I just did the test for ports between 10000 and 10100 (for 20000, displays a lot =) ):
3CX Firewall Checker, v1.0. Copyright (C) 3CX Ltd. All rights reserved.
<14:08:56>: Phase 1, checking servers connection, please wait...
<14:08:56>: Stun Checker service is reachable. Phase 1 check passed.
<14:08:56>: Phase 2a, Check Port Forwarding to UDP SIP port, please wait...
<14:08:57>: UDP SIP Port is set to 5060. Response received correctly with no translation. Phase 2a check passed.
<14:08:57>: Phase 2b. Check Port Forwarding to TCP SIP port, please wait...
<14:08:57>: TCP SIP Port is set to 5060. Response received correctly with no translation. Phase 2b check passed.
<14:08:57>: Phase 3. Check Port Forwarding to TCP Tunnel port, please wait...
<14:08:58>: TCP TUNNEL Port is set to 5090. Response received correctly with no translation. Phase 3 check passed.
<14:08:58>: Phase 4. Check Port Forwarding to RTP external port range, please wait...
<14:09:10>: UDP RTP Port 10000. Response received correctly with no translation. Phase 4-01 check passed.
<14:09:10>: UDP RTP Port 10001. Response received correctly with no translation. Phase 4-02 check passed.
<14:09:10>: UDP RTP Port 10002. Response received correctly with no translation. Phase 4-03 check passed.
<14:09:10>: UDP RTP Port 10003. Response received correctly with no translation. Phase 4-04 check passed.
<14:09:10>: UDP RTP Port 10004. Response received correctly with no translation. Phase 4-05 check passed.
<14:09:10>: UDP RTP Port 10005. Response received correctly with no translation. Phase 4-06 check passed.
<14:09:10>: UDP RTP Port 10006. Response received correctly with no translation. Phase 4-07 check passed.
<14:09:10>: UDP RTP Port 10007. Response received correctly with no translation. Phase 4-08 check passed.
<14:09:10>: UDP RTP Port 10008. Response received correctly with no translation. Phase 4-09 check passed.
<14:09:10>: UDP RTP Port 10009. Response received correctly with no translation. Phase 4-10 check passed.
<14:09:10>: UDP RTP Port 10010. Response received correctly with no translation. Phase 4-11 check passed.
<14:09:10>: UDP RTP Port 10011. Response received correctly with no translation. Phase 4-12 check passed.
<14:09:10>: UDP RTP Port 10012. Response received correctly with no translation. Phase 4-13 check passed.
<14:09:10>: UDP RTP Port 10013. Response received correctly with no translation. Phase 4-14 check passed.
<14:09:10>: UDP RTP Port 10014. Response received correctly with no translation. Phase 4-15 check passed.
<14:09:10>: UDP RTP Port 10015. Response received correctly with no translation. Phase 4-16 check passed.
<14:09:10>: UDP RTP Port 10016. Response received correctly with no translation. Phase 4-17 check passed.
<14:09:10>: UDP RTP Port 10017. Response received correctly with no translation. Phase 4-18 check passed.
<14:09:10>: UDP RTP Port 10018. Response received correctly with no translation. Phase 4-19 check passed.
<14:09:10>: UDP RTP Port 10019. Response received correctly with no translation. Phase 4-20 check passed.
<14:09:10>: UDP RTP Port 10020. Response received correctly with no translation. Phase 4-21 check passed.
<14:09:10>: UDP RTP Port 10021. Response received correctly with no translation. Phase 4-22 check passed.
<14:09:10>: UDP RTP Port 10022. Response received correctly with no translation. Phase 4-23 check passed.
<14:09:10>: UDP RTP Port 10023. Response received correctly with no translation. Phase 4-24 check passed.
<14:09:10>: UDP RTP Port 10024. Response received correctly with no translation. Phase 4-25 check passed.
<14:09:10>: UDP RTP Port 10025. Response received correctly with no translation. Phase 4-26 check passed.
<14:09:10>: UDP RTP Port 10026. Response received correctly with no translation. Phase 4-27 check passed.
