wdiff draft-srisuresh-ospf-te-00.txt draft-srisuresh-ospf-te-01.txt

Network Working Group P. Srisuresh
INTERNET-DRAFT P. Joseph Kuokoa Networks
Expires as of December 25, 2001 January 20, 2002 P. Joseph
Jasmine Networks
June,
July, 2001

New

TE LSAs to extend OSPF for Traffic Engineering
<draft-srisuresh-ospf-te-00.txt>
<draft-srisuresh-ospf-te-01.txt>

Status of this Memo

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Abstract

OSPF is a well established link state routing protocol used for
topology discovery and computing forwarding table based on
shortest-Path criteria. Traffic Engineering extensions (OSPF-TE)
will use criteria different from shortest-path so as to route
traffic around congestion paths and meet varying Service Level
agreements. OSPF-TE may also be used by non-IP networks such as
photonic and TDM (SONET/SDH) circuit switch networks for
light-path or TDM circuit setup between two end-points. The
approach outlined in this document differs from that of
[OPQLSA-TE]. The document does not suggest the use of Opaque LSAs
to add TE extensions to OSPF. Rather, new TE LSAs, modeled after
existing LSAs and flooding scope are proposed to overcome the
scaling limitations of the approach outlined in [OPQLSA-TE]. The
document draws a distinction between TE and non-TE topologies and
restricts flooding of TE LSAs into non-TE topology. The document
covers OSPF extensions for packet and non-packet networks alike,
providing a unified extension mechanism for all networks. As such,
this approach improves interoperability between peer network
elements. Lastly, the document specifies a transition path for
vendors currently using opaque LSAs to transition to using new
TE LSAs outlined here.

Table of Contents

1. Introduction ................................................3
2. Traffic Engineering .........................................4
3. Terminology .................................................5
3.1. OSPF-TE router (or) TE-compliant OSPF router ...........5
3.2. Native OSPF router .....................................5
3.3. TE nodes vs. non-TE (native) nodes .....................6
3.4. TE links vs. non-TE (native) links .....................6
3.5. Packet interface vs. non-packet interface ..............6
3.6. TE topology vs. non-TE topology ........................6
3.7. TLV ....................................................7
3.8. Router-TE TLVs .........................................7
3.9. Link-TE TLVs ...........................................7
4. Motivation and Implicit assumptions for the TE extensions ...7
5. The OSPF Options field ......................................9
6. Bringing up TE adjacencies; TE vs. Non-TE topologies .......10
6.1. The Hello Protocol ...................................10
6.2. Flooding and the Synchronization of Databases .........10
6.3. The Designated Router ................................11
6.4. The Backup Designated Router .........................12
6.5. The graph of adjacencies .............................12
7. TE LSAs ....................................................13
7.1. TE-Router LSA .........................................14
7.2. Changes to Network LSA ................................20
7.2.1. Positional-Ring type network LSA ...............20
7.3. TE-Summary LSAs .......................................20
7.3.1. TE-Summary Network LSA (0x83) ..................20
7.3.2. TE-Summary router LSA (0x84) ...................21
7.4. TE-AS-external LSAs (0x85) ............................23
7.5. TE-Circuit-paths LSA (0x8C) ...........................24
7.6. TE-Link-Update LSA (0x8d) .............................25
7.7. TE-Router-Proxy LSA (0x8e) ............................27
8. Link State Databases .......................................28
9. Abstract topology representation with TE support ...........29
10. Changes to Data structures in OSPF-TE routers ..............32
10.1. Changes to Router data structure .....................32
10.2. Two set of Neighbors .................................32
10.3. Changes to Interface data structure ..................32
11. Motivations to this approach ...............................33
11.1. TE flooding isolated to TE-only nodes ................33
11.2. Clean separation between native and TE LSDBs .........34
11.3. Scalability across a hierarchical Area topology ......35
11.4. Usable across packet and non-packet TE networks ......35
11.5. SLA enforceable network modeling .....................36
11.6. Framework for future extensibility ...................36
11.7. Real-world scenarios benefiting from this approach ...37
12. Transition strategy for implementations using Opaque LSAs ..37
13. IANA Considerations ........................................38
13.1. TE-compliant-SPF routers Multicast address allocation 38
13.2. New TE-LSA Types .....................................38
13.3. New TLVs (Router-TE and Link-TE TLVs) ................38
13.3.1. TE-selection-Criteria TLV (Tag ID = 1) .......38
13.3.2. MPLS-Signaling protocol TLV (Tag ID = 3) .....38
13.3.3. Constraint-SPF algorithms-Support TLV (Tag ID=4)
13.3.4. SRLG-TLV (Tag ID = 0x81) .....................38
13.3.5. BW-TLV (Tag ID = 0x82) .......................38
13.3.6. CO-TLV (Tag ID = ox83) .......................38
14. Acknowledgements ...........................................39
15. Security Considerations ....................................39
References .....................................................40

1. Introduction

There is substantial industry experience with deploying OSPF link
state routing protocol. That makes OSPF a good candidate to adapt
for traffic engineering purposes. The dynamic discovery of network
topology, flooding algorithm and the hierarchical organization of
areas can all be used effectively in creating and tearing traffic
links on demand. The intent of the document is to build an abstract
view of the topology in conjunction with the traffic engineering
characteristics of the nodes and links involved.

The connectivity topology may remain relatively stable, except when
the existing links or networking nodes go down or flap or new nodes
and links are added to the network. The objective of traffic
engineering is to set up circuit path(s) across a pair of nodes or
links, as the case may be, so as to forward traffic of a certain
forwarding equivalency class. Circuit emulation in a packet network
is accomplished by each MPLS intermediary node performing label
swapping. Whereas, circuit emulation in a TDM or Fiber cross-connect
network is accomplished by configuring the switch fabric in each
intermediary node to do the appropriate switching (TDM, fiber or
Lamda) for the duration of the circuit.

The objective of this document is not how to set up traffic circuits,
but rather provide the necessary TE parameters for the nodes and
links that constitute the TE topology. Unlike the traditional OSPF,
the TE extended OSPF will be used to build circuit paths, meeting
certain TE criteria. The only requirement is that end-nodes and/or
end-links of a circuit be identifiable with an IP address. For
non-IP networks (such as TDM or photonic cross connect networks),
Mapping IP addresses to a well-known name can be done through a
DNS-like mechanism.

The approach suggested in this document is different from the
Opaque-LSA-based approach outlined in [OPQLSA-TE]. Section 10
compares 11
describes the two approaches motivations behind conceiving this approach and
why the authors claim the benefits of the approach significantly
substantial over the opaque LSA based approach. Section 12
outlines a strategy to transition from Opaque-LSA based deployments
to the new-TE-LSA approach outlined here.

2. Traffic Engineering

A traffic engineered circuit may be identified by the tuple of
(Forwarding Equivalency Class, TE parameters for the circuit,
Origin Node/Link, Destination node/Link).

The forwarding Equivalency class(FEC) may be constituted of a number
of criteria such as (a) Traffic arriving on a specific interface,
(b) Traffic meeting a certain classification criteria (ex: based on
fields in the IP and transport headers), (c) Traffic in a certain
priority class, (d) Traffic arriving on a specific set of TDM (STS)
circuits on an interface, (e) Traffic arriving on a certain
wave-length of an interface, (f) Traffic arriving at a certain time
of day, and so on. A FEC may be constituted as a combination of one
or more of the above criteria. Discerning traffic based on the FEC
criteria is a mandatory requirement on Label Edge Routers (LERs).
Traffic content is transparent to the Intermediate Label Switched
Routers (LSRs), once a circuit is formed. LSRs are simply
responsible for keeping the circuit in-tact for the lifetime of the
circuit(s). As such, this document will not address FEC or the
associated signaling to setup circuits. [MPLS-TE] and [GMPLS-TE]
address the FEC criteria. Whereas, [RSVP-TE] and [CR-LDP] address
different types of signaling protocols.

As for TE parameters for the circuit, this refers to the TE
parameters for all the nodes and links constituting a circuit.
Typically, TE parameters for a node in a TE circuit may include
the following.

* Traffic prioritization ability,
* Ability to provision bandwidth on interfaces,
* Support of CSPF algorithms,
* TE-Circuit switch type,
* Automatic protection switching.

TE parameters for the link include:

* Bandwidth availability,
* reliability of the link,
* color assigned to the link
* cost of bandwidth usage on the link.
* membership to a Shared Risk Link Group and so on.

Only the unicast paths circuit paths are considered here. Multicast
variations are currently considered out of scope for this document.
The requirement is that the originating as well as the terminating
entities of a TE path are identifiable by their IP address.

