MPLS Multilink PPP Support
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MPLS-Multilink PPP Support

Last Updated: November 16, 2011

The MPLS--Multilink PPP Support feature ensures that MPLS Layer 3 Virtual Private Networks (VPNs) with quality of service (QoS) can be enabled for bundled links. This feature supports Multiprotocol Label Switching (MPLS) over Multilink PPP (MLP) links in the edge (provider edge [PE]-to-customer edge [CE]) or in the MPLS core (PE-to-PE and PE-to-provider router [P]).

Service providers that use relatively low-speed links can use MLP to spread traffic across them in their MPLS networks. Link fragmentation and interleaving (LFI) should be deployed in the CE-to-PE link for efficiency, where traffic uses a lower link bandwidth (less than 768 kbps).

Finding Feature Information

Your software release may not support all the features documented in this module. For the latest feature information and caveats, see the release notes for your platform and software release. To find information about the features documented in this module, and to see a list of the releases in which each feature is supported, see the Feature Information Table at the end of this document.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Prerequisites for MPLS--Multilink PPP Support

The MPLS--Multilink PPP Support feature requires the following:

  • Cisco Express Forwarding or distributed Cisco Express Forwarding enabled
  • MPLS enabled on PE and P routers
  • Cisco Express Forwarding switching enabled on the interface with the ip route-cache cefcommand

The first table below lists the required port adapters and processors for the MPLS--Multilink PPP Support feature on the Cisco 7200 series routers. The second table below lists the required port adapters and processors for the MPLS--Multilink PPP Support feature on the Cisco 7500 series routers.

Table 1Required Cisco 7200 Port Adapters and Processors for MPLS--Multilink PPP Support

Port Adapter

Processor

PA-4T+

PA-8T

Channelized adapters

  • PA-MC-2E1/120
  • PA-MC-2T1
  • PA-MC-2T3+
  • PA-MC-4T1
  • PA-MC-8E1/120
  • PA-MC-8T1
  • PA-MC-E3
  • PA-MC-STM-1MM
  • PA-MC-STM-1SMI
  • PA-MC-T3
  • PA-MC-8TE1+

Network processing engine models

  • NPE-400
  • NPE-G1
  • NSE-1

Table 2Required Cisco 7500 Port Adapters and Processors for MPLS--Multilink PPP Support

Port Adapter

Processor

PA-4T+

PA-8T

Channelized adapters

  • PA-MC-2E1/120
  • PA-MC-2T1
  • PA-MC-2T3+
  • PA-MC-4T1
  • PA-MC-8E1/120
  • PA-MC-8T1
  • PA-MC-E3
  • PA-MC-STM-1MM
  • PA-MC-STM-1SMI
  • PA-MC-T3
  • PA-MC-8TE1+

Route Switch Processors

  • RSP16
  • RSP8
  • RSP4+

Versatile interface processors

  • VIP4-50
  • VIP4-80
  • VIP6-80

Restrictions for MPLS--Multilink PPP Support

The MPLS--Multilink PPP Support feature is limited byplatform-specific restrictions that apply to the use of MLP and distributed MLP (dMLP).

For restrictions that apply to dMLP on the Cisco 7500 routers, see the Distributed Multilink Point-to-Point Protocol for Cisco 7500 Series Routers feature module.

Information About MPLS--Multilink PPP Support

MPLS Features Supported for Multilink PPP

The following topics provide information about MPLS features supported for MLP:

MPLS Layer 3 Virtual Private Network Features Supported for Multilink PPP

The table below lists MPLS Layer 3 VPN features supported for MLP and indicates if the feature is supported on CE-to-PE links, PE-to-P links, and Carrier Supporting Carrier (CSC) CE-to-PE links.

Table 3MPLS Layer 3 VPN Features Supported for MLP

MPLS L3 VPN Feature

CE-to-PE Links

PE-to-P Links

CSC CE-to-PE Links

Static routes

Supported

--1

--

External Border Gateway Protocol (eBGP)

Supported

Not applicable to this configuration

Supported

Intermediate System-to-Intermediate System (IS-IS)

--

Supported

--

Open Shortest Path first (OSPF)

Supported

Supported

--

Enhanced Interior Gateway Routing Protocol (EIGRP)

Supported

Supported

--

Interprovider (Inter-AS) VPNs (with Label Distribution Protocol [LDP])

Not applicable to this configuration

Supported (MLP between Autonomous System Border routers {ASBRs])

Not applicable to this configuration

Inter-AS VPNs with IPv4 Label Distribution

Not applicable to this configuration

Supported (MLP between ASBRs]

Not applicable to this configuration

CSC VPNs (with LDP)

--

Not applicable to this configuration

Supported

CSC VPNs with IPv4 label distribution

Supported

Not applicable to this configuration

Supported

External and internal BGP (eiBGP) Multipath

--

--

Not applicable to this configuration

Internal BGP (iBGP) Multipath

Not applicable to this configuration

--

Not applicable to this configuration

eBGP Multipath

--

--

--

1 An em dash (--) indicates that the configuration is not supported.

MPLS Quality of Service Features Supported for Multilink PPP

The table below lists the MPLS QoS features supported for MLP and indicates if the feature is supported on CE-to-PE links, PE-to-P links, and CSC-CE-to-CSC-PE links.

