Table of Contents
Advertisement
Outbound Proxy
SIP defines a model of the "outbound proxy" similar to
a http proxy, that handles all messages that come
from a phone. By pointing the outbound proxy to the
sipnat gateway, it can be ensured that all messages
go through the application layer gateway, even if they
don't traverse the NAT.
To avoid unnecessary traffic, the phones can be
pointed to another proxy that is within the private
network which devices if messages have to traverse
the SIP NAT gateway. This keeps traffic away from the
NAT gateway and avoid unnecessary opening of RTP
tunnels. The snom 4S proxy supports this feature.
IP Gateway
Unfortunately, not all phones on the market support
the feature of an outbound proxy.
In Linux, the kernel can be configured to forward all
packets to an application, e.g. the NAT gateway. You
need to set up a filter rule like this (using –sip-port
5069):
iptables –t nat –A PREROUTING –i eth0 –p UDP -
-dport 5060 –j REDIRECT –to-port 5069
In many installations, the NAT gateway is used as
firewall as well. For SuSe installations, setting up the
iptables does not work in these cases, because the
startup script for the firewall clears the iptable setup.
In this case you'll need to set up the ports in
/etc/rc.config.d/firewall2.rc.config like this:
...
FW_SERVICES_EXT_UDP="5060 10000:10999"
FW_REDIRECT="192.168.0.0/16,0/0,udp,5060,5061"
...
For the snom 100 VoIP phone, you find the
TIP
outbound proxy in the menu Settings, SIP,
Outbound Proxy.
11
Advertisement
Table of Contents