3. Terminology

Definitions for majority of the terms used in this document with
regard to OSPF protocol may be found in [OSPF-V2]. MPLS and traffic
engineering terms may be found in [MPLS-ARCH]. RSVP-TE and CR-LDP
signaling specific terms may be found in [RSVP-TE] and [CR-LDP]
respectively.

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALLNOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in
this document are to be interpreted as described in RFC 2119.

Below are definitions for the terms used within this document.

3.1. OSPF-TE router node (or) TE-compliant OSPF router node

This is a router that supports the OSPF TE extensions described
in this document. This requires that document and at least one of the links attached to the router links support TE extensions and,
extensions. Further, this requires that at least one of the links
attached to the router links support Packet termination and run the OSPF-TE
protocol.

An OSPF-TE router node supports native OSPF as well as the TE extensions
outlined here.

3.2. Native OSPF router

A native OSPF router is an OSPF router that does not support
the TE extensions described in this document. document or does not have
a TE link attached to it. An autonomous system (AS) could be
constituted of a combination of native OSPF
routers native-OSPF and OSPF-TE routers. nodes.

A native OSPF router, when enhanced to include the extensions
described in this document can become a OSPF-TE router. node.

3.3. TE nodes vs. non-TE (bormal) (native) nodes

A TE-Node is an intermediate or edge node taking part in the
traffic engineered (TE) network. Specifically, a TE circuit
is constituted of a series of TE nodes connected to each other
via the TE links.

A non-TE node or a normal native node is a node that does not have any
TE links attached to it and does not take part in a TE network.
Specifically, native OSPF-nodes OSPF nodes that do not take part in a TE
network fall under this category.

3.4. TE links vs. non-TE (normal) (native) links

A TE Link is a network attachment that supports traffic
engineering. Specifically, a TE circuit can only be setup using
a combination of TE nodes and TE links connected to each other.

Non-TE links link or a normal native link is one that that supports IP packet
communication, but does not support traffic engineering. engineering on the
link. For example, native OSPF protocol and least cost least-cost criteria
may be used to determine reachability of subnets in a network
constituted of normal native OSPF nodes and
normal native OSPF links.

3.5. Packet interface vs. non-packet interface

Interfaces on an OSPF-TE router node may be characterized as those that can
terminate (i.e., send and receive) IP packet data and those that can
do not. Both types of links can be part of a traffic engineered
network. In contrast, a native OSPF router does not support
non-packet interfaces.

Needless to say, the OSPF protocol and its TE extensions can only
be enabled on interfaces supporting IP packet termination. While
the OSPF protocol can be run only on interfaces terminating IP
packets - the protocol can advertise link state information of
non-packet interfaces attached to it - thereby allowing for traffic
engineering over non-packet links. For example - control interfaces
can advertise link state information of the SONET interfaces on a
SONET Add-Drop Multiplexer.

3.6. TE topology vs. non-TE topology
A TE topology is constituted of a set of contiguous TE nodes and
TE links. Associated with each TE node and TE link is a set of TE
criteria that may be supported at any given time. A TE topology
allows circuits to be overlayed statically or dynamically based
on a specific TE criteria.

A non-TE topology specifically refers to the network that does not
support TE. Control protocols such as OSPF may be run on the non-TE
topology. IP forwarding table used to forward IP packets on this
network is built based on the control protocol specific algorithm,
such as OSPF shortest-path criteria.

3.7. TLV

A TLV, strictly stands for an object in the form of Tag-Length-Value.
However, this term is also used in the document, at times, to simply
refer a Traffic Engineering attribute of a TE-node or TE-link.

All TLVs are assumed to be of the following format, unless specified
otherwise. The Tag and length are 16 bits wide each. The length
includes the 4 bytes required for Tag and Length specification.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tag | Length (4 or more) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

3.8. Router-TE TLVs

TLVs used to describe the TE capabilities of a TE-node.

3.9. Link-TE TLVs

TLVs used to describe the TE capabilities of a TE-link.

4. Motivation and Implicit assumptions for the TE extensions

The motivation behind the OSPF-TE described in this document is to
dynamically discover the TE-network topology, devise a scalable
flooding methodology and benefit from the hierarchical area
organization and other techniques of the native OSPF. The result
would be the ability to build an abstract view of a network
topology with all the traffic engineering characteristics.

With traditional OSPF, the goal is to build a forwarding table to
reach various subnets in the IP network with least-cost as the
basis. However, the goal of OSPF-TE is to determine a circuit path
(that can be pinned-down for a desired duration) meeting a certain
set of traffic engineering criteria. Further, the circuit path
could consist entirely of nodes and links that do not carry IP
traffic.

The following assumptions are made throughout the document for
the discussion of OSPF-TE.

1. Interfaces on an OSPF-TE router node may be characterized as those
that can terminate (i.e., send and receive) IP packet data and
those that wont. Both types of links can be part of a traffic
engineered network. Needless to say, the OSPF-TE protocol can
only be enabled on interfaces that support IP packet data
termination. And, As such, the control network over which TE LSAs
are exchanged may be exchanged over constituted of a combination of non-TE links.
links and TE links that also permit non-TE packet traffic.

2. Unlike traditional OSPF, OSPF-TE protocol must be capable of
advertising link state of interfaces that are not capable of
handling packet data. As such, the OSPF-TE protocol cannot be
required to synchronize its link-state database with neighbors
across all its links. It is sufficient to synchronize
link-state database in an area, across a subset of the links -
say, the packet terminating interfaces. Yet, the TE LSDB
(LSA database) should be synchronized across all OSPF-TE nodes
within an area.

All interfaces or links described by the TE LSAs will be
present in the TE topology database (a.k.a. TE LSDB).

3. An OSPF-TE router node with links in an OSPF area will need to
establish router adjacency with at least one other OSPF-TE neighboring router
OSPF-TE node in order for the router's database to be
synchronized with other routers in the area. Failing this, the
OSPF router will not be in the TE calculations of other TE
routers in the area. Refer [OSPF-FL1] for flooding
optimizations.

However, two routers that are physically connected to the same
link (or broadcast network) neednt be router adjacent via the
Hello protocol, if the link is not packet terminated.

4. Each IP subnet on a TE-configurable network MUST have a minimum
of one node with an interface running OSPF-TE protocol. This is
despite the fact that all nodes on the subnet may take part in
Traffic Engineering. (Example: SONET/SDH TDM ring with a single
Gateway Network Element, a.k.a. GNE running the OSPF protocol,
yet all other nodes in the ring are also full members of a TE
circuit).

An OSPF-TE node may advertise more than itself and the links
it is directly attached to. It may also advertise other TE
participants and their links, on their behalf.

5. As a general rule, all nodes and links that may be party
to a TE circuit should be uniquely identifiable by an IP
address. As for router ID, a separate loopback IP address
for the router, independent of the links attached, is
recommended.

6. This document does not require any changes to the existing OSPF
LSDB implementation. Rather, it suggests the use of another
database, the TE-LSDB, comprised of the TE LSAs, for TE
purposes. TE nodes may have 2 types of link state databases -
a normal native OSPF LSDB and a TE-LSDB. A normal native OSPF LSDB,
constituted of non-TE native links and nodes attached to these links(i.e., links
(i.e., non-TE as well as TE nodes), will use shortest-path
criteria to forward IP packets over normal non-TE native links. The TE-LSDB,
constituted only of TE nodes and TE links, may be used to setup
TE circuit paths along the TE topology.

5. The OSPF Options field

A new TE flag is introduced to identify TE extensions to the OSPF.
With this, the OSPF v2 will have no more reserved bits left for
future option extensions. This bit will be used to distinguish
between routers that support Traffic engineering extensions and
those that do not.

The OSPF options field is present in OSPF Hello packets, Database
Description packets and all link state advertisements. See
[OSPF-V2], [OSPF-NSSA] and [OPAQUE] for a description of the
bits in options field. Only the TE-Bit is described in this
section.

--------------------------------------
|TE | O | DC | EA | N/P | MC | E | * |
--------------------------------------
The OSPF options field - TE support

TE-Bit: This bit is set to indicate support for Traffic Engineering
extensions to the OSPF. The Hello protocol which is used for
establishing router adjacency and bidirectionality of the
link will use the TE-bit to build adjacencies between two
nodes that are either both TE-compliant or not. Two routers
will not become TE-neighbors unless they agree on the state
of the TE-bit. TE-compliant OSPF extensions are advertised
only to the TE-compliant routers. All other routers may
simply ignore the advertisements.

6. Bringing up TE adjacencies; TE vs. Non-TE topologies

OSPF creates adjacencies between neighboring routers for the purpose
of exchanging routing information. In the following subsections, we
describe the use of Hello protocol to establish TE capability
compliance between neighboring routers of an area. Further, the
capability is used as the basis to build a TE vs. non-TE network
topology.