Table 4MPLS QoS Features Supported for MLP

MPLS QoS Feature

CE-to-PE Links

PE-to-P Links

CSC-CE-to-PE Links

Default copy of IP Precedence to EXP bits and the reverse

Supported

--2

--

Set MPLS EXP bits using the modular QoS Command-Line Interface (MQC)

Supported

Supported

Supported

Matching on MPLS EXP using MQC

Supported

Supported

Supported

Low Latency Queueing (LLQ)/ Class-Based Weighted Fair Queueing (CBWFQ) support

Supported

Supported

Supported

Weighted Random Early Detection (WRED) based on EXP bits using MQC

Supported

Supported

Supported

Policer with EXP bit-marking using MQC-3 action

Supported

Supported

Supported

Support for EXP bits in MPLS accounting

Supported

Supported

Supported

2 An em dash (--) indicates that the configuration is not supported.

MPLS--Multilink PPP Support and PE-to-CE Links

The figure below shows a typical MPLS network in which the PE router is responsible for label imposition (at ingress) and disposition (at egress) of the MPLS traffic.

In this topology, MLP is deployed on the PE-to-CE links. The VPN routing and forwarding instance (VRF) interface is in a multilink bundle. There is no MPLS interaction with MLP; all packets coming into the MLP bundle are IP packets.

Figure 1MLP and Traditional PE-to-CE Links


The PE-to-CE routing protocols that are supported for the MPLS--Multilink PPP Support feature are eBGP, OSPF, and EIGRP. Static routes are also supported between the CE and PE routers.

QoS features that are supported for the MPLS--Multilink PPP Support feature on CE-to-PE links are LFI, compressed Real-Time Transport Protocol (cRTP), policing, marking, and classification.

MPLS--Multilink PPP Support and Core Links

The figure below shows a sample topology in which MPLS is deployed over MLP on PE-to-P and P-to-P links. Enabling MPLS on MLP for PE-to-P links is similar to enabling MPLS on MLP for P-to-P links.

Figure 2MLP on PE-to-P and P-to-P Links


You employ MLP in the PE-to-P or P-to-P links primarily so that you can reduce the number of Interior Gateway Protocol (IGP) adjacencies and facilitate the load sharing of traffic.

In addition to requiring MLP on the PE-to-P links, the MPLS--Multilink PPP Support feature requires the configuration of an IGP routing protocol and LDP.

MPLS--Multilink PPP Support in a CSC Network

The figure below shows a typical MPLS VPN CSC network where MLP is configured on the CSC-CE-to-CSC-PE links.

Figure 3MLP on CSC-CE-to-CSC-PE Links with MPLS VPN Carrier Supporting Carrier


The MPLS--Multilink PPP Support feature supports MLP between CSC-CE and CSC-PE links with LDP or with EBGP IPv4 label distribution. This feature also supports LFI for an MPLS VPN CSC configuration. The figure below shows all MLP links that this feature supports for CSC configurations.

Figure 4MLP Supported Links with MPLS VPN Carrier Supporting Carrier


MPLS--Multilink PPP Support in an Interautonomous System

The figure below shows a typical MPLS VPN interautonomous system (Inter-AS) network where MLP is configured on the PE-to-CE links.

Figure 5MLP on ASBR-to-PE Links in an MPLS VPN Inter-AS Network


The MPLS--Multilink PPP Support feature supports MLP between ASBR links for Inter-AS VPNs with LDP and with eBGP IPv4 label distribution.

How to Configure MPLS--Multilink PPP Support

Service providers that use relatively low-speed links can use MLP to spread traffic across them in their MPLS networks. LFI should be deployed in the CE-to-PE link for efficiency, where traffic uses lower link bandwidth (less than 768 kbps). The MPLS--Multilink PPP Support feature can reduce the number of IGP adjacencies and facilitate load sharing of traffic.

The tasks in this section can be performed on CE-to-PE links, PE-to-P links, P-to-P links, and CSC CSC-CE-to-CSC-PE links.

Enabling Cisco Express Forwarding or Distributed Cisco Express Forwarding Switching

Perform the following task to enable Cisco Express Forwarding or distributed Cisco Express Forwarding switching.

Before You Begin

Multilink PPP requires the configuration of standard Cisco Express Forwarding. Distributed MLP (dMLP) requires the configuration of distributed Cisco Express Forwarding.

Cisco Express Forwarding is enabled by default on most Cisco platforms running Cisco IOS software Release12.0 or a later release. To find out if Cisco Express Forwarding is enabled on your platform, enter theshowipcefcommand. If Cisco Express Forwarding is enabled, you receive output that looks like this:

Router# show ip cef 
Prefix              Next Hop            Interface
10.2.61.8/24        192.168.100.1       FastEthernet1/0/0
                    192.168.101.1       FastEthernet6/1

If Cisco Express Forwarding is not enabled on your platform, the output for the showipcefcommand looks like this:

Router# show ip cef
%CEF not running

Distributed Cisco Express Forwarding is enabled by default on devices such as the Catalyst 6500 series switch, the Cisco 7500 series router, and the Cisco 12000 series Internet router.


