dharanikota-interarea-mpls-te-ext-01.txt

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draft-dharanikota-interarea-mpls-te-ext

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draft-dharanikota-interarea-mpls-te-ext-01.txt April 2001

MPLS Working group S. Dharanikota
Internet Traffic Engineering Working Group Nayna Networks
Internet Draft
Document: S. Venkatachalam
Alcatel USA

Category: Expiration

OSPF, IS-IS, RSVP, CR-LDP extensions to support
inter-area traffic engineering using MPLS TE

Status of this Memo

This document is an Internet-Draft and is in full conformance with all
provisions of Section 10 of RFC2026 except that the right to produce
derivative works is not granted.

This document is an Internet-Draft and is NOT offered in accordance
with Section 10 of RFC2026, and the author does not provide the IETF
with any rights other than to publish as an Internet-Draft

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.

1. Abstract

In this draft, we propose the extensions required to the routing
protocols, signaling protocols, and the MIB to support the idea of
inter-area LSPs. A companion document [INTER_AREA_REQ] provides the
architectural requirements for such a concept. This document also
provides the signaling extensions to support the crankback as defined
in the architecture document [INTER_AREA-REQ].

2. Notation and Conventions used in this document

ABR Area Border Router
ASBR Autonomous System Border Router
CR-LDP Constraint Based Routing LDP
CSPF Constraint-based Shortest Path First
ER Explicit Route
ERO Explicit Route Object
IACO Inter Area Criteria Object
IACUO Inter Area Criteria Used Object
IGP Interior Gateway Protocol
ISIS Intermediate System to Intermediate System
ISP Internet Service Provider
LDP Label Distribution Protocol
LER Label Edge Router
LSA Link State Attribute
LSR Label Switch Router
LSP Label Switched Path
MIB Management Information Base
MPLS Multi Protocol Label Switching
OSPF Open Shortest Path First
PDU Protocol Data Unit
PLRO Primary LSP Route Object
PRO Path Route Object
PV Path Vector
RSVP Resource Reservation Protocol
TBD To Be Defined
TE Traffic Engineering
TLV Type Length Value
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].

3. Introduction

Current work in the MPLS traffic engineering group (such as
[TE_FRAMEWORK], [QOS_CONST]) focuses only on the intra-area LSP setup
issues. In this work we propose an architecture to extend the traffic
engineering capability across IGP areas and recommend relevant
modifications to the routing protocols, the signaling protocols and
the MIBs.

The ISP’s networks are divided into Autonomous Systems (ASs), where
each AS is divided into Interior Gateway Protocol (IGP) areas to allow
the hiding and aggregating of routing information. Although this
concept of hierarchical routing by an IGP makes sense from the routing
perspective, it is a bottleneck for traffic engineering - as it hides
the path taken by a packet to destinations in the other routing areas.
Hence, from the Traffic Engineering (TE) perspective, requirements
such as path selection and crankback need different architectural
additions to the existing IGPs and signaling protocols for inter-area
Label Switched Path (LSP) setup.

Traffic engineering practice currently involves the setup and use of
LSPs as dedicated bandwidth pipes between two end points. LSPs can be
setup across several routers, either through the use of manually
specified routes, or routes that are computed. The routes can be
computed offline through the use of a dedicated tool, or through the
use of online constraint based routing using an IGP [IGP_REQ,
RSVP_EXT].

The offline tool will be centralized, and has the advantage of being
able to consider the traffic pattern history over a large period of
time, and hence will be efficient in optimizing the resources over
time, not just the particular instant when the request is received.
The offline traffic engineering tool, if also used for LSP setup in
addition to routing, may be able to optimize the resources across
LSPs. This would include mechanisms to tear down LSP segments and
reroute them when better resources become available or new requests
arrive.

The online constraint based routing model [IGP_REQ] requires (1) a
constraint based routing process implemented on certain Label Switched
Routers (LSRs) that serve as Label Edge Routers (LERs) to the LSPs,
and (2) a set of mechanisms to flood out and maintain the TE
characteristics of the topology.

