Information Technology Reference
In-Depth Information
For a complete description of the MMP commands referenced herein, refer to the
Cisco Dial Solutions
Command Reference
. To locate documentation of other commands that appear in this chapter, use the
command reference master index or search online.
MMP is supported on the Cisco 7500, 4500, and 2500 series platforms, and on synchronous serial,
asynchronous serial, ISDN BRI, ISDN PRI, and dialer interfaces.
MMP does not require reconfiguration of telephone company switches.
Configuration
Routers or access servers are configured to belong to groups of peers, called
stack groups
. All members
of the stack group are peers; stack groups do not need a permanent lead router. Any stack group member
can answer calls coming from a single access number, which is usually an ISDN PRI hunt group. Calls
can come in from remote user devices, such as routers, modems, ISDN terminal adapters, or PC cards.
When a connection is established with one member of a stack group, that member owns the call. If a
second call comes in from the same client and a different router answers the call, the router establishes
a tunnel and forwards all packets belonging to the call to the router that owns the call. Establishing a
tunnel and forwarding calls through it to the router that owns the call is sometimes called
projecting the
PPP link to the call master
.
If a more powerful router is available, it can be configured as a member of the stack group, and the other
stack group members can establish tunnels and forward all calls to it. In such a case, the other stack
group members are just answering calls and forwarding traffic to the more powerful
offload
router.
High-latency WAN lines between stack group members can make stack group operation
inefficient.
Note
MMP call handling, bidding, and Layer 2 forwarding operations in the stack group proceed as follows,
as shown in Figure 16-11:
When the first call comes in to the stack group, Router A answers.
1.
In the bidding, Router A wins because it already has the call. Router A becomes the
call master
for
that session with the remote device. (Router A might also be called the
host to the master bundle
interface
.)
2.
When the remote device that initiated the call needs more bandwidth, it makes a second multilink
PPP call to the group.
3.
When the second call comes in, Router D answers it and informs the stack group. Router A wins the
bidding because it already is handling the session with that remote device.
4.
Router D establishes a tunnel to Router A and forwards the raw PPP data to Router A.
5.
Router A reassembles and resequences the packets.
6.
If more calls come in to Router D and they, too, belong to Router A, the tunnel between A and D
enlarges to handle the added traffic. Router D does not establish an additional tunnel to A.
7.
If more calls come in and are answered by any other router, that router also establishes a tunnel to
A and forwards the raw PPP data.
8.
The reassembled data is passed on the corporate network as if it had all come through one physical
link.
9.
