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This feature module describes the Distributed Multilink Point to Point Protocol (MLPPP) feature for Cisco 7500 series routers. It includes information on the benefits of the new feature, supported platforms, related documents, configuration examples and a command reference.
This document contains the following sections:
The Distributed Multilink Point to Point Protocol (MLPPP) feature allows you to combine T1/E1 lines in a Versatile Interface Processor (VIP) on a Cisco 7500 series router into a bundle that has the combined bandwidth of multiple T1/E1 lines. This is done by using a VIP MLPPP link. You choose the number of bundles and the number of T1/E1 lines in each bundle. This allows you to increase the bandwidth of your network links beyond that of a single T1/E1 line without having to purchase a T3 line. Non-distributed MLPPP can only perform limited links, with CPU utilization quickly reaching 90% with only a few T1/E1 lines running MLPPP. With distributed MLP, you can increase the router's total capacity.
Figure 1 shows a typical network using a VIP MLPPP link. The Cisco 7500 series router is connected to the network with a CT3 line that has been configured with VIP MLPPP to carry two bundles of four T1 lines each. Each of these bundles goes out to separate remote Cisco 7200 series routers, which each have one MLPPP bundle of four T1 lines. The Cisco 7500 series router is also connected to another CT3 line that has been configured with VIP MLPPP to carry two bundles of two T1 lines. One of these bundles goes out to a Cisco 2500 series router and the other goes out to a Cisco 3800 series router.
The Multilink PPP Inverse Multiplexer feature is geared towards ISPs who want to have the bandwidth of multiple T1 lines with performance comparable to that of an inverse multiplexer without having to buy stand alone inverse-multiplexing equipment. A Cisco router supporting VIPs can now bundle multiple T1 lines in a CT3 or CE3 interface. This is more economical than purchasing an inverse multiplexer, and eliminates the need to configure another piece of equipment and extra shelf space.
This feature supports the CT3 or CE3 data rate without taxing the RSP and CPU by moving the data path to the VIP.
This feature also allows remote sites to purchase multiple T1 lines instead of a T3 line for additional bandwidth. This is especially useful when the remote site does not need the bandwidth of an entire T3 line.
This feature allows multilink fragmentation to be disabled, so multilink packets can be Cisco Express Forwarded (CEF) on all platforms, if fragmentation is disabled.
CEF is now supported with fragmentation enabled or disabled.
The following restrictions apply to the Multilink PPP Inverse Multiplexer feature:
Cisco 7500 series
No MIBs are supported by this feature.
This feature supports the following RFC:
RFC 1990
CEF distributed switching must be enabled
You will need the following port adapter to use the Distributed MLPPP feature:
CT3IP (Channelized T3 Interface Processor)
Perform the following tasks to configure a multilink bundle:
In order to enable Distributed MLPPP, you must first enable Distributed CEF switching. To enable dCEF, use the ip cef distributed command in global configuration mode:
| Command | Purpose |
|---|---|
ip cef distributed | Enable distributed CEF switching. |
To create a multilink bundle, use the following commands beginning in global configuration mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| interface multilink group-number | Enter multilink interface configuration mode. | ||
| ip address address mask | Assign an IP address to the multilink interface. | ||
| encapsulation ppp | Enable PPP encapsulation. | ||
| ppp multilink | Enable Multilink PPP. |
To assign an interface to a multilink bundle, use the following commands in interface configuration mode:
| Step | Command | Purpose | ||
|---|---|---|---|---|
| no ip address | Remove any specified IP address. | ||
| keepalive | Set the frequency of keepalive packets. | ||
| encapsulation ppp | Enable PPP encapsulation. | ||
| multilink-group group-number | Assign the interface to a multilink bundle. | ||
| ppp multilink | Enable Multilink PPP. | ||
| ppp authentication chap | (Optional) Enable Challenge Handshake Authentication Protocol (CHAP) authentication. |
By default, PPP multilink fragmentation is enabled. To disable PPP multilink fragmentation, use the following command in interface configuration mode:
| Command | Purpose |
|---|---|
no ppp multilink fragmentation | Disable PPP multilink fragmentation. |
Enabling fragmentation reduces the delay latency among bundle links, but adds some load to the CPU. Disabling fragmentation may result in better throughput.
If your data traffic is consistently of a similar size, we recommend disabling fragmentation. In this case, the benefits of fragmentation may be outweighed by the added load on the CPU.
Use the show ppp multilink command to display information about the newly created multilink bundle:
Router# show ppp multilink Multilink1, bundle name is group1 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 not set, min not set) Serial1/0/0:1 Serial1/0/0/:2 Serial1/0/0/:3 Serial1/0/0/:4
This section provides the following configuration examples:
In the following example, Distributed Cisco Express Forwarding is turned on in a Cisco 7500 series router:
ip cef distributed
In the following example, the T3 controller is configured and four channelized interfaces are created:
controller T3 1/0/0 framing m23 cablelength 10 t1 1 timeslots 1-24 t1 2 timeslots 1-24 t1 3 timeslots 1-24 t1 4 timeslots 1-24
In the following example, four multilink interfaces are created with distributed CEF switching and MLPPP enabled. Each of the newly created interfaces are added to a multilink bundle:
interface multilink1 ip address 10.0.0.0 10.255.255.255 ppp chap hostname group 1 ppp multilink multiling-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 1
This section documents new or modified commands. All other commands used with this feature are documented in the Cisco IOS Release 12.0 command references.
