SIP and NAT traversal

[ciscoforum]

Has anybody done sip with NAT traversal?Here is the situation I have: we would like users working from home or travel with sip phones can call enterprise network. We have CUCM 5.x, but we do not want those external SIP phones to register with CUCM for sure. I read some documentation and find SIP NAT traversal may solve this. Here is what I what to plan, please comment back if something is wrong or need to be concerned:

add a SBC(2851 router maybe) facing internet. Configure this SBC with NAT traversal using CUCM 5.x as proxy server. External phones will point to this SBC router. Will this work?

If this works, do I really need to two LAN interfaces on this SBC?

[#2]

Enable or disable NAT with the nat_enable parameter. You can configure the address of the NAT or firewall server using the nat_address parameter. You can configure the IP address and port number of the outbound proxy server. When outbound proxy is enabled, all SIP requests are sent to the outbound proxy server instead of to the proxyN_address. All responses

continue to reconcile the normal Using processing rules. The media stream is not routed through the outbound proxy.

You can enable or disable NAT and outbound proxy modes independently. The received= tag is added to the Via header of all responses if there is no received= tag in the uppermost Via header and the source IP address is different from the IP address in the uppermost Via header. Responses are sent back to the source under the following conditions:

-If a received= tag is in the uppermost Via header, the response is sent back to the IP address contained in the received= tag.

-If there is no received= tag and the IP address in the uppermost Via header is different from the source IP address, the response is sent back to the source IP address. Otherwise the response is sent back to the IP address in the uppermost Via header

[nickdavitashvili]

Where do you put the nat_enable parameter?