Quantum and Evolution Series Installation and Operating Handbook
8-35
8.12 IP Functionality
8.12.1 Base Modem IP
As shown below, the base modem has one RJ45 auto-sensing 10/100Mbps Ethernet port
for M&C and one for sending and receiving satellite IP traffic.
Base Modem Ethernet Ports
Both of the Ethernet connections by default form part of an Ethernet bridge and share an IP
address. Essentially, the bridge makes the modem disappear from the network in relation to
passing IP traffic over satellite. Consequently, for simple point-to-point communications, little
or no user set up is required to pass IP traffic over satellite. If both Ethernet ports are
configured to be part of the bridge (which is the default) then a single Ethernet connection to
the modem can be used for both IP traffic and modem M&C control (using either of the two
RJ45 connectors). If the M&C port is configured to be outside of the bridge then one Ethernet
port is dedicated to IP traffic and the other to M&C control (as labeled on the connectors).
To communicate with the modem itself for M&C purposes, an IP address and subnet mask
must be set. Note that settings an IP address of 0.0.0.0 causes the modem to request an IP
address from a DHCP (Dynamic Host Control Porotocol) server on the network. Typically an
external router will be required to perform complex network IP routing functions (such as
dynamic routing). Static routes are supported allowing routing decisions to be made based
on a set of explicit routing rules that can be entered via the web user interface. The use of a
default gateway IP address is also supported. When specified (i.e. the value is not 0.0.0.0)
then the gateway provides a next-hop IP address for all destinations that are not on the local
subnet. Typically this is the address of a router that has been set up to forward packets to the
correct network.
The bridge has to learn what devices are on which network segment in order to avoid
creating bridging loops, where Ethernet frames circulate endlessly, using up valuable
bandwidth. The bridge therefore maintains information on how to forward frames, based on
replies that are received from each device.
The M&C port can be taken out of the bridge (via the ‘
Bridge M&C port
’ menu option) in
which case each port has its own IP address. If the modem has an IP traffic card fitted then
