Cisco 10000 - Manual (Page 423)

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Cisco 10000 Series Router Software Configuration Guide
OL-2226-23
Chapter 19 Configuring Multilink Point-to-Point Protocol Connections
Cisco 10000 series routers do not support VAI bundle interfaces in a PTA configuration. VAI bundles are supported
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.
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 19-5 ).
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.
How MLP Determines the Link a Bundle Joins
A link joins a bundle when the identification keys for that link match the identification keys for an
existing bundle.
Two keys define the identity of a remote system: the PPP username and the MLP endpoint discriminator.
The PPP authentication mechanisms (for example, PAP or CHAP) learn the PPP username. The endpoint
discriminator is an option negotiated by the Link Control Protocol (LCP). Therefore, a bundle consists
of all of the links that have the same PPP username and endpoint discriminator.
A link that does not provide a PPP username or endpoint discriminator is an anonymous link. MLP
collects all of the anonymous links into a single bundle referred to as the anonymous bundle or default
bundle. Typically, there can be only one anonymous bundle. Any anonymous links that negotiate MLP
join (or create) the anonymous bundle.
When using multilink group interfaces, more than one anonymous peer is allowed. When you preassign
a link to an MLP bundle by using the ppp multilink group command, and the link is anonymous, the
link joins the bundle interface it is assigned to if the interface is not already active and associated with
a nonanonymous user.
MLP determines the bundle a link joins in the following steps:
1. When a link connects, MLP creates a bundle name identifier for the link.
2. MLP then searches for a bundle with the same bundle name identifier.
– If a bundle with the same identifier exists, the link joins that bundle.
– If a bundle with the same identifier does not exist, MLP creates a new bundle with the same
identifier as the link, and the link is the first link in the bundle.
Table 19-2 describes the commands and associated algorithm used to generate a bundle name. In the
table, “username” typically means the authenticated username; however, an alternate name can be used
instead. The alternate name is usually an expanded version of the username (for example, VPDN tunnels
might include the network access server name) or a name derived from other sources.