Q-Lite Satellite Modem Installation and Operating Handbook
6-66
6.2.4.4 Ethernet DHCP Server
This is an On/Off control that enables a DHCP server within the modem. This can be
used to serve a configurable range of IP addresses to local network devices, as required.
6.2.4.5 Enable NAT
This is an On/Off control that enables a NAT firewall within the modem. The DHCP server
must be enabled before it can be used. The NAT sits between the terrestrial IP traffic
port(s) and the satellite port on the modem and converts all local IP addresses as defined
by the DHCP server address range to (and from) a single IP address (as defined by the
Traffic IP address
) when viewed from the far end of the satellite link.
The use of NAT is optional but it can only be used when DHCP is also enabled.
6.2.4.6 DHCP Server Start/End Addresses and Traffic IP Address
The DHCP server start and end addresses allow a range of IP addresses to be defined
that are managed by the modem. It will allocate these to local network devices when they
make DHCP IP address allocation requests to the DHCP server on the modem.
DHCP requests will also result in the
Traffic IP address
being returned as the location of a
DNS server. This is actually the address of a proxy DNS server on the modem, as well as
being the address of the DHCP server.
6.2.4.7 DNS IP Address
This is the address of an actual DNS server that the modem can use to satisfy any DNS
requests that it receives. The modem supports a proxy DNS server (defined by the
Traffic
IP address
) and, when DHCP and NAT are enabled, will cache DNS results in order to
reduce the number of satellite round trips that are required. The DNS server IP address is
normally included as part of the network connection details on Windows PCs.
6.2.4.8 Ethernet Address Learning
By default, Ethernet (or MAC) address learning is not enabled on the modem. This helps
to protect against the possibility of traffic storms caused by inadvertent loops in the
network.
However, when the 4-port Ethernet expansion switch is fitted to the modem then it is
strongly recommended that Ethernet address learning is enabled. If address learning is
disabled when the 4-port switch is fitted then traffic sent to one port will also be flooded
onto all other ports since the modem will be unaware of which devices are connected to
which switch port. While a small amount of flooding is acceptable as a means of
automatically detecting and adapting to changes in the network, it is undesirable to do it
all the time. This problem does not arise when only a single IP traffic port is available on
the modem.
