Help Broadcasting a UDP packet on the LAN:URGENT

[Charles Swiger]

On Thursday, October 23, 2003, at 11:52 AM, Barney Wolff wrote:
> On Thu, Oct 23, 2003 at 01:55:55AM -0700, Wes Peters wrote:
[ ... ]
> What are you going to do when IPv6 comes into more general use, since
> it has no broadcast address?

Are you asking what a IPv4-to-IPv6 translator (like gif?) should do, or 
are you worried about the case of a machine configured for IPv6 only 
and not for IPv4?  I expect that most people will be using IPv4 for 
quite some time; we don't have to do something for the IPv6-only case 
to still have this be useful.

>> Interactions with VLANs, for instance.  If you send an
>> all-ones broadcast on an interface that has one or more VLANs 
>> configured,
>> do you repeat them "on" each VLAN as well?  Ugh.  What about
>> point-to-point links?  Are those always considered gateways to a 
>> foreign
>> network, or just another form of locally attached network?
>
> The multicast notion would suggest that this be handled as a special
> case of multicast, with a pseudo group that can't occur naturally.
> That way you get "for free" to control which interfaces should send
> the broadcast, based on group membership.

Multicast and broadcast addressing are working at layer-3, but the 
point of using VLAN tags is to create logically 'seperate' networks 
where the flow of traffic is being handled/segregated at layer-2 rather 
than layer-3.

> The whole VLAN thing is nasty, but I'd say that the general issue is
> does the box itself have a virtual interface on the VLAN, or is it
> merely switching on it.  If the former, you send packets and process
> received packets up the stack.  If the latter, you just do what any
> switch/bridge would do, because "you" (ie, higher layers) are not 
> really
> on that layer-3 network.

The all-ones broadcast is supposed to go to all physically connected 
network segments, regardless of whether a particular interface is 
ifconfig'ured with an IP that is part of a particular layer-3 subnet.  
You should be able to send the broadcast packet out from an interface 
which is up but does not have an IPv4 address assigned, right?

-- 
-Chuck