diff --git a/lib/regbot.js b/lib/regbot.js
index 89354dc..4d5b7c1 100644
--- a/lib/regbot.js
+++ b/lib/regbot.js
@@ -6,7 +6,7 @@ const {
   REGISTER_RESPONSE_REMOVE,
   JAMBONES_REGBOT_USER_AGENT
 } = require('./config');
-const {isValidDomainOrIP} = require('./utils');
+const {isValidDomainOrIP, isValidIPv4} = require('./utils');
 const DEFAULT_EXPIRES = (parseInt(JAMBONES_REGBOT_DEFAULT_EXPIRES_INTERVAL) || 3600);
 const MIN_EXPIRES = (parseInt(JAMBONES_REGBOT_MIN_EXPIRES_INTERVAL) || 30);
 const assert = require('assert');
@@ -119,7 +119,8 @@ class Regbot {
         proxy = `sip:${this.outbound_sip_proxy};transport=${transport}`;
         this.logger.debug(`sending via proxy ${proxy}`);
       } else {
-        proxy = `sip:${this.ipv4}:${this.port};transport=${transport}`;
+        const isIPv4 = isValidIPv4(this.ipv4);
+        proxy = `sip:${this.ipv4}${isIPv4 ? `:${this.port}` : ''};transport=${transport}`;
         this.logger.debug(`sending to registrar ${proxy}`);
       }
       const req = await srf.request(`${scheme}:${this.sip_realm}`, {
@@ -203,14 +204,14 @@ class Regbot {
         }));
 
         // for reg trunks, create ephemeral set of IP addresses for inbound gateways
-        if (this.trunk_type === 'reg') {
+        if (this.trunk_type === 'reg' && !isValidIPv4(this.ipv4)) {
           this.addresses = [];
           if (this.port) {
-            const addrs = await dnsResolverA(this.logger, this.sip_realm);
+            const addrs = await dnsResolverA(this.logger, this.ipv4);
             this.addresses.push(...addrs);
           }
           else {
-            const addrs = await dnsResolverSrv(this.logger, this.sip_realm, this.transport);
+            const addrs = await dnsResolverSrv(this.logger, this.ipv4, this.transport);
             this.addresses.push(...addrs);
           }