User's Manual

380
identify and receive message of the two types.
(1) Allowing Translating from Directed Broadcast to Physical Broadcast
By default, the IP directional broadcast packets will be dropped, rather than being forwarded. Dropping the IP
directional broadcast packet is conducive to prevent the routing SWITCH from attacks of "refusal service".
You can activate the function of forwarding directed IP broadcast on the interface where the directed broadcast
is transformed to the physical message. If the forwarding function is activated, all the directed broadcast
message of the network that connects the interface will be forwarded to the interface. The message then will
be sent as the physical broadcast message.
You can designate an access table to control the forwarding of broadcast message. After the access table is
specified, only IP message that the access table allows can be transformed from the directed broadcast to the
physical broadcast.
Run the following command in interface configuration mode to activate the forwarding of the directed broadcast.
Command Purpose
ip directed-broadcast [access-list-name]
Allows the translation from the directed broadcast
to the physical broadcast on the interface.
(2) Forwarding UDP Broadcast Message
Sometimes, the host uses the UDP broadcast message to determine information about the address,
configuration and name, and so on. If the network where the host is located has no corresponding server to
forward the UDP message, the host cannot receive any of the UDP message. To solve the problem, you can
do some configuration on the corresponding interface to forward some types of broadcast message to an
assistant address. You can configure multiple assistant addresses for an interface.
You can designate a UDP destination port to decide which UDP message is to be forwarded. Currently, the
default forwarding destination port of the system is UDP packet of NetBIOS name service (port 137).
Run the following command in interface configuration mode to allow message forwarding and to specify the
destination address:
Command Purpose
ip helper-address address
Allows to forward the UDP broadcast message and
to specify the destination address.
Run the following command in global configuration mode to specify protocols to be forwarded:
Command Purpose
ip forward-protocol udp [port]
Specifies which interfaces’ UDP protocols will be
forwarded.