2 a.m.
Hey there,
I hope anyone can bring some light in the following problem.
<interface type='bridge'>
<source bridge='cloudbr0'/>
<mtu size='2000'/>
<mac address='02:00:74:76:00:01'/>
<model type='virtio'/>
<virtualport type='openvswitch'>
</virtualport>
<vlan trunk='no'>
<tag id='2097'/>
</vlan><link state='up'/>
</interface>
we have an base bridge for example and cloudbr0. After we add an mtu to the vm bridge here
it seems the base bridge gets the same mtu like the vnet adapter.
Is this normal behaviour of libvirt together with OVS?
—ovs-vsctl show
5b154321-534d-413e-9761-60476ae06640
Bridge "cloudbr0"
Port "cloudbr0"
Interface "cloudbr0"
type: internal
—MTU from the bridge after set an MTU into the XML File (before we had here 9000)
mtu : 2000
mtu_request : []
name : "cloudbr0"
ofport : 65534
—MTU of the vnet interface
mac_in_use : "fe:00:74:76:00:01"
mtu : 1450
mtu_request : 1450
name : „vnet2"
Thanks for help…
__
Sven Vogel
Teamlead Platform
EWERK RZ GmbH
Brühl 24, D-04109 Leipzig
P +49 341 42649 - 11
F +49 341 42649 - 18
S.Vogel(a)ewerk.com
www.ewerk.com
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Registergericht: Leipzig HRB 17023
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7:19 p.m.
On 7/23/19 8:00 PM, Sven Vogel wrote:
Hey there,
I hope anyone can bring some light in the following problem.
<interface type='bridge'>
<source bridge='cloudbr0'/>
<mtu size='2000'/>
<mac address='02:00:74:76:00:01'/>
<model type='virtio'/>
<virtualport type='openvswitch'>
</virtualport>
<vlan trunk='no'>
<tag id='2097'/>
</vlan><link state='up'/>
</interface>
we have an base bridge for example and cloudbr0. After we add an mtu to the vm bridge
here it seems the base bridge gets the same mtu like the vnet adapter.
Is this normal behaviour of libvirt together with OVS?
I wouldn't say it is 'normal', but this behaviour is not specific to
libvirt. I mean, if you create a tap device yourself by hand and then
plug it into an ovs bridge the same thing will happen. If you don't want
to change MTU of the bridge then just don't set it for <interface/> and
libvirt will copy whatever MTU the bridge has over to the new TAP device.
Michal
3:23 a.m.
Hi Michal,
Thanks for your answer.
I don’t understand why an interface created without mtu gets only 1500 visible in the
virtual machine but if I create an interface with mtu higher than 1500 e.g. 2000 the
bridge will change too. Before the bridge was e.g. by 9000.
I ask because you wrote if I don’t set an mtu of the interface I will get the mtu of the
bridge. But it seems so.
Can you clarify it a little better for me?
Cheers
Sven
Von meinem iPhone gesendet
__
Sven Vogel
Teamlead Platform
EWERK RZ GmbH
Brühl 24, D-04109 Leipzig
P +49 341 42649 - 11
F +49 341 42649 - 18
S.Vogel(a)ewerk.com
www.ewerk.com
Geschäftsführer:
Dr. Erik Wende, Hendrik Schubert, Frank Richter
Registergericht: Leipzig HRB 17023
Zertifiziert nach:
ISO/IEC 27001:2013
DIN EN ISO 9001:2015
DIN ISO/IEC 20000-1:2011
EWERK-Blog | LinkedIn | Xing | Twitter | Facebook
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Am 29.07.2019 um 13:20 schrieb Michal Privoznik
<mprivozn(a)redhat.com>:
> On 7/23/19 8:00 PM, Sven Vogel wrote:
> Hey there,
> I hope anyone can bring some light in the following problem.
> <interface type='bridge'>
> <source bridge='cloudbr0'/>
> <mtu size='2000'/>
> <mac address='02:00:74:76:00:01'/>
> <model type='virtio'/>
> <virtualport type='openvswitch'>
> </virtualport>
> <vlan trunk='no'>
> <tag id='2097'/>
> </vlan><link state='up'/>
> </interface>
> we have an base bridge for example and cloudbr0. After we add an mtu to the vm bridge
here it seems the base bridge gets the same mtu like the vnet adapter.
