User manual

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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 radio 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.
4.4 PORT FORWARDING
NAT functionality is only useful for traffic flows that are initiated by the Vanguard or by a device that is physically connected
to the Vanguard. Port forwarding can be enabled to allow remote devices connecting through the Internet to initiate traffic
flows with a local device connected to a Vanguard router.
In the example configuration shown below, a host from the Internet can create either a TCP or UDP connection with the
local host at 192.168.1.250 on port 7000 by sending a packet to the cellular IP address of the Vanguard radio at port 8010.
When the Vanguard radio receives a packet destined for port 8010 it will look through the Port Forwarding table to see if a
matching rule exists. It finds the rule that instructs it to forward this packet to port 7000 of IP address 192.168.1.250. The
Vanguard then modifies the destination IP address and port number before forwarding the packet onto the local area
network.