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34 • Confi guration
[ S N O M 4 S N A T F I L T E R ]
messages are written, a log level of 9 means that all possible log mes-
sages are written.
If the Log Filename is set, all log messages are also written to
the indicated file. If the file name contains a dollar character, the dollar
will be replaced with the current date. Using this method, the NAT Filter
will write a log file for every day. This way you can keep a certain history
of log files and remove them from the file system as soon as you think the
information contained there is not relevant any more.
The Log Length number indicates how many log entries the NAT
Filter should keep in internal memory. The NAT Filter writes log mes-
sages using the first-in-first-out principle, so that there is no memory leak
caused by log messages. The log messages written to the log file are not
affected by this setting.
4.3.2 Preparing Recovery
You should specify a file name, so that the NAT Filter can Save
Registrations to File. The filter will append an XML line for each reg-
istration that is being refreshed to a file that has the same name as the
registration file appended with a tilde symbol (for example, if you specify
“regs.xml”, it will write it to “regs.xml~”). After the Registration Log-
ging Time (see in timeout handling below, in seconds) the filter will move
the tilde file to the main file. When the server is restarted it will read both
files and this way restore the registration status on the filter. This allows
the continuation of the service without waiting for the user agents to re-
register. This interval should be longer than the maximum time that you
give user agents for reregistration.
4.3.3 General Outound Proxy
The Outbound Proxy indicates where messages that are not
coming from a UA behind NAT should be sent. Typically, this is the address
of the proxy handling the traffic for the domain the NAT Filter is respon-
sible for.
The outbound proxy is a SIP URI, which means it has the format
sip:host. If the host contains a number behind a semicolon (as in “sip:
proxy.com:5060”, for example), the NAT Filter will just do a DNS A query
on the address. If not, it will follow RFC3263 (Locating SIP Servers) to
find the proxy. If you use DNS SRV, you can put a server farm behind the
4.