[CentOS-virt] Networking in KVM

Paul,


On Thu, Mar 17, 2016 at 5:47 PM, Digimer <lists at alteeve.ca> wrote:

> On 17/03/16 04:47 PM, paul.greene.va at verizon.net wrote:
> > Thanks, I followed the 2nd article, and it got the existing virtual
> > machines communicating with each other.
>

Right, so your VMs are on the same bridge group now (at Layer2 of OSI).


> >
> > However, any new virtual machines I created after making the changes
> > can't communicate with anything, they can't even get out to the
> > internet, even if I manually set the IP address info. Any suggestions on
> > that?
> >
> > Paul
>

Have you verified connectivity to the VMs' default gateway?
Does the ARP (address resolution protocol) process succeed?
arp -a | grep <Default_Gateway_IP_here>
http://linux-ip.net/html/ether-arp.html

You may not have a NIC connected to your physical network in that bridge
group.
If so you need to modify your network-scripts to make that happen
automatically on boot.
You do not necessarily need an IP address on your bridge interface unless
the VM host is acting as a router (default gateway).
https://access.redhat.com/documentation/en-US/Red_Hat_Enterprise_Linux/6/html/Deployment_Guide/s2-networkscripts-interfaces_network-bridge.html

Here's an example:
~]# cat /etc/sysconfig/network-scripts/ifcfg-XX_br0
DEVICE=XX_br0
TYPE=Bridge
BOOTPROTO=static
ONBOOT=yes
DELAY=0
NM_CONTROLLED=no

You can temporarily add an interface to the bridge group for testing
purposes though.
brctl addif <bridge> <interface>
http://www.tldp.org/HOWTO/BRIDGE-STP-HOWTO/set-up-the-bridge.html


>
> Check that they're using your static bridge. 'virsh dumpxml <vm>' will
> have a section like:
>
> ====
>     <interface type='network'>
>       <mac address='52:54:00:71:20:fa'/>
>       <source network='bcn_bridge1' bridge='bcn_bridge1'/>
>       <target dev='vnet2'/>
>       <model type='e1000'/>
>       <alias name='net2'/>
>       <address type='pci' domain='0x0000' bus='0x00' slot='0x05'
> function='0x0'/>
>     </interface>
> ====
>
> That tells you that the interface is MAC '52:54:00:71:20:fa' is "plugged
> in" to the bridge 'bcn_bridge1'. If that doesn't connect to the right
> bridge, then you need to change it (virt-manager has a simple to use GUI
> for this, or you can use 'virsh edit <vm>' if you're comfortable editing
> XML).


An additional command to run to verify your Ethernet bridge(s) operation is:
brctl show
brctl show <bridge>

~]# brctl show XX_br0
bridge name bridge id STP enabled interfaces
XX_br0 8000.00151713fdbc no p1p1
vnet0
vnet1
vnet11
vnet12
vnet13
vnet19
vnet2
vnet4
vnet6
vnet7


-- 
---~~.~~---
Mike
//  SilverTip257  //
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