----- Original Message ----- > From: "Igor Lvovsky" <ilvov...@redhat.com> > To: "Saggi Mizrahi" <smizr...@redhat.com> > Cc: "Simon Grinberg" <si...@redhat.com>, "VDSM Project Development" > <vdsm-devel@lists.fedorahosted.org> > Sent: Wednesday, November 28, 2012 6:10:27 PM > Subject: Re: [vdsm] MTU setting according to ifcfg files. > > > > ----- Original Message ----- > > From: "Saggi Mizrahi" <smizr...@redhat.com> > > To: "Simon Grinberg" <si...@redhat.com> > > Cc: "VDSM Project Development" <vdsm-devel@lists.fedorahosted.org>, > > "Igor Lvovsky" <ilvov...@redhat.com> > > Sent: Wednesday, November 28, 2012 5:30:17 PM > > Subject: Re: [vdsm] MTU setting according to ifcfg files. > > > > I suggest we don't have a default. If you don't specify an MTU it > > will use whatever is already configured. > > There is no way to "go back to the defaults" only to set a new > > value. > > The engine can assume 1500 (in case of ethernet devices) is the > > "recommended value". > > > > This is not related to engine. You are right that the actually MTU > will the last configured one, > but this is exactly a problem. > As I already mentioned, if you will add another bridge without custom > MTU its users (VMs) > can assume that the MTU is 1500
Assumption is the mother of all ____. What needs to be done is reverting to the old value. Can be done easily by inserting a comment in the ifcfg-file with the MTU prior to the change. When we (hopefully) go into a stateless configuration controlled by the engine/any other manager then it should be determined solely by the manager, and reverted to user defined on reboot. > > > ----- Original Message ----- > > > From: "Simon Grinberg" <si...@redhat.com> > > > To: "Igor Lvovsky" <ilvov...@redhat.com> > > > Cc: "VDSM Project Development" > > > <vdsm-devel@lists.fedorahosted.org> > > > Sent: Wednesday, November 28, 2012 9:53:48 AM > > > Subject: Re: [vdsm] MTU setting according to ifcfg files. > > > > > > > > > > > > ----- Original Message ----- > > > > From: "Igor Lvovsky" <ilvov...@redhat.com> > > > > To: "VDSM Project Development" > > > > <vdsm-devel@lists.fedorahosted.org> > > > > Cc: "Simon Grinberg" <si...@redhat.com> > > > > Sent: Wednesday, November 28, 2012 2:58:52 PM > > > > Subject: [vdsm] MTU setting according to ifcfg files. > > > > > > > > Hi, > > > > > > > > I am working on one of the vdsm bugs that we have and I found > > > > that > > > > initscripts (initscripts-9.03.34-1.el6.x86_64) > > > > behaviour doesn't fits our needs. > > > > So, I would like to raise this issue in the list. > > > > > > > > The issue is MTU setting according to ifcfg files. > > > > I'll try to describe the flow below. > > > > > > > > 1. I started with ifcfg file for the interface without MTU > > > > keyword > > > > at > > > > all > > > > and the proper interface (let say eth0) had the *default* > > > > MTU=1500 > > > > (according to /sys/class/net/eth0/mtu). > > > > 2. I created a bridge with MTU=9000 on top of this interface. > > > > Everything went OK. > > > > After I wrote MTU=9000 on ifcfg-eth0 and ifdown/ifup it, > > > > eth0 > > > > got > > > > the proper MTU. > > > > 3. Now, I removed the bridge and deleted MTU keyword from the > > > > ifcfg-eth0. > > > > But after ifup/ifdown the actual MTU of the eth0 stayed > > > > 9000. > > > > > > > > The only way to change it back to 1500 (or something else) is > > > > explicitly set MTU in ifcfg file. > > > > According to Bill Nottingham it is intentional behaviour. > > > > If so, we have a problem in vdsm, because we never set MTU > > > > value > > > > until user ask it explicitly. > > > > > > Actually you are, > > > > > > You where asked for MTU 9000 on the network, > > > As implementation specif you had to do this all the way down the > > > chain > > > Now it's only reasonable that when you cancel the 9000 request > > > then > > > you'll do what is necessary to rollback the changes. > > > It's pity that ifcfg-files don't have the option to set > > > MTU='default', but as you can read this default before you > > > change, > > > then please keep it somewhere and revert to that. > > > > > > > > > > It means that if we have interface with MTU=9000 on it just > > > > because > > > > once there was a bridge with such MTU > > > > attached to it and now we want to attach regular bridge with > > > > *default* MTU=1500 we have a problem. > > > > The only thing we can do to avoid this it's set explicitly > > > > MTU=1500 > > > > in interface's ifcfg file. > > > > IMHO it's a bit ugly, but it looks like we have no choice. > > > > > > > > As usual comments more than welcome... > > > > > > > > Regards, > > > > Igor Lvovsky > > > > _______________________________________________ > > > > vdsm-devel mailing list > > > > vdsm-devel@lists.fedorahosted.org > > > > https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel > > > > > > > _______________________________________________ > > > vdsm-devel mailing list > > > vdsm-devel@lists.fedorahosted.org > > > https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel > > > > > > _______________________________________________ > vdsm-devel mailing list > vdsm-devel@lists.fedorahosted.org > https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel > _______________________________________________ vdsm-devel mailing list vdsm-devel@lists.fedorahosted.org https://lists.fedorahosted.org/mailman/listinfo/vdsm-devel
