3Com OfficeConnect 3C8861, User Manual

Page: 23 / 116

Understanding VPNs and PPTP 23
Figure 7 IP Address Translation
Understanding VPNs
and PPTP
Virtual private networks (VPN) are private, secure networks created in public
networks such as the Internet. A VPN is essentially a secure, private tunnel within
the Internet. Since VPN calls are placed through a local ISP, they eliminate long
distance charges that would occur from directly dialing to a remote private
network.
One of the protocols which enables a VPN to be created is PPTP. The PPTP protocol
allows for multiple workstations to establish a secure multi-protocol connection to
a remote, private network via a single, locally-dialed ISP account as shown in
Figure 8. Any networking protocols such as IP, IPX and NetBEUI can be supported
transparently through the tunnel. While the LAN Modem supports PPTP, it does
not play an active role in creating or terminating a tunnel.
Figure 8 Connection to an Remote Private Network via an ISP
192.168.1.5
19
2.168.1.2
19
2.
168.1.4
OfficeConnect 56K LAN Modem
192.168.1.1
Analog POTS line
Internet/Intranet or
online service
3 Com
Jack’s PC
192.168.1.2
Chrissy’s PC
192.168.1.3
Larry’s PC
192.168.1.4
Janet’s PC
192.168.1.5
198.6.1.1
19
8.6.1
.1
19
8.6.1
.1
198
.6.1.1
IP address
assigned by ISP
Translates PC IP
addresses to IP
address assigned
by ISP
Analog POTS line
Public telephone
network
3C886
56K LAN Modem
PWR AA RD SD
Alert
Tx Coll 1 2 3 4 CD OH
LAN STATUS
From the Edge to the Heart of the Network. 3 Com
POWER ISDN Alert B1 B2 TX COLL 1 2 3 4
3 Com
LAN STATUS
ISDN LAN Modem
3C892 OK
Internet Service
Provider
LAN Modem
Tunnel
terminator
Corporate
network