6.1. The Hello Protocol

The Hello Protocol is primarily responsible for dynamically
establishing and maintaining neighbor adjacencies. In a TE network,
it may not be required or possible for all links and neighbors to
establish adjacency using this protocol.

The Hello protocol will use the TE-bit to establish Traffic
Engineering capability (or not) between two OSPF routers.

For NBMA and broadcast networks, this protocol is responsible for
electing the designated router and the backup designated router.
For a TDM ring network, the designated and backup designated
routers may either be preselected (ex: GNE, backup-GNE) or
determined via the same Hello protocol. In any case, routers
supporting the TE option shall be given a higher precedence
for becoming a designated router over those that donot support TE.

6.2. Flooding and the Synchronization of Databases

In OSPF, adjacent routers within an area must synchronize their
databases. However, as observed in [OSPF-FL1], the requirement
may be stated more concisely that all routers in an area must
converge on the same link state database. To do that, it suffices
to send single copies of LSAs to the neighboring routers in an
area, rather than send one copy on each of the connected
interfaces. [OSPF-FL1] describes in detail how to minimize
flooding (Initial LSDB synchronization as well as the
asynchronous LSA updates) within an area.

With the OSPF-TE described here, a TE-only network topology is
constructed based on the TE option flag in the Hello packet.
Subsequent to that, TE LSA flooding in an area is limited to
TE-only routers in the area, and do not impact non-TE routers
in the area. A network may be constituted of a combination of
a TE topology and a non-TE (control) topology. Standard IP
packet forwarding and routing protocols are possible along the
control topology.

In the case where some of the neighbors are TE compliant and
others are not, the designated router will exchange different
sets of LSAs with its neighbors. TE LSAs are exchanged only
with the TE neighbors. Normal Native LSAs do not include description
for TE links. As such, normal native LSAs are exchanged with all
neighbors (TE and non-TE alike) over a shared non-TE link.

Flooding optimization in a TE network is essential
for two reasons. First, the control traffic for a TE network is
likely to be much higher than that of a non-TE network. Flooding
optimizations help to minimize the announcements and the
associated retransmissions and acknowledgements on the network.
Secondly, the TE nodes need to converge at the earliest to keep
up with TE state changes occuring occurring throughout the TE network.

This process of flooding along a TE topology cannot be folded
into the Opaque-LSA based TE scheme ([OPQLSA-TE]), because
Opaque LSAs (say, LSA #10) have a pre-determined flooding
scope. Even as a TE topology is available from the use of
TE option flag, the TE topology is not usable for flooding
unless a new TE LSA is devised, whose boundaries can be set to
span the TE-only routers in an area.

NOTE, a new All-SPF-TE Multicast address may be used for the
exchange of TE compliant database descriptors.

6.3. The Designated Router

The Designated Router is elected by the Hello Protocol on broadcast
and NBMA networks. In general, when a router's interface to a
network first becomes functional, it checks to see whether there is
currently a Designated Router for the network. If there is, it
accepts that Designated Router, regardless of its Router Priority,
so long as the current designated router is TE compliant. Otherwise,
the router itself becomes Designated Router if it has the highest
Router Priority on the network and is TE compliant.

Clearly, TE-compliance must be implemented on the most robust
routers only, as they become most likely candidates to take on
additional role as designated router.

Alternatively, there can be two sets of designated routers, one for
the TE compliant routers and another for the native OSPF routers
(non-TE compliant).

6.4. The Backup Designated Router

The Backup Designated Router is also elected by the Hello
Protocol. Each Hello Packet has a field that specifies the
Backup Designated Router for the network. Once again, TE-compliance
must be weighed in conjunction with router priority in determining
the backup designated router. Alternatively, there can be two sets
of backup designated routers, one for the TE compliant routers and
another for the native OSPF routers (non-TE compliant).

6.5. The graph of adjacencies

An adjacency is bound to the network that the two routers have
in common. If two routers have multiple networks in common,
they may have multiple adjacencies between them. The adjacency
may be split into two different types - Adjacency between
TE-compliant routers and adjacency between non-TE compliant
routers. A router may choose to support one or both types of
adjacency.

Two graphs are possible, depending on whether a Designated
Router is elected for the network. On physical point-to-point
networks, Point-to-MultiPoint networks and virtual links,
neighboring routers become adjacent whenever they can
communicate directly. The adjacency can only be one of
(a) TE-compliant or (b) non-TE compliant. In contrast, on
broadcast and NBMA networks the Designated Router and the
Backup Designated Router may maintain two sets of adjacency.
However, the remaining routers will participate in either
TE-compliant adjacency or non-TE-compliant adjacency, but not
both. In the Broadcast network below, you will notice that
routers RT7 and RT3 are chosen as the designated and backup
routers respectively. Within the network, Routers RT3, RT4
and RT7 are TE-compliant. RT5 and RT6 are not. So, you will
notice the adjacency variation with RT4 vs. RT5 or RT6.

+---+ +---+
|RT1|------------|RT2| o---------------o
+---+ N1 +---+ RT1 RT2

RT7
o::::::::::
+---+ +---+ +---+ /|: :
|RT7| |RT3| |RT4| / | : :
+---+ +---+ +---+ / | : :
| | | / | : :
+-----------------------+ RT5o RT6o oRT4 :
| | N2 * * ; :
+---+ +---+ * * ; :
|RT5| |RT6| * * ; :
+---+ +---+ **; :
o::::::::::
RT3

Figure 6: The graph of adjacencies with TE-compliant routers.

7. New TE LSAs

The native OSPF protocol protocol, as of now, has a total of 11 LSA types. Definitions
for
LSA types 1 through 5 may be found in [OSPF-v2]. LSA type 6 is are defined in [MOSPF]. [OSPF-v2]. LSA type types 6, 7 definition may be found in [NSSA].
LSA type
and 8 may be found are defined in [BGP-OSPF]. [MOSPF], [NSSA] and [BGP-OSPF] respectively.
Lastly, LSA types 9 through 11 are defined in [OPAQUE].

Each of the LSA types defined are different in content and have a unique flooding
scope. For instance, scope defined.
Opaque LSA types 9 through 11 are general purpose LSAs, with
flooding scope set to link-local, area-local and AS-wide (except into
stub areas) respectively. As will become apparent soon, from this
document, the boundaries for general purpose content format and the coarse
flooding scope of Opaque LSAs are not appropriate suitable for flooding disseminating
TE data.

In the following subsections, we define new LSAs for Traffic
engineering use. The Values for the new TE LSAs are largely modeled after the
existing LSAs for content format and flooding scope. The LSA types are assigned
such that the high bit of the LS-type octet is set to 1. Standard link-state database The new
TE LSAs are largely modeled after the existing LSAs for content
format and have a custom suited flooding mechanisms (with scope. Flooding
optimizations discussed in previous sections) are sections shall be used for
distribution of to
disseminate TE LSAs along the TE-restricted topology.

A TE-router LSA is defined to advertise TE characteristics
of the router and all the TE-links attached to the TE-router.
TE-Link-Update LSA is defined to advertise individual link
specific TE updates. Flooding scope for both these LSAs is the
TE topology within the area to which the links belong. I.e.,
only those OSPF nodes within the area with TE links will receive
these TE LSAs.

TE-Summary network and router LSAs are defined to advertise
the reachability of area-specific TE networks and Area border
routers(along with router TE characteristics) to external
areas. Flooding Scope of the TE-Summary LSAs is the TE topology
in the entire AS less the non-backbone area for which the
the advertising router is an ABR. Just as with native OSPF
summary LSAs, the TE-summary LSAs do not reveal the topological
details of an area to external areas. But, the two summary LSAs
do differ in some respects. The flooding scope of TE summary
LSAs is also defined different. As for each content, TE summary network LSAs
simply describe reachability without summarization of network
access costs. And, unlike the newly native summary router LSA,
TE-summary router LSA content includes TE capabilities of the
advertising TE router.

TE-AS-external LSA and TE-Circuit-Path LSA are defined to
advertise AS external network reachability and pre-engineered
TE
LSAs. circuits respectively. While flooding scope for both
these LSAs can be the TE-topology in the entire AS, flooding
scope for the pre-engineered TE circuit LSA may optionally be
restricted to just the TE topology within an area.

Lastly, the new TE LSAs are defined so as to permit peer
operation of packet networks and non-packet networks alike.
As such, a new TE-Router-Proxy LSA is defined to allow
advertisement of a TE router, that is not OSPF capable, by
an OSPF-TE node as a proxy.

