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Specialized Models User Guide 6 MPLS Model User Guide

Modeler/Release 10.0 SPM-6-1

6 MPLS Model User Guide

Multi-ProtocolLabelSwitching(MPLS)isamulti-layerswitchingtechnologythat

uses labels to determine how packets are forwarded through a network. The

firstpartofthisdocumentdescribeskeyfeaturesoftheMPLSspecializedmodel

and the second part focuses on procedures for configuring MPLS in your

network model.

Model Features

This section contains a list of the main features available in the Multi-Protocol

Label Switching model:

• The MPLS model captures the following protocol behavior:

Table 6-1 MPLS Model Features

Feature Description

LSP (Label Switched Path) configuration • LSPs can be created manually or

automatically from traffic conversation

pairs.

• LSPs are easily reused in other scenarios

or projects by using the LSP import and

export features.

• Both dynamic and static LSPs are created

using the path object.

Differential Services (DiffServ) • DiffServ extensions, as defined in

RFC-2475, are provided.

• The model enables you to perform QoS

(quality of service) analyses by accounting

for different types of service.

Traffic Engineering Traffic engineered routes are computed

using Constrained Shortest Path First

(CSPF)withOSPForIS-ISroutingprotocols.

End of Table 6-1

Specialized Models User Guide 6 MPLS Model User Guide

SPM-6-2 Modeler/Release 10.0

• MPLS models are implemented based on information available from the

following sources.

Table 6-2 Reference Documents

Model Features Document

Traffic Engineering

MPLS TE RFC-2702—Requirements for Traffic Engineering

Over MPLS

FECs RFC-3031—Multiprotocol Label Switching

Architecture

IGP shortcuts draft-hsmit-mpls-igp-spf-00

Label Switched Paths

Dynamic LSPs

Static LSPs RFC-3031—Multiprotocol Label Switching

Architecture

LSP routing

OSPF TE

IS-IS TE RFC-2676—QoS Routing and OSPF Extensions

Label distribution

LDP RFC-3036—LDP Specification

CR-LDP RFC-3212—Constraint-based LSP Setup Using LDP

RSVP-TE RFC-3209—RSVP-TE: Extensions to RSVP for LSP

Tunnels

PP-VPNs

A framework for layer-3 PP VPNs RFC-2547—BGP/MPLS VPNs

BGP/MPLS VPNs draft-ietf-ppvpn-framework-05

Quality of Service

QOS Architecture RFC-2475—An Architecture for Differentiated

Services

MPLS Support of Differentiated

Services RFC-3270—Multi Protocol Label Switching

draft-ietf-mpls-diff-ext-08

Restoration and Resiliency

Fast reroute with bypass tunnels

LSP protection with ingress backup

draft-ietf-mpls-rsvp-lsp-fastreroute-00

End of Table 6-2

Specialized Models User Guide 6 MPLS Model User Guide

Modeler/Release 10.0 SPM-6-3

Node Models

The MPLS model suite supports workstation, server, router, and link models

from the standard model library. The LER (Label Edge Router) and LSR (Label

SwitchingRouter) node models in the MPLS object paletteare preconfigured to

support MPLS. However, you can configure any of the router models in the

standard model library to model LERs and LSRs.

Figure 6-1 MPLS Object Palette

Model Attributes

Global MPLS attributes, which are used to configure network-wide MPLS

parameters, are grouped in the MPLS configuration object. Router-specific

MPLS attributes are grouped in the MPLS Parameters attribute on each router.

They are described in Router Attributes on page SPM-6-6.

MPLS Configuration Object Attributes

Some of the important MPLS configuration object attributes are described

below.

•FEC Specifications This attribute specifies the Forwarding Equivalence

Class (FEC) parameters used by MPLS in the network. FECs classify and

group packets so that all packets in a group are forwarded the same way.

FECs are based on any of the IP header fields—ToS, Protocol, Source

Address Range, Destination Address Range, Source Port, and Destination

Port can all be used to define a FEC. Figure 6-2 Specifying FEC Attributes

on page SPM-6-4 shows the attribute sequence for defining an FEC.

Specialized Models User Guide 6 MPLS Model User Guide

SPM-6-4 Modeler/Release 10.0

Figure 6-2 Specifying FEC Attributes

The FEC Details Table helps define the FEC through a set of match rules,

which are combinations of TCP, UDP, and IP header fields. FECs are

determined by taking a logical AND of the column settings in a row and by

taking a logical OR of each of the rows. In other words, for a packet to qualify

for a particular FEC, the IP header fields must satisfy every condition of at

least one row of the defined FEC. For example, a FEC that consists only of

email and ftp traffic would be specified as shown in Figure 6-3.

Figure 6-3 FEC Details for E-mail and FTP Traffic

Therefore,iftheIPheaderofapacketcontained eitheremailor FTP, it would

qualify for the FEC defined in Figure 6-3, and would be sent over the

corresponding LSP.

Specialized Models User Guide 6 MPLS Model User Guide

Modeler/Release 10.0 SPM-6-5

•LSP Specification File This attribute indicates whether the network LSPs

should be configured according to the text file specified. You can update the

text file by clickingOK in the LSP Browser. Updating the file recreates the file

based on the current network LSP settings, including LSPs that might not

have been in the original file (such as those created manually).

•Traffic Trunk Profiles This attribute specifies out-of-profile actions and

traffic classes for traffic trunks in the network. Traffic trunks capture traffic

characteristics such as peak rate,average rate, and average burst size. The

default Trunk Details setting configures a trunk with a value of

32,000 bits/sec for maximum and average bit rate and 32,000 bits for

maximum burst size.

