diff --git a/check-plugins/network-io/network-io b/check-plugins/network-io/network-io
index 24b937b13..485055868 100755
--- a/check-plugins/network-io/network-io
+++ b/check-plugins/network-io/network-io
@@ -1,4 +1,4 @@
-#!/usr/bin/env python3
+#!/usr/lib64/linuxfabrik-monitoring-plugins/venv/bin/python
 # -*- coding: utf-8; py-indent-offset: 4 -*-
 #
 # Author:  Linuxfabrik GmbH, Zurich, Switzerland
@@ -12,7 +12,7 @@
 
 import argparse
 import sys
-
+import re
 import lib.args
 import lib.base
 import lib.cache
@@ -48,6 +48,21 @@ DEFAULT_IGNORE = [
 ]
 DEFAULT_NO_MATCH_SEVERITY = 'ok'
 
+def parse_speed_units(speed):
+    """Parse the unit and convert speed from bit to byte"""
+    if speed.endswith("k"):
+        return int(speed[0:-1]) * 1000 / 8
+    elif speed.endswith("m"):
+        return int(speed[0:-1]) * 1000 ** 2 / 8
+    elif speed.endswith("g"):
+        return int(speed[0:-1]) * 1000 ** 3 / 8
+    elif speed.endswith("t"):
+        return int(speed[0:-1]) * 1000 ** 4 / 8
+    else:
+        if re.search(r"\w$", speed):
+            lib.base.cu(f"Unsupported speed unit: {speed}")
+            sys.exit(STATE_UNKNOWN)
+        return int(speed) / 8
 
 def parse_args():
     """Parse command line arguments using argparse."""
@@ -124,6 +139,16 @@ def parse_args():
         default=DEFAULT_WARN,
     )
 
+    parser.add_argument(
+        '--interface-speed',
+        help='Set a fixed interface speed (max throughput). Use "<interface>:<speed>" for per-interface or just "<speed>" (or ":<speed>") to apply to all interfaces. '
+        'The speed is given in bits. Units can be: k, m, g, t. '
+        'Can be specified multiple times. Examples: --interface-speed eth0:1g --interface-speed 100m',
+        dest='INTERFACE_SPEED',
+        action='append',
+        default=[],
+    )
+
     args, _ = parser.parse_known_args()
     return args
 
@@ -145,6 +170,39 @@ def main():
     except SystemExit:
         sys.exit(STATE_UNKNOWN)
 
+    # parse interface speed mappings
+    iface_speeds = {}
+    global_iface_speed = None
+    for entry in args.INTERFACE_SPEED:
+        if not entry:
+            lib.base.cu(f'Invalid --interface-speed entry "{entry}", expected format "<interface>:<speed>" or "<speed>"')
+            sys.exit(STATE_UNKNOWN)
+
+        # split into name:speed if possible. Accept either "name:speed", ":speed", or "speed"
+        if ':' in entry:
+            name_part, speed_part = entry.split(':', 1)
+            name = name_part.strip() or None
+            speed = speed_part.strip()
+        else:
+            name = None
+            speed = entry.strip()
+
+        if not speed:
+            lib.base.cu(f'Invalid --interface-speed entry "{entry}", missing speed value')
+            sys.exit(STATE_UNKNOWN)
+
+        try:
+            bit_per_second = parse_speed_units(speed)
+        except ValueError as e:
+            lib.base.cu(f'Invalid speed value in --interface-speed "{entry}": {e}')
+            sys.exit(STATE_UNKNOWN)
+
+        if name is None:
+            # global speed for all interfaces (last one wins)
+            global_iface_speed = bit_per_second
+        else:
+            iface_speeds[name] = bit_per_second
+
     conn = lib.base.coe(
         lib.db_sqlite.connect(filename='linuxfabrik-monitoring-plugins-network-io.db')
     )
@@ -257,30 +315,47 @@ def main():
             lib.db_sqlite.close(conn)
             lib.base.oao('Waiting for more data.', state)
 
-        # store the max. measured throughput in cache
+        # store/get the max. measured throughput in cache or use user-provided interface speed
         throughput_db = lib.cache.get(
             f'network-io-{interface}-throughput-max',
             filename='linuxfabrik-monitoring-plugins-network-io.db',
         )
-        if throughput_db is False:
-            # unknown interface, no value
-            throughput_max = (
-                10 * 1024 * 1024
-            )  # interface should be capable of 10 MB/sec
+
+        # precedence: per-interface CLI > global CLI > cache/discovery
+        if interface in iface_speeds:
+            throughput_max = int(iface_speeds[interface])
             lib.cache.set(
                 f'network-io-{interface}-throughput-max',
                 throughput_max,
                 filename='linuxfabrik-monitoring-plugins-network-io.db',
             )
-        elif throughput1 > int(throughput_db):
-            throughput_max = throughput1
+        elif global_iface_speed is not None:
+            throughput_max = int(global_iface_speed)
             lib.cache.set(
                 f'network-io-{interface}-throughput-max',
                 throughput_max,
                 filename='linuxfabrik-monitoring-plugins-network-io.db',
             )
         else:
-            throughput_max = int(throughput_db)
+            if throughput_db is False:
+                # unknown interface, no value
+                throughput_max = (
+                    10 * 1024 * 1024
+                )  # interface should be capable of 10 MB/sec
+                lib.cache.set(
+                    f'network-io-{interface}-throughput-max',
+                    throughput_max,
+                    filename='linuxfabrik-monitoring-plugins-network-io.db',
+                )
+            elif throughput1 > int(throughput_db):
+                throughput_max = throughput1
+                lib.cache.set(
+                    f'network-io-{interface}-throughput-max',
+                    throughput_max,
+                    filename='linuxfabrik-monitoring-plugins-network-io.db',
+                )
+            else:
+                throughput_max = int(throughput_db)
 
         # per-second rates for the remaining cumulative counters (packets,
         # errors, drops), computed like the byte rates above instead of