[ovs-discuss] in-band mode

Andreas Brinner andreas at brinner.de
Thu Jul 4 23:58:41 UTC 2013


Hello,

I was trying to cascadate an OpenFlow switch (Linksys with OpenWRT) behind 
an Open vSwitch like this:
OF Switch (Linksys) <-> Open vSwitch <-> OF Controller

I configured in-band mode for the Open vSwitch and I can see the 
additional, hidden flow rules with ovs-appctl. But still the Linksys 
couldn't connect to the controller.

The reason was, that ARP requests from the Linksys were not forwarded to 
the controller.

So I had a look into the DESIGN paper and the in-band.c code. In the DESIGN 
guide the rules (d) and (e) are specified as follows:
   (d) ARP replies to the next hop's MAC address.
   (e) ARP requests from the next hop's MAC address.
The exact same rules are set up by in-band.c and can be found in my flow 
table. So atleast everything seems consistent here.

Now my problem: these two rules should fire exactly in my case and should 
enable my Linksys to retrive the MAC address of the OF controller. At least 
if I understand the list of "supported" scenarios correctly:
   - Between Switch and Remote.  This switch is between another
     switch and the remote, and we want to allow the other
     switch's traffic through.  This uses rules (d), (e), (h), and
     (i).  It uses (b) and (c) indirectly in order to know the MAC
     address for rules (d) and (e).

But for this to work, rule (d) would have to allow ARP _requests_ to the 
controler and (e) ARP _replies_ from the controller to pass! If I manually 
add these rules to the flow table, the Linksys successfully connects to the 
controller via the Open vSwitch.

Do I miss anything here?

Cheers,

   Andreas

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