Chapter 8 Configuration of network services
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Enable DNS forwarding
The DNS module allows forwarding of certain DNS requests to specific DNS servers. This
feature can be helpful for example when we intend to use a local DNS server for the local
domain (the other DNS queries will be forwarded to the Internet directly — this will speed
up the response). DNS forwarder’s settings also play role in configuration of private networks
whereit is necessary to provide correct forwarding of requests for names in domains of remote
subnets (for details, check chapter 23).
Request forwarding is defined by rules for DNS names or subnets. Rules are ordered in a list
which is processed from the top. If a DNS name or a subnet in a request matches a rule, the
request is forwarded to the corresponding DNS server. Queries which do not match any rule
are forwarded to the “default” DNS servers (see above).
Note: If Simple DNS resolution is enabled (see below), the forwarding rules are applied only if
the DNS module is not able to respond by using the information in the hosts system file and/or
by the DHCP lease table.
Clicking on the Define button in the DNS module configuration (see figure 8.1) opens a dialog
for setting of rules concerning forwarding of DNS queries.
Figure8.3 Specificsettings of DNS forwarding
The rule can be defined for:
•DNS name — queries requiring names of computers will be forwarded to this DNS
server (so called Aqueries)
•a subnet — queries requiring IP addresses of the particular domain will be forwarded
to the DNS server (reverse domain — PTR queries)
Rulescan be reordered by arrow buttons. Thisenables creating of more complex combinations
ofrules — e.g. exceptionsfor certain workstations or subdomains. Asthe rule list is processed
from the top downwards, rules should be ordered starting by the most specific one (e.g. name
of a particular computer) and with the most general one at the bottom (e.g. the main domain
of the company). Similarly to this, rules for reversed DNS queries should be ordered by subnet
mask length (e.g. with 255.255.255.0 at the top and 255.0.0.0 at the bottom). Rules for