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[Alan Pevec <1386041@xxxxxxxxxxxxxxxxxx>]

** Also affects: neutron/juno
   Importance: Undecided
       Status: New

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https://bugs.launchpad.net/bugs/1386041

Title:
  can't connect external network using default snat from tenant network

Status in OpenStack Neutron (virtual network service):
  Fix Committed
Status in neutron juno series:
  In Progress

Bug description:
  See the following example:
  ---
     ------+----------------- external network 192.168.10.0/24
           |
           | 192.168.10.10
       +---+---+
       |  r1   |  routes [{nexthop: 10.0.0.2, destination: 20.0.0.0/24}]
       +---+---+ 
           | 10.0.0.1
           |
      -----+-----+----------- tenant network1 10.0.0.0/24  (gw: 10.0.0.1)
                 |
                 | 10.0.0.2
             +---+---+
             |  r2   |  routes [{nexthop: 10.0.0.1, destination: 0.0.0.0/0}]
             +---+---+
                 | 20.0.0.1
                 |
      -----------+------------ tenant network2 20.0.0.0/24 (gw: 20.0.0.1)
  ---

  Users want to access external network from tenant network2 using default SNAT but can't access.
  (tenant network2 is connected to r1 indirectly and set routes properly.)
  Users can access external network only from tenant network1 (it is directly connected to r1) currently.

  I think it is a bug since this restriction is unnecessary.

  It is easy to fix. How about this ?
  ---
  diff --git a/neutron/agent/l3_agent.py b/neutron/agent/l3_agent.py
  index ff8ad47..097fa36 100644
  --- a/neutron/agent/l3_agent.py
  +++ b/neutron/agent/l3_agent.py
  @@ -1445,9 +1445,8 @@ class L3NATAgent(firewall_l3_agent.FWaaSL3AgentRpcCallback,
           rules = [('POSTROUTING', '! -i %(interface_name)s '
                     '! -o %(interface_name)s -m conntrack ! '
                     '--ctstate DNAT -j ACCEPT' %
  -                  {'interface_name': interface_name})]
  -        for cidr in internal_cidrs:
  -            rules.extend(self.internal_network_nat_rules(ex_gw_ip, cidr))
  +                  {'interface_name': interface_name}),
  +                 ('snat', '-j SNAT --to-source %s' % ex_gw_ip)]
           return rules
   
       def _snat_redirect_add(self, ri, gateway, sn_port, sn_int):
  @@ -1560,11 +1559,6 @@ class L3NATAgent(firewall_l3_agent.FWaaSL3AgentRpcCallback,
               self.driver.unplug(interface_name, namespace=ri.ns_name,
                                  prefix=INTERNAL_DEV_PREFIX)
   
  -    def internal_network_nat_rules(self, ex_gw_ip, internal_cidr):
  -        rules = [('snat', '-s %s -j SNAT --to-source %s' %
  -                 (internal_cidr, ex_gw_ip))]
  -        return rules
  -
       def _create_agent_gateway_port(self, ri, network_id):
           """Create Floating IP gateway port.
  ---

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