SUMMARY STEPS

1.    enable

2.    configure terminal

3.   Do one of the following:

  • ip cef
  • ip cef distributed

4.    exit


DETAILED STEPS
 Command or ActionPurpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
Do one of the following:
  • ip cef
  • ip cef distributed


Example:

Router(config)# ip cef



Example:



Example:

Router(config)# ip cef distributed

 

Enables standard Cisco Express Forwarding switching.

or

Enables distributed Cisco Express Forwarding switching.

 
Step 4
exit


Example:

Router(config)# exit

 

Exits to privileged EXEC mode.

 

Creating a Multilink Bundle

Perform this task to create a multilink bundle for the MPLS--Multilink PPP Support feature. This can reduce the number of IGP adjacencies and facilitate load sharing of traffic.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface multilink group-number

4.    ip address address mask [secondary]

5.    encapsulation encapsulation-type

6.    ppp multilink

7.    end


DETAILED STEPS
 Command or ActionPurpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
interface multilink group-number


Example:

Router(config)# interface multilink 1

 

Creates a multilink bundle or enters multilink interface configuration mode.

  • The group-number argument is the number of the multilink bundle (a nonzero number).
 
Step 4
ip address address mask [secondary]


Example:

Router(config-if)# ip address address mask

 

Sets a primary or secondary IP address for an interface.

  • The address argument is the IP address.
  • The mask argument is the mask for the associated IP subnet.
  • The secondary keyword specifies that the configured address is a secondary IP address. If this keyword is omitted, the configured address is the primary IP address.

This command is used to assign an IP address to the multilink interface.

 
Step 5
encapsulation encapsulation-type


Example:

Router(config-if)# encapsulation ppp

 

Sets the encapsulation method used by the interface.

  • The encapsulation-type argument specifies the encapsulation type. The keyword ppp enables PPP encapsulation.
 
Step 6
ppp multilink


Example:

Router(config-if)# ppp multilink

 

Enables MLP on an interface.

 
Step 7
end


Example:

Router(config-if)# end

 

Exits to privileged EXEC mode.

 

Assigning an Interface to a Multilink Bundle

Perform this task to assign an interface to a multilink bundle for the MPLS--Multilink PPP Support feature.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    controller {t1 | e1} slot / port

4.    channel-group channel-number timeslots range

5.    exit

6.    interface serial slot / port : channel-group

7.    ip route-cache [cef | distributed]

8.    no ip address

9.    keepalive [period [retries]]

10.    encapsulation encapsulation-type

11.    multilink-group group-number

12.    ppp multilink

13.    ppp authentication chap

14.    end


DETAILED STEPS
 Command or ActionPurpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
controller {t1 | e1} slot / port


Example:

Router# controller t1 1/3

 

Configures a T1 or E1 controller and enters controller configuration mode.

  • The t1keyword indicates a T1 line card.
  • The e1 keyword indicates an E1 line card.
  • The slot / portarguments are the backplane slot number and port number on the interface. Refer to your hardware installation manual for the specific slot numbers and port numbers.
 
Step 4
channel-group channel-number timeslots range


Example:

Router(config-controller)# channel-group 1 timeslots 1

 

Defines the time slots that belong to each T1 or E1 circuit.

  • The channel-number argument is the channel-group number. When a T1 data line is configured, channel-group numbers can be values from 0 to 23. When an E1 data line is configured, channel-group numbers can be values from 0 to 30.
  • The timeslots range keyword-argument pair specifies one or more time slots or ranges of time slots belonging to the channel group. The first time slot is numbered 1. For a T1 controller, the time slot range is from 1 to 24. For an E1 controller, the time slot range is from 1 to 31. You can specify a time slot range (for example, 1-29), individual time slots separated by commas (for example 1, 3, 5), or a combination of the two (for example 1-14, 15, 17-31).
 
Step 5
exit


Example:

Router(config-controller)# exit

 

Exits to global configuration mode.

 
Step 6
interface serial slot / port : channel-group


Example:

Router(config)# interface serial 1/0:1

 

Configures a serial interface for a Cisco 7500 series router with channelized T1 or E1 and enters interface configuration mode.

  • The slot argument indicates the slot number. Refer to the appropriate hardware manual for slot and port information.
  • The /port argument indicates the port number. Refer to the appropriate hardware manual for slot and port information.
  • The :channel-group argument indicates the channel group number. Cisco 7500 series routers specify the channel group number in the range of 0 to 4 defined with the channel-groupcontroller configuration command.
 
Step 7
ip route-cache [cef | distributed]


Example:

Router(confg-if)# ip route-cache cef

 

Controls the use of switching methods for forwarding IP packets

  • The cef keyword enables Cisco Express Forwarding operation on an interface after Cisco Express Forwarding operation was disabled.
  • The distributed keyword enables distributed switching on the interface.
 
Step 8
no ip address


Example:

Router(config-if)# no ip address

 

Removes any specified IP address.

 
Step 9
keepalive [period [retries]]


Example:

Router(config-if)# keepalive

 

Enables keepalive packets and specifies the number of times that the Cisco IOS software tries to send keepalive packets without a response before bringing down the interface or before bringing the tunnel protocol down for a specific interface.

  • The period argument is an integer value, in seconds, greater than 0. The default is 10.
  • The retriesargument specifies the number of times that the device will continue to send keepalive packets without response before bringing the interface down. Enter an integer value greater than 1 and less than 255. If you do not enter a value, the value that was previously set is used; if no value was specified previously, the default of 5 is used.

