NXU-2A Operations Manual
6-4 Interoperability Now
What do I do if my network has a firewall?
If you know (or suspect) the network you are on has a firewall, go ahead and try to connect the
two units. The firewall may already be properly configured. If it is not, then the following
things should be considered.
If a server unit is behind a firewall, then the server unit’s VoIP port needs to be opened on the
firewall for both TCP and UDP. This is called “opening a hole in the firewall” and should only
be done by (or with the cooperation of) the network administrator. This will allow TCP and
UDP packets through the firewall so they can be received by the server unit. There is no
security risk in doing this since the NXU-2A cannot be made to access files or forward
information to or from other systems.
If a client unit is behind a firewall, then nothing needs to be configured on the firewall. Most
firewalls will allow traffic back through them that is related to a connection that was initiated
by a computer on its network.
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 NXU-2A?
Using NAT does not directly affect the operation of the NXU-2A. Special considerations
should be made only in the event that multiple server units will be located behind a NAT
router. In that case, each unit will need to be assigned a different VoIP port and the NAT
router configured to allow both TCP and UDP traffic for the VoIP ports of all the units behind
it. Client units are not affected by NAT and no special considerations need be made.
Should I use NAT with the NXU-2A?
The only time it is advisable to use NAT with the NXU-2A is when you wish to have multiple
units on a network, but have only one public IP address. An example of this would be a bank
of NXU-2As sharing a broadband type connection such as DSL or cable modem where only
one IP address is allocated by your ISP.
After installing a pair of NXU-2A's, the LINK ACTIVE light comes on, stays on for about 20
seconds, and then goes out. This cycle repeats endlessly. What's going on?
The most likely cause is a firewall, which is preventing UDP traffic on port 1221. See the
question above about firewall configuration.
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