Chapter 9. Connect an instance to the physical network

The packet flow for traffic leaving an instance and arriving directly at an external network: Once you configure br-ex, add the physical interface, and spawn an instance to a Compute node, your resulting interfaces and bridges will be similar to those in the diagram below (if using the iptables_hybrid firewall driver):

1. Packets leaving the eth0 interface of the instance will first arrive at the linux bridge qbr-xx.

2. Bridge qbr-xx is connected to br-int using veth pair qvb-xx <-> qvo-xxx. This is because the bridge is used to apply the inbound/outbound firewall rules defined by the security group.

3. Interface qvbxx is connected to the qbr-xx linux bridge, and qvoxx is connected to the br-int Open vSwitch (OVS) bridge.

qbr269d4d73-e7		8000.061943266ebb	no		qvb269d4d73-e7
							tap269d4d73-e7

  Bridge br-int
        fail_mode: secure
            Interface "qvof63599ba-8f"
        Port "qvo269d4d73-e7"
            tag: 5
            Interface "qvo269d4d73-e7"

The packet is then moved to the br-ex OVS bridge using the patch-peer int-br-ex <-> phy-br-ex.

Example configuration of the patch-peer on br-int:

    Bridge br-int
        fail_mode: secure
       Port int-br-ex
            Interface int-br-ex
                type: patch
                options: {peer=phy-br-ex}

Example configuration of the patch-peer on br-ex:

    Bridge br-ex
        Port phy-br-ex
            Interface phy-br-ex
                type: patch
                options: {peer=int-br-ex}
        Port br-ex
            Interface br-ex
                type: internal

When this packet reaches phy-br-ex on br-ex, an OVS flow inside br-ex strips the VLAN tag (5) and forwards it to the physical interface.

In the example below, the output shows the port number of phy-br-ex as 2.

# ovs-ofctl show br-ex
OFPT_FEATURES_REPLY (xid=0x2): dpid:00003440b5c90dc6
n_tables:254, n_buffers:256
capabilities: FLOW_STATS TABLE_STATS PORT_STATS QUEUE_STATS ARP_MATCH_IP
actions: OUTPUT SET_VLAN_VID SET_VLAN_PCP STRIP_VLAN SET_DL_SRC SET_DL_DST SET_NW_SRC SET_NW_DST SET_NW_TOS SET_TP_SRC SET_TP_DST ENQUEUE

 2(phy-br-ex): addr:ba:b5:7b:ae:5c:a2
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max

The output below shows any packet that arrives on phy-br-ex (in_port=2) with a VLAN tag of 5 (dl_vlan=5). In addition, the VLAN tag is stripped away and the packet is forwarded (actions=strip_vlan,NORMAL).

# ovs-ofctl dump-flows br-ex
NXST_FLOW reply (xid=0x4):
 cookie=0x0, duration=4703.491s, table=0, n_packets=3620, n_bytes=333744, idle_age=0, priority=1 actions=NORMAL
 cookie=0x0, duration=3890.038s, table=0, n_packets=13, n_bytes=1714, idle_age=3764, priority=4,in_port=2,dl_vlan=5 actions=strip_vlan,NORMAL
 cookie=0x0, duration=4702.644s, table=0, n_packets=10650, n_bytes=447632, idle_age=0, priority=2,in_port=2 actions=drop

This packet is then forwarded to the physical interface. If the physical interface is another VLAN-tagged interface, then the interface will add the tag to the packet.

This section describes the flow of incoming traffic from the external network until it arrives at the instance’s interface.

1. Incoming traffic first arrives at eth1 on the physical node.

2. The packet is then passed to the br-ex bridge.

3. The packet then moves to br-int using the patch-peer phy-br-ex <--> int-br-ex.

In the example below, int-br-ex uses port number 15. See the entry containing 15(int-br-ex):

ovs-ofctl show br-int
OFPT_FEATURES_REPLY (xid=0x2): dpid:00004e67212f644d
n_tables:254, n_buffers:256
capabilities: FLOW_STATS TABLE_STATS PORT_STATS QUEUE_STATS ARP_MATCH_IP
actions: OUTPUT SET_VLAN_VID SET_VLAN_PCP STRIP_VLAN SET_DL_SRC SET_DL_DST SET_NW_SRC SET_NW_DST SET_NW_TOS SET_TP_SRC SET_TP_DST ENQUEUE
 15(int-br-ex): addr:12:4e:44:a9:50:f4
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max

# ovs-ofctl dump-flows br-int
NXST_FLOW reply (xid=0x4):
 cookie=0x0, duration=5351.536s, table=0, n_packets=12118, n_bytes=510456, idle_age=0, priority=1 actions=NORMAL
 cookie=0x0, duration=4537.553s, table=0, n_packets=3489, n_bytes=321696, idle_age=0, priority=3,in_port=15,vlan_tci=0x0000 actions=mod_vlan_vid:5,NORMAL
 cookie=0x0, duration=5350.365s, table=0, n_packets=628, n_bytes=57892, idle_age=4538, priority=2,in_port=15 actions=drop
 cookie=0x0, duration=5351.432s, table=23, n_packets=0, n_bytes=0, idle_age=5351, priority=0 actions=drop

2. The second rule manages packets that arrive on int-br-ex (in_port=15) with no VLAN tag (vlan_tci=0x0000): It adds VLAN tag 5 to the packet (actions=mod_vlan_vid:5,NORMAL) and forwards it on to qvoxxx.