If you are using this command with a tunnel interface, the command specifies the number of times that the device will continue to send keepalive packets without response before bringing the tunnel interface protocol down.

 
Step 10
encapsulation encapsulation-type


Example:

Router(config-if)# encapsulation ppp

 

Sets the encapsulation method used by the interface.

  • The encapsulation-type argument specifies the encapsulation type. The keyword ppp enables PPP encapsulation.
 
Step 11
multilink-group group-number


Example:

Router(config-if)# multilink-group 1

 

Designates an interface as part of a multilink leased line bundle.

  • The group-number argument is the number of the multilink bundle (a nonzero number).
 
Step 12
ppp multilink


Example:

Router(config-if)# ppp multilink

 

Enables MLP on an interface.

 
Step 13
ppp authentication chap


Example:

Router(config-if)# ppp authentication chap

 

(Optional) Enables Challenge Handshake Authentication Protocol (CHAP) authentication on a serial interface.

 
Step 14
end


Example:

Router(config-if)# end

 

Exits to privileged EXEC mode.

 

Disabling PPP Multilink Fragmentation

Perform this task to disable PPP multilink fragmentation. PPP multilink fragmentation is enabled by default.

Enabling fragmentation reduces the delay latency among bundle links, but adds some load to the CPU. Disabling fragmentation might produce better throughput.

If your data traffic is consistently of a similar size, we recommend disabling fragmentation. In this case, the benefits of fragmentation can be outweighed by the added load on the CPU.

SUMMARY STEPS

1.    enable

2.    configure terminal

3.    interface type number

4.    ppp multilink fragmentation disable

5.    end


DETAILED STEPS
 Command or ActionPurpose
Step 1
enable


Example:

Router> enable

 

Enables privileged EXEC mode.

  • Enter your password if prompted.
 
Step 2
configure terminal


Example:

Router# configure terminal

 

Enters global configuration mode.

 
Step 3
interface type number


Example:

Router(config)# interface serial 1/0/0

 

Configures an interface type and enters interface configuration mode.

  • The type argument indicates the type of interface to be configured.
  • The number argument specifies the port, connector, or interface card number. The numbers are assigned at the factory at the time of installation or when the interface is added to a system, and can be displayed with the show interfaces command.
 
Step 4
ppp multilink fragmentation disable


Example:

Router(config-if)# ppp multilink fragmentation disable

 

Disables packet fragmentation.

 
Step 5
end


Example:

Router(config-if)# end

 

Exits to privileged EXEC mode.

 

Verifying the Multilink PPP Configuration

SUMMARY STEPS

1.    enable

2.    show ip interface brief

3.    show ppp multilink

4.    show ppp multilink interface interface-bundle

5.    show interface interface-name interface-number

6.    show mpls forwarding-table

7.    exit


DETAILED STEPS
Step 1   enable

Use this command to enable privileged EXEC mode. Enter your password if prompted. For example:



Example: 
Router> enable
Router#
Step 2   show ip interface brief

Use this command to verify logical and physical MLP interfaces. For example:



Example: 
Router# show ip interface brief
Locolrface                  IP-Address      OK? Method Status                Prot
FastEthernet1/0/0         10.3.62.106      YES NVRAM  up                    up
FastEthernet0/0/1          unassigned      YES NVRAM  administratively down down
FastEthernet0/0/0          unassigned      YES NVRAM  administratively down down
FastEthernet0/0/1          unassigned      YES NVRAM  administratively down down
FastEthernet0/0/2          unassigned      YES NVRAM  administratively down down
FastEthernet0/1/0          unassigned      YES NVRAM  administratively down down
FastEthernet0/1/1          unassigned      YES NVRAM  administratively down down
FastEthernet0/1/2          unassigned      YES NVRAM  administratively down down
FastEthernet1/2/0          unassigned      YES NVRAM  administratively down down
FastEthernet1/0/1          unassigned      YES NVRAM  administratively down down
FastEthernet1/1/0          unassigned      YES NVRAM  administratively down down
FastEthernet1/1/1          unassigned      YES NVRAM  administratively down down
FastEthernet1/1/2          unassigned      YES NVRAM  administratively down down
Serial1/1/0:1              unassigned      YES NVRAM  administratively down down
Serial1/1/0:2              unassigned      YES NVRAM  administratively down down
Serial1/1/1:1              unassigned      YES NVRAM  up                    up
Serial1/1/1:2              unassigned      YES NVRAM  up                    down
Serial1/1/3:1              unassigned      YES NVRAM  up                    up
Serial1/1/3:2              unassigned      YES NVRAM  up                    up
Multilink6                 10.30.0.2       YES NVRAM  up                    up
Multilink8                 unassigned      YES NVRAM  administratively down down
Multilink10                10.34.0.2       YES NVRAM  up                    up
Loopback0                  10.0.0.1        YES NVRAM  up                    up
Step 3   show ppp multilink

Use this command to verify that you have created a multilink bundle. For example:



