I have a cisco 887 ADSL router. I use it for small bussiness, and I have Siemens phone system behind it. Normal users go through to internet by NAT, but this Siemens phone system use SIP protocol to link SIP Server in the internet, I configrate static translate. I configrate cisco 887 as blow:
no ip nat service sip udp port 5060
ip nat inside source static tcp 192.168.1.251 5060 x.x.x.x 5060 extendable
***192.168.1.251 is phone system IP address, x.x.x.x is public IP address that ADSL vendor gave to me.
everything is ok.
One day, I need add anther Siemens phone system behind this Cisco 887. For example, using ip address 192.168.1.200, I can't configrate a translation to a same IP address + port. How can I solve it.
In anther word, this translation is necessary or not. Intead of Cisco 887, I have ever used other ADSL Router, there is no translation, but I can use Siemens phone system.