3. qvoxxx accepts the packet and forwards to qvbxx, after stripping the away the VLAN tag.

4. The packet then reaches the instance.

The output provided in the section above - How does the packet flow work? - provides sufficient debugging information for troubleshooting a flat provider network, should anything go wrong. The steps below would further assist with the troubleshooting process.

1. Review bridge_mappings:

Verify that physical network name used (for example, physnet1) is consistent with the contents of the bridge_mapping configuration. For example:

# grep bridge_mapping /etc/neutron/plugins/ml2/openvswitch_agent.ini
bridge_mappings = physnet1:br-ex

# neutron net-show provider-flat
...
| provider:physical_network | physnet1
...

2. Review the network configuration:

Confirm that the network is created as external, and uses the flat type:

# neutron net-show provider-flat
...
| provider:network_type     | flat                                 |
| router:external           | True                                 |
...

3. Review the patch-peer:

Run ovs-vsctl show, and verify that br-int and br-ex is connected using a patch-peer int-br-ex <--> phy-br-ex.

This connection is created when the neutron-openvswitch-agent service is restarted. But only if bridge_mapping is correctly configured in /etc/neutron/plugins/ml2/openvswitch_agent.ini. Re-check the bridge_mapping setting if this is not created, even after restarting the service.

4. Review the network flows:

Run ovs-ofctl dump-flows br-ex and ovs-ofctl dump-flows br-int and review whether the flows strip the internal VLAN IDs for outgoing packets, and add VLAN IDs for incoming packets. This flow is first added when you spawn an instance to this network on a specific Compute node.

For example, the output below shows eth1 is a port in br-ex:

    Bridge br-ex
        Port phy-br-ex
            Interface phy-br-ex
                type: patch
                options: {peer=int-br-ex}
        Port "eth1"
            Interface "eth1"

The example below demonstrates that eth1 is configured as an OVS port, and that the kernel knows to transfer all packets from the interface, and send them to the OVS bridge br-ex. This can be observed in the entry: master ovs-system.

# ip a
5: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master ovs-system state UP qlen 1000

This section describes the packet flow for traffic leaving an instance and arriving directly to a VLAN provider external network. This example uses two instances attached to the two VLAN networks (171 and 172). Once you configure br-ex, add a physical interface to it, and spawn an instance to a Compute node, your resulting interfaces and bridges will be similar to those in the diagram below:

1. As illustrated above, packets leaving the instance’s eth0 first arrive at the linux bridge qbr-xx connected to the instance.

2. qbr-xx is connected to br-int using veth pair qvbxx <→ qvoxxx.

3. qvbxx is connected to the linux bridge qbr-xx and qvoxx is connected to the Open vSwitch bridge br-int.

# brctl show
bridge name	bridge id		STP enabled	interfaces
qbr84878b78-63		8000.e6b3df9451e0	no		qvb84878b78-63
							tap84878b78-63

qbr86257b61-5d		8000.3a3c888eeae6	no		qvb86257b61-5d
							tap86257b61-5d

                options: {peer=phy-br-ex}
        Port "qvo86257b61-5d"
            tag: 3

            Interface "qvo86257b61-5d"
        Port "qvo84878b78-63"
            tag: 2
            Interface "qvo84878b78-63"

    Bridge br-int
        fail_mode: secure
       Port int-br-ex
            Interface int-br-ex
                type: patch
                options: {peer=phy-br-ex}

Example configuration of the patch peer on br-ex:

    Bridge br-ex
        Port phy-br-ex
            Interface phy-br-ex
                type: patch
                options: {peer=int-br-ex}
        Port br-ex
            Interface br-ex
                type: internal

The output of the following command shows that the port number of phy-br-ex is 4:

# ovs-ofctl show br-ex
 4(phy-br-ex): addr:32:e7:a1:6b:90:3e
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max

The below command displays any packet that arrives on phy-br-ex (in_port=4) which has VLAN tag 2 (dl_vlan=2). Open vSwitch replaces the VLAN tag with 171 (actions=mod_vlan_vid:171,NORMAL) and forwards the packet on. It also shows any packet that arrives on phy-br-ex (in_port=4) which has VLAN tag 3 (dl_vlan=3). Open vSwitch replaces the VLAN tag with 172 (actions=mod_vlan_vid:172,NORMAL) and forwards the packet on. These rules are automatically added by neutron-openvswitch-agent.

