[ovs-discuss] Why OVS needs arp?

[Hao Wu]

Hi Abhishek and Justin,

    Got it! Thanks for your kind help.

+++++++++++++++++
Best,
Hao

On Fri, Jul 17, 2015 at 9:51 PM, Abhishek Verma <abhishekv.verma at gmail.com>
wrote:

> Hao,
>
> OVS doesnt need ARP -- its L3 forwarding that needs it.
>
> When you ping, the kernel needs to know the destination MAC address that
> it needs to slap on to the packet. Unless it gets this the packet will not
> be forwarded. When it sends out the ARP request, OVS must forward it so
> that the other end can receive it and respond to it. If OVS is dropping the
> ARPs, then the other end will never receive it and the sender will never be
> able to send out the IP packet.
>
> You could try out by adding static ARPs. In that case, OVS with just the
> IP rules installed will be able to send out IP packets.
>
> Hope this helps.
>
> Thanks, Abhishek
>
> On Sat, Jul 18, 2015 at 10:04 AM, Justin Pettit <jpettit at nicira.com>
> wrote:
>
>>
>> > On Jul 18, 2015, at 12:03 AM, Hao Wu <wuhao.thu at gmail.com> wrote:
>> >
>> > Hi,
>> >
>> >    I'm curious that why OVS forwarding also needs arp? I find if I add
>> a flow in flow table as
>> "idle_timeout=0,ip,dst_scr=10.0.0.2,actions=output:2", the packets can't be
>> forwarded unless I also add the arp part:
>> "idle_timeout=0,arp,dst_scr=10.0.0.2,actions=output:2". For OVS, I think it
>> can work without the help of arp because it uses OF table which can match
>> IP part.
>>
>> ARP isn't IP--it has a different Ethertype--so you have to tell OVS to
>> forward it.
>>
>> --Justin
>>
>>
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>>
>
>
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