Cisco IOS MPLS configuration

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Cisco IOS MPLS configuration

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Corso di Laurea Specialistica in Ingegneria delle Telecomunicazioni

Introduction

MPLS can be configured over different platforms

It can be implemented

on a purely router-based Internet backbone

over an ATM switched network - MPLS enables an ATM switch to perform virtually all of the functions of an IP router

A.A. 2012/13

Univ. CA - Corso di Laurea Specialistica in Ingegneria delle Telecomunicazioni

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router

The key difference between a conventional ATM switch and an ATM label switch is the latter uses the control software to establish VCs

Tecnologie per reti multiservizio

Introduction

Several different types of LSR exist

LSR - Forwards labeled packets

Edge-LSR – Performs label pushing or popping and

Layer 3 lookup

ATM-LSR - Runs MPLS protocols in the control plane to

set up ATM virtual circuits. Forwards labeled packets as set up ATM virtual circuits. Forwards labeled packets as ATM cells

Traditional ATM switches can be redeployed

as ATM-LSRs through a software upgrade

ATM edge-LSR - Runs MPLS protocols in the control

plane, segmenting a packet into ATM cells or reassembling cells into the original packet

MPLS Supported Platforms

MPLS is supported on the following Cisco

platforms

Cisco LightStream 1010 ATM Cisco 2600 series routers

Cisco RSP7000 route switch processor Cisco 7200 series routers

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Command Line Interface

Cisco router has an operating system called IOS

IOS configuration is made through the command

line interface (CLI)

CLI is divided into many different modes

When you log in to a Cisco device, the device is initially

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When you log in to a Cisco device, the device is initially in user EXEC mode

User EXEC mode contains only a limited subset of commands

The EXEC commands are not saved when the software reboots.

To have access to all commands, privileged EXEC mode is required

Accessing Command Modes

Command

Mode

Prompt

User EXEC Router>

Privileged EXEC

Router> enable Password: <password>

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Router#

Global configuration

Router# configure terminal

Enter configuration commands, one per line. End with CNTL/Z.

Router(config)#

Interface configuration

Router(config)# interface interface_name Router(config-if)#

Cisco Express Forwarding

Every MPLS node must run one or more IP

routing protocols to exchange IP routing

information with other MPLS nodes in the

network

In this sense, every MPLS node (including ATM switches) is an IP router on the control plane switches) is an IP router on the control plane

Similar to traditional routers, the IP routing

protocols populate the IP routing table

In traditional IP routers, the IP routing table is used to build the IP forwarding table (Forwarding Information Base [FIB] in Cisco IOS) used by Cisco Express

Cisco Express Forwarding

Label switching on a router requires that Cisco

Express Forwarding (CEF) be enabled on that

router

To enable CEF on a router

IOS Prompt

IOS Command

Prompt

IP cef Router# configure terminal

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MPLS/Tag Switching CLI Command

Beginning with Cisco IOS Release 12.1, the Tag

Switching distribution protocol has been replaced

with the MPLS distribution protocol

MPLS supports the following

Tag Switching features

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Tag Switching features Tag Switching CLI commands

Label Binding Protocols

Cisco IOS software implements two label binding

protocols

Tag Distribution Protocol (TDP) - Cisco's proprietary

protocol available in IOS software release 11.1CT, as well as 12.0 and all subsequent IOS releases

Label Distribution Protocol (LDP) - IETF standard

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Label Distribution Protocol (LDP) - IETF standard

label binding protocol available in 12.2T release

TDP and LDP functionally are equivalent and can

be used concurrently within the network, even

on different interfaces of the same LSR

Start MPLS on an Interface

Task IOS Command

Start MPLS packet labeling and run TDP globally or on the specified interface

tag-switching ip

Start MPLS packet labeling globally or on mpls ip

Start MPLS packet labeling globally or on the specified interface. TDP is used as the default label distribution protocol.

