DETEWE opencom 100 - Nat

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Useful Information on Internet Access Configuration Examples
counts on a mail server. Mail servers
are operated by, for example, ISPs.
With the OpenCom 100 you can set
up one or more e-mail accounts for
every user account configured on
the OpenCom 100. These e-mail
accounts are then checked at regular
intervals.
If there are new e-mails in an e-mail
account, and the OpenCom 100 has
been configured for this function,
the user specified in the OpenCom
100 user account is notified of the
new e-mail on his system terminal.
System telephones of the Open-
Phone 6x and 2x families can also
display information such as the
sender or the subject of the e-mail.
NAT
Network Address Translation (NAT) is
activated on accessing the Internet
(ISP). You require this feature in or-
der 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. You thus re-
quire no addresses valid world-
wide for your LAN.
■ Only TCP/IP connections trig-
gered from a workstation can be
established. Consequently, while
you can call up Web pages from
a workstation, you cannot install
a Web server visible in the Inter-
net on a workstation.
Certain protocols can not be used
when NAT is being used. This affects
protocols with the following proper-
ties:
■ TCP/IP addresses are trans-
ported in the useful load, e.g.
NetBIOS over TCP/IP.
■ The protocol requires an active,
inwards-directed connection es-
tablishment, e.g. ICQ.
■ The protocol functions without
TCP/UDP port numbers, e.g.
ICMP or IGMP.
The OpenCom 100 NAT has suitable
processes for ensuring the functions
of all important protocols affected
by these rules. These are the proto-
cols FTP (in “Active” mode), Cu-
SeeMe (“Videoconferencing”), IRC
(“Chat”), ICMP errors (“Traceroute”)
and ICMP echo (“Ping“).