Mary
SearchIRC Admin
Joined: 03 May 2003
Posts: 692
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 Posted: Mar 12, 2004 9:49am Post subject: |
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File transfer protocol causes problems for firewalls.
The client initiates a connection with the ftp host, usually on port 21. When asked for a file, the ftp server responds by trying to connect to the client's port 20.
The whole idea of a firewall is to block unwanted connections from external hosts. It keeps a list of the connections made by hosts behind the firewall. When the ftp server tries to connect to the client, the firewall checks that list to see if it should allow the connection. A stateful firewall can handle the connection, while a non-stateful firewall will not allow the connection.
Using DCC through your IRC client is a type of protocol bender too, as you connect to the IRC server on 6667, but when you attempt to do a DCC, the sender tells the recipient what IP and what port to use for the transfer, it doesn't happen through 6667. |
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