Note: This command is equivalent to the tag-switching ip command

mpls ip

Start MPLS on an Interface

IOS Command Prompt

mpls ip (global configuration)

Router(config)# configure terminal Router(config-if)# mpls ip

mpls ip Router(config)# configure terminal

Global configuration is not sufficient to initiate

label distribution

Interface configuration is necessary

mpls ip

(interface configuration)

Router(config)# configure terminal

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Label Distribution Protocol

Configuration

To configure a Label Distribution Protocol to

operate in an MPLS network, the following

configuration tasks are performed

Configuring LDP/TDP (required)

Verifying LDP/TDP Configuration (optional)

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Configuring LDP/TDP

IOS Command Task

mpls label protocol {ldp | tdp}

(global configuration)

Configures LDP or TDP for all interfaces

mpls label protocol {ldp | tdp | both}

Configures LDP, TDP or both for a specific interface

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{ldp | tdp | both} (interface

configuration)

interface

The both keyword is intended for use with interfaces to multiaccess networks, such as Ethernet and FDDI, where some peers might use LDP while others use TDP.

When you specify the both keyword, the LSR sends both LDP and TDP discovery Hello messages and responds to both types of messages

Configuring LDP/TDP

IOS Command Prompt

mpls label protocol {ldp | tdp}

(global

Router(config-if)# mpls label protocol ldp (global configuration) mpls label protocol {ldp | tdp | both} (interface configuration)

Router(config-if)# interface Ethernet 0/2 Router(config-if)# mpls label protocol ldp

Configuring LDP/TDP

Prompt Purpose

Step1 Router# configure terminal Enables configuration

mode

Step2 Router(config)# ip cef [distributed] Configures Cisco Express Forwarding Step3 Router(config)# interface interface Specifies the interface

to configure

Step4 Router(config-if)# mpls ip Configures MPLS for a

specified interface Step5 Router(config-if)# mpls label protocol

ldp

Configures LDP for a specific interface

Step6 Router# configure terminal Configures LDP on all

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Verifying LDP/TDP Configuration

Step 1 - Verify that the interfaces in question

have been configured to use LDP

Command: show mpls interfaces

Step 2 - Verify that the interface is up and

sending LDP Discovery Hello messages (as

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sending LDP Discovery Hello messages (as

opposed to TDP Hello messages)

Command: show mpls ldp discovery

Step 3 - Verify the acceptance of the

configuration commands

Command: show run

Configuring Traffic Engineering

Cisco DS-TE functionalities can be configured

through bandwidth reservation functionalities

The bandwidth reservable on each link for

constraint-based routing (CBR) can be managed

through two bandwidth pools

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through two bandwidth pools

global pool

sub-pool: can be limited to a smaller portion of the link

bandwidth

Tunnels using the sub-pool bandwidth can be

used with MPLS Quality of Service (QoS)

mechanisms to deliver guaranteed bandwidth

services

Configuring Traffic Engineering

Cisco DS-TE should be considered as a

pre-standard implementation of IETF DiffServ-aware

MPLS Traffic Engineering

However, it is in line with the IETF requirements

The concept of "Class-Type" defined in that IETF draft The concept of "Class-Type" defined in that IETF draft corresponds to the concept of bandwidth pool

implemented by DS-TE

Because DS-TE supports two bandwidth pools (global pool and sub-pool), DS-TE should be seen as supporting two Class-Types (CT0 and CT1)

DS-TE commands

Command Purpose

ip rsvp bandwidth x y sub-pool z

To configure the size of the sub-pool on every link

x = the size of the global pool z = the size of the sub-pool

tunnel mpls traffic- To enable a TE tunnel to reserve bandwidth tunnel mpls

traffic-eng bandwidth sub-pool b

To enable a TE tunnel to reserve bandwidth from the sub-pool

tunnel mpls traffic-eng bandwidth b

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DS-TE configuration

To establish a sub-pool TE tunnel, a

configuration at three levels is required

the device (router or switch router) the physical interface

the tunnel interface

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The first two levels activate traffic engineering