<14:09:10>: UDP RTP Port 10027. Response received correctly with no translation. Phase 4-28 check passed.
<14:09:10>: UDP RTP Port 10028. Response received correctly with no translation. Phase 4-29 check passed.
<14:09:10>: UDP RTP Port 10029. Response received correctly with no translation. Phase 4-30 check passed.
<14:09:10>: UDP RTP Port 10030. Response received correctly with no translation. Phase 4-31 check passed.
<14:09:10>: UDP RTP Port 10031. Response received correctly with no translation. Phase 4-32 check passed.
<14:09:10>: UDP RTP Port 10032. Response received correctly with no translation. Phase 4-33 check passed.
<14:09:10>: UDP RTP Port 10033. Response received correctly with no translation. Phase 4-34 check passed.
<14:09:10>: UDP RTP Port 10034. Response received correctly with no translation. Phase 4-35 check passed.
<14:09:10>: UDP RTP Port 10035. Response received correctly with no translation. Phase 4-36 check passed.
<14:09:10>: UDP RTP Port 10036. Response received correctly with no translation. Phase 4-37 check passed.
<14:09:10>: UDP RTP Port 10037. Response received correctly with no translation. Phase 4-38 check passed.
<14:09:10>: UDP RTP Port 10038. Response received correctly with no translation. Phase 4-39 check passed.
<14:09:10>: UDP RTP Port 10039. Response received correctly with no translation. Phase 4-40 check passed.
<14:09:10>: UDP RTP Port 10040. Response received correctly with no translation. Phase 4-41 check passed.
<14:09:10>: UDP RTP Port 10041. Response received correctly with no translation. Phase 4-42 check passed.
<14:09:10>: UDP RTP Port 10042. Response received correctly with no translation. Phase 4-43 check passed.
<14:09:10>: UDP RTP Port 10043. Response received correctly with no translation. Phase 4-44 check passed.
<14:09:10>: UDP RTP Port 10044. Response received correctly with no translation. Phase 4-45 check passed.
<14:09:10>: UDP RTP Port 10045. Response received correctly with no translation. Phase 4-46 check passed.
<14:09:10>: UDP RTP Port 10046. Response received correctly with no translation. Phase 4-47 check passed.
<14:09:10>: UDP RTP Port 10047. Response received correctly with no translation. Phase 4-48 check passed.
<14:09:10>: UDP RTP Port 10048. Response received correctly with no translation. Phase 4-49 check passed.
<14:09:10>: UDP RTP Port 10049. Response received correctly with no translation. Phase 4-50 check passed.
<14:09:10>: UDP RTP Port 10050. Response received correctly with no translation. Phase 4-51 check passed.
<14:09:10>: UDP RTP Port 10051. Response received correctly with no translation. Phase 4-52 check passed.
<14:09:10>: UDP RTP Port 10052. Response received correctly with no translation. Phase 4-53 check passed.
<14:09:10>: UDP RTP Port 10053. Response received correctly with no translation. Phase 4-54 check passed.
<14:09:10>: UDP RTP Port 10054. Response received correctly with no translation. Phase 4-55 check passed.
<14:09:10>: UDP RTP Port 10055. Response received correctly with no translation. Phase 4-56 check passed.
<14:09:10>: UDP RTP Port 10056. Response received correctly with no translation. Phase 4-57 check passed.
<14:09:10>: UDP RTP Port 10057. Response received correctly with no translation. Phase 4-58 check passed.
<14:09:10>: UDP RTP Port 10058. Response received correctly with no translation. Phase 4-59 check passed.
<14:09:10>: UDP RTP Port 10059. Response received correctly with no translation. Phase 4-60 check passed.
<14:09:10>: UDP RTP Port 10060. Response received correctly with no translation. Phase 4-61 check passed.
<14:09:10>: UDP RTP Port 10061. Response received correctly with no translation. Phase 4-62 check passed.
<14:09:10>: UDP RTP Port 10062. Response received correctly with no translation. Phase 4-63 check passed.
<14:09:10>: UDP RTP Port 10063. Response received correctly with no translation. Phase 4-64 check passed.
