Juniper JUNOS OS 10.3 - SOFTWARE, Manual, Page: 1205 / 3946

Related
Documentation
Example: Configuring Unicast RPF on an EX Series Switch on page 1134
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•
Configuring Unicast RPF (CLI Procedure) on page 1162
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Disabling Unicast RPF (CLI Procedure) on page 1163
Understanding IP Directed Broadcast for EX Series Switches
IP directed broadcast helps you implement remote administration tasks such as backups
and wake-on-LAN (WOL) application tasks by sending broadcast packets targeted at
the hosts in a specified destination subnet. IP directed broadcast packets traverse the
network in the same way as unicast IP packets until they reach the destination subnet.
When they reach the destination subnet and IP directed broadcast is enabled on the
receiving switch, the switch translates (“explodes”) the IP directed broadcast packet
into a broadcast that floods the packet on the target subnet. All hosts on the target
subnet receive the IP directed broadcast packet.
This topic covers:
•
IP Directed Broadcast for EX Series Switches Overview on page 1109
•
IP Directed Broadcast Implementation for EX Series Switches on page 1109
• When to Enable IP Directed Broadcast on page 1110
• When Not to Enable IP Directed Broadcast on page 1110
IP Directed Broadcast for EX Series Switches Overview
IP directed broadcast packets have a destination IP address that is a valid broadcast
address for the subnet that is the target of the directed broadcast (the target subnet).
The intent of an IP directed broadcast is to flood the target subnet with the broadcast
packets without broadcasting to the entire network. IP directed broadcast packets cannot
originate from the target subnet.
When you send an IP directed broadcast packet, as it travels to the target subnet, the
network forwards it in the same way as it forwards a unicast packet. When the packet
reaches a switch that is directly connected to the target subnet, the switch checks to see
whether IP directed broadcast is enabled on the interface that is directly connected to
the target subnet:
• If IP directed broadcast is enabled on that interface, the switch broadcasts the packet
on that subnet by rewriting the destination IP address as the configured broadcast IP
address for the subnet. The switch converts the packet to a link-layer broadcast packet
that every host on the network processes.
• If IP directed broadcast is disabled on the interface that is directly connected to the
target subnet, the switch drops the packet.
IP Directed Broadcast Implementation for EX Series Switches
You configure IP directed broadcast on a per-subnet basis by enabling IP directed
broadcast on the Layer 3 interface of the subnet’s VLAN. When the switch that is
1109 Copyright © 2010, Juniper Networks, Inc.
Chapter 50: Interfaces—Overview