fix_nated_contact() is meant for changing the IP address of the Contact header when SER has a public address and the UA has a private (i.e. behind NAT). This means that it will rewrite Contact to contain the source ip address:port found in the UDP/TCP header. This is probably correct, because I assume the UA cannot be reached from the outside anyway. If you record-route, subsequent requests should go through your ser.

If you have problems with responses not being returned, have a look at Via headers as they control how answers to i.e an INVITE are routed back to the UA. You may want to have a look at the rr module double record route parameter to make sure that SER creates one record-route for the internal and one for the external interface. g-)

Sebastian Gabris wrote:

After reading a bit more mails, I came to two possible problems:

1. fix_nated_contact() needs a registrar to work properly I dont use a registrar, since i register at the VoIP - Provider.

or

2. fix_nated_contact() is not ment to be used on this scenario

Any ideas on this?

Sebastian

...

Hi everybody,

need some help on nattraversal.

i use a multihomed SER, one private IP & one public IP.

MyUA(privateIP) <-> (privateIP)SER(publicIP) <-> UA-(VoIP - Provider, pubicIP)

If i try to make a call from private net to public net, SER doesnt change the contact address. He changes the sdp - connection field but he, puts in the wrong IP - address. Instead o writing down his public IP, SER writes his private IP. Then SER forwards the call on his public interface to the provider, which will get wrong Contact & SDP information.

After reviewing my logs i saw that SER does the nat_uac_test, but the fix_nat_contact & fix_sdp dont work dont do what they should do :)

Here are the important bits of my config:

fork=yes log_stderror=no

mhomed=1 listen=10.x.x.x listen=193.x.x.x

loadmodule "/usr/lib/ser/modules/nathelper.so" modparam("usrloc", "db_mode", 0)

modparam("registrar", "nat_flag", 6) modparam("nathelper", "natping_interval", 30) # Ping interval 30 s modparam("nathelper", "ping_nated_only", 1) # Ping only clients behind NAT

if (nat_uac_test("3")) {

            if (method == "REGISTER" || ! search("^Record-Route:")) {
                log(2,"LOG: Someone trying to register from private IP, rewriting\n");             

                fix_nated_contact(); # Rewrite contact with source IP of signalling
                if (method == "INVITE") {
                    fix_nated_sdp("1"); # Add direction=active to SDP
                };
                force_rport(); # Add rport parameter to topmost Via
                setflag(6);    # Mark as NATed
            };
    };

... and so on.

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