[ovs-discuss] OpenFlow 1.3 Groups with type select

[Ben Pfaff]

On Thu, May 29, 2014 at 05:23:45PM -0700, Chris Small wrote:
> I am taking a look at using OVS to load balance traffic over a number of
> ports. I was initially thinking of implementing the application by using
> group tables with type=select but the fact that the current OVS code
> uses dl_dst as the basis of the hash complicates the implementation.
> This is especially an issue especially if trying to divide traffic by
> flows. 
> 
> I could see that for TCP and UDP flows using a hash based on
> nw_src/nw_dst/tp_src/tp_dst/proto_type (or a more complex tuple) could
> be useful for load balancing. Is there any reason why this couldn't be
> added or is there a simpler solution to allow for load balancing, using
> group tables or not, that I am missing.
> 
> If not I was thinking of coding up a patch that would replace the
> current dl_dst hash with a function that chose the tuple based on type
> of traffic. If the flow is a TCP or UDP one the new function would hash
> based on the 5-tuple. Other traffic would just use the dl_dst based
> hash. 

I don't know why the current code uses only destination MAC.  I don't
see any rationale in the code or the history.  I guess changing it to
5-tuple would be fine.

> Also is there any plans to add some way to toggle what type of hashes
> could be used for the select group tables. The OF spec specifically says
> you can't specify the hashing mechanism for select groups through the OF
> protocol itself but it still may be useful to allow for setting how you
> wanted to created for load balancing or ECMP through another mechanism.

I'd be OK with adding a way to configure it.  The trickiest part would
be finding a place to put the configuration--the "group mod" command
doesn't seem to be extensible.