[ovs-dev] [PATCH ovn v4] Broadcast DHCPREPLY when BROADCAST flag is set

[Ben Pfaff]

On Thu, Mar 05, 2020 at 05:16:04PM -0500, Ihar Hrachyshka wrote:
> On Thu, Mar 5, 2020, 15:15 Ben Pfaff <blp at ovn.org> wrote:
> 
> > On Thu, Mar 05, 2020 at 02:56:17PM -0500, Ihar Hrachyshka wrote:
> > > As per RFC2131, section 4.1:
> > >    A server or relay agent sending or relaying a DHCP message directly
> > >    to a DHCP client (i.e., not to a relay agent specified in the
> > >    'giaddr' field) SHOULD examine the BROADCAST bit in the 'flags'
> > >    field.  If this bit is set to 1, the DHCP message SHOULD be sent as
> > >    an IP broadcast using an IP broadcast address (preferably 0xffffffff)
> > >    as the IP destination address and the link-layer broadcast address as
> > >    the link-layer destination address.
> > >
> > > This patch changes destination IP address to 255.255.255.255 when client
> > > set BROADCAST flag in their DHCPREQUEST. Note: the offered IP address is
> > > still part of the DHCP payload.
> > >
> > > Reported-at: https://bugzilla.redhat.com/show_bug.cgi?id=1801006
> > >
> > > Signed-off-by: Ihar Hrachyshka <ihrachys at redhat.com>
> >
> > Does the reply actually get broadcast to all the VMs in the logical
> > network?  Or is it just the IP destination that gets changed and it's
> > actually unicast just to the requester?  The latter is what I'm inclined
> > to prefer.
> >
> 
> DHCP responder flow sets outport=inport and then runs 'output' so I assume
> it's delivered to the original port only, just with broadcast ip address.
> (I believe all DHCP responses are looped back.)

Great.  (It'd be nice to add that to the commit message.)