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Configuring Subscriber-End Broadband Access Router Features
Subscriber-End Broadband Access Router Data Operations
MC-616
Cisco IOS Multiservice Applications Configuration Guide
Figure 112 Cisco uBR900 Series Cable Access Router in a Routing Configuration with a Hub
L2TP Protocol
L2TP is an emerging Internet Engineering Task Force (IETF) standard that combines the best features
of two existing tunneling protocols: Cisco Layer 2 Forwarding (L2F) and Microsoft Point-to-Point
Tunneling Protocol (PPTP). L2TP is an extension of PPP, which is an important component for access
VPNs.
Traditional dialup networking services only supported registered IP addresses, which limited the types
of applications that could be implemented over VPNs. L2TP supports multiple protocols and
unregistered and privately administered IP addresses over the Internet. This allows the existing access
infrastructure such as the Internet, modems, access servers, and ISDN terminal adapters (TAs) to be
used.
L2TP can be initiated wherever PPTP or L2F is currently deployed, and can be operated as a client
initiated tunnel such as PPTP, or a network access server-initiated tunnel such as L2F.
The current implementation of L2TP in Cisco IOS software is dependent on a PPP connection supported
on one of the directly attached interfaces. A dialup PPP connection is required in order to initiate an
L2TP tunnel connection. This is a requirement of the L2TP Access Concentrator (LAC). Currently the
Cisco uBR900 series cable access router cannot function as the LAC; it can only function as the L2TP
Network Server (LNS), which terminates a tunnel created elsewhere in the network.
Easy IP
DHCP Server
Cisco uBR900 series cable access routers support Intelligent DHCP Relay and DHCP Client
functionality. A DHCP Relay Agent is any host that forwards DHCP packets between clients and servers.
A DHCP Relay Agent enables the client and server to reside on separate subnets. If the Cisco IOS DHCP
server cannot satisfy a DHCP request from its own database, it can forward the DHCP request to one or
more secondary DHCP servers defined by the network administrator using standard Cisco IOS IP
helper-address functionality.
Network Address Translation and Port Address Translation
Network address translation (NAT) reduces the need for globally unique IP addresses. NAT allows an
organization with addresses that are not globally unique to connect to the Internet by translating those
addresses into globally routable address space.
CATV
coaxial cable
Cable
Modem
Ethernet Ethernet
HUB
LAN
13306
Cisco uBR7246
CMTS
HFC network