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816 PowerConnect B-Series FCX Configuration Guide
53-1002266-01
Configuring IP parameters – Layer 3 Switches
26
NOTE
A less common type, the all-subnets broadcast, goes to all directly-attached subnets. Forwarding for
this broadcast type also is supported, but most networks use IP multicasting instead of all-subnet
broadcasting.
Forwarding for all types of IP directed broadcasts is disabled by default. You can enable forwarding
for all types if needed. You cannot enable forwarding for specific broadcast types.
To enable forwarding of IP directed broadcasts, enter the following command.
PowerConnect(config)# ip directed-broadcast
Syntax: [no] ip directed-broadcast
Dell software makes the forwarding decision based on the router's knowledge of the destination
network prefix. Routers cannot determine that a message is unicast or directed broadcast apart
from the destination network prefix. The decision to forward or not forward the message is by
definition only possible in the last hop router.
To disable the directed broadcasts, enter the following command in the CONFIG mode.
PowerConnect(config)# no ip directed-broadcast
To enable directed broadcasts on an individual interface instead of globally for all interfaces, enter
commands such as the following.
PowerConnect(config)# interface ethernet 1/1
PowerConnect(config-if-1/1)# ip directed-broadcast
Syntax: [no] ip directed-broadcast
Disabling forwarding of IP source-routed packets
A source-routed packet specifies the exact router path for the packet. The packet specifies the path
by listing the IP addresses of the router interfaces through which the packet must pass on its way to
the destination. The Layer 3 Switch supports both types of IP source routing:
• Strict source routing – requires the packet to pass through only the listed routers. If the Layer 3
Switch receives a strict source-routed packet but cannot reach the next hop interface specified
by the packet, the Layer 3 Switch discards the packet and sends an ICMP Source-Route-Failure
message to the sender.
NOTE
The Layer 3 Switch allows you to disable sending of the Source-Route-Failure messages. Refer
to “Disabling ICMP messages” on page 817.
• Loose source routing – requires that the packet pass through all of the listed routers but also
allows the packet to travel through other routers, which are not listed in the packet.
The Layer 3 Switch forwards both types of source-routed packets by default. To disable the feature,
use either of the following methods. You cannot enable or disable strict or loose source routing
separately.
To disable forwarding of IP source-routed packets, enter the following command.
PowerConnect(config)# no ip source-route
Syntax: [no] ip source-route
To re-enable forwarding of source-routed packets, enter the following command.