From [TOOL_VS_RP] discussion, it is clear that traffic engineering can
be implemented with the help of tools and routing protocol extensions,
as initiated by [IGP_REQ]. Although there has been some work in the
area of realizing some of the issues such as TE crankback [CRANKBACK]
and DiffServ realizations [QOS_CONST], [QOS_TE_EXT], no work has been
performed that directly related to the inter-area extensions and a
framework for such in the TE working group.

In our solution, we propose to send across IGP areas, the summary
routes containing criteria-based route attributes, which will be used
at the Autonomous System Border Routers (ASBRs) in their TE path
computation. Since an off-line TE tool cannot compute the complete
explicit path from ASBR to ASBR unless it knows the complete routing
table of the AS, we expect to have loose path specification, which can
be translated into explicit path in-steps at the intermediate Area
Border Routers (ABRs). The solutions we are providing in this draft
are applicable to the destination networks inside the AS or outside
the AS. For the sake of simplicity we consider the customer networks
inside an autonomous system.

The companion document [INTER_AREA_REQ] presents the architectural
requirements for such a solution. In this document, the extensions to
provide such a solution of criteria-based inter-area routing are
separated into routing protocol extensions, signaling protocol
extensions and configuration extensions. In section 4, we present the
OSPF and IS-IS extensions. The signaling extensions for RSVP and CR-
LDP are presented in section 5. The configuration extensions for such
architectural changes are presented in section 6. Security
considerations, references and acknowledgements follow in sections 7,
8, and 9 respectively.

4. Routing protocol extensions

4.1 Intra-area requirements

OSPF or ISIS implementation SHOULD support the [INTRA_TE],
[ISIS_INTRA_TE] extensions to advertise and distribute the TE
information of the interfaces of the area. In addition, [QOS_TE_EXT]
may be supported to flood the bandwidth per class type of each
interface.

[INTRA_TE], [ISIS_INTRA_TE] defines the following TE attributes:

- Traffic engineering metric
- Maximum bandwidth
- Maximum reservable bandwidth
- Unreserved bandwidth
- Resource class/color

[QOS_TE_EXT] defines the unreserved bandwidth for different class
types.

Not all of the TE attributes specified in [INTRA_TE], [ISIS_INTRA_TE]
and [QOS_TE_EXT] need to be supported - in fact a subset may be chosen
that reflects the traffic engineering condition of the network and
does not impose a burden on the storage and flooding of the TE
information.

Specific to OSPF:

When a request for the setup of a constraint based LSP within the area
is received, a CSPF computation will be performed on the TE resources
of the area (as specified by the intra-area TE-LSAs) to determine the
best path that satisfies the constraints. The constraints on the LSP
can be one or more of the TE attributes flooded by OSPF in the intra-
area TE LSA.

Specific to ISIS:

When a request for the setup of a constraint based LSP within the area
is received, a CSPF computation will be performed on the TE resources
of the area (as specified by the intra-area TE-LSAs) to determine the
best path that satisfies the constraints of the LSP. The constraints
on the LSP can be one or more of the TE attributes flooded by ISIS in
the L1 extended IS reachability TE sub-TLVs.

4.2 Inter-area requirements

The route computation process uses the inter-area TE summary
information.

- to determine if a path to the inter-area destination that
satisfies the constraints does exist, and
- to determine the ABR to reach the next area.

TE attribute summarization is similar to the route summarization that
is already a part of OSPF or ISIS. The TE attributes can be summarized
through the use of a dijkstra based algorithm as described in section
. The value of the TE summary attribute to a destination advertised by
an ABR represents the TE resources of the best path available from the
ABR to that destination based on that TE attribute alone.

A separate route calculation is necessary to determine the summary
value for each TE attribute that needs to be summarized. Since these
route calculations are based on the intra-area TE attribute values,
the set of TE attributes to be summarized should be a subset of the
set of TE attributes supported inside the areas.

