diff --git a/platformio/commands/upgrade.py b/platformio/commands/upgrade.py
index 57615826..80e22bb1 100644
--- a/platformio/commands/upgrade.py
+++ b/platformio/commands/upgrade.py
@@ -40,8 +40,7 @@ def cli(dev):
     # kill all PIO Home servers, they block `pioplus` binary
     shutdown_servers()
 
-    to_develop = dev or not all(
-        [c.isdigit() for c in __version__ if c != "."])
+    to_develop = dev or not all([c.isdigit() for c in __version__ if c != "."])
     cmds = ([
         "pip", "install", "--upgrade",
         "https://github.com/platformio/platformio-core/archive/develop.zip"
diff --git a/platformio/maintenance.py b/platformio/maintenance.py
index 51fe0c6c..abbd7ca2 100644
--- a/platformio/maintenance.py
+++ b/platformio/maintenance.py
@@ -52,7 +52,8 @@ def on_platformio_end(ctx, result):  # pylint: disable=W0613
         check_platformio_upgrade()
         check_internal_updates(ctx, "platforms")
         check_internal_updates(ctx, "libraries")
-    except (exception.GetLatestVersionError, exception.APIRequestError):
+    except (exception.InternetIsOffline, exception.GetLatestVersionError,
+            exception.APIRequestError):
         click.secho(
             "Failed to check for PlatformIO upgrades. "
             "Please check your Internet connection.",
@@ -240,6 +241,8 @@ def check_platformio_upgrade():
     last_check['platformio_upgrade'] = int(time())
     app.set_state_item("last_check", last_check)
 
+    util.internet_on(raise_exception=True)
+
     # Update PlatformIO's Core packages
     update_core_packages(silent=True)
 
@@ -285,6 +288,8 @@ def check_internal_updates(ctx, what):
     last_check[what + '_update'] = int(time())
     app.set_state_item("last_check", last_check)
 
+    util.internet_on(raise_exception=True)
+
     pm = PlatformManager() if what == "platforms" else LibraryManager()
     outdated_items = []
     for manifest in pm.get_installed():
diff --git a/platformio/util.py b/platformio/util.py
index 129d3752..80cd1858 100644
--- a/platformio/util.py
+++ b/platformio/util.py
@@ -18,6 +18,7 @@ import json
 import os
 import platform
 import re
+import socket
 import stat
 import subprocess
 import sys
@@ -540,6 +541,7 @@ def _get_api_result(
 
 
 def get_api_result(url, params=None, data=None, auth=None, cache_valid=None):
+    internet_on(raise_exception=True)
     from platformio.app import ContentCache
     total = 0
     max_retries = 5
@@ -559,8 +561,6 @@ def get_api_result(url, params=None, data=None, auth=None, cache_valid=None):
             return result
         except (requests.exceptions.ConnectionError,
                 requests.exceptions.Timeout) as e:
-            if not internet_on():
-                raise exception.InternetIsOffline()
             from platformio.maintenance import in_silence
             total += 1
             if not in_silence():
@@ -575,16 +575,34 @@ def get_api_result(url, params=None, data=None, auth=None, cache_valid=None):
         "Please try later.")
 
 
-def internet_on():
-    for url in ("http://dl.bintray.com", "http://dl.platformio.org"):
+@memoized
+def _internet_on():
+    ips = [
+        "193.222.52.25",  # dl.platformio.org
+        "159.122.18.156"  # dl.bintray.com
+    ]
+    timeout = 2
+    socket.setdefaulttimeout(timeout)
+    for ip in ips:
         try:
-            requests.get(url, timeout=3)
+            if os.getenv("HTTP_PROXY", os.getenv("HTTPS_PROXY")):
+                requests.get("http://%s" % ip, timeout=timeout)
+            else:
+                socket.socket(socket.AF_INET, socket.SOCK_STREAM).connect((ip,
+                                                                           80))
             return True
         except:  # pylint: disable=bare-except
             pass
     return False
 
 
+def internet_on(raise_exception=False):
+    result = _internet_on()
+    if raise_exception and not result:
+        raise exception.InternetIsOffline()
+    return result
+
+
 def get_pythonexe_path():
     return os.environ.get("PYTHONEXEPATH", normpath(sys.executable))