diff --git a/src/testsuites/test_iperf.py b/src/testsuites/test_iperf.py
index b658116..b5bcc03 100644
--- a/src/testsuites/test_iperf.py
+++ b/src/testsuites/test_iperf.py
@@ -9,6 +9,7 @@ class IperfTest(ITestSuite):
     def __init__(self, config: TestConfig) -> None:
         super().__init__(config)
         self.is_udp_mode = False
+        self.is_port_forward = False
         if self.config.packet_type == "udp":
             self.is_udp_mode = True
             if self.config.bitrate == 0:
@@ -67,8 +68,12 @@ def _run_test(self, network: INetwork, proto_info: IProtoInfo):
                 tun_ip = client.IP()
             receiver_ip = tun_ip
         else:
-            if upper_proto_name in ["BTP", "BRTP"] and self.is_udp_mode:
+            if upper_proto_name in ["BTP", "BRTP"] and self.is_port_forward:
+                # iperf3 default port 5201 is set as udp port-forwarding port in h0.
+                # send data to h0:5201, then forward to the last node in the chain.
                 receiver_ip = client.IP()
+                logging.debug(
+                    "Test iperf3 with port forwarding from %s:5201 to %s", receiver_ip, server.IP())
             else:
                 tun_ip = proto_info.get_tun_ip(
                     network, self.config.server_host)
diff --git a/src/tools/cfg_generator.py b/src/tools/cfg_generator.py
index 04afa18..7ef6340 100644
--- a/src/tools/cfg_generator.py
+++ b/src/tools/cfg_generator.py
@@ -163,13 +163,16 @@ def _generate_node_ips(self, num_nodes):
     def generate_cfg(self, num_nodes, virtual_ip_prefix):
         node_ips = self._generate_node_ips(num_nodes)
         tun_mappings = self._generate_tun_cfg(node_ips, virtual_ip_prefix)
-        for i in range(len(node_ips)):
+        for i in range(num_nodes):
             link_cnt, links = self._generate_link_cfg(node_ips, i)
             route_cnt, routes = self._generate_route_cfg(node_ips, i)
             tcp_proxy_cnt, tcp_proxies = self._generate_tcp_proxy_cfg(
                 node_ips, i)
             port_forward = ""
-            if i == 0:
+            # oasis core didn't support port forward but ini configs have port forward rules.
+            # port forward rules for h0, h1, ..., h(n-1) to h(n)
+            if i != num_nodes - 1:
+                # generate port forward from h0 to the last node in the chain.
                 port_forward = self._generate_port_forward_item(
                     node_ips[-1][0])
             with open(f"{self.path}/h{i}.ini", "w", encoding="utf-8") as f:
@@ -177,7 +180,7 @@ def generate_cfg(self, num_nodes, virtual_ip_prefix):
                                              route_cnt=route_cnt, routes=routes,
                                              tcp_proxy_cnt=tcp_proxy_cnt, tcp_proxies=tcp_proxies,
                                              port_forward=port_forward,
-                                             tun_ip=f"{virtual_ip_prefix}{i+1}", tun_mapping_cnt=len(node_ips),
+                                             tun_ip=f"{virtual_ip_prefix}{i+1}", tun_mapping_cnt=num_nodes,
                                              tun_mappings=tun_mappings))
                 logging.info("Generated %s/h%d.ini", self.path, i)