Useful Information on Internet Access
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Configuration Examples
NAT
Network address translation (NAT) is activated on accessing the Internet (ISP).
You require this feature in order to translate internal IP addresses to valid
external IP addresses. This has three important consequences for Internet
access:
●
Several workstations can share a single Internet access. You do not require
a LAN access, only a single account with the Internet service provider.
●
The IP addresses used in the LAN are translated into IP addresses valid
worldwide. So you require no such addresses for your LAN.
●
Only IP connections triggered from a workstation computer can be estab-
lished. Consequently, while you can call up Web pages from a workstation,
you cannot install a Web server visible in the Internet on a workstation.
Certain protocols cannot be used when NAT is being used. This affects
protocols with the following properties:
●
IP addresses are transported in the useful load, e.g. NetBIOS over IP or SIP.
●
The protocol requires an active, inward-directed connection establishment,
e.g. ICQ.
●
The protocol will function without TCP/UDP port numbers, e.g. ICMP or
IGMP.
The Forum 523/524 NAT has suitable processes for ensuring the functions of
many important protocols affected by these rules. These are the protocols
FTP (in “active” mode), CuSeeMe (“videoconferencing”), IRC (“chat”), ICMP
errors (“traceroute”) and ICMP echo (“ping”).
Depending on the internet telephony protocol (VoIP, SIP) the required NAT
extension (“Full Cone NAT”) or RTP-Proxy is activated on the Media Gateway
Card.
Protocols which require inward-directed connection establishment can be
configured in the
Network
:
Port Access
menu. For further information, refer
to the online help of this menu.
