HP ProCurve 7102dl Reference Manual page 800

SROS Command Line Interface Reference Guide BVI Interface Config Command Set
ip directed-broadcast <name>
Use the ip directed broadcast command to allow reception/forwarding of directed broadcasts. Use the no
form of this command to disable this command.
Syntax Description
<name> Specifies IP access control list name.
Default Values
By default, this command is disabled.
Functional Notes
A directed broadcast is a packet intended for all nodes on a nonlocal network. For example, the broadcast
address 255.255.255.255 reaches all nodes on a network; the directed broadcast address 128.1.255.255
is intended for all nodes whose network address is 128.1.0.0. A router not directly attached to 128.1.0.0
simply forwards the directed broadcast packet to the next hop. A router on network 128.1.0.0 that has ip
directed-broadcast enabled, accepts and forwards the packet to all nodes whose network address is
128.1.0.0. Routers connecting subnets of 128.1.0.0 also accept and forward the packet to the nodes on
their respective subnets. When a directed broadcast packet reaches a router that is directly connected to
its destination subnet, that packet is distributed as a broadcast on the destination subnet. The packet is
then sent as a link-layer broadcast.
The ip directed-broadcast command controls the distribution of directed broadcasts when they reach
their target subnets. Only the final transmission of the directed broadcast on its ultimate destination subnet
is affected. It does not affect the transit unicast routing of IP directed broadcasts.
If ip directed-broadcast is enabled for this interface, incoming IP packets whose addresses identify them
as directed broadcasts intended for the subnet to which this interface is attached will be forwarded as
broadcasts on that subnet. Forwarding of the packets can be limited by specifying an access control list
with this command. In this case, only directed broadcasts that are permitted by the specified access
control list will be forwarded, and all other directed broadcasts directed to this interface subnet will be
dropped.
Disabling the ip directed-broadcast command will cause directed broadcasts destined for the subnet to
which this interface is attached to be dropped.
This option is a requirement for routers as described in RFC1812, section 4.2.2.11. Furthermore, it is
disabled by default (RFC2644), with the intended goal of reducing the efficacy of certain types of
denial-of-service attacks.
Usage Examples
The following example enables forwarding of directed broadcasts on BVI interface 1:
ProCurve(config)#interface bvi 1
ProCurve(config-bvi 1)#ip directed-broadcast
5991-2114 © Copyright 2007 Hewlett-Packard Development Company, L.P. 798