User manual

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Cooper Bussmann 615M-1 Cellular Data Modem and IP Router Series Manual
Rev Version 1.0
ChapTEr 4 - Ip aDDrESSING
4.1 Overview
When 615M-1 cellular router is connected to a cellular carrier, it will always have two IP addresses. The first is
the local area network (LAN) address. The 615M-1 can be accessed through either the LAN 1 or LAN 2 Ethernet
connectors on the front panel using this IP address. This IP address is user configurable and is saved locally in the
615M-1. The factory default IP address is 192.168.1.50, with a subnet mask of 255.255.255.0.
The second 615M-1 IP address is assigned by the cellular carrier each time the 615M-1 connects to the cellular
network. Often this IP address is publicly accessible from the Internet. However, in some instances the cellular
carrier may assign an IP address that is protected by firewalls. When a publicly accessible IP address is assigned,
data flows can be initiated from either the 615M-1 or from the Internet. When an IP address is protected by cellular
firewalls, data flows can only be initiated from the 615M-1. In either case, after a data flow has been established,
data is free to move in both directions.
4.2 IP Addressing Tutorial
The default LAN subnet of the 615M-1 consists of addresses from 192.168.1.0 to 192.168.1.255. The first and last
IP address a subnet is always reserved, no matter the subnet size . The first IP address in the subnet is the
Network ID. The last IP address in the subnet is the Broadcast Address.
The following example illustrates a sample 615M-1 network. The subnet consists of IP addresses ranging from
192.168.1.0 to 192.168.1.255. The subnet mask is 255.255.255.0. This is sometimes written in shorthand notation
as: 192.168.1.50/24 since the subnet mask 255.255.255.0 contains 24 ones then 8 zeros when it is converted to
binary.
The first address 192.168.1.0 is reserved for the Network ID. The last address 192.168.1.255 is reserved for the
broadcast address. There are 254 valid IP addresses that may be assigned to hosts on the LAN network.
Ethernet Subnet Mask 255.255.255.0
Network ID 192.168.1.0 (reserved—first IP address in subnet)
Broadcast Address: 192.168.1.255 (reserved—last IP address in subnet)
615M-1 192.168.1.50/24
PLC/RTU #1 192.168.1.10/24
Computer #1 192.168.1.125/24
By changing the subnet mask, the network can be made to include as many or as few IP addresses as desired.
Ethernet devices can only communicate directly to other devices that have IP addresses within the same IP subnet.
For example, Computer #1 in the example above can only communicate with locally connected devices that have
IP addresses between 192.168.1.1 and 192.168.1.254. When Computer #1 wants to communicate with another
server on the Internet, it sends its data packet to the local gateway. In this case, the local gateway is the 615M-1
router. Since the 615M-1 has two IP addresses (each IP address is on a separate subnet), it can forward the packet
from the LAN network (192.168.1.0/24) to the cellular network. The packet will continue to be forwarded in a similar
fashion from subnet to subnet until it reaches its final destination.
4.3 Private vs. Public IP Addresses
Certain address ranges in the in IPv4 address space have been reserved as private IP address. Private IP
addresses can be used by anyone, without the need to register for an IP address assignment from the Internet
Assigned Numbers Authority (IANA). However, private IP addresses are not routable on the Internet. Routers on the
Internet will typically drop any packets that are destined for a private IP address. These addresses are reserved for
local use only.