Kerio Tech Firewall6, Administrator'S Manual

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Chapter 6 Internet Connection
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Advanced settings (optimization, dedicated links, etc.)
In basic configuration, network load balancing is applied automatically with respect to their
proposed speeds (see above). It is possible to use traffic rules to modify this algorithm (e.g. by
dedicating one link for a particular traffic). This issue is described in detail in chapter 7.5 .
Probe hosts
Functionality of individual Internet links is regularly tested by sending an ICMP request for
a response ( PING ) to certain hosts or network interfaces. By default, the default gateway of
the particular link is used as the probe host. If the default gateway is not available, the tested
link is not working (correctly).
If the primary default gateway (i.e. the default gateway set for the tested link) cannot be used
as the testing computer by any reason, it is possible to specify IP addresses of other (one or
more) testing computers upon clicking on Advanced . If at least one of the tested devices is
available, the Internet connection in question is considered as functioning.
The specified probe hosts will be used for testing of availability of all Internet links. Therefore,
the group of testing computers should include a few hosts belonging to various subnets of the
Internet.
Figure 6.16 Network load balancing — setting probe hosts
Note:
1. Probe hosts must not block ICMP Echo Requests ( PING ) since such requests are used to test
availability of these hosts — otherwise the hosts will be always considered as unavailable.
This is one of the cases where the default gateway cannot be used as the testing computer.
2. Probe hosts must be represented by computers or network devices which are permanently
running (servers, routers, etc.). Workstations which are running only a few hours per day
are irrelevant as probe hosts.
3. ICMP queries sent to probe hosts cannot be blocked by the firewall’s traffic rules.