7.1. TE-Router LSA

Router LSAs are Type 1 LSAs. The TE-router LSA is modeled after the
router LSA with the same flooding scope as the router-LSA, except
that the scope is further restricted to TE-only nodes within the
area. A value of 0x81 is assigned to TE-router LSA. The TE-router
LSA describes the router-TE metrics as well as the link-TE metrics
of the TE links attached to the router. Below is the format of the
TE-router LSA. Unless specified explicitly otherwise, the fields
carry the same meaning as they do in a router LSA. Only the
differences are explained below.

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 | 0x81 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |V|E|B| 0 | Router-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-TE flags (contd.) | Router-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .... | # of TE links |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | 0 | Link-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE flags (contd.) | Zero or more Link-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |

Option
In TE-capable router nodes, the TE-compliance bit is set to 1.

Router-TE flags field (TE capabilities of the router node)

Below is an initial set of definitions. More may be standardized
if necessary. The TLVs are not expanded in the current rev. Will
be done in the follow-on revs. The field imposes a restriction
of no more than 32 flags to describe the TE capabilities of a
router-TE.

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|L|L|P|T|L|F| |S|S|S|C|
|S|E|S|D|S|S| |T|E|I|S|
|R|R|C|M|C|C| |A|L|G|P|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|<---- Boolean TE flags ------->|<- TE flags pointing to TLVs ->|

Bit LSR
When set, the router is considered to have LSR capability.

Bit LER
When set, the router is considered to have LER capability.
All MPLS border routers will be required to have the LER
capability. When the E bit is also set, that indicates an
AS Boundary router with LER capability. When the B bit is
also set, that indicates an area border router with LER
capability.

Bit PSC
Indicates the node is Packet Switch Capable.

Bit TDM
Indicates the node is TDM circuit switch capable.

Bit LSC
Indicates the node is Lamda switch Capable.

Bit FSC
Indicates the node is Fibre Fiber (can also be a non-fibre non-fiber link
type) switch capable.

Bit STA
Label Stack Depth limit TLV follows. This is applicable only
when the PSC flag is set.

Bit SEL
TE Selection Criteria TLV, supported by the router, follows.

Bit SIG
MPLS Signaling protocol support TLV follows.

BIT CSPF
CSPF algorithm support TLV follows.

Router-TE TLVs
The following Router-TE TLVs are defined.

TE-selection-Criteria TLV (Tag ID = 1)

The values can be a series of resources that may be used
as the criteria for traffic engineering (typically with the
aid of a signaling protocol such as RSVP-TE or CR-LDP or LDP).

- Bandwidth based LSPs (1)
- Priority based LSPs (2)
- Backup LSP (3)
- Link cost (4)

Bandwidth criteria is often used in conjunction with Packet
Switch Capable nodes. The unit of bandwidth permitted to be
configured may however vary from vendor to vendor. Bandwidth
criteria may also be used in conjunction with TDM nodes. Once
again, the granularity of bandwidth allocation may vary from
vendor to vendor.

Priority based traffic switching is relevant only to Packet
Switch Capable nodes. Nodes supporting this criteria will
be able to interpret the EXP bits on the MPLS header to
prioritize the traffic across the same LSP.

Backup criteria refers to whether or not the node is capable
of finding automatic protection path in the case the
originally selected link fails. Such a local recovery is
specific to the node and may not need to be notified to the
upstream node.

MPLS-Signaling protocol TLV (Tag ID = 3)
The value can be 2 bytes long, listing a combination of
RSVP-TE, CR-LDP and LDP.

Constraint-SPF algorithms-Support TLV (Tag ID = 4)
List all the CSPF algorithms supported. Support for CSPF
algorithms on a node is an indication that the node may be
requested for all or partial circuit path selection during
circuit setup time. This can be beneficial in knowing
whether or not the node is capable of expanding loose
routes (in an MPLS signaling request) into an LSP. Further,
the CSPF algorithm support on an intermediate node can be
beneficial when the node terminates one or more of the
hierarchical LSP tunnels.

Label Stack Depth TLV (Tag ID = 5)
Applicable only for PSC-Type traffic. A default value of 1
is assumed. This indicates the depth of label stack the
node is capable of processing on an ingress interface.

The following fields are used to describe each router link (i.e.,
interface). Each router link is typed (see the below Type field).
The Type field indicates the kind of link being described.

Type
A new link type "Positional-Ring Type" (value 5) is defined.
This is essentially a connection to a TDM-Ring. TDM ring network
is different from LAN/NBMA transit network in that, nodes on the
TDM ring donot necessarily have a terminating path between
themselves. Secondly, the order of links is important in
determining the circuit path. Third, the protection switching
and the number of fibers from a node going into a ring are
determined by the ring characteristics. I.e., 2-fibre 2-fiber vs
4-fibre
4-fiber ring and UPSR vs BLSR protected ring.

Type Description
__________________________________________________
1 Point-to-point connection to another router
2 Connection to a transit network
3 Connection to a stub network
4 Virtual link
5 Positional-Ring Type.

Link ID
Identifies the object that this router link connects to.
Value depends on the link's Type. For a positional-ring type,
the Link ID shall be IP Network/Subnet number, just as with a
broadcast transit network. The following table summarizes the
updated Link ID values.

Type Link ID
______________________________________
1 Neighboring router's Router ID
2 IP address of Designated Router
3 IP network/subnet number
4 Neighboring router's Router ID
5 IP network/subnet number

Link Data
This depends on the link's Type field. For type-5 links, this
specifies the router interface's IP address.

Link-TE options (TE capabilities of a link)

+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|T|N|P|T|L|F|D| |S|L|B|C|
|E|T|K|D|S|S|B| |R|U|W|O|
| |E|T|M|C|C|S| |L|G|A|L|
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|<---- Boolean TE flags ------->|<- TE flags pointing to TLVs ->|

TE - Indicates whether TE is permitted on the link. A link
can be denied for TE use by setting the flag to 0.

NTE - Indicates whether non-TE traffic is permitted on the
TE link. This flag is relevant only when the TE
flag is set.

PKT - Indicates whether or not the link is capable of
packet termination.

TDM, LSC, FSC bits
- Same as defined for router TE options.

DBS - Indicates whether or not Database synchronization
is permitted on this link.

SRLG Bit - Shared Risk Link Group TLV follows.

LUG bit - Link usage cost metric TLV follows.

BWA bit - Data Link bandwidth TLV follows.

COL bit - Data link Color TLV follows.

Link-TE TLVs

SRLG-TLV
This describes the list of Shared Risk Link Groups the link
belongs to. Use 2 bytes to list each SRLG.

BWA-TLV
This indicates the maximum bandwidth, available bandwidth,
reserved bandwidth for later use etc. This TLV may also
describe the Data link Layer protocols supported and the
Data link MTU size.

LUG-TLV
This indicates the link usage cost - Bandwidth unit, Unit
usage cost, LSP setup cost, minimum and maximum durations
permitted for setting up the TLV etc., including any time
of day constraints.

COLOR-TLV
This is similar to the SRLG TLV, in that an autonomous
system may choose to issue colors to link based on a
certain criteria. This TLV can be used to specify the
color assigned to the link within the scope of the AS.

7.2. Changes to Network LSAs

Network-LSAs are LSA

Network-LSA is the Type 2 LSAs. LSA. With the exception of the following,
no additional changes will be required to this LSA for TE
compatibility. The LSA format and flooding scope remains unchanged.

A network-LSA is originated for each broadcast, NBMA and
Positional-Ring type network in the area which supports two or
more routers. The TE option is also required to be set while
propagating the TDM network LSA.

7.2.1. Positional-Ring type network LSA - New Network type for TDM-ring.
- Ring ID: (Network Address/Mask)
- No. of elements in the ring (a.k.a. ring neighbors)
- Ring Bandwidth
- Ring Protection (UPSR/BLSR)
- ID of individual nodes (Interface IP address)
- Ring type (2-Fibre (2-Fiber vs. 4-Fibre, 4-Fiber, SONET vs. SDH)

Network LSA will be required for SONET RING. Unlike the broadcast
type, the sequence in which the NEs are placed on a RING-network
is pertinent. The nodes in the ting must be described clock wise,
assuming the GNE as the starting element.

7.3. TE-Summary LSAs

TE-Summary-LSAs are the Type 0x83 and 0x84 LSAs. These LSAs are
originated by area border routers. TE-Summary-network-LSA (0x83)
describes the reachability of TE networks in a non-backbone
area, advertised by the Area Border Router. Type 0x84
summary-LSA describes the reachability of Area Border Routers
and AS border routers and their TE capabilities.

One of the benefits of having multiple areas within an AS is
that frequent TE advertisements within the area donot impact
outside the area. Only the TE abstractions as befitting the
external areas are advertised.