The third level establishes the sub-pool tunnel

Configuring the Device

At this level, the device (router or switch router)

is configured to use

Cisco Express Forwarding (CEF) MultiProtocol Label Switching (MPLS) Traffic Engineering tunneling

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either the OSPF or IS-IS routing algorithm

Configuring the Device

Step1 Router# configure terminal Enables configuration mode

Step2 Router(config)# ip access-list

standard access-list-number

Enables MPLS and its traffic engineering tunnel capability

Step3 Router(config)# router ospf Invokes OSPF and puts

the device into router configuration mode

Step4 Router(config-router)# mpls

traffic-eng router-id loopback0

Specifies that the traffic engineering router identifier is the IP address associated with the loopback0 interface

Step5 Router(config-router)# mpls

traffic-eng area num

Turns on MPLS traffic engineering for a particular

Configuring the Network Interface

At this level, the interface through which the

tunnel will run is configured with the following

steps

Put the router into interface-configuration mode Enable Resource Reservation Protocol (RSVP)

This is used to signal (set up) a TE tunnel, and to tell devices along the tunnel path to reserve a specific amount of bandwidth for the tunnel traffic

At this step, the maximum size of the sub-pool is established

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Configuring the Network Interface

Step1 Router(config)# interface interface-id

Enables interface-configuration mode

Step2 Router(config-if)# ip rsvp

bandwidth interface-kbps

Enables RSVP on this interface and limits the amount of

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bandwidth interface-kbps

sub-pool kbps bandwidth RSVP can reserve on this_interface.

The sum of bandwidth used by all tunnels on this interface cannot exceed interface-kbps, and the sum of bandwidth used by all sub-pool tunnels cannot exceed sub-pool kbps

Step3 Router(config-if)# mpls

traffic-eng tunnels

Enables the MPLS traffic TE feature on this interface

Configuring the Tunnel Interface

At this level, a set of attributes for the tunnel is

defined on the “tunnel interface”

Step1 Router(config)# interface Creates a tunnel interface (named in this

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tunnel1

Creates a tunnel interface (named in this

example tunnel1) and enters interface

configuration mode Step2 Router(config-if)# tunnel

destination A.B.C.D

Specifies the IP address of the tunnel tail

device Step3 Router(config-if)# tunnel

mode mpls traffic-eng

Sets the tunnel’s encapsulation mode to

MPLS TE

Configuring the Tunnel Interface

Step4 Router(config-if)# tunnel

mpls traffic-eng bandwidth {sub-pool | [global]}

bandwidth

Configures the tunnel’s bandwidth and assigns it either to the sub-pool or the global sub-pool

Step5 Router(config-if)# tunnel Sets the priority to be used when system determines which existing

Router(config-if)# tunnel

mpls

traffic-eng priority

system determines which existing tunnels are eligible to be preempted

Step6 Router(config-if)# tunnel

mpls traffic-eng path-option

Configures the paths (hops) a tunnel should use. The user can enter an explicit path (can specify the IP addresses of the hops) or can specify a dynamic path (the router figures out the best set of hops)

Verifying the Configurations

To verify TE configuration, the EXEC command

show running-config has to be used a and its

output display has to be checked for correctness

To check one tunnel’s configuration, enter show

interfaces tunnel followed by the tunnel

interface number

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DiffServ Using DS-TE Global Pool

Tunnels

A tunnel can be configured using global pool

bandwidth to carry several classes of traffic

Traffic from each class can receive differentiated

service with the following:

Select a separate queue (a distinct diffserv PHB) for

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Select a separate queue (a distinct diffserv PHB) for each traffic class. For example, if there are three classes (gold, silver, and bronze) there must be three queues (diffserv AF2, AF3, and AF4)

Mark each class of traffic using a unique value in the MPLS experimental bits field (for example gold = 4, silver = 5, bronze = 6)

Ensure that packets marked as Gold are placed in the gold queue, Silver in the silver queue, and so on