[ovs-discuss] Regarding openvswitch group, type=select, hashing

[Ben Pfaff]

No, select buckets don't use mod-n to select a bucket.  Instead, for
each live bucket, OVS hashes flow data with the bucket ID and multiplies
by the bucket weight to obtain a "score", and then selects the bucket
with the highest score.

On Mon, Apr 24, 2017 at 12:27:16AM +0530, Ahmed Khan wrote:
> Hi ben,
> Let me rephrase.
> 
> Does hashing involve mod on number of buckets in a group ? If a new bucket
> is added/deleted in a group, would it result in different hash value and
> hence a selection of different bucket for the same 5 tuple ?
> 
> Also, how many buckets per group does ovs support ? And how many group
> tables are supported ?
> 
> Thanks.
> 
> On 22 Apr 2017 02:34, "Ben Pfaff" <blp at ovn.org> wrote:
> 
> > On Thu, Apr 20, 2017 at 04:12:20PM +0530, Ahmed Khan wrote:
> > > I understand that,
> > >
> > > *"""*
> > >
> > > *Open vSwitch 2.4 and later by default hashes the source and
> > > **destination Ethernet address, VLAN ID, Ethernet type, IPv4/v6
> > > **source and destination address and protocol, and for TCP and SCTP
> > > **only, the source and destination ports.  The hash is "symmetric",
> > > **meaning that exchanging source and destination addresses does not
> > > **change the bucket selection.*
> > >
> > > *"""*
> > >
> > > *How does bucket size impact selection ? If entries are added/deleted
> > > to/from bucket, then for the same 5tuple is it rehashed and new entry
> > > could get selected ?*
> >
> > OpenFlow groups do contain buckets, but buckets do not have entries.
> > Therefore, entries cannot be added or deleted within buckets, so I don't
> > understand the question.  Can you rephrase it?
> >
> > Thanks,
> >
> > Ben.
> >