On Oct 12, 2012 8:16 AM, "James B. Byrne" <byrnejb@harte-lyne.ca> wrote:
>
> This cross-posted from the main Centos discussion list.
>
> I installed a new CentOS-6.3 kvm guest on a recently provisioned kvm
> host also running CentOS-6.3.  This guest will not connect to the
> network and the host cannot connect to it via its public IP address. I
> had previously installed a guest system on thst same kvm host using
> the same ISO and that system connects to the network without problem.
>
> I next created a third guest instance and this too does not connect
> with either the kvm host or the gateway.
>
> I have shutdown all the guests, restarted networking on the host and
> restarted the gueests and the problem persists on the two most
> recently added guests but does not happen on the first guest instance.
>
>
> I have installed litterally dozens of kvm guests this past year and I
> have never encountered this situation.  Has anyone else?  Does anyone
> have any idea what might be going on?
>
> ip addr
> 1: lo <LOOPBACK,UP,LOWER_UP> mtu 16436 qdisc noqueue state UNKNOWN
>     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
>     inet 127.0.0.1/8 scope host lo
>     inet6 ::1/128 scope host
> 2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast
> state UP qlen 1000
>     link/ether 52:54:00:a0:26:47 brd ff:ff:ff:ff:ff:ff
>     inet 216.185.71.243/24 brd 216.185.71.255 scope global eth0
>     inet6 fe80::5054:ff:fea0:2647/64 scope link
>        vaslid_lft forever preferred_lft forever
>
> ip route
> 216.185.71.0/24 dev eth0  proto kernel  scope link  scr 216.185.71.243
> 169.254.0.0/16 dev eth0  scope link  metric 1002
> default via 216.185.71.1 dev eth0
>
> netstat -r
> Kernel IP routing table
> Destination    Gateway      Genmask        Flags  MSS Window  irtt Iface
> 216.185.71.0   *            255.255.255.0  U        0 0          0 eth0
> link-local     *            255.255.0.0    U        0 0          0 eth0
> default        216.185.71.1 0.0.0.0        UG       0 0          0 eth0
>
> service iptables stop
> .  .  .
>
> ping 216.185.71.1
> PING 216.185.71.1 (216.185.71.1) 56(84) bytes of data.
> >From 216.185.71.243 icmp_seq=2 Destination Host Unreachable
> >From 216.185.71.243 icmp_seq=3 Destination Host Unreachable
> >From 216.185.71.243 icmp_seq=4 Destination Host Unreachable
> ^C
>
>
> --
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Did you configure your KVM host's public interface with a bridge?  what is the output of 'brctl show'?

Also Ive run into VM host issues on corporate networks where port security limits number of unique MAC addresses able to communicate on one physical switch port.

- Trey