User Manual

373
Users Manual of XGS-6350-24X4C
identify the broadcast message through special address. Some protocols, including some important Internet
protocols, frequently use the broadcast message. One primary task of the IP network administrator is to
control the broadcast message. The system supports the directed broadcast, that is, the broadcast of
designated network. The system does not support the broadcast of all subnets in a network.
Some early-stage IP’s do not adopt the current broadcast address standard. The broadcast address adopted
by these IP’s is represented completely by the number “0”. The system can simultaneously identify and
receive message of the two types.
1. Allowing translating from directed broadcast to physical broadcast
The directed IP broadcast message will be dropped by default, preventing the switch from attacking by
message “service rejected”.
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.
Run… To…
ip directed-broadcast
[access-list-name]
Allow 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 port 137.
Run the following command in interface configuration mode to allow message forwarding and to specify the
destination address:
Run… To…
ip helper-addressaddress
Allow to forward the UDP broadcast
message and to specify the destination
address.