Administrator's Guide - Kerio Software Archive

8.3 Special Security Settings
Anti-Spoofing
Anti-Spoofing checks whether only packets with allowed source IP addresses are received at
individual interfaces of the Kerio Control host. This function protects Kerio Control host from
attacks from the internal network that use false IP addresses (so called spoofing).
For each interface, any source IP address belonging to any network connected to the interface
is correct (either directly or using other routers). For any interface connected to the Internet
(so called external interface), any IP address which is not allowed at any other interface is
correct.
Detailed information on networks connected to individual interfaces is acquired in the routing
table.
The Anti-Spoofing function can be configured in the
Anti-Spoofing folder in Configuration → Advanced Options.
Enable Anti-Spoofing
This option activates Anti-Spoofing.
Log
If this option is on, all packets that have not passed the anti-spoofing rules will be logged
in the Security log (for details see chapter 22.11).
Connections Count Limit
This security function defines a limit for the maximum number of network connections which
can be established from one local host (workstation) to the Internet or from the Internet to the
local server via a mapped port.
Incoming and outgoing connections are monitored separately. If number of all connections
established from/to a single local host in any direction reaches the specified value, Kerio
Control block any further connections in the particular direction.
These restrictions protects firewall (Kerio Control host) from overload and may also help
protect it from attacks to the target server, reduce activity and impact of a worm or Trojan
horse.
Count limit for outgoing connections is useful for example when a local client host is attacked
by a worm or Trojan horse which attempts to establish connections to larger number of
various servers. Limiting of number of incoming connections can for example prevent the
target from so called SYN flood attacks (flooding the server by opening too many concurrent
connections without any data transferred).
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