Filter
Top Products
22-5
Cisco 10000 Series Router Software Configuration Guide
OL-2226-23
Chapter 22 Configuring Multilink Point-to-Point Protocol Connections
MLP Groups
• Virtual access interfaces (VAIs)
• Multilink group interfaces
Both of these types of interfaces provide the same level of PPP and multilink functionality once a bundle
is established, and all PPP and multilink-related features run identically on the bundle.
A VAI is the primary type of interface used for MLP bundles. It is created dynamically for a multilink
connection and released as soon as the connection is torn down. A bundle interface of this type exists
only as long as a user is connected. As soon as the user disconnects, the bundle interface no longer exists.
VAIs are the default type of bundle interface. If you do not configure a multilink group interface, the
bundle interface is automatically a VAI, which has the following advantages and disadvantages:
• The number of bundle interfaces depends only on the number of currently active multilink users and
not on the size of your user database.
• Because a local configuration source does not exist for per-user information, this information is
derived from another source, such as an AAA (authentication, authorization, and accounting) server.
• Because a dedicated interface does not exist for you to monitor, you must track a user’s activity
using another means, such as the accounting mechanism of an AAA server.
Note Cisco 10000 series routers do not support VAI bundle interfaces in a PTA configuration. VAI
bundles are supported only on the L2TP network server (LNS) for MLPoLNS.
Multilink group interfaces are static interfaces that exist whether or not they are being used at a particular
point in time. Multilink group interfaces are dedicated to specific remote users and are primarily used in
leased-line environments in which you already know where all of your physical links are connected and
the number of users is primarily defined by the number of physical connections your system has.
Multilink group interfaces allow you to track a specific user’s activity. By examining a user’s associated
interface, you can easily see if a user is connected and how much traffic the user has sent or received.
You can monitor the state of the multilink group interface for such things as network outages.
MLP Groups
When you configure the ppp multilink group command on a link, the command applies a restriction to
the link that indicates the link is not allowed to join any bundle other than the indicated group interface,
and that the connection is to be terminated if the peer system attempts to join a different bundle.
A link actually joins a bundle when the identification keys for that link match the identification keys for
an existing bundle (see the
“How MLP Determines the Link a Bundle Joins” section on page 22-6).
Configuring the ppp multilink group command on a link does not allow the link to bypass this process,
unless a bundle does not already exist for this particular user. When matching links to bundles, the
identification keys are always the determining factors.
Because the ppp multilink group command merely places a restriction on the link, any MLP-enabled
link that is not assigned to a particular multilink group can join the dedicated bundle interface if it
provides the correct identification keys for that dedicated bundle. Removing the ppp multilink group
command from an active link that currently is a member of a multilink group does not make that link
leave the bundle because the link is still a valid member. It is just no longer restricted to this one bundle.