Example: 
Router# show ppp multilink 
Multilink1, bundle name is group 1
 Bundle is Distributed
0 lost fragments, 0 reordered, 0 unassigned, sequence 0x0/0x0 rcvd/sent
0 discarded, 0 lost received, 1/255 load
Member links: 4 active, 0 inactive (max no set, min not set)
 Serial1/0/0/:1
 Serial1/0/0/:2
 Serial1/0/0/:3
 Serial1/0/0/:4
Step 4   show ppp multilink interface interface-bundle

Use this command to display information about a specific MLP interface. For example:



Example: 
Router# show ppp multilink interface multilink6
Multilink6, bundle name is router
  Bundle up for 00:42:46, 1/255 load
  Receive buffer limit 24384 bytes, frag timeout 1524 ms
  Bundle is Distributed
    0/0 fragments/bytes in reassembly list
    1 lost fragments, 48 reordered
    0/0 discarded fragments/bytes, 0 lost received
    0x4D7 received sequence, 0x0 sent sequence
  Member links: 2 active, 0 inactive (max not set, min not set)
    Se1/1/3:1, since 00:42:46, 240 weight, 232 frag size
    Se1/1/3:2, since 00:42:46, 240 weight, 232 frag size
Step 5   show interface interface-name interface-number

Use this command to display information about serial interfaces in your configuration. For example:



Example: 
Router# show interface serial 1/1/3:1
Serial1/1/3:1 is up, line protocol is up
  Hardware is Multichannel T1
  MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation PPP, LCP Open, multilink Open, crc 16, Data non-inverted
  Last input 00:00:01, output 00:00:01, output hang never
  Last clearing of "show interface" counters 00:47:13
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     722 packets input, 54323 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     697 packets output, 51888 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions no alarm present
  Timeslot(s) Used:1, subrate: 64Kb/s, transmit delay is 0 flags
  Transmit queue length 25
Router# show interface serial 1/1/3:2
Serial1/1/3:2 is up, line protocol is up
  Hardware is Multichannel T1
  MTU 1500 bytes, BW 64 Kbit, DLY 20000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation PPP, LCP Open, multilink Open, crc 16, Data non-inverted
  Last input 00:00:03, output 00:00:03, output hang never
  Last clearing of "show interface" counters 00:47:16
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  5 minute input rate 0 bits/sec, 0 packets/sec
  5 minute output rate 0 bits/sec, 0 packets/sec
     725 packets input, 54618 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     693 packets output, 53180 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 output buffer failures, 0 output buffers swapped out
     1 carrier transitions no alarm present
  Timeslot(s) Used:2, subrate: 64Kb/s, transmit delay is 0 flags
  Transmit queue length 26

You can also use the show interface command to display information about the multilink interface:



Example: 
Router# show interface multilink6
Multilink6 is up, line protocol is up
  Hardware is multilink group interface
  Internet address is 10.30.0.2/8
  MTU 1500 bytes, BW 128 Kbit, DLY 100000 usec,
     reliability 255/255, txload 1/255, rxload 1/255
  Encapsulation PPP, LCP Open, multilink Open
  Open: CDPCP, IPCP, TAGCP, loopback not set
  DTR is pulsed for 2 seconds on reset
  Last input 00:00:00, output never, output hang never
  Last clearing of "show interface" counters 00:48:43
  Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
  Queueing strategy: fifo
  Output queue: 0/40 (size/max)
  30 second input rate 0 bits/sec, 0 packets/sec
  30 second output rate 0 bits/sec, 0 packets/sec
     1340 packets input, 102245 bytes, 0 no buffer
     Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
     0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
     1283 packets output, 101350 bytes, 0 underruns
     0 output errors, 0 collisions, 1 interface resets
     0 output buffer failures, 0 output buffers swapped out
     0 carrier transitions
Step 6   show mpls forwarding-table

Use this command to display contents of the MPLS Label Forwarding Information Base (LFIB) and look for information on multilink interfaces associated with a point2point next hop. For example:



Example: 
Router# show mpls forwarding-table
Local  Outgoing    Prefix            Bytes tag  Outgoing   Next Hop
tag    tag or VC   or Tunnel Id      switched   interface
16     Untagged    10.30.0.1/32      0          Mu6        point2point
17     Pop tag     10.0.0.3/32       0          Mu6        point2point
18     Untagged    10.0.0.9/32[V]    0          Mu10       point2point
19     Untagged    10.0.0.11/32[V]   6890       Mu10       point2point
20     Untagged    10.32.0.0/8[V]    530        Mu10       point2point
21     Aggregate   10.34.0.0/8[V]    0
22     Untagged    10.34.0.1/32[V]   0          Mu10       point2point

Use the show ip bgp vpnv4command to display VPN address information from the Border Gateway Protocol (BGP) table:



Example: 
Router# show ip bgp vpnv4 all summary
BGP router identifier 10.0.0.1, local AS number 100
BGP table version is 21, main routing table version 21
10 network entries using 1210 bytes of memory
10 path entries using 640 bytes of memory
2 BGP path attribute entries using 120 bytes of memory
1 BGP extended community entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP using 1994 total bytes of memory
BGP activity 10/0 prefixes, 10/0 paths, scan interval 5 secs
10.0.0.3  4 100 MsgRc52 MsgSe52  TblV21  0  0 00:46:35 State/P5xRcd
Step 7   exit

Use this command to exit to user EXEC mode. For example:



Example: 
Router# exit
Router>

Configuration Examples for MPLS--Multilink PPP Support

Sample MPLS--Multilink PPP Support Configurations

The following examples show sample configurations for MLP on a Cisco 7200 router, on a Cisco 7500 router, and on a CSC network. The configuration of MLP on an interface is the same for PE-to-CE links, PE-to-P links, and P-to-P links.

