Appendix B
:
Netmask
Network Prefix
Bits
Host Part Bits
Maximum Number of
Devices in the Subnet
2
255.255.255.252
30
2
2
255.255.255.248
29
3
6
255.255.255.240
28
4
14
255.255.255.224
27
5
30
255.255.255.192
26
6
62
255.255.255.128
25
7
126
255.255.255.0
24
8
253
255.255.254.0
23
9
510
255.255.252.0
22
10
1022
255.255.248.0
21
11
2046
…
…
…
…
255.128.0.0
9
23
8,388,606
255.0.0.0
8
24
16,777,214
B.2
The Gateway Parameter
Whenever a device is attempting to make a connection to another device on the network,
the device compares the address of the remote device to its own netmask and IP address.
If the remote device's IP address is in the same subnet (i.e. it shares the same network
address), a direct connection to the remote device can be made.
Going back to our example, assume that the Instreamer ICE has an IP address of
192.168.0.40 and a netmask of 255.255.255.0. For the sake of this example, assume that
the Instreamer ICE wants to send a stream to a device at 192.168.0.32. Since this device is
on the same subnet, (it shares the 192.10.0 portion of the IP address) the stream can be
sent directly to the device at 192.10.0.32.
If, however, the stream is going to a device at 192.10.12.15, the remote device is not in the
same subnet (remember, all devices in the Instreamer ICE´s subnet share the same first
three octets, because the netmask is 255.255.255.0). When the remote device is not in the
same subnet, the Instreamer ICE must communicate through the "gateway", which is a
device that routes traffic between two subnets. Thus, the Instreamer ICE contacts the
gateway and asks it to send the stream to the remote IP address. The gateway handles the
routing required to deliver the message to the remote subnet.
The gateway parameter specifies the IP address of the gateway that routes traffic to another
subnet. The gateway IP address must always be in the same subnet as the device. The
gateway device actually has at least two IP addresses—one on the local subnet, and one on
the other subnet(s) it routes to).
If you are statically assigning an IP address to the Instreamer ICE, and it will need to
connect to other computers or devices outside its own subnet, you must fill in the gateway IP
address. If the Instreamer ICE is not communicating with any devices outside its own
subnet, you can leave the gateway parameter blank.
If the Instreamer ICE is obtaining its IP address automatically from a DHCP server, the
DHCP server will assign the IP address and netmask, and may also supply the gateway
address.
B.3
Special IP Addresses
Some ranges of IP addresses have special meaning, and therefore aren't available for
assignment to a device on the subnet.
2
Keep in mind that two of the host addresses in the range (all zeros and all ones) are not valid for assignment to devices, so the
maximum number of hosts is actually two less than the number of host addresses in the host address range. The next section discusses
these special IP addresses that are not available for assignment to a device.
