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A directed broadcast is a frame sent to the subnet broadcast address on a remote IP subnet. Forwarding directed broadcast traffic can be enabled or disabled on an IP-interface basis. By disabling or suppressing directed broadcast on an interface, all frames sent to the subnet broadcast address for a local router interface will be dropped. Disabling this function protects hosts from possible denial of service (DOS) attacks such as "smurfing".
The table below describes the item in the Direct Broadcast tab.
DirectBroadcastEnable
If enabled, an Isolated Routing Port (IRP) can forward directed broadcast traffic. A directed broadcast is a frame sent to the subnet broadcast address on a remote IP subnet. By disabling or suppressing directed broadcast on an interface, all frames sent to the subnet broadcast address for a local router interface are dropped. Disabling this function protects a host from possible denial of service (DOS) attacks.
Note: This feature is enabled by default. With the feature enabled, the CPU does not receive a copy of the directed broadcast. As a result, the switch does not respond to a subnet broadcast ping sent from a remote subnet.
Note:
With directed broadcast enabled, the CPU does not receive a copy of the directed broadcast. As a result, the switch does not respond to the subnet broadcast ping sent from the remote subnet. In earlier software releases, the switch replied to a directed broadcast subnet ping.