In the general case of TE attribute summarization, any number of TE
attributes such as bandwidth, delay to a destination can be
summarized. However, since a large number of TE attributes to be
summarized will result in an increase in processing required, the
number of TE attributes to be summarized should be kept small.

Specific to OSPF:

The summarized TE attributes will be distributed inside the areas by
the use of a new link state message (called TE summary LSA) as defined
in [INTER_TE_OSPF]. The definitions for the various TE attributes in
the TE summary LSA are also described in [INTER_TE_OSPF]. In addition
to those TE attributes, the following three TLVs are proposed to be
added in the TE summary LSA.

Specific to ISIS:

The summarized TE attributes will be distributed inside the areas by
extending the IP reachability TLV in the L1 and L2 link state PDU to
include TE sub-TLVs as described below.

4.3 Requirements for OSPF

4.3.1 Unreserved Bandwidth for CT1 to CT3

The unreserved bandwidth for class-types 1, 2 and 3 [QOS_CONST] to the
destination are each individually described in a TLV. The units is
bytes/second and the representation is IEEE floating point. The TLV
types are 7, 8, and 9, respectively and the length is 32 octets each.

4.4. Requirements for ISIS

4.4.1 Traffic Engineering Extensions to the IP Reachability TLV

This draft extends the IP Reachability TLV in the L1 and L2 link state
PDUs to allow the representation of TE information in the form of TE
sub-TLVs. Each TE sub-TLV in the IP Reachability TLV carries the type
and value of a traffic engineering attribute to the remote
destination.

An L2 link state PDU containing the IP reachability TLV with the TE
extensions will be originated by an L1/L2 router and flooded
throughout the L2 domain. This PDU will contain IP reachability TLV
with the TE sub-TLVs for each reachable address in the connected
areas. The value for each TE attribute will have been computed through
the use of a dijkstra based algorithm as detailed in the next section.
(This is the 'up' part of the redistribution as detailed in
[ISIS_TE]).

An L1 link state PDU containing the IP reachability TLV with the TE
extensions will be originated by an L1/L2 router and flooded
throughout its connected areas. This PDU will contain IP reachability
TLV with the TE sub-TLVs for each reachable address in a remote area.
(This is the 'down' part of the redistribution as detailed in
[ISIS_TE]).

4.4.2 Format of the IP reachability TLV with TE Sub-TLVs

The extended IP reachability TLV as described in [ISIS_TE] with TYPE =
135 is further extended with the addition of the TE sub-TLVs
describing the traffic engineering attributes to the destination
network.

Hence the IP reachability TLV has a structure as described in
[ISIS_TE], followed by zero or more TE sub-TLVs, each of which is of
the form:

4.4.3 The Traffic Engineering Sub-TLVs

The following traffic engineering attributes are defined:

Sub-TLV type Length (octets) Name
3 4 Resource Class/Color
9 4 Maximum Bandwidth
10 4 Reservable Bandwidth
11 32 Unreserved Bandwidth
18 3 TE Default Metric
TBD 4 Delay
TBD 32 Unreserved Bandwidth for CT1
TBD 32 Unreserved Bandwidth for CT2
TBD 32 Unreserved Bandwidth for CT3

Most of these traffic engineering attributes have sizes and types the
same as in [ISIS_TE]. Note that new traffic engineering attributes and
sub-TLVs to represent them may be defined in the future. The TE
attributes are described below.

4.4.3.1 Resource Class/Color

The resource class or color of the destination network is a
combination of the colors for the various paths to the network. The
sub-TLV type of the resource class/color attribute is 3, and the
length is 4 octets.

4.4.3.2 Maximum Bandwidth

The maximum bandwidth to the destination is described in bytes/second
as an IEEE floating point number. The sub-TLV type is 9, and the
length is 4 octets.

4.4.3.3 Reservable Bandwidth

The reservable bandwidth to the destination is described in
bytes/second as an IEEE floating point number. The sub-TLV type is 10,
and the length is 4 octets.

