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MBOX® USER MANUAL
To obtain the subnet broadcast address for a particular subnet:
Step 1. Take the IP address for a device on that subnet and the subnet mask for that device.
Step 2. Line the address and subnet mask up one above the other, in four columns with each octet being a column.
Step 3. In columns where the subnet mask has a value of 255, write down the value from the IP address’ octet.
Step 4. In columns where the subnet mask a value of 0, write down a value of 255.
+ Unicast - packets using a specic, unique destination IP address. This is most comparable to two people having a
single face-to-face conversation without anyone else able to hear them. Interfaces can have more than one unicast
communication at a time. Unicasting cuts down on network overhead as it places the minimum amount of data on
the network and because packets are addressed specically, it eliminates the requirements that a device lter out
data it doesn’t need to listen to.
+ Multicast - packets that are sent to an IP address belonging to a predetermined range of IP addresses. Interface’s
may join a multicast group to be able to send and receive packets within the group. This is comparable to a group of
listeners who all choose to listen to one speaker, or to other members of the group who take on the role as speaker.
The conversation doesn’t leave the group.
It is possible for interfaces to send packets to or receive packets sent to a multicast address without joining the
corresponding multicast group. But unless the interfaces join the multicast group, switches between the devices may not
forward the multicast packets correctly.
Most of the time a /8 subnet mask (255.0.0.0) can be used with Mbox. When using multiple interfaces on the same
computer, with each having a /8 subnet mask, a general rule is to make sure that each interface has a different rst octet.
Otherwise there may be ambiguity when trying to determine which interface to use for various communications. While
all interfaces on a computer may receive packets from any source, packets sent by the computer almost always should
leave through only one interface. If that interface is not on the correct subnet (or indeed the correct physical network)
then the packets will never get to the intended destination.
CAUTION! IP addresses starting with 2 and 192 and having a subnet mask of 255.0.0.0 are actually publicly routable IP
addresses. Therefore, if the computer has an interface connected to a router (e.g. connecting to the internet), and also
has an interface with a 2./8 or 192./8 then there may be some connection issues with certain websites.
For example, if two interfaces are congured with IP addresses of 2.0.0.1 and 2.1.0.1 and both have a subnet mask of
255.0.0.0. -> Both interfaces are on the same sub-network (i.e. 2.x.x.x), but have unique IDs on that network. Because
this is a valid IP scheme, the computer will allow this; but using this setup will cause issues with Mbox software. One or
both of these interfaces should use a /16 subnet mask instead of the /8 subnet mask, thereby placing the two interfaces
onto different subnets. -> 2.1.x.x and 2.0.x.x
With all protocols, especially those detailed below, it’s best that one and only one interface on the computer be on the
same subnet as the destination devices. When the computer is told to output data to a specic destination device it
avoids confusion if only one interface can “talk” to that device.
IP Address: 192 168 000 123
Subnet Mask: 255 255 000 000
Subnet Broadcast Address: 192 168 255 255
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