[Serusers] Multihomed SER & NAT

[Greger V. Teigre]

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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>
>
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