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USER’S GUIDE
256 CyberSWITCH
EXAMPLE OF AN IP FILTER CONFIGURATION
This example provides a simple filtering scenario in which a corporate LAN utilizes a
CyberSWITCH to provide WAN access to both dial-in devices as well as the global Internet. A
Netserver resides on the LAN to provide configuration support for the CyberSWITCH. Also on the
LAN are an anonymous FTP server and a WWW server.
The following are the requirements/restrictions to be addressed by IP filters:
• No outside access allowed to the Netserver or the CyberSWITCH.
• The FTP and WWW servers must be accessible from anywhere.
• Corporate hosts (including dial-in devices) may initiate TCP-based sessions with the Internet,
but not vice-versa. This covers the main IP applications such as TELNET, FTP, SMTP server
and HTTP. An assumption for FTP is that the client program supports the “PASV” option, in
which the data-transfer TCP connection is initiated by the client.
• No UDP traffic.
The interface to the Internet is via a numbered IP interface, which has the following filter applied
to its Input stage. Using a final action of DISCARD, the strategy for the filter is to restrict everything
but an explicitly permitted set of traffic.
128.131.25.10
128.131.25.12
128.131.25.11
128.131.25.15
193.57.50.1
Remote User
Remote User
Remote User
Internet
FTP
Server
SFVRA
Manager
WWW
Server
Host
Host
Host
Host
ISDN
CSX1200
POWER
SERVICE
TX
RX
10BASE - T
LAN B-CHANNELS E1 ONLY
B2 B4
B6 B8
B26 B28
B22 B24
B18 B20
B14 B16
B10 B12
B30 L1
B1 B3
B5 B7
B25 B27
B21 B23
B17 B19
B13 B15
B9 B11
B29 B31
E1
D
T1
D