ARA-1 Operations Manual
INTEROPERABILITY NOW
6-3
What happens if two ARA-1s have the same IP address (or an ARA-1 has the same address
as some other device)?
The ARA-1s will not work properly. Both units will respond at the same time, causing network
errors. The extreme case would be if an ARA-1 is programmed to have the same IP address as
an existing computer on the same network. This would likely render that computer unusable for
network functions, and could cause other users to have problems as well. The bottom line is that
two devices on the same network cannot share the same IP address.
What is a firewall?
A firewall is a security device that prevents people outside of a network from accessing
computers or devices inside the network. A company firewall prevents incoming network
connections so no one outside the company can access the company’s computers via the Internet.
How does a firewall affect the ARA-1?
A firewall may prevent a connection to an ARA-1 if it is behind the firewall and the SIP proxy
or other connecting device is not. This problem can often be overcome through the use of STUN,
which is described in the configuration section of this manual.
Should I use a firewall with the ARA-1?
Strictly speaking from the standpoint of the ARA-1, there is no reason to use a firewall. The
ARA-1 is a standalone network device that poses minimal security risks. However, if the network
the ARA-1 is on is shared with computers, servers, or other network devices, then a firewall may
be advisable. Talk to your network administrator about such situations.
What is NAT?
NAT (Network Address Translation) is a scheme by which many network devices can share one
IP address. The NAT router translates packets passed through it between the single public IP
address it holds and the private IP addresses used by devices on its network. This means that no
computers behind the NAT router are directly accessible from outside the network since none of
them have public (or routable) IP addresses.
How does NAT affect the ARA-1?
Using NAT does not adversely affect the operation of the ARA-1. The use of the STUN protocol
may be necessary when the unit is located behind a NAT device. Special considerations should
be made in the event that multiple ARA-1 units will be located behind a NAT router. In that
case, each unit will need to be assigned a different local VoIP port, and the device will need to
be configured to use the STUN protocol.