[Serusers] Multihomed SER & NAT

[Sebastian Gabris]

Thanks for the response, will try it and see what happens. :-)

While waiting for help, i tried a new config, without fix_nat_contact.
It works (Audio & signalling) for outgoing calls.(private -> public)
Contact header has a private IP but SDP information is correct due to RTPProxy.
At incoming calls the force_rtp_proxy command didn't change anything, meaning that SDP Information is not correct -> no audio, only signalling.

I tried to start rtpproxy without options and in bridged mode. Also in bridged mode i tried both possibilities -l private/public & -l public/private, but it didn't influence the outcome.

Perhaps someone could help me out on this. :-)

Here are the changes to my config.

route[1]
{

         if(dst_ip == 10.x.x.x)
        {
                force_rtp_proxy("","193.x.x.x");
        };
        if (dst_ip == 193.x.x.x)
        {
                force_rtp_proxy("","10.x.x.x");
        };


        t_on_reply("1");

        if (!t_relay()) {
                sl_reply_error();
        };
}

onreply_route[1] {

    if (status =~ "(183)|2[0-9][0-9]") {
        if(dst_ip == 10.x.x.x)
        {
                force_rtp_proxy("e");
                log(2,"RTP_PROXY: Reply-Route1 dst 10.x.x.x\n");
        };
        if (dst_ip == 193.x.x.x)
        {
                force_rtp_proxy("i");
                log(2,"RTP_PROXY: Reply-Route1 dst 193.x.x.x\n");
        };

        };
}




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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