BinTec X4000, User Manual

Page: 341 / 498

X4000 User’s Guide 341
Access Security
10
uniquely identify data connections. The FTP client creates a number, e.g. xyz,
which is used as source port. As destination port, the client uses the number
under which the FTP server offers the FTP service, e.g. 21. The FTP server
then answers with IP packets that use 21 as source port and xyz as destination
port:
Figure 10-3: Example: FTP connection
B
IA
N C
A
/B
R
IC
K -X
M
ISDN
1
2
192.168.1.1
192.168.1.2
192.168.1.3
X4000D
Bin Tec
4000
FTP Server
10.1.1.2
FTP-Server
10.1.1.2
Your Local Area Network
Network of your
WAN Partner
Src IP = 192.168.1.1
Src Port = xyz
Dest IP = 10.1.1.2
Dest Port = 21
Src IP = 192.168.1.1
Src Port = xyz
Dest IP = 10.1.1.2
Dest Port = 21