Configuring Multichassis Multilink PPP

This chapter describes the use of Multichassis Multilink Point-to-Point Protocol (MMP) on the Cisco AccessPath-TS3 Integrated Access System. The chapter begins with the principles of MMP and how it works, and then includes procedures for configuring MMP.

To enable MMP on the AccessPath-TS3 system, you must configure the Access Server Shelves.

Topics in this section include the following:

Understanding MMP

This section presents a brief overview of MMP operations and includes the following topics:

MMP is a feature in Cisco IOS Release 11.2 and later that extends Multilink PPP Protocol (MP, also known as MLP) functionality across multiple chassis.

MP gives users additional bandwidth on demand by splitting and recombining packets across a logical pipe (bundle) formed by multiple links. On the transmit end, MP provides for the fragmentation of a single packet into multiple packets for transmission across multiple PPP links. On the receive end, MP provides packet reassembly from multiple PPP links.

MMP enhances MP by permitting MP links from a single client to terminate on different access servers. The whole process is invisible to the user.

MMP allows Internet service providers (ISPs) and enterprise system administrators the flexibility to group multiple access servers into a single rotary group that users can access from a single number. The MMP client is unaware that the MP bundle is made up of links terminating on different access servers.

Why Use MMP?

MMP is particularly suited to the Cisco AccessPath-TS3 Integrated Access System for the following reasons:

Scalability--You can add Access Server Shelves to the AccessPath-TS3 system.
Dialup pooling--MMP permits the AccessPath-TS3 system to use Access Server Shelves for the dialup pool and to reassemble and resequence MP packets.
Stack grouping--All Access Server Shelves can be designated as a stack group. The stack group can support a variety of technologies.
Single access number--Any stack group member can answer a call coming into a single access number. This single access number would normally be applied via a telco hunt group (a single number the telco applies to a group of physical connections). The central office switch can assign any call made to the access number to any ISDN B channel on any PRI within this hunt group.

How MMP Works

MMP works with the Stack Group Bidding Protocol (SGBP), which supports bidding and arbitration across multiple shelves in the AccessPath-TS3 system.

Figure 8-1: MMP Operation

In Figure 8-1, User X (connected to Router Y) takes advantage of the added bandwidth provided by MP when dialing into the AccessPath-TS3 system stack. The Access Server Shelf that answers the first call will host the master bundle for MMP calls. The following sequence illustrates a typical scenario when the AccessPath-TS3 system is configured in a peer stack group:

Call 1 is made and Access Server Shelf A asks other shelves whether anyone has received the first call from Router Y.
If no one received the first call from Router Y, Access Server Shelf A will accept the call.
When User X needs more bandwidth, Call 2 is made and, in this example, Access Server Shelf C accepts the call and informs the stack group.
The stack group members bid for ownership of the call, but Access Server Shelf A wins the bid because it already has an MP session with User X.
Access Server Shelf A sets up an L2F tunnel to pass raw PPP data between the Access Server Shelf C and itself.

Configuring MMP on the Access Server Shelves

The Access Server Shelves in the AccessPath-TS3 system use MMP by default, for multi-channel operation. SGBP is used to control channel termination.

Configure MMP

**Table 8-1: Configuring MMP--Access Server Shelf**
Step	Command	Purpose
1	`AS01>` `enable` `Password:` `AS01#`	Enter enable mode. Enter the password. You have entered enable mode when the prompt changes to `AS01#`.
2	`AS01#` `config term` `Enter configuration commands, one per line. End with CNTL/Z.` `AS01(config)#`	Enter global configuration mode. You have entered global configuration mode when the prompt changes to `AS01(config)#`.
3	`AS01(config)#` `sgbp group mystack`	Create a stack group and assign this Access Server Shelf to it. Substitute your stack group name for `mystack`.
4	`AS01(config)#` `sgbp member AS02 172.16.1.34` `AS01(config)#` `sgbp member AS03 172.16.1.35` `AS01(config)#` `sgbp member AS04 172.16.1.36` `AS01(config)#` `sgbp member AS05 172.16.1.37` `AS01(config)#` `sgbp member AS06 172.16.1.38` `AS01(config)#` `sgbp member AS07 172.16.1.39` `AS01(config)#` `sgbp member AS08 172.16.1.40` `AS01(config)#` `sgbp member AS09 172.16.1.41` `AS01(config)#` `sgbp member AS10 172.16.1.42` `AS01(config)#` `sgbp member AS11 172.16.1.43` `AS01(config)#` `sgbp member AS12 172.16.1.44` `AS01(config)#` `sgbp member AS13 172.16.1.45` `AS01(config)#` `sgbp member AS14 172.16.1.46` `AS01(config)#` `sgbp member AS15 172.16.1.47` `AS01(config)#` `sgbp member AS16 172.16.1.48` `AS01(config)#` `sgbp member AS17 172.16.1.49` `AS01(config)#` `sgbp member AS18 172.16.1.50` `AS01(config)#` `sgbp member AS19 172.16.1.51` `AS01(config)#` `sgbp member AS20 172.16.1.52` `AS01(config)#` `sgbp member AS21 172.16.1.53`	Specify the host name and IP address of the peer member of the stack group. In this example, there are 21 peers.
5	`AS01(config)#` `sgbp seed-bid default`	Set the bidding level for a stack group member. Default indicates that the Access Server Shelf will only bid for an external call if it is already bundling the first channel of the same set.
6	`AS01(config)#` `sgbp source-ip 172.16.1.33`	Set the source IP address for SGBP packets. The AccessPath-TS3 system uses Loopback 0 addresses for SGBP source IP addresses.
7	`AS01(config)#` `username mystack password mypassword`	Assign a password for the SGBP peers to exchange. The username must match the stack group name. The same password must be configured in each Access Server Shelf in the SGBP group. Substitute your stack group name for `mystack`, and your SGBP password for `mypassword`.
8	`AS01(config)#` `end` `AS01#` `%SYS-5-CONFIG_I: Configured from console by console`	Return to privileged EXEC mode. This message is normal and does not indicate an error.

Verify the MMP Configuration

To verify the MMP configuration on each Access Server Shelf:

Enter the show sgbp command:

AS01# show sgbp
Group Name: test Ref: 0x4780B252
Seed bid: default, 50, default seed bid setting
 
  Member Name: AS02 State: active Id: 9
  Ref: 0x4780B54D
  Address: 172.16.1.34
AS02# show sgbp
Group Name: test Ref: 0x4780B54D
Seed bid: default, 50, default seed bid setting
 
  Member Name: AS01 State: active Id: 1
  Ref: 0x4780B252
  Address: 172.16.1.33

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