Enterasys SecureStack C2

ip helper-address
16-12 IP Configuration
Defaults
None.
Mode
Interfaceconfiguration:C2(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,thedirectedbroadcastaddresswouldbe192.168.255.255.Forasubnet
withtheaddress192.168.12.0,thedirectedbroadcastaddresswouldbe192.168.12.255.
InordertominimizebroadcastDoSattacks,forwardingofdirectedbroadcastsis
disabledby
defaultontheSecureStackC2,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C2hasfiveroutedinterfacesfor
the10,20,30,40,and50networks,enablingdirected
broadcastonlyonthe30networkinterfacewillallowanyonefromanyothernetworks(10,20,40,
50)tosenddirectedbroadcasttothe30network.
Example
ThisexampleshowshowtoenableIPdirectedbroadcastsonVLAN1:
C2(su)->router(Config)#interface vlan 1
C2(su)->router(Config-if(Vlan 1))#ip directed-broadcast
ip helper-address
UsethiscommandtoenabletheDHCP/BOOTPrelayagentonaSecureStackC2routedinterface.
EnablingtherelayagentallowsforwardingofclientDHCP/BOOTPrequeststoaDHCP/BOOTP
serverthatdoesnotresideonthesamebroadcastdomainastheclient.Upto6IPhelperaddresses
maybeconfiguredper
interface.
ThenoformofthiscommanddisablestheforwardingofUDPdatagramstothespecifiedaddress.
Syntax
ip helper-address address
no ip helper-address address
Parameters
Defaults
None.
Mode
Interfaceconfiguration:C2(su)‐>Router1(Config‐if(Vlan1))#
address AddressofthehostwhereUDPbroadcastpacketsshouldbeforwarded.