> Is this normal behaviour of libvirt together with OVS?
I wouldn't say it is 'normal', but this behaviour is not specific to libvirt.
I mean, if you create a tap device yourself by hand and then plug it into an ovs bridge
the same thing will happen. If you don't want to change MTU of the bridge then just
don't set it for <interface/> and libvirt will copy whatever MTU the bridge has
over to the new TAP device.
Michal
4:39 p.m.
On 7/29/19 9:23 PM, Sven Vogel wrote:
Hi Michal,
Thanks for your answer.
I don’t understand why an interface created without mtu gets only 1500 visible in the
virtual machine but if I create an interface with mtu higher than 1500 e.g. 2000 the
bridge will change too. Before the bridge was e.g. by 9000.
I ask because you wrote if I don’t set an mtu of the interface I will get the mtu of the
bridge. But it seems so.
Can you clarify it a little better for me?
I don't know enough about OVS internals to answer that, sorry. Maybe we
should ask OVS developers why OVS bridge behaves this way.
Michal
9:50 p.m.
In general if no MTU is set on interface creation the default value is 1500.
On OVS the bridge MTU is automatically set to the smallest port MTU. So
you just have to set the MTU of each port of the bridge.
Take a look at: https://bugzilla.redhat.com/show_bug.cgi?id=1160897
It is a bit of a pain to read but seems to confirm the statement about
the OVS MTU value being set by the MTU of the ports.
I have been using OVS with Xen and a few years ago I had to wrap my head
around this problem.
Once you start setting the MTU to something other than 1500 you will
find you need to set ALL the MTU values of ALL your interfaces.
Otherwise some inherited default will bite you.
On 7/31/19 4:39 AM, Michal Privoznik wrote:
On 7/29/19 9:23 PM, Sven Vogel wrote:
> Hi Michal,
>
> Thanks for your answer.
>
> I don’t understand why an interface created without mtu gets only
> 1500 visible in the virtual machine but if I create an interface with
> mtu higher than 1500 e.g. 2000 the bridge will change too. Before the
> bridge was e.g. by 9000.
> I ask because you wrote if I don’t set an mtu of the interface I will
> get the mtu of the bridge. But it seems so.
>
> Can you clarify it a little better for me?
I don't know enough about OVS internals to answer that, sorry. Maybe
we should ask OVS developers why OVS bridge behaves this way.
Michal
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Alvin Starr || land: (647)478-6285
Netvel Inc. || Cell: (416)806-0133
alvin(a)netvel.net ||
5:02 p.m.
Hi Alvin,
Thanks for the help. :) This sounds good. My head also wrap about this problem.
The question for me is why they use the smallest?
Cheers
Sven
__
Sven Vogel
Teamlead Platform
EWERK DIGITAL GmbH
Br?hl 24, D-04109 Leipzig
P +49 341 42649 - 11
F +49 341 42649 - 18
S.Vogel(a)ewerk.com
www.ewerk.com
Gesch?ftsf?hrer:
Dr. Erik Wende, Hendrik Schubert, Frank Richter
Registergericht: Leipzig HRB 17023
Zertifiziert nach:
ISO/IEC 27001:2013
DIN EN ISO 9001:2015
DIN ISO/IEC 20000-1:2011
ISAE 3402 Typ II Assessed
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Am 31.07.2019 um 15:50 schrieb Alvin Starr
<alvin@netvel.net<mailto:alvin@netvel.net>>:
In general if no MTU is set on interface creation the default value is 1500.
On OVS the bridge MTU is automatically set to the smallest port MTU. So you just have to
set the MTU of each port of the bridge.
Take a look at: https://bugzilla.redhat.com/show_bug.cgi?id=1160897
It is a bit of a pain to read but seems to confirm the statement about the OVS MTU value
being set by the MTU of the ports.
I have been using OVS with Xen and a few years ago I had to wrap my head around this
problem.
Once you start setting the MTU to something other than 1500 you will find you need to set
ALL the MTU values of ALL your interfaces.
Otherwise some inherited default will bite you.
5:43 p.m.
