Quidway® NetEngine 40 Series Universal Switching Router Service Boards
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http://www.huawei.com/products/datacomm/
4
PSTN/ISDN
Internal server
PC
Remote user
Remote branch office
L2TP tunnel
Internet Backbone
LAC
NAS
LNS
VPDN typical networking via L2TP
The L2TP Access Concentrator (LAC) is the equipment deployed in the switching network, having
the PPP-end system and L2TP processing capability. A LAC is usually a Network Access Server
(NAS) that provides access services to users through the PSTN/ISDN network. As the end point on
the other side of a L2TP tunnel, the L2TP Network Server (LNS) is the equipment on the peer end
of LAC and also the logical end point for the PPP session transmitted by the LAC over the tunnel.
With a dedicated L2TP service board, the NE40 can work as LNS to construct a VPDN, and its GE
interface can reach the wire speed. In networking, the NE40 can switch internal user data of the
LNS or directly access users to the MPLS L3 VPN.
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GRE Service Board
Generic Routing Encapsulation (GRE) is used to encapsulate packets of some network layer
protocols (such as IP and IPX) to make it possible to transmit the encapsulated packets over
another network layer protocol (such as IP).
As the layer 3 tunnel protocol of VPN, GRE can adopt tunnel technology between protocol layers. A
tunnel is a virtual point-to-point connection. It can be regarded as a virtual interface supporting only
point-to-point connections. This interface provides a tunnel for transmission of encapsulated
packets, and encapsulates and decapsulates packets on both ends of the tunnel.
GRE is used to implement the following service types:
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Transmit data of a multi-protocol local network through single-protocol backbone network.
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Widen the working scope of networks that use hop-limited protocols (such as IPX).
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Connect discontinuous subnets to construct a VPN.
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Access the MPLS VPN through GRE tunnel.
The dedicated GRE service board of the NE40 can implement the services listed above and the
multicast VPN service.
