p-asserted header

 I have an incoming INVITE come into our application with a p-asserted header. After we proxy it once within the application router it is stripped. When we process the call through the app router and eventually send out the proxied invite, it does not have this header. We need to forward this on to the next endpoint. How do I keep the container from stripping this header. We have tried adding the IP address of the remote user to the trusted authentication hosts table in the sip server/sip security tab of the admin console. thanks.