7.3.1. TE-Summary Network LSA (0x83)

TE-summary network LSA may be used to advertise reachability of
TE-networks accessible to areas external to the originating
area. The scope of flooding is AS wide, with the exception of
the originating area and the stub areas. For example, the
TE-summary network LSA advertised by the border router of a
non-backbone area is readvertised to all other areas, not just
the backbone area. The area border router for each
non-backbone area is responsible for advertising the
reachability of backbone networks into the area.

The flooding scope of TE-summary network LSA is unlike that
of the summary network LSA (type 0x03), which simply uses this
as an inter-area exchange of network accessibility and limits
the flooding scope to just the backbone area.

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 | 0x83 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID (IP Network Number) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router (Area Border Router) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

7.3.2. TE-Summary router LSA (0x84)

TE-summary router LSA may be used to advertise the availability of
Area Border Routers (ABRs) and AS Border Routers (ASBRs) that are
TE capable. The TE-summary router LSAs are originated by the Area
Border Routers. The scope of flooding for the TE-summary router LSA
is the entire AS, with the exception of the non-backbone areas the
advertising ABRs belong to.

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 | 0x84 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router (ABR) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |E|B| 0 | No. of Areas |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Area-ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| .... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Link State ID
The ID of the Area border router or the AS border router whose
TE capability is being advertised.

Advertising Router
The ABR that advertises its TE capabilities (and the OSPF areas
it belongs to) or the TE capabilities of an ASBR within one of
the areas the ABR is a border router of.

No. of Areas
Specifies the number of OSPF areas the link state ID belongs to.

Area-ID
Specifies the OSPF area(s) the link state ID belongs to. When
the link state ID is same as the advertising router ID, this
lists all the areas the ABR belongs to. In the case the
link state ID is an ASBR, this simply lists the area the
ASBR belongs to. The advertising router is assumed to be the
ABR from the same area the ASBR is located in.

Summary-router-TE flags

Bit E - When set, the advertised Link-State ID is an AS boundary
router (E is for external). The advertising router and
the Link State ID belong to the same area.

Bit B - When set, the advertised Link state ID is an Area

border router (B is for Border)

Router-TE flags,
Router-TE TLVs (TE capabilities of the link-state-ID router)

TE Flags and TE TLVs are as applicable to the ABR/ASBR
specified in the link state ID. The semantics is same as
specified in the Router-TE LSA.

7.4. TE-AS-external LSAs (0x85)

TE-AS-external-LSAs are the Type 0x85 LSAs. This is modeled after
AS-external LSA format and flooding scope. These LSAs are originated
by AS boundary routers with TE extensions (say, a BGP node which can
communicate MPLS labels across to external ASes), and describe
networks and pre-engineered TE links external to the AS. The
flooding scope of this LSA is similar to that of an AS-external LSA.
I.e., AS wide, with the exception of stub areas.

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 | 0x85 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Mask |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Forwarding address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Route Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # of Virtual TE links | 0 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE-Forwarding address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| External Route TE Tag |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |

Network Mask
The IP address mask for the advertised TE destination. For
example, this can be used to specify access to a specific
TE-node or TE-link with an mask of 0xffffffff. This can also
be used to specify access to an aggregated set of destinations
using a different mask, ex: 0xff000000.

Link-TE flags,
Link-TE TLVs
The TE attributes of this route. These fields are optional and
are provided only when one or more pre-engineered circuits can
be specified with the advertisement. Without these fields,
the LSA will simply state TE reachability info.

Forwarding address
Data traffic for the advertised destination will be forwarded to
this address. If the Forwarding address is set to 0.0.0.0, data
traffic will be forwarded instead to the LSA's originator (i.e.,
the responsible AS boundary router).

External Route Tag
A 32-bit field attached to each external route. This is not
used by the OSPF protocol itself. It may be used to communicate
information between AS boundary routers; the precise nature of
such information is outside the scope of this specification.

7.5. TE-Circuit-paths LSA (0x8C)

TE-Circuit-paths LSA may be used to advertise the availability of
pre-engineered TE circuit path(s) originating from any router in
the network. The flooding scope may be Area wide or AS wide.

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 | 0x84 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 |S|E|B| 0 | # of TE circuit paths |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE-Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE-Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | 0 | Link-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE flags (contd.) | Zero or more Link-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE-Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TE-Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |

Link State ID
The ID of the router to which the TE circuit path(s) is being
advertised.

TE-circuit-path(s) flags

Bit S - When set, the flooding scope is set to be AS wide.
Otherwise, the flooding scope is set to be area wide.

Bit E - When set, the advertised Link-State ID is an AS boundary
router (E is for external). The advertising router and
the Link State ID belong to the same area.

Bit B - When set, the advertised Link state ID is an Area border
router (B is for Border)

No. of Virtual TE Links
This indicates the number of pre-engineered TE links between the
advertising router and the router specified in the link state ID.

TE-Link ID
This is the ID by which to identify the virtual link on the
advertising router. This can be any private interface index or
handle that the advertising router uses to identify the
pre-engineered TE virtual link to the ABR/ASBR.

TE-Link Data
This specifies the IP address of the physical interface
on the advertising router.

7.6. TE-Link-Update LSA (0x8d)

A significant difference between a non-TE OSPF network and a TE OSPF
network is that the latter is subject to dynamic circuit pinning and
is more likely to undergo state updates. Specifically, some links
might undergo more changes and more frequently than others.
Advertising the entire TE-router LSA in response to a change in any
single link could be repetitive. Flooding the network with TE-router
LSAs at the aggregated speed of all the dynamic changes is simply
not desirable. Hence, the new TE-link-update LSA, that advertises
link specific updates alone.

The TE-link-Update LSA will be advertised as frequently as the link
state is changed. The TE-link sequence is largely the advertisement
of a sub-portion of router LSA. The sequence number on this will be
incremented with the TE-router LSA's sequence as the basis. When an
updated TE-router LSA is advertised within 30 minutes of the
previous advertisement, the updated TE-router LSA will assume a
sequence no. that is larger than the most frequently updated of
its links.

Below is the format of the TE-link update LSA.

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 | 0x8d |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID (same as Link ID) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | 0 | Link-TE options |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE options | Zero or more Link-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| # TOS | metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TOS | 0 | TOS metric |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Link State ID
This would be exactly the same as would have been specified as
as Link ID for a link within the router-LSA.

Link Data
This specifies the router ID the link belongs to. In majority of
cases, this would be same as the advertising router.

The tuple of (LS Type, LSA ID, Advertising router) uniquely identify
the LSA and replace LSAs of the same tuple with an older sequence
number. However, there is an exception to this rule in the context
of TE-link-update LSA. TE-Link update LSA will initially assume the
sequence number of the TE-router LSA it belongs to. Further,
when a new TE-router LSA update with a larger sequence number is
advertised, the newer sequence number is assumed by al the link
LSAs.

7.7. TE-Router-Proxy LSA (0x8e)

This is a variation to the TE-router LSA in that the TE-router LSA
is not advertised by the network element, but rather by a trusted
TE-router Proxy. This is typically the scenario in a non-packet
TE network, where some of the nodes donot have OSPF functionality
and count on a helper node to do the advertisement for them. One
such example would be the SONET/SDH ADM nodes in a TDM ring. The
nodes may principally depend upon the GNE (Gateway Network Element)
to do the advertisement for them. TE-router-Proxy LSA shall not be
used to advertise Area Border Routers and/or AS border Routers.

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 | 0x8e |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link State ID (Router ID of the TE Network Element) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Advertising Router |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS sequence number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LS checksum | length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0 | Router-TE flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Router-TE flags (contd.) | Router-TE TLVs |
+---------------------------------------------------------------+
| .... |
+---------------------------------------------------------------+
| .... | # of TE links |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | 0 | Link-TE options |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link-TE flags | Zero or more Link-TE TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Link Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |

8. Link State Databases

With the new TE-LSA scheme, an OSPF-TE node will have two types
of Link state databases (LSDB). A native LSDB that describes the
control (non-TE) topology and a TE-LSDB that describes the TE
topology. Shortest-Path-First algorithm will be used to forward
IP packets along the native control network. OSPF neighbors data
structure will be used for flooding along the control topology.

The TE-LSDB is constituted only of TE nodes and TE links. A variety
of CSPF algorithms may be used to dynamically setup TE circuit
paths along the TE network. A new TE-neighbors data structure will
be used to flood TE LSAs along the TE-only topology. Clearly, the
the TE nodes will need the control (non-TE) network for OSPF
communication. The control network may also be used for pinging
OSPF-TE nodes and performing any debug and monitoring tasks on
the nodes. However, the ability to make distinction between
TE and non-TE topologies, allows the bandwidth on TE links to be
strictly SLA enforceable, even as a TE link is packet-capable.
The actual characteristics of the TE-link are irrelevant from the
OPSF-TE perspective. As such, that allows for packet and non-packet
networks to operate in peer mode.

