I've found a bug in the Private Gateway functionality, when Source NAT is
enabled for the Private Gateway. When the SNAT is added to iptables, it has
the source CIDR of the private gateway subnet. Since no VMs live in that
private gateway subnet, the SNAT doesn't work. Below is an example:
- VMs have IP addresses in the 10.0.0.0/24 subnet.
- The Private Gateway address is 10.101.141.2/30
See the outputs below, see how the SOURCE field for the new SNAT (eth3) only
matches if the source is 10.101.141.0/30? Since the VM has an IP address in
10.0.0.0/24, the VMs don't get SNAT'd as they should when talking across the
private gateway. The SOURCE should be set to ANYWHERE.
BEFORE ADDING PRIVATE GATEWAY
-----------------------------------------------
Chain POSTROUTING (policy ACCEPT 1 packets, 52 bytes)
pkts bytes target prot opt in out source destination
2 736 SNAT all -- any eth2 10.0.0.0/24 anywhere
to:10.0.0.1
16 1039 SNAT all -- any eth1 anywhere anywhere
to:46.99.52.18
AFTER ADDING PRIVATE GATEWAY W/ SNAT
-----------------------------------------------
Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 SNAT all -- any eth3 10.101.141.0/30 anywhere
to:10.101.141.2
2 736 SNAT all -- any eth2 10.0.0.0/24 anywhere
to:10.0.0.1
23 1515 SNAT all -- any eth1 anywhere anywhere
to:46.99.52.18
It looks like CsAddress.py treats the creation of the Private Gateway SNAT as
if it is a GUEST network, which works fine, except for the SNAT problem shown
above. Here is the code from MASTER (line 479 is SNAT rule):
if self.get_type() in ["guest"]:
...
...
self.fw.append(["nat", "front",
"-A POSTROUTING -s %s -o %s -j SNAT --to-source %s" %
(guestNetworkCidr, self.dev, self.address['public_ip'])])
I am thinking we just change that to the following. I can't think of any
reason we need the source/guest CIDR specified:
if self.get_type() in ["guest"]:
...
...
self.fw.append(["nat", "front",
"-A POSTROUTING -o %s -j SNAT --to-source %s" %
(self.dev, self.address['public_ip'])])
THE NAT TABLE IF THE ABOVE CODE CHANGE IS MADE
-----------------------------------------------
Chain POSTROUTING (policy ACCEPT 0 packets, 0 bytes)
pkts bytes target prot opt in out source destination
0 0 SNAT all -- any eth3 anywhere anywhere
to:10.101.141.2
2 736 SNAT all -- any eth2 anywhere anywhere
to:10.0.0.1
23 1515 SNAT all -- any eth1 anywhere
Thoughts everyone?