Sample Multilink PPP Configuration on Cisco 7200 Series Router

Following is a sample configuration of a Cisco 7200 router, which is connected with a T1 line card and configured with an MPLS Multilink PPP interface:

controller T1 1/3
 framing esf
 clock source internal
 linecode b8zs
 channel-group 1 timeslots 1
 channel-group 2 timeslots 2
 no yellow generation
 no yellow detection
!
interface Multilink6
 ip address 10.37.0.1 255.0.0.0
 ppp multilink interleave
 tag-switching ip
 load-interval 30
 multilink-group 6
!
interface Serial1/3:1
 encapsulation ppp
 no ip address
 ppp multilink
 tx-queue-limit 26
 multilink-group 6
 peer neighbor-route
!
interface Serial1/3:2
 encapsulation ppp
 no ip address
 ppp multilink
 tx-queue-limit 26
 multilink-group 6
 peer neighbor-route

Sample Multilink PPP Configuration for Cisco 7500 Series Router

Following is a sample configuration of a Cisco 7500 router, which is connected with a T1 line card and configured with an MPLS Multilink PPP interface:

controller T1 1/1/3
 framing esf
 clock source internal
 linecode b8zs
 channel-group 1 timeslots 1
 channel-group 2 timeslots 2
 no yellow generation
 no yellow detection
!
interface Multilink6
 ip address 10.37.0.2 255.0.0.0
 ppp multilink interleave
 tag-switching ip
 load-interval 30
 multilink-group 6
!
interface Serial1/1/3:1
 encapsulation ppp
 no ip address
 ppp multilink
 tx-queue-limit 26
 multilink-group 6
 peer neighbor-route
!
interface Serial1/1/3:2
 encapsulation ppp
 no ip address
 ppp multilink
 tx-queue-limit 26
 multilink-group 6
 peer neighbor-route

Sample Multilink PPP Configuration on an MPLS CSC PE Router

Following is a sample configuration for an MPLS CSC PE router. An EBGP session is configured between the PE and CE routers. 

PE-Router# show running-config interface Serial1/0:1
Building configuration...
!
mpls label protocol ldp
ip cef
ip vrf vpn2
 rd 200:1
 route-target export 200:1
 route-target import 200:1
!
controller T1 1/0
 framing esf
 clock source internal
 linecode b8zs
 channel-group 1 timeslots 1
 channel-group 2 timeslots 2
 no yellow generation
 no yellow detection
!
interface Serial1/0:1
 no ip address
 encapsulation ppp
 tx-ring-limit 26
 ppp multilink
 ppp multilink group 1
!
interface Serial1/0:2
 no ip address
 encapsulation ppp
 tx-ring-limit 26
 ppp multilink
 ppp multilink group 1
!
interface Multilink1
 ip vrf forwarding vpn2
 ip address 10.35.0.2 255.0.0.0
 no peer neighbor-route
 load-interval 30
 ppp multilink
 ppp multilink interleave
 ppp multilink group 1
!
!
router ospf 200
 log-adjacency-changes
 auto-cost reference-bandwidth 1000
 redistribute connected subnets
 passive-interface Multilink1
 network 10.0.0.7 0.0.0.0 area 200
 network 10.31.0.0 0.255.255.255 area 200
!
!
 router bgp 200
 no bgp default ipv4-unicast
 bgp log-neighbor-changes
 neighbor 10.0.0.11 remote-as 200
 neighbor 10.0.0.11 update-source Loopback0
 !
 address-family vpnv4
 neighbor 10.0.0.11 activate
 neighbor 10.0.0.11 send-community extended
 bgp scan-time import 5
 exit-address-family
 !
 address-family ipv4 vrf vpn2
 redistribute connected
 neighbor 10.35.0.1 remote-as 300
 neighbor 10.35.0.1 activate
 neighbor 10.35.0.1 as-override
 neighbor 10.35.0.1 advertisement-interval 5
 no auto-summary
 no synchronization
 exit-address-family

Enabling Cisco Express Forwarding or Distributed Cisco Express Forwarding Example

The following example shows how to enable Cisco Express Forwarding for MLP configurations:

enable
configure terminal 
ip cef

The following example shows how to enable distributed Cisco Express Forwarding for dMLP configurations:

enable
configure terminal 
ip cef distribute

Creating a Multilink Bundle Example

The following example shows how to create a multilink bundle for the MPLS--Multilink PPP Support feature: 

interface multilink 1
 ip address 10.0.0.0 10.255.255.255
 encapsulation ppp
 ppp chap hostname group 1
 ppp multilink
 multilink-group 1

Assigning an Interface to a Multilink Bundle Example

The following example shows how to create four multilink interfaces with distributed Cisco Express Forwarding switching and MLP enabled. Each of the newly created interfaces is added to a multilink bundle.

