The OVS buffers are sized by packets, not by bytes.

On Sat, Apr 16, 2016 at 05:09:24PM +0000, ‪Majid Taleqani‬ ‪ wrote:
> Thank you Ben for answering my questionBen you mentioned that OVS have the 
> capacity to buffer 256 packets per connection. i guess OVS buffer size should 
> be in byte not in packet count. i mean if i send 256 packets that each packet 
> size is 1024 byte should overflow OVS buffer sooner that sending 256 packets 
> with the size of 20 byte. also consider that these 256 packets do not match 
> flow table and therefore will be buffered and sent to controller and also 
> suppose that controller just drop Packt_IN messages to test overflowing OVS 
> buffer.am i right or OVS just care about packet count?
> thank you    
> 
> 
>       From: Ben Pfaff <b...@ovn.org>
>  To: Ali Volkan Atli <volkan.a...@argela.com.tr> 
> Cc: ‪Majid Taleqani‬ ‪‬ <majid.taleq...@yahoo.com>; "discuss@openvswitch.org" 
> <discuss@openvswitch.org>
>  Sent: Friday, 15 April 2016, 10:17:22
>  Subject: Re: [ovs-discuss] open vSwitch port input buffer capacity
>    
> OK, so you're asking how many packets does OVS buffer on an OpenFlow
> connection?  That was not clear from the question.  It is documented in
> ovs-vswitchd(8):
> 
>   Packet buffering.
>       The OpenFlow specification, version 1.2, says:
> 
>               Switches  that  implement  buffering  are  expected  to  expose,
>               through  documentation,  both the amount of available buffering,
>               and the length of time before buffers may be reused.
> 
>       Open vSwitch maintains a separate set of 256 packet  buffers  for  each
>       OpenFlow  connection.  Any given packet buffer is preserved until it is
>       referenced by an OFPT_FLOW_MOD or OFPT_PACKET_OUT request or for 5 sec‐
>       onds, whichever comes first.
> 
> Also, PKTBUF_CNT isn't 512, it's 256.
> 
> On Fri, Apr 15, 2016 at 05:42:02AM +0000, Ali Volkan Atli wrote:
> > Hi Ben
> > 
> > No doubt you are a legend but you are wrong in this question or I'm
> > totally screwed :)
> > 
> > I think you did not understand the question correctly. OvS has a
> > buffer mechanism for each controller. While trying to add a flow_mod
> > with max_length is not OFPCML_NO_BUFFER, the packets are stored in the
> > buffer. If the maximum capacity is exceeded, OvS start sending the
> > whole packets instead of related parts in the packet-in
> > messages. Finally, its size (PKTBUF_CNT) is 512.
> > 
> > @Majid, just set max-lenght (different than 0xFFFF) and then drop the 
> > packet-in messages in the controller and then you'll see the whole packets 
> > after 512th packet-in.
> > 
> > - Volkan
> > 
> > ________________________________________
> > From: discuss [discuss-boun...@openvswitch.org] on behalf of Ben Pfaff 
> > [b...@ovn.org]
> > Sent: Thursday, April 14, 2016 6:56 PM
> > To: ‪Majid Taleqani‬ ‪‬
> > Cc: discuss@openvswitch.org
> > Subject: Re: [ovs-discuss] open vSwitch port input buffer capacity
> > 
> > On Thu, Apr 14, 2016 at 01:52:31PM +0000, ‪Majid Taleqani‬ ‪ wrote:
> > > i am writing a DDOS mitigation for openflow networks using pox
> > > controller and open vSwitch version 1.9. as DDOS attacks aim at
> > > Flooding flow tables and input buffers, i wonder what is the maximum
> > > capacity of each switch port input buffer.
> > 
> > OVS ports themselves don't have buffers, so this is a question of your
> > NIC driver's buffering strategy.
> > 
> > > i know after the switch input buffer overflows then the switch sends
> > > the whole packet to the controller
> > 
> > No, that's wrong.  Buffer overflow has nothing to do with sending
> > packets to the controller.
> > 
> > > and then the controller responses by sending packet out message which
> > > contains the whole packet and also the action.  i want to know how
> > > much data and at what rate should a host send data to overflow a
> > > switch port input buffer and if is it possible to change the switch
> > > port input buffers? is it possible to change the amount of time that a
> > > packet stays in buffer before timeouts?  thanks
> > _______________________________________________
> > discuss mailing list
> > discuss@openvswitch.org
> > http://openvswitch.org/mailman/listinfo/discuss
> 
> 
>   
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