# ovs-ofctl dump-flows br-ex
NXST_FLOW reply (xid=0x4):
NXST_FLOW reply (xid=0x4):
 cookie=0x0, duration=6527.527s, table=0, n_packets=29211, n_bytes=2725576, idle_age=0, priority=1 actions=NORMAL
 cookie=0x0, duration=2939.172s, table=0, n_packets=117, n_bytes=8296, idle_age=58, priority=4,in_port=4,dl_vlan=3 actions=mod_vlan_vid:172,NORMAL
 cookie=0x0, duration=6111.389s, table=0, n_packets=145, n_bytes=9368, idle_age=98, priority=4,in_port=4,dl_vlan=2 actions=mod_vlan_vid:171,NORMAL
 cookie=0x0, duration=6526.675s, table=0, n_packets=82, n_bytes=6700, idle_age=2462, priority=2,in_port=4 actions=drop

The below command shows int-br-ex with port number 18:

# ovs-ofctl show br-int
 18(int-br-ex): addr:fe:b7:cb:03:c5:c1
     config:     0
     state:      0
     speed: 0 Mbps now, 0 Mbps max

# ovs-ofctl dump-flows br-int
NXST_FLOW reply (xid=0x4):
 cookie=0x0, duration=6770.572s, table=0, n_packets=1239, n_bytes=127795, idle_age=106, priority=1 actions=NORMAL
 cookie=0x0, duration=3181.679s, table=0, n_packets=2605, n_bytes=246456, idle_age=0, priority=3,in_port=18,dl_vlan=172 actions=mod_vlan_vid:3,NORMAL
 cookie=0x0, duration=6353.898s, table=0, n_packets=5077, n_bytes=482582, idle_age=0, priority=3,in_port=18,dl_vlan=171 actions=mod_vlan_vid:2,NORMAL
 cookie=0x0, duration=6769.391s, table=0, n_packets=22301, n_bytes=2013101, idle_age=0, priority=2,in_port=18 actions=drop
 cookie=0x0, duration=6770.463s, table=23, n_packets=0, n_bytes=0, idle_age=6770, priority=0 actions=drop

The second rule says a packet that arrives on int-br-ex (in_port=18) which has VLAN tag 172 in it (dl_vlan=172), replace VLAN tag with 3 (actions=mod_vlan_vid:3,NORMAL) and forward. The third rule says a packet that arrives on int-br-ex (in_port=18) which has VLAN tag 171 in it (dl_vlan=171), replace VLAN tag with 2 (actions=mod_vlan_vid:2,NORMAL) and forward.

Note that the VLAN tag 2 and 3 is an example that was used on a test Compute node for the VLAN provider networks (provider-171 and provider-172). The required configuration may be different for your VLAN provider network, and can also be different for the same network on two different Compute nodes.

Refer to the packet flow described in the section above when troubleshooting connectivity in a VLAN provider network. In addition, review the following configuration options:

1. Verify that physical network name is used consistently. In this example, physnet1 is used consistently while creating the network, and within the bridge_mapping configuration:

# grep bridge_mapping /etc/neutron/plugins/ml2/openvswitch_agent.ini
bridge_mappings = physnet1:br-ex

# neutron net-show provider-vlan171
...
| provider:physical_network | physnet1
...

2. Confirm that the network was created as external, is type vlan, and uses the correct segmentation_id value:

# neutron net-show provider-vlan171
...
| provider:network_type     | vlan                                 |
| provider:physical_network | physnet1                             |
| provider:segmentation_id  | 171                                  |
...

3. Run ovs-vsctl show and verify that br-int and br-ex are connected using the patch-peer int-br-ex <→ phy-br-ex.
This connection is created while restarting neutron-openvswitch-agent, provided that the bridge_mapping is correctly configured in /etc/neutron/plugins/ml2/openvswitch_agent.ini.
Recheck the bridge_mapping setting if this is not created even after restarting the service.

4. To review the flow of outgoing packets, run ovs-ofctl dump-flows br-ex and ovs-ofctl dump-flows br-int, and verify that the flows map the internal VLAN IDs to the external VLAN ID (segmentation_id). For incoming packets, map the external VLAN ID to the internal VLAN ID.
This flow is added by the neutron OVS agent when you spawn an instance to this network for the first time. If this flow is not created after spawning the instance, make sure that the network is created as vlan, is external, and that the physical_network name is correct. In addition, re-check the bridge_mapping settings.

5. Finally, re-check the ifcfg-br-ex and ifcfg-ethx configuration. Make sure that ethX is added as a port inside br-ex, and that both of them have UP flag in the output of the ip a command.
For example, the output below shows that eth1 is a port in br-ex.

    Bridge br-ex
        Port phy-br-ex
            Interface phy-br-ex
                type: patch
                options: {peer=int-br-ex}
        Port "eth1"
            Interface "eth1"

The command below shows that eth1 has been added as a port, and that the kernel is aware to move all packets from the interface to the OVS bridge br-ex. This is demonstrated by the entry: master ovs-system.

# ip a
5: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq master ovs-system state UP qlen 1000