4.4.3.4 Unreserved Bandwidth

The unreserved bandwidth to the destination is described in
bytes/second as an IEEE floating point number. The sub-TLV type is 11,
and the length is 4 octets.

4.4.3.5 Traffic Engineering Metric

The traffic engineering metric represents the traffic engineering cost
of reaching the destination network from the advertising L2 router.
The sub-TLV type is 18, and the length of this attribute is 3 octets.

4.4.3.6 Delay

The delay attribute is the delay cost to reach the destination network
in milliseconds, represented as an unsigned (4-byte) long integer. The
TLV-type is TBD, and the length is 4 octets.

4.4.3.7 Unreserved Bandwidth for CT1 to CT3

The unreserved bandwidth for class-types 1, 2 and 3 [QOS_CONST] to the
destination are each individually described in a sub-TLV. The units is
bytes/second and the representation is IEEE floating point. The sub-
TLV types are TBD, and the length is 4 octets.

4.5 Summarization of Traffic Engineering Attributes

The traffic engineering metric is an additive metric similar to the
OSPF/ISIS metrics, but need not be the same. The traffic engineering
and metric advertised by the router for the given summary destination
will have been computed in a manner similar to the dijkstra
computation for the OSPF/ISIS metric.

The delay is an additive metric. The value of the delay attribute for
a summary destination will have been determined through a dijkstra
computation based on the delay.

The maximum bandwidth to the summary destination is the largest of all
path-capacities, each associated with a possible path to the
destination. The path-capacity is the smallest link capacity of all
the links in the path. Hence, the maximum bandwidth is the maximum
amount of traffic that can be sent to that destination, when there is
no other traffic on the links.

The unreserved bandwidth to the summary destination is the largest of
all path-unreserved bandwidths, each associated with a possible path
to the destination. The path-unreserved bandwidth is the smallest
unreserved bandwidth of all the links in the path. Hence, the
unreserved bandwidth is the maximum amount of traffic that can
currently be sent to that destination, the other traffic on the links
being steady. The unreserved bandwidth for Class-Types 1, 2, and 3
[QOS_CONST] will be computed similarly.

The value of the color attribute to the summary destination is some
combination of the path-colors, each associated with a possible path
to the destination. The path-color is a combination of the colors of
the links in the path. This combination can be a "logical and" of the
colors, or a concatenation.

5. Signaling Extensions

The signaling protocol requirements for the setup of the inter-area
LSP are (as mentioned in [INTE_AREA_REQ]):

1. Signaling SHOULD be extended to carry the criteria based
elements, such as: Primary criteria (Attribute 1, …, Attribute N);
Secondary criteria (Attribute 1, …, Attribute N).
2. Signaling SHOULD trigger IGP computation for the explicit route
in an area at the transit ABRs. If the path, which satisfies the primary
criteria, is not available then it should trigger for the IGP computation
of the path for the secondary criteria.
3. It MAY inform the initiating node about the change the criteria
for the path set up in the intermediate path. This deliberate
notification can also be derived when the actual setup is completed.
4. The intermediate ABRs SHOULD know the difference between the
primary and the backup LSPs. This enables the signaling component to
distinguish between the paths taken by the primary LSP during the
computation of the backup LSP.
5. The same mechanisms used for the primary LSP setup SHOULD be used
for the backup LSP setup also.
6. Crankback in an area SHOULD always be performed from the starting
ABR of that LSP section. If the path is not available send the
information one area back and try to perform the computation.

5.1 RSVP extensions

In this section we describe extensions to RSVP for the support of
Inter-Area LSP setup as described in [INTER_AREA_REQ]. These
extensions are in addition to the extensions to RSVP as defined in
[RSVP_EXT] and includes attributes from [QOS_TE_EXT] [TE_FRAMEWORK] as
sub-objects.

