L2Tp Architectures; L2Tp To Virtual Routing And Forwarding Architecture - Cisco 10000-2P2-2DC Software Configuration Manual

Chapter 1 Broadband Aggregation and Leased-Line Overview
In the figure, PPPoX sessions are placed in the proper virtual routing and forwarding (VRF) instance
based on the virtual template to which they map. This model is identical to the one in
access side. However, the two models differ on the network side. The model in
and a tag interface on the network side and separates traffic at Layer 3. The
Model"

L2TP Architectures

Figure 1-4
Figure 1-4
In the figure, the clients and the LACs exchange PPP packets that are typically encapsulated in PPPoA
or PPPoE and typically carried on ATM circuits. However, the protocols used between the clients and
the LAC do not affect LNS requirements. The LAC creates L2TP tunnels to all of the LNSs at which its
clients want to terminate. Multiple tunnels might exist between each LAC and each LNS. For each client
PPP session the LAC signals the LNS to add another session to a tunnel. The LAC forwards all traffic to
the LNS, including the PPP control traffic. The LNS terminates the PPP sessions and routes any client
IP packets on to the ISP or corporate network toward their final destination. The LNS performs
authentication, authorization, and accounting (AAA) actions on the PPP sessions.

L2TP to Virtual Routing and Forwarding Architecture

Figure 1-5
OL-2226-23
in Figure 1-2 uses VRFs does not use a tag interface, and separates traffic at Layer 2.
shows an L2TP network server (LNS) model.
LNS Architectural Model
Client
PPP sessions,
typically PPPoA
and PPPoEoA
LAC
LAC
LAC
PPP sessions
in L2TP tunnels
Client
shows an L2TP to VRF model.
Typically OC-12 ATM or
OC-12 POS physical
links containing
L2TP tunnel flows
ATM
network
1000s of tunnels,
multiple physical
links
AAA servers
Cisco 10000 Series Router Software Configuration Guide
Broadband Architecture Models
Figure 1-2
Figure 1-3
"PTA to VRF Architectural
100K routed
Cisco
subscribers
10000 ESR
ISP/corporate
Typically GigEthernet
or OC-12 POS IP
routed traffic
EMS/NMS
on the
uses MPLS
network
1-5