. Security Considerations
This document does not raise any security issues that are not already
covered in [OSPF].
Psenak, et al. Expires September 27, 2005 [Page 13]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
8. IANA Considerations
The T-bit as defined in [RFC1583] for a router's TOS capability is
redefined as the MT-bit in this document. Similarly, the TOS field
for Router-LSAs, Summary-LSAs, NSSA-LSAs, and AS-External LSAs as
defined in [OSPF] is redefined as MT-ID in this document.
Psenak, et al. Expires September 27, 2005 [Page 14]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
9. References
9.1 Normative References
[NSSA] Murphy, P., "The OSPF Not-So-Stubby Area (NSSA) Option",
RFC 3101, January 2003.
[OSPF] Moy, J., "OSPF Version 2", RFC 2328, April 1998.
[RFC1583] Moy, J., "OSPF Version 2", RFC 1583, March 1994.
[RFC2119] Bradner, S., "Key words for use in RFC's to Indicate
Requirement Levels", RFC 2119, March 1997.
9.2 Informative References
[M-ISIS] Przygienda, T., Shen, N. and N. Sheth, "M-ISIS: Multi
Topology (MT) Routing in IS-IS",
draft-ietf-isis-wg-multi-topology-07.txt (work in
progress).
[STUB] Retana, A., Nguyen, L., White, R., Zinin, A. and D.
McPherson, "OSPF Stub Router Advertisement", RFC 3137, June
2001.
Authors' Addresses
Peter Psenak
Cisco Systems
Parc Pegasus, De Kleetlaan 6A
1831 Diegem
Belgium
EMail: ppsenak@cisco.com
Sina Mirtorabi
Cisco Systems
225 West Tasman Drive
San Jose, CA 95134
USA
EMail: sina@cisco.com
Psenak, et al. Expires September 27, 2005 [Page 15]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
Abhay Roy
Cisco Systems
225 West Tasman Drive
San Jose, CA 95134
USA
EMail: akr@cisco.com
Liem Nguyen
Cisco Systems
7025 Kit Creek Road
Research Triangle Park, NC 27709
USA
EMail: lhnguyen@cisco.com
Padma Pillay-Esnault
Cisco Systems
225 West Tasman Drive
San Jose, CA 95134
USA
EMail: ppe@cisco.com
Psenak, et al. Expires September 27, 2005 [Page 16]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
Appendix A. Acknowledgments
The authors would like to thank Scott Sturgess, Alvaro Retana, and
David Kushi for their comments on the document. Thanks to Acee
Lindem for review and editing.
Psenak, et al. Expires September 27, 2005 [Page 17]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
Appendix B. OSPF data formats
LSA content defined in [OSPF] is modified to introduce the MT-ID.
B.1 Router-LSAs
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
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
concerning the construction of router-LSAs, see Section 12.4.1
[OSPF].
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|*|*|*|N|W|V|E|B| 0 | # links |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | # MT-ID | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID | 0 | MT-ID metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID | 0 | MT-ID metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
Psenak, et al. Expires September 27, 2005 [Page 18]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
B.2 Network-LSAs
Network-LSAs are the Type 2 LSAs. A network-LSA is originated for
each broadcast and NBMA network in the area which supports two or
more routers. The network-LSA is originated by the network's
Designated Router. The LSA describes all routers attached to the
network, including the Designated Router itself. The LSA's Link
State ID field lists the IP interface address of the Designated
Router.
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
details concerning the construction of network-LSAs, see Section
12.4.2 [OSPF].
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 | 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Attached Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
Note that network LSA does not contain any MT-ID fields as the cost
of the network to the attached routers is 0 and DR is shared by all
topologies.
B.3 Summary-LSAs
Summary-LSAs are the Type 3 and 4 LSAs. These LSAs are originated by
area border routers. Summary-LSAs describe inter-area destinations.
For details concerning the construction of summary- LSAs, see Section
12.4.3 [OSPF].
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
Psenak, et al. Expires September 27, 2005 [Page 19]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
(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). When
the destination is an AS boundary router, a Type 4 summary-LSA is
used, and the Link State ID field is the AS boundary router's OSPF
Router ID. (To see why it is necessary to advertise the location of
each ASBR, consult Section 16.4 of [OSPF]). Other than the
difference in the Link State ID field, the format of Type 3 and 4
summary-LSAs is identical.
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 | 3 or 4 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID | MT-ID metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MT-ID | MT-ID metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
B.4 AS-External-LSAs
AS-external-LSAs are the Type 5 LSAs. These LSAs are originated by
AS boundary routers, and describe destinations external to the AS.
For details concerning the construction of AS-external-LSAs, see
Section 12.4.3 [OSPF].
AS-external-LSAs usually describe a particular external destination.
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
network's "host" bits set; see Appendix E [OSPF] for details).
AS-external-LSAs are also used to describe a default route. Default
routes are used when no specific route exists to the destination.
Psenak, et al. Expires September 27, 2005 [Page 20]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
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.
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 | 5 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| 0 | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Route Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| MT-ID | MT-ID metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Route Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| MT-ID | MT-ID metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Route Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
B.5 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].
Psenak, et al. Expires September 27, 2005 [Page 21]
Internet-Draft Multi-Topology (MT) Routing in OSPF March 2005
Intellectual Property Statement
The IETF takes no position regarding the validity or scope of any
Intellectual Property Rights or other rights that might be claimed to
pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
assurances of licenses to be made available, or the result of an
attempt made to obtain a general license or permission for the use of
such proprietary rights by implementers or users of this
specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Psenak, et al. Expires September 27, 2005 [Page 22]