<14:09:10>: UDP RTP Port 10064. Response received correctly with no translation. Phase 4-65 check passed.
<14:09:10>: UDP RTP Port 10065. Response received correctly with no translation. Phase 4-66 check passed.
<14:09:10>: UDP RTP Port 10066. Response received correctly with no translation. Phase 4-67 check passed.
<14:09:10>: UDP RTP Port 10067. Response received correctly with no translation. Phase 4-68 check passed.
<14:09:10>: UDP RTP Port 10068. Response received correctly with no translation. Phase 4-69 check passed.
<14:09:10>: UDP RTP Port 10069. Response received correctly with no translation. Phase 4-70 check passed.
<14:09:10>: UDP RTP Port 10070. Response received correctly with no translation. Phase 4-71 check passed.
<14:09:10>: UDP RTP Port 10071. Response received correctly with no translation. Phase 4-72 check passed.
<14:09:10>: UDP RTP Port 10072. Response received correctly with no translation. Phase 4-73 check passed.
<14:09:10>: UDP RTP Port 10073. Response received correctly with no translation. Phase 4-74 check passed.
<14:09:10>: UDP RTP Port 10074. Response received correctly with no translation. Phase 4-75 check passed.
<14:09:10>: UDP RTP Port 10075. Response received correctly with no translation. Phase 4-76 check passed.
<14:09:10>: UDP RTP Port 10076. Response received correctly with no translation. Phase 4-77 check passed.
<14:09:10>: UDP RTP Port 10077. Response received correctly with no translation. Phase 4-78 check passed.
<14:09:10>: UDP RTP Port 10078. Response received correctly with no translation. Phase 4-79 check passed.
<14:09:10>: UDP RTP Port 10079. Response received correctly with no translation. Phase 4-80 check passed.
<14:09:10>: UDP RTP Port 10080. Response received correctly with no translation. Phase 4-81 check passed.
<14:09:10>: UDP RTP Port 10081. Response received correctly with no translation. Phase 4-82 check passed.
<14:09:10>: UDP RTP Port 10082. Response received correctly with no translation. Phase 4-83 check passed.
<14:09:10>: UDP RTP Port 10083. Response received correctly with no translation. Phase 4-84 check passed.
<14:09:10>: UDP RTP Port 10084. Response received correctly with no translation. Phase 4-85 check passed.
<14:09:10>: UDP RTP Port 10085. Response received correctly with no translation. Phase 4-86 check passed.
<14:09:10>: UDP RTP Port 10086. Response received correctly with no translation. Phase 4-87 check passed.
<14:09:10>: UDP RTP Port 10087. Response received correctly with no translation. Phase 4-88 check passed.
<14:09:10>: UDP RTP Port 10088. Response received correctly with no translation. Phase 4-89 check passed.
<14:09:10>: UDP RTP Port 10089. Response received correctly with no translation. Phase 4-90 check passed.
<14:09:10>: UDP RTP Port 10090. Response received correctly with no translation. Phase 4-91 check passed.
<14:09:10>: UDP RTP Port 10091. Response received correctly with no translation. Phase 4-92 check passed.
<14:09:10>: UDP RTP Port 10092. Response received correctly with no translation. Phase 4-93 check passed.
<14:09:10>: UDP RTP Port 10093. Response received correctly with no translation. Phase 4-94 check passed.
<14:09:10>: UDP RTP Port 10094. Response received correctly with no translation. Phase 4-95 check passed.
<14:09:10>: UDP RTP Port 10095. Response received correctly with no translation. Phase 4-96 check passed.
<14:09:10>: UDP RTP Port 10096. Response received correctly with no translation. Phase 4-97 check passed.
<14:09:10>: UDP RTP Port 10097. Response received correctly with no translation. Phase 4-98 check passed.
<14:09:10>: UDP RTP Port 10098. Response received correctly with no translation. Phase 4-99 check passed.
<14:09:10>: UDP RTP Port 10099. Response received correctly with no translation. Phase 4-100 check passed.
<14:09:10>: UDP RTP Port 10100. Response received correctly with no translation. Phase 4-101 check passed.
Application exit code is 0