Internet Security Diagnostics: Outgoing Filters

Diagnostics / Security

To improve the security of internet communications, global filters can be used in the FRITZ!Box. A number of filters are enabled by default in the FRITZ!Box, others are disabled upon delivery. The filters enabled in the FRITZ!Box by default filter packets which are normally not required for communication.

  • Disable the enabled filters only if you want to run applications that require these packets.
  • Enable the disabled filters only if you want to block the unsecured dispatch of email, or if you want to make it more difficult to identify your FRITZ!Box.

Firewall Stealth Mode

In stealth mode the firewall rejects unsolicited queries from the internet without comment, instead of replying with ICMP control messages. It continues to reply to queries frequently required by programs.

Filter SettingMeaning
disabled

The filter is not enabled in the FRITZ!Box by default.
enabled Enable this option if you want to make it more difficult to identify your FRITZ!Box through port scans.

SMTP Filter

The SMTP filter blocks SMTP packets. SMTP is an email transport protocol that serves to exchange email in computer networks.

The SMTP filter blocks the dispatch of e-mail via the unsecured port 25.

Filter SettingMeaning
disabled The filter is not enabled in the FRITZ!Box by default.
enabled Enable this filter in order to block uncontrolled sending of email messages (for instance, by malware on devices in the home network). Use only secure email servers if you would like to enable this filter.

NetBIOS Filter

The NetBIOS-Filter blocks NetBIOS packets. NetBIOS packets are usually not required for communication in the internet.

Filter SettingMeaning
NetBIOS filter enabled

This is the default setting in the FRITZ!Box.

When this setting is enabled, NetBIOS packets are blocked by the FRITZ!Box's packet filter.
NetBIOS filter disabled

When this setting is disabled, NetBIOS packets are allowed to pass through the FRITZ!Box's packet filter.

Disable the NetBIOS filter only if you are using applications that have to exchange NetBIOS packets with the internet, as would be the case, for instance, for SMB access to the Strato HiDrive.

Teredo Filter

The Teredo filter blocks Teredo packets. Teredo is a tunnel protocol that uses UDP to tunnel IPv6 packets over IPv4. With Teredo individual devices in the home network can establish their own IPv6 connections. IPv6 connections with Teredo are not usually necessary if the FRITZ!Box provides a native IPv6 connection for the home network.

Filter SettingMeaning
Teredo filter enabled

This is the default setting in the FRITZ!Box.

When this setting is enabled, Teredo packets are blocked by the FRITZ!Box's packet filter. Devices in the home network cannot use Teredo to establish IPv6 tunnels.
Teredo filter disabled

When this setting is disabled, Teredo packets are allowed to pass through the FRITZ!Box's packet filter. With Teredo devices in the home network can establish their own IPv6 connections.

Note the following if the FRITZ!Box provides a native IPv6 connection:

  • An IPv6 connection with Teredo is not protected by the FRITZ!Box IPv6 firewall.
  • Disable this filter only if a device in the home network absolutely requires Teredo and you are willing to accept the risk that the Teredo connection is not protected by the FRITZ!Box IPv6 firewall.