Three new objects are introduced as follows:

- <INTER AREA CRITERIA> object (from now on is also abbreviated as
IACO) introduced to carry the primary and the secondary criteria in the
PATH message.
- <INTER AREA CRITERIA USED> object (from now on is also
abbreviated as IACUO) is introduced in the RESV message to capture the
route taken by the primary or the secondary PATH message.
- <PRIMARY LSP ROUTE> object (from now on abbreviated as PLRO) to
carry the path followed by the primary LSP in the PATH message.

In the following sections we also demonstrate different uses of ERO
(EXPLICIT ROUTE OBJECT) and RRO (RECORD ROUTE OBJECT) from the
[RSVP_EXT] draft. Note that constraint-related objects such as
<CLASSTYPE> as mentioned in [QOS_TE_EXT] can be sub-objects in the
IACO. The following table illustrates the objects discussed that are
relevant for this draft.

Object type Message Importance
--------------------------------------------------------------------
<INTER AREA CRITERIA> Path Mandatory
<INTER AREA CRITERIA USED> Resv Mandatory
<PRIAMRY LSP ROUTE> Path Mandatory
<DIFFSERV><CLASSTYPE> Path Optional
<TE CONSTRAINTS> Path Optional
<EXPLICIT ROUTE> Path Optional
<RECORD ROUTE> Path, Resv Optional but recommended

5.1.1 PATH and RESV message format changes

The format of the Path message is changed as follows:

<Path Message> ::=

<Common Header> [<INTEGRITY>]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[<EXPLICIT_ROUTE>]
<LABEL_REQUEST>
[<SESSION_ATTRIBUTE>]
[<INTER AREA CRITERIA>] (For Primary Criteria)
[<DIFFSERV>][<CLASSTYPE>]
[<TE CONSTRAINTS>]
[<INTER AREA CRITERIA>] (For Secondary Criteria)
[<DIFFSERV>][<CLASSTYPE>]
[<TE CONSTRAINTS>]
[<PRIMARY LSP ROUTE>]
[<POLICY_DATA> ... ]
[<sender descriptor>]

<sender descriptor> ::= <SENDER_TEMPLATE> [<SENDER_TSPEC>]
[<ADSPEC>]
[<RECORD_ROUTE>]

The format of the Resv message is changed as follows:

<Resv Message> ::=

<Common Header> [ <INTEGRITY> ]
<SESSION> <RSVP_HOP>
<TIME_VALUES>
[<RESV_CONFIRM>] [<SCOPE>]
[<POLICY_DATA>...]
<STYLE> <flow descriptor list>
[<RECORD ROUTE>]
[<INTER AREA CRITERIA USED>]

5.1.2 Handling of the new objects

The following are the message formats for the new objects that are
introduced in this document.

INTER AREA CRITERIA Object (IACO):

C-Number:
To be defined by IANA
C-Type:
0 for the Primary Criteria
1 for the Secondary Criteria
Attribute:
Constraints from the traffic engineering related drafts.

INTER AREA CRITERIA USED Object (IACUO):

C-Number:
To be defined by IANA
C-Type:
0 for the Primary Criteria
1 for the Secondary Criteria
2 for none

PRIMARY LSP ROUTE Object (PLRO):

+-------------------------------------------------------------------+
| Length = N*4 or 16 | C-Number = TBD | C-Type = 0 for IPV4 |
| | (8 bits) | (8 bits)1 for IPV6 |
| | | 2 for unavailable|
+-------------------------------------------------------------------+
| IP Address 1 (V4 or V6) |
+-------------------------------------------------------------------+
| ……… |
+-------------------------------------------------------------------+
| IP Address N (V4 or V6) |
+-------------------------------------------------------------------+

C-Number:
To be defined by IANA
C-Type:
0 for the IPV4 address
1 for the IPV6 address
2 for the unavailability of the objects.

The IACO can be used very effectively in conjunction with the ERO and
RRO objects. It is possible that the ERO and RRO options are enabled
to specify a preferred path and to know the path taken by the LSP
respectively.

