Switch User Manual

Configuring Broadcast Settings
19-16 IP Configuration
Configuring Broadcast Settings
Purpose
ToconfigureIPbroadcastsettings.Bydefault,interfacesontheSecureStackC3donotforward
broadcastpackets.
Commands
ip directed-broadcast
UsethiscommandtoenableordisableIPdirectedbroadcastsonaninterface.Bydefault,
interfacesontheSecureStackC3donotforwarddirectedbroadcasts.Thenoformofthis
commanddisablesIPdirectedbroadcastontheinterface.
Syntax
ip directed-broadcast
no ip directed-broadcast
Parameters
None.
Defaults
None.
Mode
Interfaceconfiguration:C3(su)‐>Router1(Config‐if(Vlan1))#
Usage
Directedbroadcastisanefficientmechanismforcommunicatingwithmultiplehostsonanetwork
whileonlytransmittingasingledatagram.Adirectedbroadcastisapacketsenttoallhostsona
specificnetworkorsubnet.Thedirectedbroadcastaddressincludesthenetworkorsubnetfields,
withthebinarybitsof
thehostportionoftheaddresssettoone.Forexample,foranetworkwith
theaddress192.168.0.0/16,thedirectedbroadcastaddresswouldbe192.168.255.255.Forasubnet
withtheaddress192.168.12.0/24,thedirectedbroadcastaddresswouldbe192.168.12.2 55.
InordertominimizebroadcastDoSattacks,forwardingofdirectedbroadcastsis
disabledby
defaultontheSecureStackC3,asrecommendedbyRFC2644.
Iftheabilitytosenddirectedbroadcaststoanetworkisrequired,youshouldenabledirected
broadcastsonlyontheoneinterfacethatwillbetransmittingthedatagrams.Forexample,ifa
SecureStackC3hasfiveroutedinterfacesfor
the10,20,30,40,and50networks,enablingdirected
For information about... Refer to page...
ip directed-broadcast 19-16
ip forward-protocol 19-17
ip helper-address 19-18