Linux KVM: Disable virbr0 NAT Interface

Author: Vivek Gite Last updated: May 6, 2017 22 comments

The virtual network (virbr0) used for Network address translation (NAT) which allows guests to access to network services. However, NAT slows down things and only recommended for desktop installations. To disable Network address translation (NAT) forwarding type the following commands:

Display Current Setup

Type the following command:
# ifconfig
Sample outputs:

virbr0    Link encap:Ethernet  HWaddr 00:00:00:00:00:00  
          inet addr:192.168.122.1  Bcast:192.168.122.255  Mask:255.255.255.0
          inet6 addr: fe80::200:ff:fe00:0/64 Scope:Link
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:0 errors:0 dropped:0 overruns:0 frame:0
          TX packets:39 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0 
          RX bytes:0 (0.0 b)  TX bytes:7921 (7.7 KiB)

Or use the following command:
# virsh net-list
Sample outputs:

Name                 State      Autostart
-----------------------------------------
default              active     yes

To disable virbr0, enter:
# virsh net-destroy default # virsh net-undefine default # service libvirtd restart # ifconfig

This entry is 9 of 14 in the CentOS / Redhat (RHEL) KVM Virtulization series. Keep reading the rest of the series:

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22 comments… add one

Pankaj Gadhari Sep 14, 2010 @ 17:25

Hi Vivek,

Whether disabling virbr0 i mean the steps you have given above needs a restart of the machine.

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- 🐧 nixCraft Sep 14, 2010 @ 18:06
  
  No just restart the libvirtd service.
  
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  - Pankaj Gadhari Sep 14, 2010 @ 18:31
    
    If we shutdown the libvirtd service as we are not using it, whether virbr0 interface will come down and not show up in ifconfig.
    
    Reply Link
Simon Hamp Nov 25, 2010 @ 18:12

How would I reverse this?

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ToddB Jan 2, 2011 @ 9:41

Thanks for this tip! I was getting frustrated for a couple of hours trying to disable this nic!

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Jony Mark Feb 5, 2011 @ 22:34

Great topic
please tell me how I can enable virbr0 if it was disable ?
Reply ASAP
Regards

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MAD-Max Aug 2, 2011 @ 15:54

Thank you

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Nignog Nov 28, 2011 @ 15:36

You can use “net-autostart default –disable” instead of “net-undefine default”. This keeps the config on disk so that you may reenable it later if you need it (with “net-autostart default”).

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- chadunplugged Mar 13, 2013 @ 22:25
  
  Negative, this did not work for me on centos 6.3. The article steps did work though.
  
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  - zizouya Aug 22, 2013 @ 20:35
    
    virsh net-autostart default –-disable then reboot worked on RHEL6.4. Thanks
    
    Reply Link
ANDRE Jun 16, 2012 @ 0:04

Thank you!

I had no idea how to disable virbr0.

Very useful to your post.

Hugs!

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jestin Paul Aug 1, 2012 @ 6:36

Thanks !

Worked very well.

Don’t know whether we can disable it at OS installation itself, if not required.

Found this on a machine installed by 3rd party and was taking lot of load.

regards

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Manuel Oct 2, 2012 @ 21:34

Thanks, you safe me really

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David Ramirez Nov 1, 2012 @ 15:38

Thanks – worked just fine on a CentOS 5.8/64 environment on a big server that I want to set up with Xen or KVM – but no NAT is needed/wanted. Next step is to set up a bridge… but not virbr0.

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Suleman Mar 31, 2013 @ 11:12

thanks, works very well

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ndawg Sep 10, 2013 @ 22:46

This tip helped me in Red Hat 6.4 also had to reboot system
now virbr0 is disabled.

Thanks a lot.

ndawg

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sharif mridha Aug 14, 2014 @ 13:07

Thanks a lot now my virbr() disabled.

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sudi Jul 31, 2015 @ 4:37

to reverse this you need to recreate default virbr0

# brctl addbr virbr0
# ip addr add 192.168.122.1/24 broadcast 192.168.122.255 dev virbr0
# ip link set dev virbr0 up

# uuidgen virbr0 < gen uuid for virbr0
# ifconfig | grep virbr0 < get the mac address

# vim /root/default.xml


  default
  6087308e-2b93-4d4d-aa24-dabd1668b11a
  

# virsh net-list
 Name                 State      Autostart     Persistent
----------------------------------------------------------

# cp default.xml /var/lib/libvirt/network/

# virsh net-define default.xml
# virsh net-autostart default
# service libvirtd restart

# virsh net-list
 Name                 State      Autostart     Persistent
----------------------------------------------------------
 default              active     yes           yes

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fusch Mar 19, 2016 @ 16:38

Why is this enabled by default after a fresh install?
I guess its related to a guest login ?

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Khang Feb 15, 2017 @ 15:03

thank you so much

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Kingneutron Mar 19, 2017 @ 21:20

Thanks, your article just helped me :)

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karan Apr 26, 2017 @ 20:51

Thanks a lot , very precise and useful

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