4.2
IP ADDRESSING TUTORIAL
The default LAN subnet of the Vanguard consists of addresses from 192.168.1.0 to 192.168.1.255. The first and last IP
addresses of a subnet are always reserved, no matter what the subnet size is. The first IP address in the subnet is the
Network ID. The last IP address in the subnet is the Broadcast Address.
The example below illustrates a sample Vanguard 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)
Vanguard 3000
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 talk directly to other devices that have IP addresses within the same IP subnet. For example,
Computer #1 from the example above can only talk with locally connected devices that have IP addresses between
192.168.1.1 and 192.168.1.254. When Computer #1 wants to talk to another server on the Internet, it will send its data
packet to the local gateway. In this case the local gateway is the Vanguard router. Since the Vanguard 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 VERSUS 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 IANA (Internet Assigned
Numbers Authority). 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.
Common Private IP Address Ranges
10.0.0.0
to
10.255.255.255
172.16.0.0
to
172.31.255.255
192.168.0.0
to
192.168.255.255
Devices using Private IP addresses must have a router with NAT (network address translation) capability to access the
Internet. By default, the Vanguard will perform the NAT function on all outgoing traffic. The Vanguard router will
change the source IP address from the private IP of the local host to the Vanguard’s public IP address which was
assigned by the cellular carrier. Since the outgoing packet has been modified, a remote server or website on the
Internet will think the packet came directly from the Vanguard radio. It will reply back to the cellular IP address of the
Vanguard. The Vanguard radio remembers which traffic flows have been established and routes the incoming return
traffic back to the desired host device on the local area network.
Vanguard 3000 Series Multicarrier Cellular Data Modem & IP Router PN 001-7300-100 Rev. B
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