Consider the following network where some of the routers and links
are TE enabled and others are native OSPF routers and links. All
nodes in the network belong to the same OSPF area.

+---+
| |--------------------------------------+
|RT6|\\ |
+---+ \\ |
|| \\ |
|| \\ |
|| \\ |
|| +---+ |
|| | |----------------+ |
|| |RT1|\\ | |
|| +---+ \\ | |
|| //| \\ | |
|| // | \\ | |
|| // | \\ | |
+---+ // | \\ +---+ |
|RT2|// | \\|RT3|------+
| |----------|----------------| |
+---+ | +---+
| |
| |
| |
+---+ +---+
|RT5|--------------|RT4|
+---+ +---+
Legend:
-- Native(non-TE) network link
| Native(non-TE) network link
\\ TE network link
|| TE network link

Figure 6: A (TE + native) OSPF network topology

In the above network, TE and native OSPF Link State Data bases
(LSDB) would have been synchronized within the area along the
following nodes.

Native OSPF LSDB nodes TE-LSDB nodes
---------------------- -------------
RT1, RT2, RT3. RT4, RT5, RT6 RT1, RT2, RT3, RT6

Nodes such as RT1 will have two LSDBs, a native LSDB and a TE-LSDB
to reach native and TE networks. The TE LSA updates will not impact
non-TE nodes RT4 and RT5.

9. Abstract topology representation with TE support

Below, we assume a TE network that is composed of three OSPF areas,
namely Area-1, Area-2 and Area-3, attached together through the
backbone area. The following figure is an inter-area topology
abstraction from the perspective of routers in Area-1. The
abstraction is similar, but not the same, as that of the non-TE
abstraction. As such, the authors claim the model is easy to
understand and emulate. The abstraction illustrates reachability
of TE networks and nodes in areas external to the local area and
ASes external to the local AS. The abstraction also illustrates
pre-engineered TE links that may be advertised by ABRs and ASBRs.

Area-1 an has a single border router, ABR-A1 and no ASBRs. Area-2
has an Area border router ABR-A2 and an AS border router ASBR-S1.
Area-3 has two Area border routers ABR-A2 and ABR-A3; and an AS
border router ASBR-S2. There may be any number of Pre-engineered
TE links amongst ABRs and ASBRs. The following example assumes a
single TE-link between ABR-A1 and ABR-A2; between ABR-A1 and
ABR-A3; between ABR-A2 to ASBR-S1; and between ABR-A3 to ASBR-S2.
All Area border routers and AS border routers are assumed to
be represented by their TE capabilities.

+-------+
|Area-1 |
+-------+
+-------------+ |
|Reachable TE | +------+
|networks in |--------|ABR-A1|
|backbone area| +------+
+-------------+ | | |
+-------------+ | +-------------------+
| | |
+-----------------+ | +-----------------+
|Pre-engineered TE| +----------+ |Pre-engineered TE|
|circuit path(s) | | Backbone | |circuit path(s) |
|to ABR-A2 | | Area | |to ABR-A3 |
+-----------------+ +----------+ +-----------------+
| | | |
+----------+ | | |
| | +--------------+ |
+-----------+ | | | | +-----------+
|Reachable | +------------+ +------+ |Reachable |
|TE networks|---| ABR-A2 | |ABR-A3|--|TE networks|
|in Area A2 | +------------+ +------+ |in Area A3 |
+-----------+ / | | | | | +-----------+
/ | | +-------------------+ | +----------+
/ | +-------------+ | | |
+-----------+ +--------------+ | | | +--------------+
|Reachable | |Pre-engineered| | | | |Pre-engineered|
|TE networks| |TE Ckt path(s)| +------+ +------+ |TE Ckt path(s)|
|in Area A3 | |to ASBR-S1 | |Area-2| |Area-3| |to ASBR-S2 |
+-----------+ +--------------+ +------+ +------+ +--------------+
| / | /
+-------------+ | / | /
|AS external | +---------+ +-------------+
|TE-network |------| ASBR-S1 | | ASBR-S2 |
|reachability | +---------+ +-------------+
|from ASBR-S1 | | | |
+-------------+ | | |
+-----------------+ +-------------+ +-----------------+
|Pre-engineered TE| |AS External | |Pre-engineered TE|
|circuit path(s) | |TE-Network | |circuit path(s) |
|reachable from | |reachability | |reachable from |
|ASBR-S1 | |from ASBR-S2 | |ASBR-S2 |
+-----------------+ +-------------+ +-----------------+

Figure 8: 9: Inter-Area Abstraction as viewed by Area-1 TE-routers

10. Changes to Data structures in OSPF-TE routers

9.1. nodes

10.1. Changes to Router data structure

The router with TE extensions must be able to include all the
TE capabilities (as specified in section 7.1) in the router data
structure. Further, routers providing proxy service to other TE
routers must also track the router and associated interface data
structures for all the TE client nodes for which the proxy
service is being provided. Presumably, the interaction between
the Proxy server and the proxy clients is out-of-band.

9.2.

10.2. Two set of Neighbors

Two sets of neighbor data structures will need to be maintained.
TE-neighbors set is used to advertise TE LSAs. Only the
TE-routers TE-nodes
will be members of the TE-neighbor set.
Normal Native neighbors set will
be used to advertise native LSAs. All neighboring nodes supporting
non-TE links canbe can be part of this set. As for flooding optimizations
based on neighbors set, readers may refer [OSPF-FL1].

9.3.

10.3. Changes to Interface data structure

The following new fields are introduced to the interface data
structure. These changes are in addition to the changes specified
in [OSPF-FL1].

TePermitted
If the value of the flag is TRUE, the interface is permissible
to be advertised as a TE-enabled interface.

NonTePermitted
If the value of the flag is TRUE, the interface permits non-TE
traffic on the interface. Specifically, this is applicable to
packet networks, where data links may permit both TE and non-TE
packets. For FSC and LSC TE networks, this flag will be set to
FALSE. For Packet networks that donot permit non-TE traffic on
TE links alos, also, this flag is set to TRUE.

PktTerminated
If the value of the flag is TRUE, the interface terminates
Packet data and hence may be used for IP and OSPF data exchange.

AdjacencySychRequired
If the value of the flag is TRUE, the interface may be used to
synchronize the LSDB across all adjacent neighbors. This is
TRUE by default to all PktTerminated interfaces that are
enabled for OSPF. However, it is possible to set this to FALSE
for some of the interfaces.

TE-TLVs
Each interface may potentially have a maximum of 16 TLVS that
describe the link characteristics.

The following existing fields in Interface data structure will take
on additional values to support TE extensions.

Type
The OSPF interface type can also be of type "Positional-RING".
The Positional-ring type is different from other types (such
as broadcast and NBMA) in that the exact location of the nodes
on the ring is relevant, even as they are all on the same
ring. SONET ADM ring is a good example of this. Complete ring
positional-ring description may be provided by the GNE on a
ring as a TE-network LSA for the ring.

List of Neighbors
The list may be statically defined for an interface, without
requiring the use of Hello protocol.

10. Comparison between Opaque-LSAs & the new TE-LSAs

The following subsections attempt

11. Motivations to identify the various issues
such this approach

Use of TE LSAs bring substantial benefits over using Opaque LSAs
as flooding scope and described below. These benefits cannot be retrofitted into
Opaque LSAs due to fundamental scalability that are fundamentally
lacking in limitations of the Opage-LSA based
Opaque-LSA approach. Section 10.2 goes on to
describe a transition strategy to eventually transition completely
to

The primary motivation behind the new TE-LSA scheme.

Once the OSPF-TE model is completely transitioned to the scheme
described in this document, that the
approach is clean (clean separation of LSDB between TE vs non-TE
networks), scalable (across more than one OSPF area), unified
(for packet and non-packet networks
can be combined alike), efficient (efficient
flooding algorithm) and issued addresses across the unified network.
As such, the traffic engineering can be based on the overlayed or
the peer SLA enforceable. The model espoused in [GMPLS-TE].

10.1. proposed also
provides the right framework for future enhancements.

11.1. TE flooding load on a non-TE network

In a non-TE network, when a link is flapping, that can cause
considerable hardship on all routers in the area. The hardship is
not so much because of the LSAs that are generated, but because
that causes the OSPF routing table isolated to be recalculated. TE-only nodes

A TE network can also have generate a large number of LSA updates due
to the many state changes the TE links undergo dynamically. These
LSA For
example, bandwidth assignment on a TE link for a specific circuit
path setup will mandate that the change in bandwidth availability
be communicated network wide. While such frequent link state
updates are is reasonable for an OSPF-TE node, neither infrequent the frequency
nor undesirable as with link
flaps.

