Protecting the system
This filter blocks the firewall against connection setups at privileged ports (0 ... 1023) for TCP and UDP. Most rele-
vant data services are offered via privileged ports (establishing names, file transfer, etc.).
IP Spoofing Blocking
This filter blocks the firewall against “fake” (spoof) packets on the “wrong side” of the firewall. As a result, data pa-
ckets which would certainly belong in the LAN based on their IP address, but would be routed to the port for the DSL
modem by an attacker from the Internet, are ignored (same applies to ISDN links to the Internet).
DNS-filter
This filter permits establishing of names (assignment of IP-addresses to URLs) by enabling outgoing UPD and TCP
packets at port 53, as well as incoming ones from port 53. Longer replies and zone transfers are also permitted by en-
abling TCP. No DNS queries can pass through the firewall when this filter is de-activated!
Active FTP - Filter
Together with the corresponding software module in the firewall this filter permits active FTP. Active FTP differs
from passive FTP in that the FTP server sets up a connection for data transfer at the request of the clients (applies
both to the response to the FTP command “ls” and to the file transfer proper). The problem here is that the connecti-
on setup by the FTP server is made at any non-privileged port, thus requiring that a large region of the firewall be
enabled.
Outgoing connections at ports 20 and 21 and incoming ones from these ports to non-privileged ports are enabled.
Passive FTP - Filter
This filter permits file transfer via FTP, with the connection always being established by the FTP client. Outgoing
connections to port 21 and incoming ones from this port to non-privileged ports are enabled.
HTTP - Filter
This filter permits Web browsing by enabling packets to ports 80 and 8080 (when using http proxies) for outgoing
connections and incoming packets from these ports to non-privileged ports.
HTTPS - Filter
This filter permits secure Web surfing by enabling packets to port 443 for outgoing connections and incoming pa-
ckets from this port to non-privileged ports. The https protocol is frequently used for home banking and online shop-
ping; http connections are used for transfer of secure packets using encryption.
HBCI - Filter
This filter permits the use of HBCI for home banking by enabling packets to port 3000 for outgoing connections and
incoming ones from this port to non-privileged ports.
E-mail send filter
This filter permits transmission of e-mails via SMTP (= sending e-mails) by enabling packets to port 25 for outgoing
connections and incoming packets from this port to non-privileged ports.
E-mail reception - Filter
This filter permits transmission of e-mails via POP (= receiving e-mails) by enabling packets to port 110 for outgoing
connections and incoming packets from this port to non-privileged ports.
Configure firewall filters
Filter Wizard
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