interface multilink1
 ip address 10.0.0.0 10.255.255.255
 ppp chap hostname group 1
 ppp multilink
 multilink-group 1
	
interface serial 1/0/0/:1
 no ip address
 encapsulation ppp
 ip route-cache distributed
 no keepalive
 ppp multilink
 multilink-group 1
interface serial 1/0/0/:2
 no ip address
 encapsulation ppp
 ip route-cache distributed
 no keepalive
 ppp chap hostname group 1
 ppp multilink
 multilink-group 1
interface serial 1/0/0/:3
 no ip address
 encapsulation ppp
 ip route-cache distributed
 no keepalive
 ppp chap hostname group 1
 ppp multilink
 multilink-group 1
interface serial 1/0/0/:4
 no ip address
 encapsulation ppp
 ip route-cache distributed
 no keepalive
 ppp chap hostname group 1
 ppp multilink
 multilink-group

Additional References

The following sections provide references related to the MPLS--Multilink PPP Support feature:

Related Documents

Related Topic

Document Title

Configuration tasks for Distributed MLP for Cisco 7500 series routers

Distributed Multilink Point-to-Point Protocol for Cisco 7500 Series Routers

Configuration tasks for media-independent PPP and Multilink PPP

Configuring Media-Independent PPP and Multilink PPP

Configuration tasks for MPLS DiffServ tunneling modes

MPLS DiffServ Tunneling Modes

Configuration tasks for the MPLS QoS multi-VC mode feature

"Configuring MPLS" chapter, Cisco IOS Multiprotocol Label Switching Configuration Guide , Release 12.4

Configuration tasks for MPLS VPNs

"MPLS Virtual Private Networks" chapter, Cisco IOS Multiprotocol Label Switching Configuration Guid e, Release 12.4

Configuration tasks for MPLS VPN CSC

"MPLS Virtual Private Networks" chapter, Cisco IOS Multiprotocol Label Switching Configuration Guid e, Release 12.4

Configuration tasks for MPLS VPN CSC with IPv4 BGP label distribution

"MPLS Virtual Private Networks" chapter, Cisco IOS Multiprotocol Label Switching Configuration Guid e, Release 12.4

Configuration tasks for MPLS VPN Inter-AS with IPv4 BGP label distribution

"MPLS Virtual Private Networks" chapter, Cisco IOS Multiprotocol Label Switching Configuration Guid e, Release 12.4

Standards

Standards

Title

No new or modified standards are supported by this feature, and support for existing standards has not been modified by this feature.

--

MIBs

MIBs

MIBs Link

No new or modified MIBs are supported by this feature, and support for existing MIBs has not been modified by this feature.

To locate and download MIBs for selected platforms, Cisco IOS releases, and feature sets, use Cisco MIB Locator found at the following URL:

http://www.cisco.com/go/mibs

RFCs

RFCs

Title

RFC 1990

The PPP Multilink Protocol (MP)

Technical Assistance

Description

Link

The Technical Support & Documentation website contains thousands of pages of searchable technical content, including links to products, technologies, solutions, technical tips, and tools. Registered Cisco.com users can log in from this page to access even more content.

http://www.cisco.com/techsupport

Command Reference

This feature uses no new or modified commands.

Feature Information for MPLS--Multilink PPP Support

The following table provides release information about the feature or features described in this module. This table lists only the software release that introduced support for a given feature in a given software release train. Unless noted otherwise, subsequent releases of that software release train also support that feature.

Use Cisco Feature Navigator to find information about platform support and Cisco software image support. To access Cisco Feature Navigator, go to www.cisco.com/go/cfn. An account on Cisco.com is not required.

Table 5Feature Information for MPLS--Multilink PPP Support

Feature Name

Releases

Feature Information

MPLS--Multilink PPP Support

12.2(8)T 12.2(15)T1012.3(5a) 12.3(7)T 12.2(28)SB 12.4(20)T

The MPLS--Multilink PPP Support feature ensures that MPLS Layer 3 Virtual Private Networks (VPNs) with quality of service (QoS) can be enabled for bundled links. This feature supports Multiprotocol Label Switching (MPLS) over Multilink PPP (MLP) links in the edge (provider edge [PE]-to-customer edge [CE]) or in the MPLS core (PE-to-PE and PE-to-provider router [P]).

Service providers that use relatively low-speed links can use MLP to spread traffic across them in their MPLS networks. Link fragmentation and interleaving (LFI) should be deployed in the CE-to-PE link for efficiency, where traffic uses a lower link bandwidth (less than 768 kbps).

In 12.2(8)T, MLP support on CE-to-PE links was introduced.

In 12.2(15)T10 and 12.3(5a), MLP support for MPLS networks was extended to PE-to-P links, PE-to-PE links, Carrier Supporting Carrier (CSC) CSC-CE-to-CSC-PE links, and interautonomous system (Inter-AS) PE-to-PE links.

In 12.3(7)T, the feature was integrated into the Cisco IOS 12.3T release.

In 12.2(28)SB, the feature was integrated into the Cisco IOS 12.2SB release.

In 12.4(20)T, the feature was integrated into the Cisco IOS 12.4T release.

Glossary

bundle --A group of interfaces connected by parallel links between two systems that have agreed to use Multilink PPP (MLP) over those links.

CBWFQ --class-based weighted fair queueing. A queueing option that extends the standard Weighted Fair Queueing (WFQ) functionality to provide support for user-defined traffic classes.

