Thank you for you post and apologies for the late response - I was scrolling through some dated posts and happened upon yours. Well it sounds like you need to create an access control list for the outside to permit SIP and then a NAT statement to NAT the traffic from port 5060 to the internal host.
If you share a sanitised configuration with me, I can tailor some commands for your router that you can put straight in to get this working. If you are just looking for some guidance however, I'll explain the process below. Refrain form entering these commands if you aren't comfortable with Cisco IOS. You may negate other configuration currently in place and tamper with the functionality of your existing system. Highly advisable to take a configuration back-up.
Is this router publicly facing? I.E - does it have a public IP address on one of its interfaces?
Lets make the assumption that Fa0/0 is your "outside" interface with an IP address of 1.1.1.1 and Fa0/1 is your "inside" interface with an IP address of 192.168.1.254. Lastly, lets assume that 192.168.1.80 is your internal CUBE/SIP Gateway/PBX that you wish the traffic from 5060 to go to.
Step 1) Create an access control list for the outside interface and assign it in an ingress direction to the outside interface. The below rule will permit traffic on 5060 from any IP address to the IP address of your outside interface and implicitly deny everything else.
ip access-list extended Outside_Access_In
permit udp any host 1.1.1.1 eq 5060
exit
interface Fa0/0
ip access-group Outside_Access_In in
exit
Step 2) Specify the logical role of the interfaces for NAT by entering the following commands in global configuration mode.
interface fa0/0
ip nat outside
interface fa0/1
ip nat inside
exit
Step 3) Lastly, create the static NAT statement (correctly know as static PAT or Port Address Translation).
ip nat inside source static udp 192.168.1.80 5060 1.1.1.1 5060
In summary, for this example, any connections from the outside trying to hit 1.1.1.1:5060 will be connected to the internal host at 192.168.1.80:5060.
I hope that helps and please, let me know if I can be of any more assistance.
Kind regards,
Luke
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