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Cisco Catalyst Blade Switch 3130 and 3032 for Dell Software Configuration Guide
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Chapter 38 Configuring IP Unicast Routing
Configuring IP Addressing
Beginning in privileged EXEC mode, follow these steps to set the IP broadcast address on an interface:
To restore the default IP broadcast address, use the
no ip broadcast-address
interface configuration
command.
Flooding IP Broadcasts
You can allow IP broadcasts to be flooded throughout your internetwork in a controlled fashion by using
the database created by the bridging STP. Using this feature also prevents loops. To support this
capability, you must configure bridging on each interface that is to participate in the flooding. If bridging
is not configured on an interface, it still can receive broadcasts. However, the interface never forwards
broadcasts it receives, and the router never uses that interface to send broadcasts received on a
different interface.
Packets that are forwarded to a single network address using the IP helper-address mechanism can be
flooded. Only one copy of the packet is sent on each network segment.
To be considered for flooding, packets must meet these criteria. (Note that these are the same conditions
to be met for packet forwarding when using IP helper addresses.)
•
The packet must be a MAC-level broadcast.
•
The packet must be an IP-level broadcast.
•
The packet must be a TFTP, DNS, Time, NetBIOS, Network Disk, or BOOTP packet, or a UDP
specified by the
ip forward-protocol udp
global configuration command.
•
The time-to-live (TTL) value of the packet must be at least 2.
A flooded UDP datagram is given the destination address specified with the
ip broadcast-address
interface configuration command on the output interface. The destination address can be set to any
address. Thus, the destination address might change as the datagram propagates through the network.
The source address never changed. The TTL value decrements.
When a flooded UDP datagram is sent on an interface (and the destination address is possibly changed),
the datagram is processed by the normal IP output routines and is, therefore, subject to ACLs, if they are
present on the output interface.
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
interface
interface-id
Enter interface configuration mode, and specify the interface to
configure.
Step 3
ip broadcast-address
ip-address
Enter a broadcast address different from the default, for example
128.1.255.255.
Step 4
end
Return to privileged EXEC mode.
Step 5
show ip interface
[
interface-id
]
Verify the broadcast address on the interface or all interfaces.
Step 6
copy running-config startup-config
(Optional) Save your entries in the configuration file.