4.4 Virtual Server
Generally NAT based router/firewall filters out all unrecog-
nized packets from WAN to protect your Internal LAN
computers; therefore all LAN computers behind Broadband
Router are invisible to the outside Internet. However, some
Internet servers (like WWW, FTP, E-mail …) should be visible
and accessible by outside Internet. As a result, Broadband
Router provide Virtual Server functions to meet this demand.
In addition, Broadband Router also protect the servers and all
other computers in LAN simultaneously.
Since all the Internet servers always handle the fixed
TCP/UDP service port number. (like WWW is 80, FTP is 21 …)
Thus any packets from WAN which destination port
number is matched with Broadband Router virtual server
port, then these packets will be forwarded to the pre-defined
LAN
IP. Certainly, the destination port number is also kept
the same.
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