© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—3-1 Frame-Mode MPLS Implementation on Cisco IOS Platforms Configuring Frame-Mode MPLS on Cisco.

© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—3-1

Frame-Mode MPLS Implementation on Cisco IOS Platforms

Configuring Frame-Mode MPLS on Cisco IOS Platforms


Outline

• Overview

• What Are MPLS Configuration Tasks?

• Configuring the MPLS ID on a Router

• Configuring MPLS on a Frame-Mode Interface

• Configuring a Label-Switching MTU

• Configuring IP TTL Propagation

• Configuring Conditional Label Distribution

• Configuring Frame-Mode MPLS on Switched WAN Media

• Summary


MPLS Configuration Tasks

Mandatory:• Enable CEF switching

• Configure LDP on every label-enabled interface

Optional:• Configure the MPLS ID

• Configure MTU size for labeled packets

• Configure IP TTL propagation

• Configure conditional label advertising


mpls ldp router-id interface [force]

Router(config)#

Specifies a preferred interface for determining the LDP router ID: • Parameters

– interface: Causes the IP address of the specified interface to be used as the LDP router ID, provided that the interface is operational

– force: Alters the behavior of the mpls ldp router-id command to force the use of the named interface as the LDP router ID

Configuring the MPLS ID on a Router


Configuring MPLS on a Frame-Mode Interface

mpls ip

Router(config-if)#

• Enables label switching on a frame-mode interface

• Starts LDP on the interface

mpls label protocol [tdp | ldp | both]

Router(config-if)#

• Starts selected label distribution protocol on the specified interface


Configuring MPLS on a Frame-Mode Interface: Example 1


Configuring MPLS on a Frame-Mode Interface: Example 2


PE51(config)# int ser 0/0.111PE51(config-if)# mpls ipPE51(config-if)# mpls label protocol ldpPE51(config-if)#^Z

PE51#show running-config int ser 0/0.111Building configuration...Current configuration : 165 bytes!interface Serial0/0.111 point-to-point ip address 192.168.5.49 255.255.255.240 mpls label protocol ldp tag-switching ip frame-relay interface-dlci 111end

PE51#

Verifying MPLS on a Frame-Mode Interface: Example


Configuring a Label-Switching MTU

mpls mtu bytes

Router(config-if)#

• Label switching increases the maximum MTU requirements on an interface because of the additional label header.

• Interface MTU is automatically increased on WAN interfaces; IP MTU is automatically decreased on LAN interfaces.

• Label-switching MTU can be increased on LAN interfaces (resulting in jumbo frames) to prevent IP fragmentation.

• The jumbo frames are not supported by all LAN switches.


Configuring Label-Switching MTU: Example


Configuring IP TTL Propagation

no mpls ip propagate-ttl

Router(config)#

• By default, IP TTL is copied into the MPLS label at label imposition, and the MPLS label TTL is copied (back) into the IP TTL at label removal.

• This command disables IP TTL and label TTL propagation.

– TTL value of 255 is inserted in the label header.

• The TTL propagation has to be disabled on ingress and egress edge LSRs.


Configuring IP TTL Propagation:Example


Configuring IP TTL Propagation:Disabling IP TTL Propagation Example


no mpls ip propagate-ttl [forwarded | local]

Router(config)#

Selectively disables IP TTL propagation for:• Forwarded traffic (Traceroute does not work for

transit traffic labeled by this router.)

• Local traffic (Traceroute does not work from the router but works for transit traffic labeled by this router.)

Configuring IP TTL Propagation:Extended Options


Configuring IP TTL Propagation:Disabling IP TTL Propagation Example


mpls ldp advertise-labels [for prefix-access-list [to peer-access-list]]

Router(config)#

• By default, labels for all destinations are announced to all LDP or TDP neighbors.

• This command enables you to selectively advertise some labels to some LDP or TDP neighbors.

• Conditional label advertisement works only over frame-mode interfaces.

• Parameters:

– for prefix-access-list—The IP access list that selects the destinations for which the labels will be generated

– to peer-access-list—The IP access list that selects the MPLS neighbors that will receive the labels

Conditional Label Distribution Configuration


• The customer is already running IP infrastructure.

• MPLS is needed only to support MPLS VPN services:

– Labels should be generated only for loopback interfaces (BGP next hops) of all routers.

– All loopback interfaces are in one contiguous address block (192.168.254.0/24).

Conditional Label Distribution Configuration: Example


ip cef!interface serial 0/0 mpls ip!interface serial 0/1 mpls ip!interface ethernet 1/0 mpls ip

Conditional Label Distribution Configuration Steps

Step 1: Enable CEF and label switching.

ip cef

mpls ip

mpls ip

mpls ip


Conditional Label Distribution Configuration Steps (Cont.)

Step 2: Enable conditional label advertisement.

!! Disable default advertisment mechanism!no mpls ldp advertise-labels!! Configure conditional advertisments!mpls ldp advertise-labels for 90 to 91!access-list 90 permit ip 192.168.254.0 0.0.0.255access-list 91 permit ip any

no mpls ldp advertise-labels

mpls ldp advertise-labels for 90 to 91!access-list 90 permit 192.168.254.0 0.0.0.255access-list 91 permit any


Configuring Frame-Mode MPLS on Switched WAN Media

Why:• Run MPLS over ATM networks that do not

support MPLS.

• This could be the potential first phase in ATM network migration.

How:• Configure MPLS over ATM point-to-point subinterfaces on

the routers.


• Routers view the ATM PVC as a frame-mode MPLS interface.

• TDP or LDP is run between the adjacent routers.

• Many LSPs can be established over one ATM PVC.

• The ATM network is not aware of MPLS between the routers.

Configuring Frame-Mode MPLS on Switched WAN Media:MPLS over ATM Forum PVCs


• Create a point-to-point ATM subinterface.

• Configure ATM PVC on the subinterface.

• Start label switching and LDP or TDP on the interface.

Configuring Frame-Mode MPLS on Switched WAN Media:

MPLS over ATM Forum PVCs (Cont.)


• Create a point-to-point or multipoint Frame Relay subinterface.

• Configure Frame Relay DLCI on the subinterface.

• Start label switching and LDP or TDP on the interface.

Configuring Frame-Mode MPLS on Switched WAN Media:MPLS over Frame Relay Networks


Summary

• Some of the MPLS configuration tasks are mandatory and some are optional.

• The command mpls ldp router-id interface [force] specifies a preferred interface for determining the LDP router ID.

• Use the mpls ip or tag-switching ip commands to enable MPLS (interface level).

• Label switching increases maximum MTU size on an interface.

• TTL propagation must be disabled on ingress and egress edge LSRs.

• Conditional label advertisement works only on frame-mode interfaces.

• When frame-mode MPLS on an ATM interface is enabled, LDP relationships are established between the PVC endpoints and not with the attached ATM switch.


© 2006 Cisco Systems, Inc. All rights reserved. MPLS v2.2—3-1 Frame-Mode MPLS Implementation on Cisco IOS Platforms Configuring Frame-Mode MPLS on Cisco.

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