Storm control direction

Unanswered Question
Jan 28th, 2009


I'm having a senior moment. Which way does storm control work on an interface ? Does it monitor incoming broadcasts and not pass them to the bus or outgoing broadcasts and not send them on the wire ?

The issue is if you want to protect a server do you need to configure broadcast suppression on all ports except the server or just the server port ?

I have this problem too.
0 votes
  • 1
  • 2
  • 3
  • 4
  • 5
Overall Rating: 0 (0 ratings)
chuckwirth Thu, 01/29/2009 - 07:42

Storm control, or traffic suppression, monitors packets passing from an interface to the switching bus and determines if the packet is unicast, multicast, or broadcast. The switch counts the number of packets of a specified type received within the one second time interval and compares the measurement with a pre-defined suppression-level threshold.

Patrick Colbeck Thu, 01/29/2009 - 07:50

Thanks. I thought that was the case but a best practice document that I read suggested enabling storm control on selected ports to protect essential service or words to that effect and it made me doubt my understanding.

Giuseppe Larosa Thu, 01/29/2009 - 11:12

Hello Patrick,

we have broadcast storm control enabled on ports including uplinks.

When a bridging loops form and a broadcast storm arises I see a lot of output drops caused by broadcast storm-control including 10GE that have never reached 100% of link utilization

(we have had an issue with 8 10 GE linecards solved with an IOS upgrade on C6500 with sup 720 3B)

My understanding is that on IOS native C6500 and IOS based 4500 the feature works outbound at least I see effects like it is outbound.

Hope to help


Patrick Colbeck Fri, 01/30/2009 - 08:12

Now I am confused. Perhaps it is different on 4500 / 6500 to fixed config switches ?

Giuseppe Larosa Fri, 01/30/2009 - 11:57

Hello Patrick,

I've reviewed documentation

and actually it says that control is inbound to the switching fabric.

However, as I wrote in my previous post I saw output drops on interfaces including tengigabit interfaces that I had thought to be caused by this feature:

we have it enabled together with spanning loop guard and this causes the link to be placed in stp inconsistent state and so it should cause a topology change not output drops on traffic.

It may be just a cosmetic effect to show output drops.

I've checked on a C3750 where the brodcast stom control triggered for an application using broadcast.

On that device I don't see frames discarded outbound and no frames discarded inbound

sh log | inc Mar 15

Mar 15 17:59:24: %LINEPROTO-5-UPDOWN: Line protocol on Interface GigabitEthernet1/0/32, changed state to down

Mar 15 17:59:25: %LINK-3-UPDOWN: Interface GigabitEthernet1/0/32, changed state to down

Mar 15 18:52:53: %STORM_CONTROL-3-FILTERED: A Broadcast storm detected on Gi1/0/48. A packet filter action has been applied on the interface.

Mar 15 18:53:26: %STORM_CONTROL-3-FILTERED: A Broadcast storm detected on Gi1/0/48. A packet filter action has been applied on the interface.

Mar 15 18:53:58: %STORM_CONTROL-3-FILTERED: A Broadcast storm detected on Gi1/0/48. A packet filter action has been applied on the interface.

the sh inteface doesn't show any form of drops:

sh int gi1/0/48

GigabitEthernet1/0/48 is up, line protocol is up (connected)

Hardware is Gigabit Ethernet, address is 0013.c4fc.3530 (bia 0013.c4fc.3530)

Description: Apparato Centrale d'Ascolto-Sig. Tuzzoli

MTU 1500 bytes, BW 1000000 Kbit, DLY 10 usec,

reliability 255/255, txload 1/255, rxload 1/255

Encapsulation ARPA, loopback not set

Keepalive set (10 sec)

Full-duplex, 1000Mb/s, media type is 10/100/1000BaseTX

input flow-control is off, output flow-control is unsupported

ARP type: ARPA, ARP Timeout 04:00:00

Last input 00:00:14, output 00:00:00, output hang never

Last clearing of "show interface" counters never

Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0

Queueing strategy: fifo

Output queue: 0/40 (size/max)

5 minute input rate 6761000 bits/sec, 1057 packets/sec

5 minute output rate 431000 bits/sec, 770 packets/sec

1709095733 packets input, 1342388493 bytes, 0 no buffer

Received 215887428 broadcasts (0 multicast)

0 runts, 0 giants, 0 throttles

0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored

0 watchdog, 4905487 multicast, 0 pause input

0 input packets with dribble condition detected

2849905040 packets output, 1920956647 bytes, 0 underruns

0 output errors, 0 collisions, 3 interface resets

0 babbles, 0 late collision, 0 deferred

0 lost carrier, 0 no carrier, 0 PAUSE output

0 output buffer failures, 0 output buffers swapped out

from the above document it says that on C6500 the following provides stats about the feature activity

Router# show interfaces [{type1 slot/port} | {port-channel number}] counters storm-control

Unfortunately I didn't check with this.

Hope to help



This Discussion