The following list of cases we will illustrate the handling of the
IACO, IACUO, and PLRO objects in conjunction with the ERO and RRO
objects.

Case 1: IACO + ERO with strict route option: Here we can have two
situations in one case the primary fails and the other in which both the
primary and the secondary fail. The following explain the operation:
i. Primary fails: Since the path is strict route a PATHErr message
will be sent to crankback to the nearest ABR in the path with error code
for “Primary Criteria Failed”. The ABR should attempt to setup the LSP
with secondary criteria.
ii. Primary and secondary fails: When both the primary and the
secondary fails the source of the LSP setup is informed with the help of
a PATHErr message with the error code “Primary and Secondary Criteria
Failed”.
Case 2: IACO + ERO with loose source route option: Here also we have the
same situation as above except for the choice of different path when
either the primary or the secondary fails. Also when both the primary and
the secondary fail we have to go only one previous ABR hop to recomputed
the path till the source is reached.
Case 3: IACUO with and without RRO: In the case of no RRO in the RESV
message the LSP initiating node (Ingress LER) will not know the path
taken by the primary LSP and hence backup LSP may have overlapping LSP
sections with the primary. Where as when the RRO object is used, above
problem can be avoided, with the use of PLRO.
Case 4: With and without PLRO: When PLRO is present we can avoid
overlapping segments between the primary and the backup LSPs.

5.1.3 Error conditions

The following are the error conditions

1 Primary Criteria Failed (with the ABRs traversed)
2 Secondary Criteria Failed (with the ABRs traversed)
3 Primary and Secondary Criteria Failed (with the ABRs traversed)
4 Unknown Criteria
5 Unknown Object

5.2 CR-LDP extensions

In this section we describe extensions to CR-LDP for the support of
Inter-Area LSP setup as described in [INTER_AREA_REQ]. These
extensions are in addition to the extensions to CR-LDP as defined in
[CR_LDP] and includes the attributes from [QOS_TE_EXT], [TE_FRAMEWORK]
as sub-objects.

Three new objects are introduced as follows:

- <INTER AREA CRITERIA TLV> (from now on is also abbreviated as
IACO) introduced to carry the primary and the secondary criteria in the
Label Request message.
- <INTER AREA CRITERIA USED TLV> (from now on is also abbreviated
as IACUO) is introduced in the Label Mapping message to capture the route
taken by the primary or the secondary Label Request message.
- <PRIMARY LSP ROUTE TLV> (from now on abbreviated as PLRO) to
carry the path followed by the primary LSP in the Label Request message.

Note that constraint-related TLVs such as <CLASSTYPE> as mentioned in
[QOS_TE_EXT] can be sub-TLVs in the IACO. The following table
illustrates the objects discussed that are relevant for this draft.

Object type Message Importance
--------------------------------------------------------------------
<INTER AREA CRITERIA TLV> Label Request Mandatory
<INTER AREA CRITERIA USED TLV> Label Mapping Mandatory
<PRIAMRY LSP ROUTE TLV> Label Request Mandatory
<DIFFSERV TLV><CLASSTYPE TLV> Label Request Optional
<TE CONSTRAINTS TLV> Label Request Optional
<EXPLICIT ROUTE TLV> Label Request Optional
<PATH VECTOR TLV> Label Request/Mapping Optional
(recommended)

5.2.1 Label Request and Label Mapping messages Encoding

The encoding for the CR-LDP Label Request message is extended as
follows, to optionally include the Inter Area Criteria TLV (which
contains the Primary and Secondary Criteria TLVs) and Primary LSP
Route TLV:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Request (0x0401) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ER-LSP TLV (CR-LDP Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PATH VECTOR TLV (Optional but Recommended) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INTER AREA CRITERIA TLV (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PRIAMRY LSP ROUTE TLV (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Other CR-LDP TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The encoding for the CR-LDP Label Mapping Message is extended as
follows, to optionally include the Inter Area Criteria Used TLV:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0| Label Mapping (0x0400) | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Message ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FEC TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label Request Message ID TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSPID TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic TLV (CR-LDP, optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| INTER AREA CRITERIA USED (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

5.2.2 Handling of the new objects

The following are the message formats for the new objects that are
introduced in this document.

