Alcatel Omni Switch/Router, User Manual

Page: 763 / 1100

Enabling/Disabling Directed Broadcasts
Page 25-41
Enabling/Disabling Directed Broadcasts
An IP directed broadcast is an IP datagram that has all zeroes or all 1’s in the host portion of
the destination IP address. The packet is sent to the broadcast address of a subnet to which
the sender is not directly attached. The datagram is routed through the network as a unicast
packet. When it arrives at the subnet, it is converted into a broadcast packet.
Directed broadcasts are used in denial-of-service smurf attacks. In a smurf attack, a continu-
ous stream of ping requests are sent from a falsified source address to a directed broadcast
address, resulting in a large stream of replies, which can overload the host of the source
address.
By default, the switch drops directed broadcasts. Typically, directed broadcasts should not be
enabled.
To enable directed broadcasts to be routed through the switch:
1. At the system prompt, enter the
ipdirbcast
command.
2. Enter
y
to enable direct broadcasts.