Custom GTP IP address configuration for UP Transport Layer Information

src/gnb.cpp

@@ -52,6 +52,9 @@ static nr::gnb::GnbConfig *ReadConfigYaml()
     result->ngapIp = yaml::GetIp4(config, "ngapIp");
     result->gtpIp = yaml::GetIp4(config, "gtpIp");
 
+    if (yaml::HasField(config, "gtpAdvertiseIp"))
+        result->gtpAdvertiseIp = yaml::GetIp4(config, "gtpAdvertiseIp");
+
     result->ignoreStreamIds = yaml::GetBool(config, "ignoreStreamIds");
     result->pagingDrx = EPagingDrx::V128;
     result->name = "UERANSIM-gnb-" + std::to_string(result->plmn.mcc) + "-" + std::to_string(result->plmn.mnc) + "-" +

src/gnb/ngap/session.cpp

@@ -233,7 +233,9 @@ std::optional<NgapCause> NgapTask::setupPduSessionResource(PduSessionResource *r
         return NgapCause::Protocol_semantic_error;
     }
 
-    resource->downTunnel.address = utils::IpToOctetString(m_base->config->gtpIp);
+    std::string gtpIp = m_base->config->gtpAdvertiseIp.value_or(m_base->config->gtpIp);
+
+    resource->downTunnel.address = utils::IpToOctetString(gtpIp);
     resource->downTunnel.teid = ++m_downlinkTeidCounter;
 
     auto *w = new NmGnbNgapToGtp(NmGnbNgapToGtp::SESSION_CREATE);

src/gnb/types.hpp

@@ -307,6 +307,7 @@ struct GnbConfig
     std::string portalIp{};
     std::string ngapIp{};
     std::string gtpIp{};
+    std::optional<std::string> gtpAdvertiseIp{};
     bool ignoreStreamIds{};
 
     /* Assigned by program */