3Com MSR 50 Series, Configuration Manual

Page: 366 / 2443

366 C
HAPTER
19: PPP
AND
MP C
ONFIGURATION
For the details of PPP, refer to RFC 1661.
MP Multilink PPP (MP) provides an approach to increasing bandwidth. It allows
multiple PPP links to form an MP bundle. After receiving a packet, MP segments (if
the packet is large) the packet into fragments and distributes them over multiple
PPP links to the remote end. After the remote end receives these fragments, it
assembles them into a packet and passes the packet to the network layer.
Implementation
You can configure MPs through virtual templates (VT) or MP-group interfaces. VTs
are used to configure virtual access interfaces. After binding multiple PPP links to
an MP, you need to create a VA interface for the MP to enable it to exchange data
with the peers. VT and MP-group differ in the following.
■
Configuring MP through VT interfaces can involve an authentication process.
The device locates the interfaces associated to a specified VT according to the
username provided by the peers, and creates a bundle (called VT channel in the
system) corresponding to an MP link based on the configurations of the
template.
■
Multiple bundles can be created on the same virtual template interface, each of
which is an MP link. From the perspective of the network layer, these links form
a point to multipoint network topology. In this sense, virtual template
interfaces are more flexible than MP-group interfaces.
■
Bundling mode can be used to distinguish multiple bundles created on a VT
interface. You can use the
ppp mp binding-mode command in VT interface
view to specify the bundling mode. Three bundling modes are available:
authentication , both (the default), and descriptor . The authentication
mode specifies to bundle links according to username, the descriptor mode
specifies to bundle links according to the peer descriptor (which is determined
during LCP negotiation), and the
both mode specifies to bundle links
according to both username and descriptor.
■
MP-group interfaces are intended only for MP. On an MP-group interface, only
one bundle is allowed. Compared with VT interfaces, the configuration of
MP-group interfaces is simpler and easier, and accordingly is fast and effective,
easy to configure and understand.
Negotiation
MP negotiation involves two processes: first LCP negotiation, and then NCP
negotiation.
■
LCP negotiation, during which both sides negotiate the common LCP
parameters and check whether their peer interface is working in the MP mode.
If not, the LCP negotiation fails. After the LCP negotiation succeeds, NCP
negotiation starts.
■
NCP negotiation, which are performed based on the NCP parameters of the
MP-group interface or the specified VT interface. NCP parameters on physical
interfaces are not effective.
MP link is established after the NCP negotiation succeeds.
Functions
MP functions to: