Router by-default doesn't forward the broadcast storm.
So any application that requires broadcast to be
forwarded to another subnet wiould be blocked by the
router. Taking the example of DHCP Server & Client. A
DHCP Client machine on bootup sends broadcast in
search of a BBOTP Server. As long as this server is in
the same subnet, an IP address will be automatically
assigned to that machine. However if the DHCP server
is on another subnet, this broadcast will no be
forwarded to that subnet (The behaviour of a Router)
unless we specify the IP HELPER-ADDRESS w.x.y.z
command on the interface that is recieving the
broadcast (i.e. the interface with subnet of client's
machine). this command actually converts the broadcast
to a unicast address, where the unicast address is
specified by the IP address of the DHCP server
specified in the Helper-address command. As long as
there is only one DHCP server you require nothing else
(i.e no requirement for IP DIRECTED-BROADCAST command)
but if there are multiple dhcp servers on the same
subnet you have to define the directed broadcast
address in the ip helper-address command. Eg if the
network is 10.1.1.0/24 then the directed-broadcast
address would be 10.1.1.255. In this case you have to
define ip directed-broadcast command on the
interfaces.
Muhammad Khalilullah
Network Engineer
CCNP, MCSE
--- norsyam ariffin <[EMAIL PROTECTED]> wrote:
> Hi guy,
>
> Could somebody explain what is the function of IP
> HELPER ADDRESS & IP
> DIRECTED BROADCAST.
>
> Thanks in advance.
>
> Syam
>
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