The INTER AREA CRITERIA TLV has the following format:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| IACO TLV | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PRIMARY CRITERIA sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SECONDARY CRITERIA sub-TLV |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

This TLV has both the primary and the secondary criteria sub-TLVs.
Notice that the U and F bits are set to ‘0’ to abort the connection
setup in case any LSP does not know how to use these mechanisms.

The PRIMARY/SECONDARY CRITERIA sub-TLV format:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|PRIMARY/SECONDARY CRITERIA | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DiffServ TLV(Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Class Type TLV (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Traffic Engineering TLV (Optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Other TLVs |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The sub TLV carries either the Primary or the Secondary criteria. Each
of these criteria has a list of constraints as exemplified in the
above message format. Also note that the U and F flags are set to ‘0’.

The INTER AREA CRITERIA USED TLV has the following format:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0| IACUO TLV | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reserved |Used |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The Inter Area Criteria Used TLV has a Criteria Used field “Used”,
which will be set to:

0 for primary criteria,
1 for secondary criteria and
15 for none

PRIMARY LSP ROUTE TLV format:

0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0|0|PRIMARY LSP ROUTE TLV | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV4/ IPV6 HOP 1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ………… |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IPV4/ IPV6 HOP N |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

This TLV contains the path taken by the Primary LSP. It can have IPV4
or IPV6 address hops taken by this path.

The IACO can be used very effectively in conjunction with the Explicit
Route (ER) TLV and Path Vector (PV) TLV. It is possible that the ER
TLV and PV TLV options are enabled to specify preferred path and to
know the path taken by the LSP respectively.

The following list of cases we will illustrate the handling of the
IACO, IACUO, and PLRO TLVs in conjunction with the ER TLV and PR TLV.

Case 1: IACO + ER TLV with strict route option: Here we can have two
situations in one case the primary fails and the other in which both the
primary and the secondary fail. The following explain the operation:
i. Primary fails: Since the path is strict route a LDP Notification
message will be sent to crankback to the nearest ABR in the path with
error code for “Primary Criteria Failed”. The ABR should attempt to setup
the LSP with secondary criteria.
ii. Primary and secondary fails: When both the primary and the
secondary fails the source of the LSP setup is informed with the help of
a LDP Notification message with the error code “Primary and Secondary
Criteria Failed”.
Case 2: IACO + ER TLV with loose source route option: Here also we have
the same situation as above except for the choice of different path when
either the primary or the secondary fails. Also when both the primary and
the secondary fail we have to go only one previous ABR hop to recomputed
the path till the source is reached.
Case 3: IACUO with and without PV TLV: In the case of no PV TLV in the
LDP Mapping message the LSP initiating node (Ingress LER) will not know
the path taken by the primary LSP and hence backup LSP may have
overlapping LSP sections with the primary. Where as when the PV TLV is
used, above problem can be avoided, with the use of PLRO.
Case 4: With and without PLRO: When PLRO is present we can avoid
overlapping segments between the primary and the secondary LSPs.

5.2.3 Status codes for the inter-area LSP setup

In the procedures described above, certain errors must be reported.
The following values are defined for the Status Code field:

Status Code E Status Data

Primary Criteria Failed 0 TBD
Secondary Criteria Failed 0 TBD
Primary and Secondary Criteria Failed0 TBD
Unknown Criteria 0 TBD
Unknown TLV 0 TBD

Note: The criteria failures should always inform the ABR path taken
for the current reservation.

6. MIB requirements (TBD)

The configuration requirements for such architecture can be divided
into:

- Routing configuration, such as criteria filtering, criteria-
constraint mapping, route filtering for criteria summarization etc.
- LSP Setup configuration, such as primary criteria and backup
criteria etc.
- Signaling configuration, such as the criteria change in the
intermediate segment notification, crankback in-progress notification
required etc.

