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

Ihar Hrachyshka ihrachys at redhat.com
Thu Mar 5 22:16:04 UTC 2020


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.)

Ihar

>


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