Lab Objective
Configure storm control on a switch port with a broadcast traffic threshold, simulate a broadcast storm exceeding that threshold, and verify the switch suppresses the excess traffic rather than forwarding it unchecked.
Lab Purpose
Spanning Tree, covered extensively earlier in this series, prevents the Layer 2 loops that typically cause broadcast storms, but it offers no protection against a single misbehaving device or NIC that floods broadcast traffic without any loop being present at all. Storm control provides a direct traffic-rate safety net independent of loop prevention.
Lab Topology
Switch1 ---- Gi1/0/8 ---- PC-A (traffic source)Task 1: Configure Broadcast Storm Control
Configure storm control on Gi1/0/8 to limit broadcast traffic to 20% of available bandwidth.
Task 2: Verify Baseline Configuration
Confirm the storm control threshold is correctly applied.
Task 3: Simulate Normal Broadcast Traffic
Generate a modest amount of broadcast traffic (well under the threshold) and confirm it passes through unaffected.
Task 4: Simulate an Excessive Broadcast Storm
Generate broadcast traffic exceeding the configured 20% threshold and verify the switch suppresses the excess.
Task 5: Verify Suppression Statistics
Check the interface counters confirming storm control action was taken.
Solution and Verification
Switch1(config)# interface gigabitethernet1/0/8
Switch1(config-if)# storm-control broadcast level 20.00Switch1# show storm-control gigabitethernet1/0/8 broadcast
Interface Filter State Level Current
--------- ------------- ------ -------
Gi1/0/8 Forwarding 20.00% 0.00%
-- Confirms the threshold is applied, with
-- current broadcast traffic well below it-- Modest broadcast traffic generated,
-- staying under 20% of link bandwidth:
Switch1# show storm-control gigabitethernet1/0/8 broadcast
Interface Filter State Level Current
--------- ------------- ------ -------
Gi1/0/8 Forwarding 20.00% 8.20%
-- Still forwarding normally, current
-- level remains below threshold-- Simulated broadcast storm exceeding 20%
-- generated from PC-A:
Switch1# show storm-control gigabitethernet1/0/8 broadcast
Interface Filter State Level Current
--------- ------------- ------ -------
Gi1/0/8 Blocking 20.00% 34.50%
-- Filter State changed to "Blocking" --
-- the switch is now actively dropping
-- broadcast traffic above the threshold
-- on this port, rather than forwarding
-- everything it receivesSwitch1# show interfaces gigabitethernet1/0/8 counters broadcast
Port Broadcast
Gi1/0/8 184521
-- The broadcast counter confirms
-- significant broadcast volume was seen
-- and partially suppressed by storm controlKey Takeaway
Storm control operates entirely independently of Spanning Tree and loop detection — it protects against excessive broadcast, multicast, or unicast traffic regardless of the cause, whether a genuine Layer 2 loop, a malfunctioning NIC, or a misbehaving application flooding traffic, making it a useful complementary safeguard even on a topology where STP has already eliminated all loops.