These configuration information will be further elaborated in the
later versions of this draft.

7. Security Considerations (TBD)

8. Acknowledgements

The authors acknowledge Darek Skalecki, Ramana Gollamudi and Rao
Vadlamani for their insightful comments.

9. References

[RFC2026] S. Bradner, “The Internet Standards Process – Revision
3,” BCP 9, RFC 2026.

[RFC2119] S. Bradner, “Key words for use in RFCs to Indicate
Requirement Levels,” BCP 14, RFC2119.

[IGP_REQ] T. Li, G. Swallow, D. Awduche, “IGP Requirements for
Traffic Engineering with MPLS,” <draft-li-mpls-igp-00.txt>

[CRANKBACK] A. Iwata, N. Fujita, G. Ash, “Crankback Routing
Extensions for CR-LDP,” <draft-fujita-mpls-crldp-crankback-
01.txt>

[TOOL_VS_RP] “Internet Traffic Engineering working group mailing
list discussion on centralized tool based TE versus constraint-
based routing protocol extensions,” ftp://ftpext.eng.uu.net/tewg

[QOS_CONST] F. Le Faucheur et al., “Requirements for support of
DiffServ-aware MPLS Traffic Engineering,” <draft-lefaucheur-diff-
te-reqts-00.txt>

[QOS_TE_EXT] F. Le Faucheus et al., “Extensions to IS-IS, OSPF,
RSVP and CR-LDP for support of DiffServ-aware MPLS Traffic
Engineering,” <draft-lefaucheur-diff-te-ext-00.txt>

[INTRA_AREA] D. Katz, D. Yeung, “Traffic Engineering Extensions
to OSPF,” <draft-katz-yeung-ospf-traffic-01.txt>

[INTER_AREA] N. Fujita, A. Iwata, “Traffic Engineering Extensions
to OSPF Summary LSA,” <draft-fujita-ospf-te-summary-00.txt>

[INTER_AREA_REQ] S. Venkatachalam, S. Dharanikota, “A frame work
for the LSP setup across IGP areas for MPLS traffic engineering,”
<draft-venkatachalam-interarea-mpls-te-00.txt>

[TE_FRAMEWORK] D. O. Awduche, et al., “A Framework for internet
Traffic Engineering,” <draft-ietf-tewg-framework-02.txt>

[OSPF_RFC] J. Moy, “OSPF Version 2,” RFC 2328.

[OPAQUE_LSA] R. Coltun, “The OSPF Opaque LSA Option,” RFC 2370.

[RSVP_EXT] D. Awduche et al., “Extensions to RSVP for LSP
Tunnels,” <draft-ietf-mpls-rsvp-lsp-tunnel-04.txt>

[INTER_TE_OSPF] S. Venkatachalam, and B. Abarbanel, “OSPF
Extensions to Support Inter-Area Traffic Engineering,” <draft-
venkatachalam-ospf-traffic-00.txt >

[ISIS_ISO] “Intermediate System to Intermediate System Intra-
Domain Routeing Exchange Protocol for use in Conjunction with the
Protocol for Providing the Connectionless-mode Network Service
(ISO 8473),” ISO DP 10589, February 1990.

[ISIS_IETF] R. Callon, “Use of OSI IS-IS for Routing in TCP/IP
and Dual Environments,” RFC 1195.

[ISIS_TE] H. Smit, and T. Li, “IS-IS Extensions for Traffic
Engineering,” <draft-ietf-isis-traffic-01.txt>

9. Author's Addresses

Sudheer Dharanikota

Nayna Networks
157 Topaz Street
Milpitas, CA 95035
Phone: (408)-956-8000 x357
Email: sudheer@nayna.com

Senthil Venkatachalam

Alcatel USA
45195 Business Court, Suite 400
Dulles, VA 20166
Phone: (703)654-8635
Email: Senthil.Venkatachalam@usa.alcatel.com