Chapter 3: System planning
Data network planning
Page 3-30
The IP address is essential for data delivery through a router interface. Address Resolution
Protocol (ARP) correlates MAC addresses to IP addresses.
For communications to outside the network segment, ARP reads the network gateway address of
the router and translates it into the MAC address of the router. Then the communication is sent to
MAC address (physical network interface card) of the router.
For each router between the sending module and the destination, this sequence applies. The ARP
correlation is stored until the ARP cache times out.
Allocating subnets
The subnet mask is a 32-bit binary number that filters the IP address. Where a subnet mask
contains a bit set to 1, the corresponding bit in the IP address is part of the network address.
Example IP address and subnet mask
In
Figure 47
, the first 16 bits of the 32-bit IP address identify the network:
Figure 47 Example of IP address in Class B subnet
Octet 1
Octet 2
Octet 3
Octet 4
IP address 169.254.1.1
10101001 11111110 00000001 00000001
Subnet mask 255.255.0.0 11111111 11111111 00000000 00000000
In this example, the network address is 169.254 and 2
16
(65,536) hosts are addressable.
Selecting non-routable IP addresses
The factory default assignments for network elements are:
Unique MAC address
IP address of 169.254.1.1
Subnet mask of 255.255.0.0
Network gateway address of 169.254.0.0
For each radio and CMM4, assign an IP address that is both consistent with the IP addressing plan
for your network and cannot be accessed from the Internet. IP addresses within the following
ranges are not routable from the Internet, regardless of whether a firewall is configured:
10.0.0.0 – 10.255.255.255
172.16.0.0 – 172.31.255.255
192.168.0.0 – 192.168.255.255
Also, the subnet mask and network gateway for each CMM4 can be assigned.
