Leaflet

OL-11615-01

Conceptually, Catalyst 6500 and 4500 Series switches implement the traffic storm feature in a similar

manner. However, there are some implementation differences. Traffic storms can consist of unicast,

multicast, or broadcast packets. Traffic storm control in Catalyst 6500 Series switches can monitor and

limit unicast, multicast, and broadcast packet storms while in Catalyst 4500, storm control can monitor

and limit multicast and broadcast packet storms only. There are other implementation differences

between the two switching platforms, as explained in the following sections.

Catalyst 6500 Broadcast Suppression (Catalyst OS)

The traffic storm control feature on Catalyst 6500 Series switches is supported for both, Catalyst OS and

Cisco IOS. In Catalyst OS, traffic storm control is implemented under the name of broadcast

suppression. In this switching platform, broadcast traffic storm control is supported on all LAN ports,

while multicast and unicast traffic storm control is supported only on Gigabit and 10 Gigabit Ethernet

ports.

Broadcast suppression on the Catalyst 6500 Series switches is implemented in the hardware. The

suppression circuitry monitors the packets passing from a port to the switching bus. Using the

Individual/Group bit in the packet destination address, the broadcast suppression circuitry determines if

the packet is unicast or broadcast, keeps track of the current count of broadcasts within the 1-second time

interval, and when a threshold is reached, filters out the subsequent broadcast packets.

Note Broadcast and multicast suppression is not supported on the WS-X6148A-GE-TX,

WS-X6148A-GE-45A, and WS-X6548-GE-TX modules.

Because hardware broadcast suppression uses a bandwidth-based method to measure the broadcast

activity, the most significant implementation factor is setting the percentage of the total available

bandwidth that can be used by the broadcast traffic. A threshold value of 100 percent means that no limit

is placed on the broadcast traffic. By entering the set port broadcast command, you can set up the

broadcast suppression threshold value.

Because the packets do not arrive at uniform intervals, the 1-second time interval during which the

broadcast activity is measured can affect the behavior of broadcast suppression.

On the Gigabit Ethernet ports, you can use broadcast suppression to filter multicast and unicast traffic.

You can suppress the multicast or unicast traffic separately on a port, both require that you configure

broadcast suppression. When you specify a percentage of the total bandwidth to be used for the multicast

or unicast traffic, the same limit applies to the broadcast traffic.

Note Multicast suppression does not drop bridge protocol data unit (BPDU) packets unless it is enabled in one

of the following modules: WS-X6724-SFP, WS-X6748-GE-TX, WS-X6748-SFP, WS-X6704-10GE,

WS-SUP32-GE-3B, and WS-SUP32-10GE-3B. Enabling multicast suppression on these modules can

cause BPDUs to be suppressed when the multicast suppression threshold is exceeded. We strongly

advise that you do not use multicast suppression on ports that need to receive BPDUs because potential

side effects can be root port loss or spanning tree loops when the suppression threshold is exceeded. As

an alternative, consider using the Layer 2 hardware-based rate limiter on Supervisor 32 and 720 if you

need to control the volume of BPDUs or other Layer 2 PDUs. Note that the hardware-based rate limiters

must be used cautiously, as they control traffic globally and can also have potential side effects on the

Layer 2 connectivity. Refer to

Configuring Hardware-Based Rate Limiters in Catalyst OS, page 82 for

more information.