diff --git a/.github/workflows/unit-test-with-cfg.yml b/.github/workflows/unit-test-with-cfg.yml
index 0991ba6519..221d7fb2a4 100644
--- a/.github/workflows/unit-test-with-cfg.yml
+++ b/.github/workflows/unit-test-with-cfg.yml
@@ -74,6 +74,10 @@ jobs:
           cmake -DCMAKE_VERBOSE_MAKEFILE=ON -DCMAKE_BUILD_TYPE=${{ inputs.build_type }} ${{ steps.cmake_flags.outputs.compiler }} ${{ inputs.build_args }} ${{ inputs.install_mbedtls && '-DBUILD_MBEDTLS=OFF' || '' }} ${{ inputs.install_tinycbor && '-DBUILD_TINYCBOR=OFF' || '' }} -DBUILD_TESTING=ON ..
           make oc-unittests
 
+      - name: Setup firewall to drop TCP IPV6 with destination port 12345 (for timeout tests)
+        run: |
+          sudo ip6tables -I OUTPUT -p tcp --dport 12345 -j DROP
+      
       - name: Run unit tests
         run: |
           cd build
diff --git a/port/linux/tcpsession.c b/port/linux/tcpsession.c
index 448a7bf6eb..521156b9b8 100644
--- a/port/linux/tcpsession.c
+++ b/port/linux/tcpsession.c
@@ -86,6 +86,7 @@ typedef struct tcp_waiting_session_t
     oc_clock_time_t start;
     uint8_t count;
     uint8_t force;
+    int error;
   } retry;
   OC_LIST_STRUCT(messages);
   on_tcp_connect_t on_tcp_connect;
@@ -1115,7 +1116,7 @@ tcp_cleanup_connected_waiting_session_locked(tcp_waiting_session_t *ws,
 }
 
 static bool
-tcp_try_connect_waiting_session_locked(tcp_waiting_session_t *ws)
+tcp_try_connect_waiting_session_locked(tcp_waiting_session_t *ws, int *err)
 {
   assert(ws != NULL && ws->sock != -1);
   int error = 0;
@@ -1125,6 +1126,7 @@ tcp_try_connect_waiting_session_locked(tcp_waiting_session_t *ws)
     return false; /* Solaris pending error */
   }
   if (error != 0) {
+    *err = error;
     OC_ERR("socket error: %d", error);
     return false;
   }
@@ -1154,6 +1156,7 @@ enum {
   TCP_WAITING_SESSION_VALID,
   TCP_WAITING_SESSION_RETRY,
   TCP_WAITING_SESSION_EXPIRED,
+  TCP_WAITING_SESSION_ERROR,
 };
 
 static int
@@ -1161,6 +1164,9 @@ tcp_waiting_session_check(const tcp_waiting_session_t *session,
                           oc_clock_time_t now,
                           oc_tcp_connect_retry_t connect_retry)
 {
+  if (session->retry.error != 0) {
+    return TCP_WAITING_SESSION_ERROR;
+  }
   bool retry = session->retry.force != 0;
   if (!retry) {
     oc_clock_time_t expires_in = connect_retry.timeout * OC_CLOCK_SECOND;
@@ -1247,6 +1253,9 @@ tcp_check_expiring_sessions(oc_clock_time_t now)
       }
       break;
     }
+    case TCP_WAITING_SESSION_ERROR:
+      free_waiting_session_locked(ws, false, false);
+      break;
     case TCP_WAITING_SESSION_EXPIRED:
       free_waiting_session_locked(ws, true, false);
       break;
@@ -1262,14 +1271,21 @@ tcp_check_expiring_sessions(oc_clock_time_t now)
 static void
 tcp_process_waiting_session_locked(tcp_waiting_session_t *ws)
 {
-  if (!tcp_try_connect_waiting_session_locked(ws)) {
+  int error = 0;
+  if (!tcp_try_connect_waiting_session_locked(ws, &error)) {
     OC_DBG("failed to connect session(%p, fd=%d)", (void *)ws, ws->sock);
     if (ws->sock >= 0) {
       tcp_context_cfds_fd_clr(&ws->dev->tcp, ws->sock);
       close(ws->sock);
       ws->sock = -1;
     }
-    ws->retry.force = 1;
+    if (error == 0) {
+      ws->retry.force = 1;
+      ws->retry.error = 0;
+    } else {
+      // close the connection
+      ws->retry.error = 1;
+    }
   }
 }
 
diff --git a/port/unittest/connectivitytest.cpp b/port/unittest/connectivitytest.cpp
index e07ff8d078..3abda32779 100644
--- a/port/unittest/connectivitytest.cpp
+++ b/port/unittest/connectivitytest.cpp
@@ -431,7 +431,7 @@ TEST_F(TestConnectivityWithServer, oc_tcp_connect_timeout)
   oc_endpoint_t ep = oc::endpoint::FromString(
     "coaps+tcp://[::1]:12345"); // reachable address, but inactive port
   // enough retries so they will run the whole duration of this test
-  oc_tcp_set_connect_retry(UINT8_MAX, 5);
+  oc_tcp_set_connect_retry(0, 5);
   auto restore_defaults = []() {
     oc_tcp_set_connect_retry(OC_TCP_CONNECT_RETRY_MAX_COUNT,
                              OC_TCP_CONNECT_RETRY_TIMEOUT);
@@ -456,8 +456,7 @@ TEST_F(TestConnectivityWithServer, oc_tcp_connect_timeout)
   EXPECT_EQ(OC_SEND_MESSAGE_QUEUED, oc_send_buffer2(msg, true));
 
   OC_DBG("oc_tcp_connect_timeout wait");
-  oc_tcp_set_connect_retry(0, 2);
-  oc::TestDevice::PoolEvents(2);
+  oc::TestDevice::PoolEvents(10);
 
   EXPECT_EQ(-1, oc_tcp_connection_state(&ep));
   oc_message_unref(msg);
diff --git a/port/unittest/dnstest.cpp b/port/unittest/dnstest.cpp
index b7fb773d91..d926365261 100644
--- a/port/unittest/dnstest.cpp
+++ b/port/unittest/dnstest.cpp
@@ -52,6 +52,7 @@ TEST_F(TestDNS, oc_dns_lookup_invalid)
                               static_cast<transport_flags>(0)));
 
   oc_string_t addr;
+  memset(&addr, 0, sizeof(oc_string_t));
   EXPECT_EQ(-1, oc_dns_lookup(nullptr, &addr, static_cast<transport_flags>(0)));
 
   EXPECT_NE(0, oc_dns_lookup("openconnectivity", &addr,
@@ -61,6 +62,7 @@ TEST_F(TestDNS, oc_dns_lookup_invalid)
 TEST_F(TestDNS, oc_dns_lookup)
 {
   oc_string_t addr;
+  memset(&addr, 0, sizeof(oc_string_t));
   EXPECT_EQ(0, oc_dns_lookup("localhost", &addr, IPV6));
   oc_free_string(&addr);
 }
@@ -70,6 +72,7 @@ TEST_F(TestDNS, oc_dns_lookup)
 TEST_F(TestDNS, oc_dns_lookup_ipv4)
 {
   oc_string_t addr;
+  memset(&addr, 0, sizeof(oc_string_t));
   EXPECT_EQ(0, oc_dns_lookup("localhost", &addr, IPV4));
   oc_free_string(&addr);
 }