How does work in QEMU guest OS work?

Question

I have a problem understanding how Qemu and the network work in a guest OS (Ubuntu). I read this guide and others. And if I understand, if you want to pick up the Internet in the guest OS, you need to do a touch on the interface in the host OS. After that, to bind the eth0 and tap0 interfaces :

• Using NAT Routing
• Using the bridge (link tap0 and eth0-host )

Now I have these interfaces in the host ( ppp0 - 3G modem - Internet, lo):

ppp0      Link encap:Point-to-Point Protocol  
      inet addr:10.245.146.78  P-t-P:10.64.64.64  Mask:255.255.255.255
      UP POINTOPOINT RUNNING NOARP MULTICAST  MTU:1500  Metric:1
      RX packets:49635 errors:0 dropped:0 overruns:0 frame:0
      TX packets:42745 errors:0 dropped:0 overruns:0 carrier:0
      collisions:0 txqueuelen:3 
      RX bytes:52405401 (52.4 MB)  TX bytes:5988643 (5.9 MB)

On gust OS ( eth0 , lo):

eth0        Link encap:Ethernet HWaddr:52:54:00:12:34:56
      inet addr:10.0.2.15  Bcast:10.0.2.255 Mask:255.255.255.0
      ...

! , ppp0 ? .

, . ?

Qemu:

qemu -hda ~/virt.disk -cdrom /dev/cdrom -boot once=dc -m 1024M -usb -smp 2 -enable-kvm 

:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.64.64.64     *               255.255.255.255 UH    0      0        0 ppp0
default         10.64.64.64     0.0.0.0         UG    0      0        0 ppp0

:

Kernel IP routing table
Destination     Gateway         Genmask         Flags Metric Ref    Use Iface
10.0.2.0        *               255.255.255.0 U    1      0        0 eth0
link-local      *               255.255.0.0   U    1000   0        0 eth0
default         10.0.2.2        0.0.0.0       UG   0      0        0 eth0

Answer 1

, TAP, . TAP, - qemu:

-net nic,model=rtl8139 -net tap

rtl8139 nic . , nic :

qemu -net nic,model=?

, TAP . script :

# For Network Bridging/TAP
# Set permissions of tun device
chown root.users /dev/net/tun 
chmod g+rw /dev/net/tun

#Add a bridge, add eth0
brctl addbr br0
ifconfig eth0 0.0.0.0 promisc
brctl addif br0 eth0
dhclient br0

# Create tap0
tunctl -t tap0 -u username #replace username by your username

# Enable tap0
brctl addif br0 tap0
ifconfig tap0 up

script, , -net, TAP.