Network Address Translation (NAT)
Since the addressing and routing of SIP is done at the application layer, the
biggest problem the SIP protocol now has is the disconnect between the IPv4
addressing and routing at the application layer versus the IPv4 addressing and
routing at the transport and network layers. Network Address Translation (NAT)
occurs at the transport and network layers, and thus the challenge.
The purpose of a Network Address Translation (NAT) firewall for businesses is to
provide the translation between a single public IP address on the WAN and
multiple private IP addresses for all of the workstations, servers and other IP
equipment within the LAN. The router running NAT should never advertise the
LAN network addresses to the WAN network backbone. Only the networks with
global addresses may be known outside the router. However, global information
that NAT receives from the border router can be advertised in the LAN network
the usual way. Typical or traditional firewalls apply NAT to the TCP/IP protocol at
the transport and network layers.
NAT's basic operation is as follows. The network addresses inside a private
domain can be reused by any other private domain. For instance, a single Class
A address could be used by many private domains. At each exit point between a
private domain and the public WAN backbone, NAT is installed. If there is more
than one exit point it is of great importance that each NAT has the same
In order for SIP to work effectively, the NAT issue must be resolved, and that is
where the Session Border Element such as the firewalls and SIParators offered by
Ingate, are very important for enabling SIP services to an enterprise network.
Learn all about how Ingate is Solving the Firewall/NAT Traversal Issue of SIP" in this pdf.
For additional information on Ingate Remote SIP Connectivity, please contact email@example.com.