On Thu, 8 Aug 2019 at 10:08, Sven Vogel <S.Vogel(a)ewerk.com> wrote:
> Am 31.07.2019 um 15:50 schrieb Alvin Starr <alvin(a)netvel.net>:
> In general if no MTU is set on
interface creation the default value is
> 1500.
> On OVS the bridge MTU is automatically set to the smallest
port MTU. So
> you just have to set the MTU of each port of the bridge.
> Take a look at:
https://bugzilla.redhat.com/show_bug.cgi?id=1160897
> It is a bit of a pain to read but seems to confirm the statement about the
> OVS MTU value being set by the MTU of the ports.
> I have been using OVS with Xen and a few years ago I had
to wrap my head
> around this problem.
> Once you start setting the MTU to something other than 1500 you will find
> you need to set ALL the MTU values of ALL your interfaces.
> Otherwise some inherited default will bite you.
The question for me is why they use the smallest?
Because otherwise some frames won't get through because the interface can't
receive them, and the job of network equipment is to enable and maintain
communication :-).
Cheers
Sven
- Peter
[...]
9:09 p.m.
Hi Peter,
Maybe my English it not good enough. I would understand the highest but not the smallest.
You know? :)
You mean if any VM has 2000 set and another will set 3000 we get 3000 for all on the
bridge? What I don’t understand is if the bridgec already has 9000 set as MTU they will be
shrined down?!?
For me I think it lags of some functionality.
__
Sven Vogel
Teamlead Platform
EWERK DIGITAL GmbH
Brühl 24, D-04109 Leipzig
P +49 341 42649 - 11
F +49 341 42649 - 18
S.Vogel(a)ewerk.com
www.ewerk.com
Geschäftsführer:
Dr. Erik Wende, Hendrik Schubert, Frank Richter
Registergericht: Leipzig HRB 17023
Zertifiziert nach:
ISO/IEC 27001:2013
DIN EN ISO 9001:2015
DIN ISO/IEC 20000-1:2011
ISAE 3402 Typ II Assessed
EWERK-Blog<https://blog.ewerk.com/> |
LinkedIn<https://www.linkedin.com/company/ewerk-group> |
Xing<https://www.xing.com/company/ewerk> |
Twitter<https://twitter.com/EWERK_Group> |
Facebook<https://de-de.facebook.com/EWERK.IT/>
Mit Handelsregistereintragung vom 09.07.2019 ist die EWERK RZ GmbH auf die EWERK IT GmbH
verschmolzen und firmiert nun gemeinsam unter dem Namen: EWERK DIGITAL GmbH, für weitere
Informationen klicken Sie hier<https://www.ewerk.com/ewerkdigital>;.
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The contents of this e-mail (including any attachments) are confidential and may be
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system. Thank you.
Am 08.08.2019 um 11:43 schrieb Peter Crowther
<peter.crowther@melandra.com<mailto:peter.crowther@melandra.com>>:
On Thu, 8 Aug 2019 at 10:08, Sven Vogel
<S.Vogel@ewerk.com<mailto:S.Vogel@ewerk.com>> wrote:
The question for me is why they use the smallest?
Because otherwise some frames won't get through because the interface can't
receive them, and the job of network equipment is to enable and maintain communication
:-).
Cheers
Sven
- Peter
[...]
Am 31.07.2019 um 15:50 schrieb Alvin Starr
<alvin@netvel.net<mailto:alvin@netvel.net>>:
In general if no MTU is set on interface creation the default value is 1500.
On OVS the bridge MTU is automatically set to the smallest port MTU. So you just have to
set the MTU of each port of the bridge.
Take a look at: https://bugzilla.redhat.com/show_bug.cgi?id=1160897
It is a bit of a pain to read but seems to confirm the statement about the OVS MTU value
being set by the MTU of the ports.
I have been using OVS with Xen and a few years ago I had to wrap my head around this
problem.
Once you start setting the MTU to something other than 1500 you will find you need to set
ALL the MTU values of ALL your interfaces.
Otherwise some inherited default will bite you.
1856
days inactive
1873
days old
7 comments
4 participants
participants (4)
-
Alvin Starr -
Michal Privoznik -
Peter Crowther -
Sven Vogel