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port the data from a more intelligent router to the
modem, PPP over Ethernet (PPPoE) is used.
Due to the shortage on IP addresses, some DSL op-
erators change the IP addresses of their clients on a
periodical basis (e.g. daily). This should prevent that
an IP address is blocked by a user that is not active.
That means, that the IP address changed sporadically
and that connections get lost during this reassignment
of IP addresses.
Therefore, SIP NAT gateway has to poll for address
changes and reflect these changes in future mes-
sages. A static set-up of the public IP address is not
enough.
Domain Proxy behind NAT
Many installations don't have only one public address
available that is used by the NAT gateway. However,
they can be reached via DNS from the public network
as well as from the private network.
Example: Company X has the domain smallcomp.com
associated with 123.123.123.123 and would like to be
reachable at e.g. sip:info@smallcomp.com.
To make this possible, all incoming packets on the SIP
NAT gateway must be forwarded to the private ad-
dress where the proxy is running. You can achieve this
by starting the gateway with the option --default
<adr>, where the address is expressed as adr:port,
e.g. 192.168.3.4:5062.
Starting
Manual Start
You can start the NAT gateway on your Linux NAT
router with the command sipnat. The following pro-
gram options are available.
--log <n>: Set the log level to a value be-
§
tween 0 and 9. 0 means only the most urgent
messages get through, 9 means the sipnat is
verbose.
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