Re: [ECOS] Re: How to send UDP broadcast to 255.255.255.255?

[Mandeep Sandhu <mandeepsandhu.chd@gmail.com>]

Hi All,

I've managed to get UDP broadcasts working w/o making any changes to
the FreeBSD stack of ecos.

Just wanted to detail out here the steps I've taken and get a feedback
from you guys on whether it's
proper or not...

I'm writing a DHCP server with limited-capability (which serves only 1
client). For this I need to send
out all my responses on the broadcast address.

* I've setup my servers eth0 statically as follows:

IP: 10.1.1.1
netmask: 255.255.255.0
Broadcast addr: 10.1.1.255
Gateway: 0
Server: 0

* After a call to init_all_network_interfaces() I setup a static "default" route
as follows:

route info:
Dest IP: 0.0.0.0/0.0.0.0 (any IP)
Gw  : 10.1.1.1 (me)
Dev : eth0

Flags: RTF_UP <--- VERY IMPORTANT!

I found that, previously I was setting the flags as "RTF_UP |
RTF_GATEWAY". Now this causes
the problem that in ip_output() function, the stack uses the
"destination" address of the gateway
(i.e 10.1.1.1) instead of the actual one (i.e the bcast IP
255.255.255.255) if RTF_GATEWAY flag
is set. This causes the packet transmission to fail when trying to
resolve the ARP. I don't know why
the ARP should fail, since its only trying to resolve for itself!

Anyways, I found this to be the cure for my problem, i.e setting the
default route and NOT putting
this flag.

* For sending bcast packets, I use raw sockets (with the relevant ioctl to set
the IP_HDRINCL flag).

This seems to be working. I've tested it on my Ubuntu machine with dhclient.

Do you think this is an acceptable workaround?

Thanks,
-mandeep


On Wed, Aug 12, 2009 at 10:32 AM, Mandeep
Sandhu<mandeepsandhu.chd@gmail.com> wrote:
>>
>> I am able to send the broadcasts as I intended.
>
> Are you using UDP or RAW sockets?
>
> I've also setup my default route to point to eth0.
>
> But when the UDP packet goes out, I see that it's corrupted.
>
> Still debugging as to where the screwup is happening?
>
> Thanks,
> -mandeep
>
>>
>> I'd vote for the inclusion of the option in the main tree.
>>
>> Thanks
>> --
>>                                Stano
>>
>> --
>> Before posting, please read the FAQ: http://ecos.sourceware.org/fom/ecos
>> and search the list archive: http://ecos.sourceware.org/ml/ecos-discuss
>>
>>
>

--
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