Hello, indeed there is a pseudo-variable that gives the environment variables. Moreover, iirc, Luis Azedo added a while ago (it may be only from 5.3) support to resolve variables inside substdef (and maybe define) -- so eventually you should be able to do this with 5.3.0: #!substdef "/PUBLICIP/$env(KAMPUBLICIP)/"  listen=udp:$(local_ip):5060 advertise  "PUBLICIP":5060 It might not work for this specific case, because listen value is a little bit complex definition, not just string values. But with 5.3 there is a command line parameter (-l -- lower case L) to specify listen socket with advertise address. So just remove listen from kamailio.cfg and the start kamailio like: kamailio -l proto:localaddr:lcoalport/publicaddr:publicport Like: kamailio -l udp:10.0.0.1:5080/1.2.3.4:5060 See kamailio -h for more details. Cheers, Daniel On 24.10.19 09:28, Rick Barenthin wrote: -- Daniel-Constantin Mierla -- www.asipto.com www.twitter.com/miconda -- www.linkedin.com/in/miconda Kamailio Advanced Training, Oct 21-23, 2019, Berlin, Germany -- https://asipto.com/u/kat