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System Services
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14.4. Telnet Server configuration
The Telnet server allows standard telnet-protocol clients (available for most client platforms) to connect to
the FB2700 and access a command-line interface (CLI). The CLI is documented in Chapter 21 and in the
Appendix I.
14.4.1. Access control
Access control can be restricted in the same way as the HTTP (web) service, including per user access
restrictions.
Note
By default, the FB2700 will only allow telnet access from machines that are on one of the locally-
attached Ethernet subnets
a
. This default is used since the CLI offers a degree of system control that
is not available via the web interface - for example, software images stored in the on-board Flash
memory can be deleted via the CLI.
The example XML below shows the telnet service configured this way :-
<telnet allow="10.0.0.0/24 10.1.0.3-98 10.100.100.88 10.99.99.0/24"
comment="telnet service access restricted by IP address"
local-only="false"/>
14.5. DNS configuration
The DNS service provides name resolution service to other tasks within the app software, and can act
as a relay for requests received from client machines. DNS typically means converting a name, like
www.firebrick.co.uk
to one or more IP addresses, but it can also be used for reverse DNS finding the
name of an IP address. DNS service is normally provided by your ISP.
The DNS service on the FB2700 simply relays requests to external DNS servers and caches replies. You can
configure a list of external DNS servers using the
resolvers
attribute. However, DNS resolvers are also
learned automatically via various systems such as DHCP and PPPoE. In most cases you do not need to set
the resolvers.
14.5.1. Blocking DNS names
You can configure names such that the FB2700 issues an NXDOMAIN response making it appear that the
domain does not exist. This can be done using a wildcard, e.g. you could block
*.xxx
.
Tip
You can also restrict responses to certain IP addresses on your LAN, making it that some devices get
different responses. You can also control when responses are given using a profile, e.g. time of day.
14.5.2. Local DNS responses
Instead of blocking names, you can also make some names return pre-defined responses. This is usually only
used for special cases, and there is a default for
my.firebrick.co.uk
which returns the FireBrick's own
IP. Faking DNS responses will not always work, and new security measures such as DNSSEC will mean these
faked responses will not be accepted.