Figure 6-4 Specifying Traffic Trunk Profiles

•EXP <--> Drop Precedence and EXP <--> PHB These attributes specify

how EXP bits in the MPLS shim header are translated into diffserv

information at each LSR. For E-LSPs, LSRs determine Per Hop Behavior

(PHB), while on L-LSPs, they determine Drop Precedence. Use the default

setting unless you are analyzing the effects of QoS.

Specialized Models User Guide 6 MPLS Model User Guide

SPM-6-6 Modeler/Release 10.0

Figure 6-5 Mapping EXP Bits to Drop Precedence and PHB

Router Attributes

Someof theimportantMPLSParametersattributessetonroutersaredescribed

below.

Traffic Mapping Configuration

This attribute specifies bindings between FECs and LSPs. Each row of the

Traffic Mapping Configuration table specifies a distinct traffic engineering (TE)

binding.EachTE bindingspecifiestheFEC,traffictrunk,andLSPthatisapplied

to the label of the incoming packet.

Only previously defined values appear in the attribute pull-down lists. If no

values appear in the attribute pull-down lists, verify that you have defined the

FECs and traffic trunks in the MPLS Configuration object, and that the LSPs

appear in the network path browser.

Specialized Models User Guide 6 MPLS Model User Guide

Modeler/Release 10.0 SPM-6-7

When an unlabeled packet arrives at an ingress LER, the following sequence

occurs to determine the correct label for the packet:

1) The TE binding is selected based on the packet FEC and the incoming

interface.

2) The packet is checked to make sure that its traffic characteristics conform

to those specified for the TE binding’s traffic trunk.

3) Thepacketis labeled forand sentthroughthe primaryLSPspecifiedforthe

TE binding.

Figure 6-6 Configuring TE Bindings

•EXP <--> Drop Precedence and EXP <--> PHB These attributes specify

which mappings, defined in the MPLS configuration object, are used by the

router.

•LDP Parameters—specifies Label Distribution Protocol parameters used by

the LSR. LDP Parameters is a compound attribute, composed of the

following sub-attributes:

—Discovery Configuration—specifies Hello message parameters

needed to learn of neighboring routers

—Session Configuration—specifies Keep-alive message parameters

used to establish LDP sessions

—Recovery Configuration—specifies how node and link failures are

detected

This weight attribute

configuration uses LER2-LER5

75%ofthetimeandLER2-site9

25% of the time.

Specialized Models User Guide 6 MPLS Model User Guide

SPM-6-8 Modeler/Release 10.0

Figure 6-7 Configuring LDP Parameters

Simulation Attributes

The following simulation attributes are available (Configure/Run Discrete Event

Simulation dialog box) when using the MPLS model suite.

•CR-LDP Routing—specifies if CR-LDP routing uses CSPF or conventional

IGP to determine routes in loosely defined LSPs. The default value is IGP.

•CSPF Retry Timer—specifieshowlongan ingressLER waitsafterdetecting

a node or link failure before rerouting an LSP that traverses the failed node

or link. The default value for this attribute is 45 seconds.

•LDP Discovery End Time—specifies when LDP discovery ends. After this

time, no more LDP discovery packets are sent through the network. This

value should occur after the network reaches a final, constant state in the

simulation since no network topology or device status changes are reflected

in the LDP routing tables after LDP Discovery End Time.

•LDP Discovery Start Time—specifies when LDP starts sending discovery

packets through the network. Set this attribute to a value other than Do Not

Start to enable LDP.

•LSP Signaling Protocol—specifies whether dynamic LSPs are signaled

using CR-LDP (constraint-based routed LDP) or RSVP. The default value is

CR-LDP.

Specialized Models User Guide 6 MPLS Model User Guide

Modeler/Release 10.0 SPM-6-9

LSP Attributes

Some of the important LSP attributes are described below. Most of these

attributes can also be configured in the LSP browser, which is described in the

next section.

Figure 6-8 Configuring an LSP’s Attributes

•Directionality—specifiesifanLSPisunidirectionalorbidirectional.Dynamic

LSPs are always unidirectional.

•LSP Type—specifies whether the LSP is of type E-LSP or L-LSP. For

E-LSP, three experimental bits in the shim header carry the Diff-Serv

information. Thisprovides eight different types ofservice (TOS)per LSP. For

L-LSP, TOS information is contained in the MPLS label and all packets

traversing the link are treated equally.

•Path Details—specifies which packets use the LSP and defines how

packets are forwarded through the LSP. This attribute is automatically

configured for dynamic LSPs. To configure this attribute for static LSPs,

select Update LSP Details from the Protocols > MPLS menu.

Figure 6-9 Path Details for a Static LSP

•Recovery Parameters—specifies recovery parameters that are used to

reroute traffic on this LSP if there is a link or node failure along the LSP.

Specialized Models User Guide 6 MPLS Model User Guide

SPM-6-10 Modeler/Release 10.0

Figure 6-10 Recovery Parameters Configuration

•Setup Parameters—specifies the duration of the LSP.

Figure 6-11 Setup Parameters Configuration

•TE Parameters—specifies the traffic engineering constraints used by

CR-LDP to find a route through the network. CR-LDP uses Constrained

Routing to find the route that is the best fit for the specified constraints. This

attribute applies to dynamic LSPs only. Make sure you account for network

bandwidth availability when configuring static LSPs.

Figure 6-12 TE Parameters Configuration

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