Now, consider the case content of TE link state is desirable for native OSPF
nodes. This can be a considerable interruption to non-TE nodes in
a network that is constituted of multiple types of nodes and links
(ex: A network constituted of packet routing nodes/links and SONET
network ADMs/links, A packet-network where Opaque the ratio of TE nodes
to non-TE nodes is quite considerable).

The wider the flooding scope (and number of TE nodes), the larger
the number of retransmissions and acknowledgements. The same
information (needed or not) may reach a router through multiple
links. Even if the router did not forward the information past the
node, it would still have to send acknowledgements across all the
multiple links on which the LSAs are used for tried to converge. By restricting
the flooding of TE
extensions. LSAs to TE-only nodes within a TE topology, we
obviate any TE based processing for non-TE nodes.

The flooding topology for opaque LSAs makes no distinction between
TE nodes and non-TE native OSPF nodes. In a network where the TE and non-TE native
nodes coexist, a non-TE native OSPF router would be bombarded with Opaque opaque
LSAs.

These It is possible for the native OSPF nodes to silently ignore
the unsupported Opaque LSAs carry TE metric state changes, which the non-TE
router does (during network migration) or add
knobs within implementation to decide whether or not care about. If the router simply dropped the a certain
opaque
LSAs and didnt recompute the dijkstra, that might be OK. LSA mandates dijkstra SPF recomputation. But, it
may the latter
can be that some routers tricky and will recompute routes (because they process
some need non-trivial amounts of the Opaque LSAs that say that a particular link is no longer
available for non-TE use). LSA
processing to make the determination. In the latter case, case where routers
donot validate the need to recompute, routers might
choose to simply recompute end up
recomputing for all new Opaque LSA advertisements. Clearly, that
would be a considerable computational demand and can be cause for
instability on non-TE routers, triggered by the frequent
opaque LSA advertisements.

Secondly, If OSPF routers.

11.2. Clean separation between native and TE LSDBs

Most vendors wishing to support MPLS based TE in their network
tend to migrate gradually to support the TE extensions. Perhaps,
add new TE links or convert existing links into TE links within
an area first and non-TE topologies are not separated (as is
the case with Opaque-LSAs), progressively advance to offer in the non-TE router could be utilizing entire
AS. As such, the TE link as its least cost link, thereby stressing network cannot be assumed to exist
independently without native OSPF network even in the long term.

Not all routers will support TE link and
effectively rendering extensions at the TE link ineffective for TE purposes.
Separating same time
during the two topologies (as advocated by this document with
new migration process. Use of TE specific LSAs and their
flooding to OSPF-TE only nodes will allow the vendor to
introduce MPLS TE option flag) ensure that without destabilizing the SLA objectives on existing network.
As such, the native OSPF-LSDB will remain undisturbed while
newer TE links are properly met.

Thirdly, added to network.

With the wider new TE-LSA scheme, native OSPF nodes will keep just the
native OSPF link state database. The OSPF-TE nodes will keep
native as well as the TE LSDB. The native LSDB describes the
control (non-TE) topology. Shortest-Path-First algorithm will be
used to forward IP packets along this network. OSPF neighbors
data structure will be used for flooding scope, along the larger control
topology.

In the number Opaque-LSA-based TE scheme, the TE-LSDB built using opaque
LSAs will be required to refer the native LSDB to build the TE
topology. Even with that, there is way to know the TE capabilities
of
retransmissions and acknowledgements. the routers. The same information or
sometimes unneeded information may reach Opaque-LSA approach does not deal with TE
capabilities for a router through multiple
links. Even if the router didnt forward router. Opaque LSAs are flooded to all nodes.
Some nodes that happen to support the information past TE extensions will have a
hit and accept the
time, it would still opaque LSAs. Others that donot support will
have to send acknowledgements across all a miss and simply drop the
multiple links received Opaque LSAs. This type of
hit-and-miss approach is not only disruptive, but also blind to
SLA requirements on which the TE links.

11.3. Scalability across a hierarchical Area topology

Use of TE LSAs tried for inter-area communication is clearly superior
to converge. By moving using Opaque LSAs with AS wide scoping. Without revealing
the
concept TE nodes and characteristics of flooding from "per interface" to "per neighbor", we
minimize the flooding, without compromising on attached links, an Opaque
LSA (type 11) simply does not disseminate reachability of TE
networks and nodes outside the untimate goal area. Stated differently,
Use of LSDB convergence opaque LSA can, work at best, for TE a single area AS.

Providing area level abstraction and non-TE networks.

Lastly, separating having this abstraction be
distinct for TE and non-TE native topologies is beneficial a necessity in inter-area
communication. When the topologies are separate, the area border
routers can advertise different summary LSAs for TE and
non-TE routers. Opaque LSAs are not adequate to establish
TE peering relationship with the neighbors. For example, a non-TE native Area Border router (ABR) could
simply announce announces the non-TE-network shortest path network summary LSAs (LSA
type 3) for non-TE networks nodes outside the area. A TE ABR, on the other hand,
could use TE-summary network LSA to advertise
just the TE-network summary LSAs (0x83). network Reachability
information - not aggregated path metric as required for a native
OSPF LSDB. Clearly, the advertised data is different. The boundary of TE-network summary LSA content and flooding
is also different. scope should be
different for the TE nodes. The flooding boundary for TE-summary
LSAs would be (AS - OriginatingArea - StubAreas - NSSAs). Clearly, the
Opaque-LSA flooding boundary will not permit this type of flooding
granularity. Without an AS-wide flooding (with the exception of stub
areas), it is impossible to know which outside-are networks are
TE-configurable and which

Opaque-LSAs are not.

In summary, lack of flexible suitable neither for content nor for flooding topology can be an operational
and functional nightmare. Folks will be forced to an unscalable,
single-area topology to get around the shortcoming of the opaque
LSAs.

10.2. Scaling concerns What is lacking scope
in Opaque-LSA-based TE scheme?

The Opaque LSA based mechanism has the following fundamental scaling
problems. These cannot be fixed by mere extensions to the same
approach. We suggest below a transition strategy to migrate to the
scheme proposed in this document.

1. context of inter-area communication. The flooding boundaries
of Opaque LSAs make the OSPF-TE approach suitable at best to single-area
topologies. Extending TE beyond one area
can cause a lot of flooding problems. e.g.: For example, Opaque LSAs cannot support the flooding
scope of TE-summary-networks. Opaque LSAs (AS-wide scope) will be
unable to restrict flooding in its own originating area.

2.
Opaque LSAs are also not adequate to establish TE peering
relationship with neighbors.

11.4. Usable across packet and non-packet TE networks

In a peer networking TE model, you are likely to want different
types of TE information flooded by various nodes, as they are
heterogenous and will remain that way. The TE LSA based approach
offers a single set of LSAs that may uniformly be used across
packet and non-packet nodes and links. Once a link is declared
as TE, the TE properties advertised of the link can be link
specific, but all advertisements would use the same LSA format.

Implementations reusing the opaque LSA with GMPLS extensions
are burden for the routers that do not need it. Clear
separation (as proposed here) between TE and native LSAs
and having independent flooding scopes for native and TE state
information will be extremely useful in inheriting the right
set of LSAs for the right application (i.e, TE vs native).

11.5. SLA enforceable network modeling

When TE and native topologies are not separated (as is the case
with Opaque-LSAs), a native OSPF node could be utilizing a TE
link as its least cost link, thereby stressing the TE link and
effectively rendering the TE link ineffective for TE purposes.
Separating the two topologies (as advocated by this document with
new TE LSAs and TE option flag) ensure that the SLA objectives on
TE links are properly met.

11.6. Framework for future extensibility

The approach outlined provides a framework for future
extensibility based on service provider needs.

There may be many types of information that should not be
disseminated along the Opaque LSA flooding boundaries. Take for
example, the TE-summary network LSA. This LSA does not follow
the scope of an area or an AS, but something in between. As a
general rule, the proposed framework can be extended to define
newer TE LSAs with a suitable flooding scope.

Having a clean framework which argues for having different
link state databases for different applications on the same network
will provide the right forum for future extensibility. Just as
the TE LSDB may be used for MPLS TE application, a different type
of LSDB may be used for yet another type of application (such as
QOS based IP forwarding) using the same IP network.

lastly, an opaque LSA is also restricted in the way format in which it can
express different types of data. Everything should be expressible
in
in the form of a TLV. Summary-TE-networks-from each-Area, each Area, TE-ABR
routers, TE-ASBR routers, TE-AS-External-networks,
TE-Router-Capabilities, TE-link-updates, TE-Router
Capabilities, TE-link updates, Pre-engineered-TE-Links - All of
these data have to be engineered to be expressible in a TLV form
with one or more sub-TLVs. Some of the TLVs will be required to
be mandatory. Some would be expected to appear in a pre-specified
order and some are expected to appear just once in the LSA.
TLVs should not be a panacea for all kinds of TE data. TLVs are
generally more difficult to process and debug than fixed format
messages.

