Internet Draft
MPLS, Internet Traffic Engineering Sudheer Dharanikota
Internet Draft Senthil K. Venkatachalam
Category: Standards Track Alcatel USA
September 2000
OSPF, IS-IS, RSVP, CR-LDP Extensions to Support
Inter-Area Traffic Engineering Using MPLS TE
<draft-dharanikota-interarea-mpls-te-ext-00.txt>
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026 [RFC2026].
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_FWK] 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_FWK].
S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 1]
Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000
2. Notations 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.
S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 2]
Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000
The ISP's networks are divided into Autonomous Systems (ASs), where
each AS is divided into 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 TE perspective, requirements such as path
selection and crankback need different architectural additions to
the existing IGPs and signaling protocols for inter-area LSP setup.
Traffic engineering practice currently involves the setup and use of
Label Switched Paths (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 LSRs that
serve as 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 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 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.
S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 3]
Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000
The requirements of criteria-based inter-area routing are separated
into routing protocol requirements, signaling protocol requirements
and configuration requirements. 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 requirements for such
architectural changes are presented in section 6. Security
considerations, references and acknowledgements follow in sections
7, 8, and 9.
4. Routing protocol extensions
4.1 Intra-area requirements
OSPF or ISIS implementation SHOULD support the [OSPF_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.
[OSPF_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 [OSPF_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.
S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 4]
Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000
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 4.3. 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.
4.2.1 Requirements for 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 [OSPF_INTER_TE]. The definitions for the various TE
attributes in the TE summary LSA are also described in
[OSPF_INTER_TE]. In addition to those TE attributes, the following
three TLVs are proposed to be added in the TE summary LSA.
4.2.1.1 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
are 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.
S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 5]
Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000
4.2.2 Requirements for 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
[ISIS_ISO], [ISIS_IETF] to include TE sub-TLVs as described below.
4.2.2.1 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_INTRA_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_INTRA_TE]).
4.2.2.2 Format of the IP reachability TLV with TE Sub-TLVs
The extended IP reachability TLV as described in [ISIS_INTRA_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_INTRA_TE], followed by zero or more TE sub-TLVs, each of which is of
the form:
No. of Octets
+---------------------------+
| CODE | 1
+---------------------------+
| LENGTH | 1
+---------------------------+
| VALUE | LENGTH
+---------------------------+
S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 6]
Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000
4.2.2.3 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_INTRA_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.
4.2.2.3.1 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.
4.2.2.3.2 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.
4.2.2.3.3 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.
4.2.2.3.4 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.
S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 7]
Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000
4.2.2.3.5 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.
4.2.2.3.6 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.
4.2.2.3.7 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.
4.3 Inter-Area 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
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.
S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 8]
Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000
5. Signaling requirements
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_FWK]. 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:
- object (from now on is also abbreviated
as IACO) introduced to carry the primary and the secondary
criteria in the PATH message.
- 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.
- object (from now on abbreviated as PLRO) to
carry the path followed by the primary LSP in the PATH message.
S. Dharanikota, S. Venkatachalam Expires March 2001 [Page 9]
Internet Draft draft-dharanikota-interarea-mpls-te-ext-00.txt Sept. 2000
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
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
--------------------------------------------------------------------
Path Mandatory
Resv Mandatory
Path Mandatory
Path Optional
Path Optional
Path Optional
Path, Resv Optional but
Recommended
5.1.1 PATH and RESV message format changes
The format of the Path message is changed as follows:
::=
[]
[]
[]
[] (For Primary Criteria)
[][]
[]
[] (For Secondary Criteria)
[][]
[]
[]
[ ... ]
[]
::= []
[]
[]
The format of the Resv message is changed as follows:
::=
[ ]
[] []
[...]