On Wed, Mar 09, 2016 at 07:09:55PM +0530, Numan Siddique wrote:
> On 12/22/2015 01:31 PM, Ben Pfaff wrote:
> > Hi Babu and Numan.
> >
> > So far, we've been able to build OVN so that the logic of the system is
> > implemented in terms of OVN logical flows. That is, the logical flow
> > table determines what happens in every significant way in OVN. It would
> > be nice to preserve this property for DHCP. A design of this form would
> > have to include a way for the flow table to extract DHCP header and
> > option information from packets, and for the flow table to create new
> > DHCP packets and set their header and option values. It would be more
> > work, but then the DHCP behavior could be controlled entirely from
> > ovn-northd by modifying the flow table.
> >
> > I'd like to discuss whether this is practical and worth the effort.
> >
> > Do you have any initial thoughts?
>
> Hi Ben and everyone,
>
> We propose to support native dhcp in OVN in the following way
>
> - For every logical switch port a new logical flow will be added if the
> Logical_Port.options has atleast "dhcp-opt-router=<ROUTER_IP>" defined.
>
> For eg. If there is a logical port "por1" with Logical_Port.options
> defined as
> ["dhcp-opt-router=10.0.0.1", "dhcp-opt-netmask=255.255.254.0"] and it has
> ip address
> "10.0.0.3", then the flow would look like
>
> table=1( ls_in_dhcp), priority= 50, match=(inport == "port1" && eth.src ==
> <ETH_ADDR> && ip4.src == 0.0.0.0 && ip4.dst == 255.255.255.255 && udp.src ==
> 68 && udp.dst == 67), action=(dhcp_offer { offerip = 10.0.0.3; router =
> 10.0.0.1; netmask = 255.255.254.0; }; eth.dst = eth.src; ip4.dst = 10.0.0.3;
> udp.src = 67; udp.dst = 68; outport = inport; inport = ""; / Allow sending
> out inport. / output;)
>
> - ovn-controller would parse the action 'dhcp_offer' and store the dhcp
> options in the
> 'userdata' of the packet-in and set 'pause' to true.
>
> The corresponding OF Flow would look like
>
> table=17, n_packets=7, n_bytes=2394, idle_age=1197, hard_age=2535,
> priority=50,udp,reg6=0x2,metadata=0x1,dl_src=fa:16:3e:0b:73:79,nw_src=0.0.0.0,nw_dst=255.255.255.255,tp_src=68,tp_dst=67
>
> actions=controller(userdata=00.00.00.02.00.00.00.00.0a.00.00.03.03.04.0a.00.00.01.01.04.ff.ff.fe.00,pause),move:NXM_OF_ETH_SRC[]->NXM_OF_ETH_DST[],mod_nw_dst:10.0.0.3,mod_tp_src:67,mod_tp_dst:68,move:NXM_NX_REG6[]->NXM_NX_REG7[],load:0->NXM_NX_REG6[],load:0->NXM_OF_IN_PORT[],resubmit(,32)
>
>
> - When the ovn-controller receives the packet-in for the dhcp request, it
> would
> frame a new dhcp packet with almost the same contents of the original
> packet
> and copy the dhcp options from the 'userdata' to the packet dhcp options
> and resume the flow. OpenvSwitch would resume and apply the other actions.
>
> We have a dirty poc code based on this approach here [1].
>
> We would like to know if this solution is reasonable, so that we can proceed
> further with the implementation.
I like it. Thank you for working on this!
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