Cisco Express Forwarding --A proprietary form of switching that optimizes network performance and scalability for networks with large and dynamic traffic patterns, such as the Internet, and for networks characterized by intensive web-based applications or interactive sessions. Although you can use Cisco Express Forwarding in any part of a network, it is designed for high-performance, highly resilient Layer 3 IP backbone switching.

EIGRP --Enhanced Interior Gateway Routing Protocol. An advanced version of the Interior Gateway Routing Protocol (IGRP) developed by Cisco. It provides superior convergence properties and operating efficiency, and combines the advantages of link-state protocols with those of distance vector protocols.

IGP --Interior Gateway Protocol. An Internet protocol used to exchange routing information within an autonomous system. Examples of common Internet IGPs include Interior Gateway Routing Protocol (IGRP), Open Shortest Path First (OSPF), and Routing Information Protocol (RIP).

IGRP --Interior Gateway Routing Protocol. An Interior Gateway Protocol (IGP) developed by Cisco to address the issues associated with routing in large, heterogeneous networks. Compare with Enhanced Interior Gateway Routing Protocol (EIGRP).

IS-IS --Intermediate System-to-Intermediate System. An Open Systems Interconnection (OSI) link-state hierarchical routing protocol, based on DECnet Phase V routing, in which IS-IS routers exchange routing information based on a single metric to determine network topology.

LCP --Link Control Protocol. A protocol that establishes, configures, and tests data link connections for use by PPP.

LFI --link fragmentation and interleaving. The Cisco IOS XE LFI feature reduces delay on slower-speed links by breaking up large datagrams and interleaving low-delay traffic packets with the smaller packets resulting from the fragmented datagram. LFI allows reserve queues to be set up so that Real-Time Protocol (RTP) streams can be mapped into a higher priority queue in the configured weighted fair queue set.

link --One of the interfaces in a bundle.

LLQ --low latency queueing. A quality of service QoS queueing feature that provides a strict priority queue (PQ) for voice traffic and weighted fair queues for other classes of traffic. It is also called priority queueing/class-based weighted fair queueing (PQ/CBWFQ).

MLP --Multilink PPP. A method of splitting, recombining, and sequencing datagrams across multiple logical links. The use of MLP increases throughput between two sites by grouping interfaces and then load balancing packets over the grouped interfaces (called a bundle). Splitting packets at one end, sending them over the bundled interfaces, and recombining them at the other end achieves load balancing.

MQC --Modular QoS CLI. MQC is a CLI structure that allows users to create traffic polices and attach these polices to interfaces. MQC allows users to specify a traffic class independently of QoS policies.

NCP --Network Control Protocol. A series of protocols for establishing and configuring different network layer protocols (such as for AppleTalk) over PPP.

OSPF --Open Shortest Path First. A link-state, hierarchical Interior Gateway Protocol (IGP) routing algorithm proposed as a successor to Routing Information Protocol (RIP) in the Internet community. OSPF features include least-cost routing, multipath routing, and load balancing. OSPF was derived from an early version of the IS-IS protocol.

PPP --Point-to-Point Protocol. A successor to the Serial Line Interface Protocol (SLIP) that provides router-to-router and host-to-network connections over synchronous and asynchronous circuits. PPP works with several network layer protocols (such as IP, Internetwork Packet Exchange [IPX], and AppleTalk Remote Access [ARA]). PPP also has built-in security mechanisms (such as Challenge Handshake Authentication Protocol [CHAP] and Password Authentication Protocol [PAP]). PPP relies on two protocols: Link Control Protocol (LCP) and Network Control Protocol (NCP).

RIP --Routing Information Protocol. A version of Interior Gateway Protocol (IGP) that is supplied with UNIX Berkeley Standard Distribution (BSD) systems. Routing Information Protocol (RIP) is the most common IGP in the Internet. It uses hop count as a routing metric.

Virtual Bundle Interface --An interface that represents the master link of a bundle. It is not tied to any physical interface. Data going over the bundle is transmitted and received through the master link.

WFQ --weighted fair queueing. A congestion management algorithm that identifies conversations (in the form of traffic streams), separates packets that belong to each conversation, and ensures that capacity is shared fairly among the individual conversations. WFQ is an automatic way of stabilizing network behavior during congestion and results in improved performance and reduced retransmission.

WRED --weighted random early detection. A queueing method that ensures that high-precedence traffic has lower loss rates than other traffic during times of congestion.

Cisco and the Cisco logo are trademarks or registered trademarks of Cisco and/or its affiliates in the U.S. and other countries. To view a list of Cisco trademarks, go to this URL: www.cisco.com/go/trademarks. Third-party trademarks mentioned are the property of their respective owners. The use of the word partner does not imply a partnership relationship between Cisco and any other company. (1110R)

Any Internet Protocol (IP) addresses and phone numbers used in this document are not intended to be actual addresses and phone numbers. Any examples, command display output, network topology diagrams, and other figures included in the document are shown for illustrative purposes only. Any use of actual IP addresses or phone numbers in illustrative content is unintentional and coincidental.

1 An em dash (--) indicates that the configuration is not supported.
2 An em dash (--) indicates that the configuration is not supported.
© 2011 Cisco Systems, Inc. All rights reserved.