libvirt users - Aug 2013 - KVM bridge wonkiness in Fedora19

Greetings,
I'm attempting to get several virtual machines setup on a Fedora19
host system, with the traditional bridge network devices (br0, br1,
etc).   I've done this many times before with older versions of Fedora
(16, 14, etc), and it just works.  However, for reasons that I cannot
figure out, the bridge doesn't seem to be working in Fedora19.  While
I can successfully connect to the outside world (local network +
internet) from inside a VM, nothing can communicate with the VM from
outside (local network).  I'm referring to something as trivial as
pinging.  From inside the VM, I can ping anything successfully (0%
packet loss).  However, from outside the VM (on the host, or any other
system on the same network), I see 100% packet loss when pinging the
IP address of the VM.

My first question is simply, does anyone else have this working
successfully in F19?  And if so, what steps did you need to follow?

I'm not using NetworkManager at all, its all the network service.
There are no firewalls involved anywhere (iptables & firewall services
are currently disabled).  Here's the current host configuration:

    # brctl show
    bridge name    bridge id        STP enabled    interfaces
    br0        8000.38eaa792efe5    no        em2
                                vnet1
    br1        8000.38eaa792efe6    no        em3
    br2        8000.38eaa792efe7    no        em4
                                vnet0
    virbr0        8000.525400db3ebf    yes        virbr0-nic

    # more /etc/sysconfig/network-scripts/ifcfg-em2
    TYPE=Ethernet
    BRIDGE="br0"
    NAME=em2
    DEVICE="em2"
    UUID=aeaa839e-c89c-4d6e-9daa-79b6a1b919bd
    ONBOOT=yes
    HWADDR=38:EA:A7:92:EF:E5
    NM_CONTROLLED="no"

    # more /etc/sysconfig/network-scripts/ifcfg-br0
    TYPE=Bridge
    NM_CONTROLLED="no"
    BOOTPROTO=dhcp
    NAME=br0
    DEVICE="br0"
    ONBOOT=yes

    # ifconfig em2 ;ifconfig br0
    em2: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
            inet6 fe80::3aea:a7ff:fe92:efe5  prefixlen 64  scopeid
0x20<link>
            ether 38:ea:a7:92:ef:e5  txqueuelen 1000  (Ethernet)
            RX packets 100093  bytes 52354831 (49.9 MiB)
            RX errors 0  dropped 0  overruns 0  frame 0
            TX packets 25321  bytes 15791341 (15.0 MiB)
            TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0
            device memory 0xf7d00000-f7e00000

    br0: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
            inet 10.31.99.226  netmask 255.255.252.0  broadcast 10.31.99.255
            inet6 fe80::3aea:a7ff:fe92:efe5  prefixlen 64  scopeid
0x20<link>
            ether 38:ea:a7:92:ef:e5  txqueuelen 0  (Ethernet)
            RX packets 19619  bytes 1963328 (1.8 MiB)
            RX errors 0  dropped 0  overruns 0  frame 0
            TX packets 11  bytes 1074 (1.0 KiB)
            TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Relevant section from /etc/libvirt/qemu/foo.xml (one of the VMs with
this problem):

    <interface type='bridge'>
          <mac address='52:54:00:26:22:9d'/>
          <source bridge='br0'/>
          <model type='virtio'/>
          <address type='pci' domain='0x0000'
bus='0x00' slot='0x03'
function='0x0'/>
    </interface>

I can provide additional information, if requested.  thanks!

(I'm at a conference, & haven't read the entire email..)

[...]
> My first question is simply, does anyone else have this working
> successfully in F19?  And if so, what steps did you need to follow?
I have it working just fine.

Can you try this?

  http://kashyapc.fedorapeople.org/virt/configuring-bridging-f19+.txt

[...]

-- 
/kashyap