Re: [ECOS] IP limited broadcasts problems

[Robin Farine <acnrf@dial.eunet.ch>]

Andrew Lunn <andrew.lunn@ascom.ch> writes:

> On Sat, May 19, 2001 at 06:54:41PM +0200, Robin Farine wrote:
> > It seems to me that the OpenBSD IP stack does not handle correctly
> > IP limited broadcasts. Take a host with N Ethernet interfaces, each
> > with an IP address on a separate IP subnet and with the flag
> > IFF_BROADCAST set. The host sends an IP limited broadcast. I would
> > expect that an Ethernet broadcast goes out of each interface
> > (provided that a route to the interface's specific IP subnet exists
> > for each interface).
> 
> > Did someone already observed & reported this problem or should I
> > rather go to sleep, and then read TCP/IP Illustrated again?
> 
> Good morning Robin, Hope you slept well.

Not too bad and, after 3 pages of TCP/IP Illustrated, I fell asleep again so
...

> 
> I just checked the Internet STD documents to see if this is broken according
> to the standards. Best i could find was, in std3, "Requirements for Internet
> Hosts"
> 
>               There has been discussion on whether a datagram addressed
>               to the Limited Broadcast address ought to be sent from all
>               the interfaces of a multihomed host.  This specification
>               takes no stand on the issue.
> 
> So it seems this falls into one of those gray areas. 
> 
> You probably want to swap mailing lists and post to an OpenBSD
> list.

Not required, the stack clearly conforms to the grey area.

> It may also be worth looking at an OpenBSD application that uses Limited
> broadcasts. rwhod should be a simple example, or DHCP server for something
> more complex.

I bet that such services work only on host with one interface. On Linux, they
have added a feature that lets an application bind a socket to a specific
interface for this purpose. It seems that the OpenBSD stack does not include
anything like this. Bad news for our DHCP relay!

Robin