Opaque LSAs demand more processing to assimilate into topology
abstraction. A single Opaque LSA type is bent in many
ways (using a variety of TLVs) to update the native OSPF topology
abstraction nodes.

One way to transition from the current Opaque-LSA-based TE scheme to
the new-TE scheme could be as follows.

1. Use the existing Opaque-LSA-based-TE scheme for single area
topologies. You will still need to find Not a way framework that a non-TE
router doesnt cannibalize a TE-link for SPF forwarding.

2. Fold in the TE option flag to construct the TE and non-TE
topologies in an area, even if the topologies cannot be used
for flooding within the area.

3. Do away with Opaque LSAs for inter-area communication. Make use
of the TE-topology within area to summarize the TE networks in
the area and advertise the same to all TE-routers in the backbone.
The TE-ABRs on the backbone area will in-turn advertise these
summaries again within their connected areas. Use new LS types
for summary LSAs, AS-external-LSAs and so forth, as specified
in this document.

4. Replace the use of Opaque LSAs with the TE LSAs within the area
as well.

10.3. Link State Database.

With the new TE-LSA scheme, a TE node will have two types of
Link state databases. The normal LSDB describes the control
(non-TE) topology. Shortest-Path-First algorithm will be used to
forward IP packets along this network. OSPF neighbors data
structure will be used for flooding along the control topology.

The TE node will have a separate TE-LSDB that describes the TE
topology, constituted only of TE nodes and TE links. A variety of
CSPF algorithms may be used to dynamically setup TE circuit paths
along this TE network. TE-neighbors data structure is used for
flooding TE LSAs alongs the TE-only topology. Having a clear
distinction between the two LSDBs (and hence topologies) makes
this approach more desirable to service providers desiring to
offer strictly enforceable SLAs (Service Level Agreements)
along their TE topology.

Whereas, in the Opaque-LSA-based TE scheme, the TE-LSDB built
using opaque LSAs will could be required to refer the normal LSDB to
build the TE topology. Even with that, there is way to know the
TE capabilities of the routers. The Opaque-LSA approach does
not deal with TE capabilities easily extended
for a router. Opaque LSAs
are flooded to all nodes. Some nodes that happen to support
the TE extensions will have a hit and accept the opaque LSAs.
Others that donot support will have a miss and simply drop the
received Opaque LSAs. This type of hit-and-miss approach is
not only disruptive, but also blind to the SLA requirements
on TE links.

10.4. future applications.

11.7. Real-world scenarios better served by the new-TE-LSAs scheme. benefiting from this approach

Many real-world scenarios are better served by the new-TE-LSAs
scheme. Here are a few examples.

1. Multi-area network.

2. Single-Area networks - The TE links are not cannibalized by the
non-TE routers for SPF forwarding.

3. Credible SLA enforcement in a (TE + non-TE) packet network.
Ability to restrict flooding to some links (say, non-TE links)
ensures the service provider is able to devote the entire
bandwidth of a TE-link for TE circuit purposes. This makes SLA
enforcement credible.

4. For a non-Packet TE network, the Opaque-LSA-based-TE scheme is
not adequate to represent
(a) "Positional-Ring" type network LSA and
(b) Router Proxying - allowing a router to advertise on behalf
of other nodes (that are not Packet/OSPF capable).

11.

12. Transition strategy for implementations using Opaque LSAs

Below is a strategy to transition current implementations to
adapt the new TE LSA scheme in a gradual fashion. Implementations
using Opaque-LSAs can take the following steps to accomplish this.
Once the OSPF-TE is completely transitioned to using the new TE
LSAs as described here, the TE network can reap the full benefits
of the scheme. Amongst other things, packet and non-packet networks
may be combined with ease into a unified network. As such, the MPLS
traffic engineering can be based on either of the overlayed or peer
models espoused in [GMPLS-TE].

1. Restrict the use of Opaque-LSAs for within an area.

2. Fold in the TE option flag to construct the TE and non-TE
topologies in an area, even if the topologies cannot be used
for flooding within the area.

3. Use TE-Summary LSAs and AS-external-LSAs for inter-area
Communication. Make use of the TE-topology within area to
summarize the TE networks in the area and advertise the same
to all TE-routers in the backbone. The TE-ABRs on the backbone
area will in-turn advertise these summaries again within their
connected areas.

4. Replace Opaque LSAs with TE LSAs within the area as well.

13. IANA Considerations

11.1. All-TE-compliant-SPF

13.1. TE-compliant-SPF routers Multicast address allocation

11.2.

13.2. New TE-LSA Types

11.3.

13.3. New TLVs (Router-TE and Link-TE TLVs)

11.3.1.

13.3.1. TE-selection-Criteria TLV (Tag ID = 1)
- Bandwidth based LSPs (1)
- Priority based LSPs (2)
- Backup LSP (3)
- Link cost (4)

11.3.2.

13.3.2. MPLS-Signaling protocol TLV (Tag ID = 3)
- RSVP-TE signaling
- LDP signaling
- CR-LDP signaling

11.3.3.

13.3.3. Constraint-SPF algorithms-Support TLV (Tag ID = 4)
- CSPF Algorithm Codes.

11.3.4.

13.3.4. SRLG-TLV (Tag ID = 0x81)
- SRLG group IDs

11.3.5.

13.3.5. BW-TLV (Tag ID = 0x82)

11.3.6

13.3.6 CO-TLV (Tag ID = ox83)

12.
14. Acknowledgements

The authors wish to thank Vishwas manral, Riyad Hartani and Tricci
So for their valuable comments and feedback on the draft.

15. Security Considerations

This memo does not create any new security issues for the OSPF
protocol. Security considerations for the base OSPF protocol are
covered in [OSPF-v2]. As a general rule, a TE network is likely
to generate significantly more control traffic than a native
OSPF network. The excess traffic is almost directly proportional
to the rate at which TE circuits are setup and torn down within
an autonomous system. It is important to ensure that TE database
sychronizations happen quickly when compared to the aggregate
circuit setup an tear-down rates.

REFERENCES

[IETF-STD] Bradner, S., " The Internet Standards Process --
Revision 3", RFC 1602, IETF, October 1996.

[RFC 1700] J. Reynolds and J. Postel, "Assigned Numbers",
RFC 1700

[MPLS-TE] Awduche, D., et al, "Requirements for Traffic
Engineering Over MPLS," RFC 2702, September 1999.

[GMPLS-TE] P.A. Smith et. al, "Generalized MPLS - Signaling
Functional Description",
draft-ietf-mpls-generalized-signaling-03.txt, work
in progress.

[RSVP-TE] Awduche, D.O., L. Berger, Der-Hwa Gan, T. Li,
V. Srinivasan and G. Swallow, "RSVP-TE: Extensions
to RSVP for LSP Tunnels", Work in progress,
draft-ietf-mpls-rsvp-lsp-tunnel-08.txt

[CR-LDP] Jamoussi, B. et. al, "Constraint-Based LSP Setup
using LDP", draft-ietf-mpls-cr-ldp-05.txt,
Work in Progress.

[OSPF-v2] Moy, J., "OSPF Version 2", RFC 2328, April 1998.

[MOSPF] Moy, J., "Multicast Extensions to OSPF", RFC 1584,
March 1994.

[NSSA] Coltun, R., V. Fuller and P. Murphy, "The OSPF NSSA
Option", draft-ietf-ospf-nssa-update-10.txt, Work in
Progress.

[OPAQUE] Coltun, R., "The OSPF Opaque LSA Option," RFC 2370,
July 1998.

[OSPF-FL1] Zinin, A. and M. Shand, "Flooding Optimizations in
link-state routing protocols", work in progress,
<draft-ietf-ospf-isis-flood-opt-01.txt>

[OSPF-FL2] Moy, J., "Flooding over a subset topology",
<draft-ietf-ospf-subset-flood-00.txt>, work in progress.

[OPQLSA-TE] Katz, D., D. Yeung and K. Kompella, "Traffic
Engineering Extensions to OSPF", work in progress,
<draft-katz-yeung-ospf-traffic-05.txt>
Authors' Addresses

Pyda Srisuresh
Jasmine Networks
3061 Zanker Road,
Kuokoa Networks, Inc.
2901 Tasman Dr., Suite B
San Jose, 202
Santa Clara, CA 95134 95054
U.S.A.
EMail: srisuresh@yahoo.com

Paul Joseph
Jasmine Networks
3061 Zanker Road, Suite B
San Jose, CA 95134
U.S.A.
EMail: pjoseph@jasminenetworks.com