In this blog post I will explain how to connect private tenant networks to an external network without the use of NAT or DNAT (floating ips) via a neutron router.

With the following configuration you will have routers that don’t do NAT on ingress or egress connections. You won’t be able to use floating ips too, at least in the explained configuration, you could add a second external network and a gateway port, plus some static routes to let the router steer traffic over each network.

This can be done, with just one limitation, tenant networks connected in such topology cannot have overlapping ips. And also, the upstream router(s) must be informed about the internal networks so they can add routes themselves to those networks. That can be done manually, or automatically by periodically talking to the openstack API (checking the router interfaces, the subnets etc..) but I’ll skip that part in this blog post.

We’re going to assume that our external provider network is “public”, with the subnet “public_subnet” and that the CIDR of such network is 192.168.1.0/24 with a gateway on 192.168.1.1. Please excuse me because I’m not using the new openstack commands, I can make an updated post later if somebody is interested in that.

Step by step

Create the virtual router

source keystonerc_admin

neutron router-create router_test

Create the private network for our test, and add it to the router

neutron net-create private_test
$PRIV_NET=$(neutron net-list | \
            awk ' /private_test/ { print $2 }')

neutron subnet-create \
       --name private_subnet $PRIV_NET 10.222.0.0/16
neutron router-interface-add router_test private_subnet

Create a security group, and add an instance

neutron security-group-create test
neutron security-group-rule-create test --direction ingress

nova boot --flavor m1.tiny --image cirros \
           --nic net-id=$PRIV_NET \
          --security-group test cirros
sleep 10
nova console-log cirros

Please note that in the console-log you may find that everything went well… and that the instance has an address through DHCP.

Create a port for the router on the external network, do it manually so we can specify the exact address we want.

SUBNET_ID=$(neutron subnet-list | awk ' /public_subnet/ { print $2 }')
neutron port-create public --fixed-ip \
    subnet_id=$SUBNET_ID,ip_address=192.168.1.102 ext-router-port

Add it to the router

PORT_ID=$(neutron port-show ext-router-port | \
          awk '/ id / { print $4 } ')
neutron router-interface-add router_test port=$PORT_ID

We can test it locally (assuming our host has access to 192.168.1.102)

# test local...
ip route add 10.222.0.0/16 via 192.168.1.102

# and assuming that our instance was created with 10.222.0.3

[root@server ~(keystone_admin)]# ping 10.222.0.3
PING 10.222.0.3 (10.222.0.3) 56(84) bytes of data.
64 bytes from 10.222.0.3: icmp_seq=1 ttl=63 time=0.621 ms
64 bytes from 10.222.0.3: icmp_seq=2 ttl=63 time=0.298 ms

Extra note, if you want to avoid issues with overlapping tenant network IPs, I recommend you to have a look at the subnet pool functionality of neutron which started in Kilo.

I hope you enjoyed it, and that this is helpful.

The next example illustrates how to create a test port on a bare-metal node connected to an specific tenant network, this can be useful for testing, or connecting specific bare-metal services to tenant networks.

The bare-metal node $HOST_ID needs to run the neutron-openvswitch-agent, which will wire the port into the right tag-id, tell neutron-server that our port is ACTIVE, and setup proper L2 connectivity (ext VLAN, tunnels, etc..)

Setup our host id and tenant network

NETWORK_NAME=private
NETWORK_ID=$(openstack network show -f value -c id $NETWORK_NAME)
HOST_ID=$(hostname)

Create the port in neutron

PORT_ID=$(neutron port-create --device-owner \  
          compute:container \
          --name test_interf0 $NETWORK_ID | awk '/ id / { print $4 }')

PORT_MAC=$(neutron port-show $PORT_ID -f value -c mac_address)

The port is not bound yet, so it will be in DOWN status

neutron port-show $PORT_ID -f value -c status
DOWN

Create the test_interf0 interface, wired to our new port

ovs-vsctl -- --may-exist add-port br-int test_interf0 \
  -- set Interface test_interf0 type=internal \
  -- set Interface test_interf0 external-ids:iface-status=active \
  -- set Interface test_interf0 external-ids:attached-mac="$PORT_MAC" \
  -- set Interface test_interf0 external-ids:iface-id="$PORT_ID"

We can now see how neutron marked this port as ACTIVE

neutron port-show $PORT_ID -f value -c status
ACTIVE

Set MAC address and move the interface into a namespace (namespace is important if you’re using dhclient, otherwise the host-wide routes and DNS configuration of the host would be changed, you can omit the netns if you’re setting the IP address manually)

ip link set dev test_interf0 address $PORT_MAC
ip netns add test-ns
ip link set test_interf0 netns test-ns
ip netns exec test-ns ip link set dev test_interf0 up

Get IP configuration via DHCP

ip netns exec test-ns dhclient -I test_interf0 --no-pid test_interf0 -v
Internet Systems Consortium DHCP Client 4.2.5
Copyright 2004-2013 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/test_interf0/fa:16:3e:6f:64:46
Sending on   LPF/test_interf0/fa:16:3e:6f:64:46
Sending on   Socket/fallback
DHCPREQUEST on test_interf0 to 255.255.255.255 port 67 (xid=0x5b6ddebc)
DHCPACK from 192.168.125.14 (xid=0x5b6ddebc)

Test connectivity (assuming we have DNS and a router for this subnet)

ip netns exec test-ns ping www.google.com
PING www.google.com (173.194.70.99) 56(84) bytes of data.
64 bytes from fa-in-f99.1e100.net (173.194.70.99): icmp_seq=1 ttl=36 time=115 ms
64 bytes from fa-in-f99.1e100.net (173.194.70.99): icmp_seq=2 ttl=36 time=114 ms
...