NAT through Dom0 on unstable branch

[Eitan Isaacson <ee.jay.eye@gmail.com>]

Hello,
I might be the first to encounter this issue, so I think it is worth posting...

I am trying to set up a configuration in which a DomU and Dom0 are on
their own subnet, and DomU accesses the real network through Dom0's
NAT.

These are the steps that I take (note, these steps worked fine in
"testing" and "stable" branches):

I first set up a bridge with a private IP:

brctl addbr mybr0
ip addr add 192.168.0.1/24 dev mybr0
ip link set mybr0 up

These are my network scripts in the xend config file:

(network-script     network-route)
(vif-script         vif-bridge)
(vif-bridge         mybr0)

I start a DomU with an IP of 192.168.0.101, and I am able to ping Dom0
(192.186.0.1).

I enable IP forwarding, and I set up NAT:

sysctl -w net.ipv4.ip_forward=1  # (if not allready done by xend)
iptables -t nat -A POSTROUTING -j MASQUERADE \
  -o eth0 -s 192.168.0.1/24

I am able to ping the outside world by IP, but name resolution, or any
other TCP/IP traffic does not work.
The very strange part is that tcpdump seems to show packets arriving
at their destination on the outside world hosts. but besides the ACKs,
the outside hosts do not respond.
I am not a networking expert, so I am sorry if my diagnoses is not full.

Here is a bit more info (on Dom0):
# iptables -t nat -L
Chain PREROUTING (policy ACCEPT)
target     prot opt source               destination

Chain POSTROUTING (policy ACCEPT)
target     prot opt source               destination
MASQUERADE  all  --  192.168.0.0/24       anywhere

Chain OUTPUT (policy ACCEPT)
target     prot opt source               destination

# ifconfig
eth0      Link encap:Ethernet  HWaddr 00:0F:1F:8C:17:D6
          inet addr: 10.0.20.10  Bcast:10.0.255.255  Mask:255.255.0.0
          UP BROADCAST NOTRAILERS RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:30868 errors:0 dropped:0 overruns:0 frame:0
          TX packets:1121 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:1000
          RX bytes:8172500 (7.7 Mb)  TX bytes:158965 (155.2 Kb)
          Base address:0xdf40 Memory:fcfe0000-fd000000

lo        Link encap:Local Loopback
          inet addr:127.0.0.1  Mask:255.0.0.0
          UP LOOPBACK RUNNING  MTU:16436  Metric:1
          RX packets:5 errors:0 dropped:0 overruns:0 frame:0
          TX packets:5 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:288 (288.0 b)  TX bytes:288 (288.0 b)

mybr0     Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
          inet addr:192.168.0.1  Bcast:0.0.0.0  Mask:255.255.255.0
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:12 errors:0 dropped:0 overruns:0 frame:0
          TX packets:13 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:834 (834.0 b)  TX bytes:938 (938.0 b)

vif1.0    Link encap:Ethernet  HWaddr FE:FF:FF:FF:FF:FF
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1
          RX packets:13 errors:0 dropped:0 overruns:0 frame:0
          TX packets:10 errors:0 dropped:0 overruns:0 carrier:0
          collisions:0 txqueuelen:0
          RX bytes:1044 (1.0 Kb)  TX bytes:812 (812.0 b)

# brctl show
bridge name     bridge id               STP enabled     interfaces
mybr0           8000.feffffffffff       no              vif1.0


Thanks!