To create a multilink bundle or enter multilink interface configuration mode, use the interface multilink global configuration command. To remove a multilink bundle, use the no form of this command.
interface multilink group-number
group-number | Number of the multilink bundle (a nonzero number). |
No interfaces are configured.
Global configuration
| Release | Modification |
|---|---|
12.0(3)T | This command was introduced. |
The following example creates multilink bundle 1:
interface multilink 1 ip address 192.168.11.4 255.255.255.192 encapsulation ppp ppp multilink keepalive
multilink-group
ppp multilink fragmentation
To designate an interface as part of a multilink leased line bundle, use the multilink-group command in interface configuration mode. To remove an interface from a bundle, use the no form of this command.
multilink-group group-number
group-number | Number of the multilink bundle (a nonzero number). |
Disabled
Interface configuration
| Release | Modification |
|---|---|
12.0(3)T | This command was introduced. |
All interfaces in a multilink bundle must have the same bandwidth.
The following example designates serial interface 1 as part of multilink bundle 1:
interface serial 1/0/0:1 encapsulation ppp multilink-group 1 ppp multilink ppp authentication chap
interface multilink
ppp multilink fragmentation
To enable PPP multilink fragmentation, use the ppp multilink fragmentation command in interface configuration mode. To disable fragmentation, use the no form of this command.
ppp multilink fragmentationThis command has no arguments or keywords.
Enabled
Interface configuration
| Release | Modification |
|---|---|
12.0(3)T | This command was introduced. |
This command first appeared in Cisco IOS Release 12.0(3)T.
Enabling fragmentation reduces the delay latency among bundle links, but adds some load to the CPU. Disabling fragmentation may result in better throughput.
If your data traffic is consistently of a similar size, we recommend disabling fragmentation. In this case, the benefits of fragmentation may be outweighed by the added load on the CPU.
The following example disables PPP multilink fragmentation:
no ppp multilink fragmentation
interface multilink
multilink-group
To display information about Multilink PPP, use the show ppp multilink EXEC command.
show ppp multilinkThis command has no arguments or keywords.
No default behaviors or values
EXEC
| Release | Modification |
|---|---|
12.0(3)T | This command was introduced. |
Display information about member links of a multilink ppp group, including interfaces, bundles, lost fragments and the state of the distributed feature.
The following example displays information about a multilink group:
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
The following debug commands are supported on the VIP for this feature:
bundle--A group of interfaces connected via parallel links between two systems that have agreed to do MLP over those links.
differential delay--The amount of time that passes between the reception of two related signals that arrive on two separate carriers.
CEF--Cisco Express Forwarding. Optimizes network performance and scalability for networks with large and dynamic traffic patterns, such as the Internet, on networks characterized by intensive Web-based applications or interactive sessions. Although you can use CEF in any part of a network, it is designed for high-performance, highly resilient Layer 3 IP backbone switching.
IMUX--Inverse multiplexer.
LCP--Link Control Protocol. A protocol that establishes, configures, and tests dat-link connections for use by PPP.
link--One of the interfaces in a bundle.
MLP--Multilink Point to Point Protocol. A method of splitting, recombining, and sequencing datagrams across multiple logical data links.
mux--A multiplexing device. A mux combines multiple signals for transmission over a single line. The signals are demultiplexed (separated) at the receiving end.
NCP--Network Control Protocol. A series of protocols for establishing and configuring different network layer protocols (such as for AppleTalk) over PPP.
OIR--online insertion and removal. A feature that permits the addition, replacement, or removal of cards without interrupting the system power, entering console commands, or causing other software or interfaces to shut down.
PCI--Peripheral Component Interconnect. An open specification of the electrical, mechanical, and protocol features of a PCI bus. The PCI bus can operate at speeds up to 33 Mhz with a synchronous data transfer size of up to 64 data bits. The initial version of the VIP motherboard supports 25 Mhz and 32 bit transfer.
PPP--Point-to-Point Protocol. A successor to SLIP that provides router-to-router and host-to-network connections over synchronous and asynchronous circuits. PPP was designed to work with several network layer protocols (such as IP, IPX, and ARA). PPP also has built-in security mechanisms (such as CHAP and PAP). PPP relies on two protocols: LCP and NCP.
RSP--Route Switch Processor. Processor module used in the Cisco 7500 series routers that integrates the functions of the Route Processor and the Switch Processor. The former contains the CPU, system software, most of the router's memory components; the latter is a processor module that acts as the administrator for all Cisco Extended Bus activities.
VIP--Versatile Interface Processor. An interface card that is used in Cisco 7000 and Cisco 7500 series routers. It can hold different port adapters to interface to various media (Ethernet, TokenRing, FDDI, Serial, ATM, etc.). The VIP supports 2 port adapters, standard packet delivery, distributed CEF and feature off-load.
Virtual Bundle Interface--An interface, which is not tied to any physical interface, that represents the master link of a bundle. Data going over the bundle is transmitted and received through the master link.
Posted: Wed Aug 16 20:44:48 PDT 2000
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