[ovs-discuss] In 'OVS Faucet Tutorial', router does not work as expected at 'Step 4: Router Broadcasts ARP Request'

Brad Cowie brad at cowie.nz
Mon Jan 15 00:55:23 UTC 2018


Hi Robin,

Glad this is working for you now.

At step 6, I'm not entirely sure why the packet doesn't end up being caught
in tcpdump (it doesn't for me either), but we see from the action from
ofproto/trace:

Datapath actions:
set(eth(src=0e:00:00:00:00:01,dst=00:10:20:30:40:50)),set(ipv4(dst=10.200.0.1,ttl=63)),4

That this packet will be sent out port 4 as expected, so we know faucet has
programmed the right rules inside of openvswitch even though the packet
doesn't show up.

Brad

On 10 January 2018 at 03:39, Robin Lee <robinlee.sysu at gmail.com> wrote:

> Thanks, Brad!
>
> ARP request broadcast is now seen with faucet 1.6.15 and the modified
> faucet.yaml.
>
> But at a follow step 'Step 6: IP Packet Delivery',
>    /usr/sbin/tcpdump -evvvr sandbox/p4.pcap ip
> does not show any IP packet even I have re-sent the UDP one.
>
> -robin
>
> On Sat, Jan 6, 2018 at 7:07 AM, Brad Cowie <brad at cowie.nz> wrote:
>
>> Hi Robin,
>>
>> I'm part of the faucet team and we reproduced your issue at our end and
>> have produced a fix/workaround.
>>
>> What happened is that in faucet 1.6.12 we added a bunch of new packet
>> handling sanity checks to help improve security of faucet's packet
>> handling. Packets made by ofproto/trace -generate will have a zero-length
>> payload which trips some of our sanity checks which will cause us to drop
>> the packet.
>>
>> We have added a new flag for disabling this check for cases like the OVS
>> tutorial where we don't care about security as much as simplicity, this
>> patch will be included in faucet 1.6.15 which is due to be released in 3
>> days:
>>
>> https://github.com/faucetsdn/faucet/pull/1459
>>
>> I have also submitted a patch to upstream OVS to update the tutorial:
>>
>> https://mail.openvswitch.org/pipermail/ovs-dev/2018-January/342689.html
>>
>> Thanks for your find! Hope you find this flag gets everything working
>> again.
>>
>> Brad
>>
>> On 25 December 2017 at 14:18, Robin Lee <robinlee.sysu at gmail.com> wrote:
>>
>>> Hi,
>>>
>>> I am new to OVS and just doing 'OVS Faucet Tutorial'.
>>>
>>> But everything is OK until 'Step 4: Router Broadcasts ARP Request',
>>> the router does not send ARP broadcast requrest in my environment.
>>>
>>> After I run:
>>> ovs-appctl ofproto/trace br0 in_port=p1,dl_src=00:01:02:03:
>>> 04:05,dl_dst=ff:ff:ff:ff:ff:ff,dl_type=0x806,arp_spa=10.100.
>>> 0.1,arp_tpa=10.100.0.254,arp_sha=00:01:02:03:04:05,arp_tha=ff:ff:ff:ff:ff:ff,arp_op=1
>>> -generate
>>>
>>> ovs-appctl ofproto/trace br0 in_port=p1,dl_src=00:01:02:03:
>>> 04:05,dl_dst=0e:00:00:00:00:01,udp,nw_src=10.100.0.1,nw_dst=10.200.0.1,nw_ttl=64
>>> -generate
>>>
>>> The sandbox/p4.pcap does not received any ARP request broadcast.
>>>
>>>
>>> My environment is also prepared following the tutorial.
>>>
>>> OVS is instalded from Fedora 27 repo:
>>> Step 4: Router Broadcasts ARP Request'
>>> and run with tutorial/ovs-sandbox in the git repo.
>>>
>>> Faucet is 1.6.14 and run in docker as instructed.
>>>
>>> -robin
>>>
>>> _______________________________________________
>>> discuss mailing list
>>> discuss at openvswitch.org
>>> https://mail.openvswitch.org/mailman/listinfo/ovs-discuss
>>>
>>>
>>
>
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