[ovs-discuss] ovswitchd : maximum MAC addresses, possibility to increase it ?

[Ben Pfaff]

I posted a patch that allows the MAC learning table limit to be chagned
at runtime:
        http://openvswitch.org/pipermail/dev/2012-October/022259.html

On Thu, Oct 18, 2012 at 10:47:55AM +0200, Benoit ML wrote:
> Hello,
> 
> Thank you for the answers.
> So we will compile a new version with '16384', primary for the central
> vswitch. Pretty sweat.
> 
> About the versions : for the older hypervisor, we are in 1.0 and 1.2.
> We have some in 1.4 too. For the central physical vswitch we are in
> 1.6.1.
> 
> We have a plan to upgrade evrything to the last version, but we need
> to test the ovsdb-tool to convert evry database to the lastest schema
> ... and no really time to do it for now ;)
> 
> In the architecture we have all hypervisors (~50 hypervs) vsiwtchd
> connected, throught gre tunnel (mtu is ok no probleme here), to the
> central vswitchd. So by port on the vswitchd we have plenty of MAC
> addr.  An arp request take some times.
> Modify the  'MAC learning age', only on the central vswitchd, hide the
> probleme : less ARP requests for communication between VM already in
> the mac table. But well it's just hiding.
> Really I don't know if it's related to the "old" version of vswitchd
> on some hypervisors, or GRE tunnels, or  mac learning processing ...
> If I can help by some data, let me know ;)
> 
> Thank you again.
> 
> Regards,
> 
> 2012/10/17 Ben Pfaff <blp at nicira.com>:
> > On Wed, Oct 17, 2012 at 10:18:58AM +0200, Benoit ML wrote:
> >> We actually using openvswitch in a large virtualised environnement (~
> >> 1000 VMs).  It's working verry nicely ! :) We use a centralised
> >> physical openvswitch server.
> >
> > I'm glad to hear that.
> >
> > Out of curiosity, what version of Open vSwitch are you using?
> >
> >> By the way, we have some questions and performances issues about the
> >> mac-adresses : an ARP request take some times (about 2 ms), and well
> >> it's not a big deal, but it's not very clean too. We have increase the
> >> 'mac learning age' to 3600 secondes, and it's better.
> >
> > Do you mean that Open vSwitch is too slow at processing ARP requests?
> > I'm not sure how the MAC learning age is related.
> >
> >> Futher more, I've seen in the documentation (ovswitchd) that the
> >> maximum mac addresses per bridge is 2048. I found that pretty low. In
> >> the last version is steel the case ?  Can we modify this behaviure,
> >> like something to 10 000 ?
> >> Because if it's really 2048 we ve reached this limit ...
> >>
> >> In the source I see a hard coded parameter in "lib/mac-learning.h" :
> >> #define MAC_MAX 2048
> >> Can we change this parameter without any side effect ?
> >
> > You can increase it to a larger power of 2, such as 8192 or 16384.
> >
> >> Another question, what's the algorithm to add a new adresse mac when
> >> the table is full ? replace the first (by age) ?
> >
> > The MAC address least recently seen on the network is replaced.
> 
> 
> 
> -- 
> --
> Benoit
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