About send packet with BROADCAST addr? Who can help me.

Hello, every body, I'm a newbie in linux network programming.
When I want to write a program that implement a request ip addr from
DHCP+ server, I encounter a problem.

According to the packet that I captured from the Carrier's Login
utility, I need to send a UDP packet, with broadcast dest addr, and 0
src addr.
But when I configure the eth0's address as 0, i can't send out a
packet.

Does anyone know what's the problem is, and how to slove it?

Thanks.

(E-Mail Removed) wrote:
> Hello, every body, I'm a newbie in linux network programming.
> When I want to write a program that implement a request ip addr from
> DHCP+ server, I encounter a problem.
>
> According to the packet that I captured from the Carrier's Login
> utility, I need to send a UDP packet, with broadcast dest addr, and 0
> src addr.
> But when I configure the eth0's address as 0, i can't send out a
> packet.
>
> Does anyone know what's the problem is, and how to slove it?

Why? There are already good DHCP client daemons.

You cannot reliably send an UDP packet with sender address
of 0.0.0.0 (as required by DHCP) without using raw sockets.

I'd recommend to tackle simpler network programming tasks first.

--

Tauno Voipio
tauno voipio (at) iki fi

Thanks for your help.

The reason that need to write this program is that the Carrier use a
mechnism called DHCP+ Authentication to control the access to Internet.
DHCP+ extends DHCP, and the Carrier only provide Windows version and
redhat version of DHCP+ Client. But I'm using Debian.

According your advice, should I encapsulate IP header by myself?

Tauno Voipio wrote:
> (E-Mail Removed) wrote:
> > Hello, every body, I'm a newbie in linux network programming.
> > When I want to write a program that implement a request ip addr from
> > DHCP+ server, I encounter a problem.
> >
> > According to the packet that I captured from the Carrier's Login
> > utility, I need to send a UDP packet, with broadcast dest addr, and 0
> > src addr.
> > But when I configure the eth0's address as 0, i can't send out a
> > packet.
> >
> > Does anyone know what's the problem is, and how to slove it?
>
> Why? There are already good DHCP client daemons.
>
> You cannot reliably send an UDP packet with sender address
> of 0.0.0.0 (as required by DHCP) without using raw sockets.
>
> I'd recommend to tackle simpler network programming tasks first.
>
> --
>
> Tauno Voipio
> tauno voipio (at) iki fi

Alex wrote:
> Tauno Voipio wrote:
>
>>(E-Mail Removed) wrote:
>>
>>>Hello, every body, I'm a newbie in linux network programming.
>>>When I want to write a program that implement a request ip addr from
>>>DHCP+ server, I encounter a problem.
>>>
>>>According to the packet that I captured from the Carrier's Login
>>>utility, I need to send a UDP packet, with broadcast dest addr, and 0
>>>src addr.
>>>But when I configure the eth0's address as 0, i can't send out a
>>>packet.
>>>
>>>Does anyone know what's the problem is, and how to slove it?
>>
>>Why? There are already good DHCP client daemons.
>>
>>You cannot reliably send an UDP packet with sender address
>>of 0.0.0.0 (as required by DHCP) without using raw sockets.
>>
>>I'd recommend to tackle simpler network programming tasks first.
>>

(-- top-posting corrected, TV --)

> Thanks for your help.
>
> The reason that need to write this program is that the Carrier use a
> mechnism called DHCP+ Authentication to control the access to Internet.
> DHCP+ extends DHCP, and the Carrier only provide Windows version and
> redhat version of DHCP+ Client. But I'm using Debian.
>
> According your advice, should I encapsulate IP header by myself?

Get the sources of a working DHCP daemon, e.g. DHCPCD,
read it and modify to accept the extras.

Yes, you do need to build the whole DHCPDISCOVER packet yourself
to create the correct addresses into it.

I assume that you know what's in the extras of the ISP.

Check once more that the necessary changes cannot be done
with DHCP options. Many clients already existing are capable
of handling the options.

For reference, read and understand the DHCP RFCs (RFC 1541 and RFC 2131
and associated RFCs) before continuing with the project.

--

Tauno Voipio
tauno voipio (at) iki fi