DHCPD broadcast question

DHCPD broadcast question

Post by sorchu.. » Wed, 01 Jun 2005 20:58:27



Dear all,

I have trying to write a program to detect the dhcpd broadcasting. I am
able to detect the client's broadcasting by listening to port 67. But I
couldn't get anything from port 68.

Is there anything that I need to set for the DHCPD to use port 68 to
broadcast, also, which broadcast ip address would be used?

My program is currently listening to 255.255.255.0

Thx

 
 
 

DHCPD broadcast question

Post by chris-use.. » Wed, 01 Jun 2005 22:57:53



> I have trying to write a program to detect the dhcpd broadcasting.
> My program is currently listening to 255.255.255.0

255.255.255.255

Chris

 
 
 

DHCPD broadcast question

Post by Moe Tr » Thu, 02 Jun 2005 08:27:13




>I have trying to write a program to detect the dhcpd broadcasting. I am
>able to detect the client's broadcasting by listening to port 67. But I
>couldn't get anything from port 68.

See RFC2131 Section 4.1

NORMALLY  client to server is broadcast to port 67, because the client
doesn't know either address.  The server monocasts to port 68.

   0.0.0.0:1025  -> 255.255.255.255:67

  IP.OF.SERV.ER:3456 -> IP.OF.CLI.ENT:68

Remember, this is Ethernet, so the packet at that level looks like

  MA:CA:DD:RE:SS:Client -> FF:FF:FF:FF:FF:FF

  Server:MA:CA:DD:RE:SS -> MA:CA:DD:RE:SS:Client

Now, if you are on a 'switched' network (rather than a hub or coax),
the switch probably won't spray the reply out all ports - you won't hear
it, unless you are on a common switch port.

        Old guy

 
 
 

1. server DHCPD ISC Linux and broadcast DHCP OFFER and ACK

Hi,
I'm a little news with Linux and DHCPD ISC server.
I set a test network with 1 DHCP client ,1 DHCP server ISC et 1 hub.
My STB boot and has an IP address and DHCP options. But I'm a little
suprise to see on Ethereal capture that DHCP ISC server send DHCP Offer
and DHCP Ack by unicast and not by broadcast (255.255.255.255).

There is any DHCP option to set for have brodcast answer from DHCP ISC
server?
Thanks
David

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