IBM 6 MPLS User Manual

Specialized Models User Guide 6 MPLS Model User Guide

6 MPLS Model User Guide

Multi-Protocol Label Switching (MPLS) is a mult i-layer switching technology that uses labels to determine how packets are forwarded through a network. The first part of this document des cribes key features of the MPLS speci alized model 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)

Traffic Engineering Traffic engineered routes are computed

End of Table 6-1

• 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.

using Constrained Shortest Path First (CSPF) with OSPF or IS-IS routing protoc ols.

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• 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

Over MPLS

FECs RFC-3031

Architecture

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

Label Switched Paths

Dynamic LSPs Static LSPs

LSP routing

OSPF TE IS-IS TE

Label distribution

LDP RFC-3036—LDP Specification

CR-LDP RFC-3212—Constraint-bas ed LSP Setup Usin g LDP

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

RFC-3031 Architecture

RFC-2676

Tunnels

—Requirements for Traffic Engineering

—Multiprotocol Label Switc hin g

—QoS Routing and OSPF Extensions

PP-VPNs

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

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

Quality of Ser vice

QOS Architecture RFC-2475—An Architecture for Differentiated

Services

MPLS Support of Differentiated Services

Restoration and Resili enc y

Fast reroute with bypass tunnels LSP protection with ingress backup

End of Table 6-2

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Node Models

The MPLS model suite supports workstation, server, router, and link models from the standard model libra ry. The LER (Label Edge Router) an d LSR (Label Switching Router) node models in t he MPLS object palette are preconfigured t o 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

MPLS Configuration Object 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 i n the MPLS Par ameters att ribute on each router . They are described in Router 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 Destinat ion Port can all be used to define a FEC. Figure 6-2 Specifying FEC Attri butes on page SPM-6-4 shows the attribute sequence for defining an FEC.

on page SPM-6-6.

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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, if the IP header of a pac ket contained either email or FTP, it would qualify for the FEC defined in Figure 6-3

, and would be sent over the

corresponding LSP.

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• LSP Specification File This attribute indicates whethe r the network LSPs should be configured according to the text file specified. You can update the text file by clicking OK in the LSP Browser. Updating the fil e 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, aver age 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.

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

Router Attributes

Some of the important MPLS Parameters attribu tes set on routers are described below.

Traffic Mapping Configuration

This attribute specifies bindings between FECs and LSPs. Each row of the Traffic Mapping Configuration table specifies a distinct traffic eng ineering (TE) binding. Each TE binding specifies the FEC, traffic trunk, and LSP that is applied 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 objec t, and that the LSPs appear in the network path browser.

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When an unlabeled packet arrives at an ingress LER, the following sequence occurs to determine the correct la bel 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) The packet is labeled for and sent t hrough the primary LSP specified for the TE binding.

Figure 6-6 Configuring TE Bindings

This weight attribute configuration uses L ER2-L ER5 75% of the time and LER2-site9 25% of the time.

• 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 Prot ocol parameters used by the LSR. LDP Parameters is a compound attribute, composed of the following sub-attributes:

— Discovery Configuration—specifi es 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 fai lures are

detected

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