Chapter 4. Monitoring OVN

You can use the ovn-trace command to monitor and troubleshoot OVN logical flows, and you can use the ovs-ofctl dump-flows command to monitor and troubleshoot OpenFlows.

4.1. Monitoring OVN logical flows

OVN uses logical flows that are tables of flows with a priority, match, and actions. These logical flows are distributed to the ovn-controller running on each Compute node. You can use the ovn-sbctl lflow-list command on the Controller node to view the full set of logical flows, as shown in this example.

$ ovn-sbctl --db=tcp:172.17.1.10:6642 lflow-list
    Datapath: "sw0" (d7bf4a7b-e915-4502-8f9d-5995d33f5d10)  Pipeline: ingress
      table=0 (ls_in_port_sec_l2  ), priority=100  , match=(eth.src[40]), action=(drop;)
      table=0 (ls_in_port_sec_l2  ), priority=100  , match=(vlan.present), action=(drop;)
      table=0 (ls_in_port_sec_l2  ), priority=50   , match=(inport == "sw0-port1" && eth.src == {00:00:00:00:00:01}), action=(next;)
      table=0 (ls_in_port_sec_l2  ), priority=50   , match=(inport == "sw0-port2" && eth.src == {00:00:00:00:00:02}), action=(next;)
      table=1 (ls_in_port_sec_ip  ), priority=0    , match=(1), action=(next;)
      table=2 (ls_in_port_sec_nd  ), priority=90   , match=(inport == "sw0-port1" && eth.src == 00:00:00:00:00:01 && arp.sha == 00:00:00:00:00:01), action=(next;)
      table=2 (ls_in_port_sec_nd  ), priority=90   , match=(inport == "sw0-port1" && eth.src == 00:00:00:00:00:01 && ip6 && nd && ((nd.sll == 00:00:00:00:00:00 || nd.sll == 00:00:00:00:00:01) || ((nd.tll == 00:00:00:00:00:00 || nd.tll == 00:00:00:00:00:01)))), action=(next;)
      table=2 (ls_in_port_sec_nd  ), priority=90   , match=(inport == "sw0-port2" && eth.src == 00:00:00:00:00:02 && arp.sha == 00:00:00:00:00:02), action=(next;)
      table=2 (ls_in_port_sec_nd  ), priority=90   , match=(inport == "sw0-port2" && eth.src == 00:00:00:00:00:02 && ip6 && nd && ((nd.sll == 00:00:00:00:00:00 || nd.sll == 00:00:00:00:00:02) || ((nd.tll == 00:00:00:00:00:00 || nd.tll == 00:00:00:00:00:02)))), action=(next;)
      table=2 (ls_in_port_sec_nd  ), priority=80   , match=(inport == "sw0-port1" && (arp || nd)), action=(drop;)
      table=2 (ls_in_port_sec_nd  ), priority=80   , match=(inport == "sw0-port2" && (arp || nd)), action=(drop;)
      table=2 (ls_in_port_sec_nd  ), priority=0    , match=(1), action=(next;)
      table=3 (ls_in_pre_acl      ), priority=0    , match=(1), action=(next;)
      table=4 (ls_in_pre_lb       ), priority=0    , match=(1), action=(next;)
      table=5 (ls_in_pre_stateful ), priority=100  , match=(reg0[0] == 1), action=(ct_next;)
      table=5 (ls_in_pre_stateful ), priority=0    , match=(1), action=(next;)
      table=6 (ls_in_acl          ), priority=0    , match=(1), action=(next;)
      table=7 (ls_in_qos_mark     ), priority=0    , match=(1), action=(next;)
      table=8 (ls_in_lb           ), priority=0    , match=(1), action=(next;)
      table=9 (ls_in_stateful     ), priority=100  , match=(reg0[1] == 1), action=(ct_commit(ct_label=0/1); next;)
      table=9 (ls_in_stateful     ), priority=100  , match=(reg0[2] == 1), action=(ct_lb;)
      table=9 (ls_in_stateful     ), priority=0    , match=(1), action=(next;)
      table=10(ls_in_arp_rsp      ), priority=0    , match=(1), action=(next;)
      table=11(ls_in_dhcp_options ), priority=0    , match=(1), action=(next;)
      table=12(ls_in_dhcp_response), priority=0    , match=(1), action=(next;)
      table=13(ls_in_l2_lkup      ), priority=100  , match=(eth.mcast), action=(outport = "_MC_flood"; output;)
      table=13(ls_in_l2_lkup      ), priority=50   , match=(eth.dst == 00:00:00:00:00:01), action=(outport = "sw0-port1"; output;)
      table=13(ls_in_l2_lkup      ), priority=50   , match=(eth.dst == 00:00:00:00:00:02), action=(outport = "sw0-port2"; output;)
    Datapath: "sw0" (d7bf4a7b-e915-4502-8f9d-5995d33f5d10)  Pipeline: egress
      table=0 (ls_out_pre_lb      ), priority=0    , match=(1), action=(next;)
      table=1 (ls_out_pre_acl     ), priority=0    , match=(1), action=(next;)
      table=2 (ls_out_pre_stateful), priority=100  , match=(reg0[0] == 1), action=(ct_next;)
      table=2 (ls_out_pre_stateful), priority=0    , match=(1), action=(next;)
      table=3 (ls_out_lb          ), priority=0    , match=(1), action=(next;)
      table=4 (ls_out_acl         ), priority=0    , match=(1), action=(next;)
      table=5 (ls_out_qos_mark    ), priority=0    , match=(1), action=(next;)
      table=6 (ls_out_stateful    ), priority=100  , match=(reg0[1] == 1), action=(ct_commit(ct_label=0/1); next;)
      table=6 (ls_out_stateful    ), priority=100  , match=(reg0[2] == 1), action=(ct_lb;)
      table=6 (ls_out_stateful    ), priority=0    , match=(1), action=(next;)
      table=7 (ls_out_port_sec_ip ), priority=0    , match=(1), action=(next;)
      table=8 (ls_out_port_sec_l2 ), priority=100  , match=(eth.mcast), action=(output;)
      table=8 (ls_out_port_sec_l2 ), priority=50   , match=(outport == "sw0-port1" && eth.dst == {00:00:00:00:00:01}), action=(output;)
      table=8 (ls_out_port_sec_l2 ), priority=50   , match=(outport == "sw0-port2" && eth.dst == {00:00:00:00:00:02}), action=(output;)

Key differences between OVN and OpenFlow include:

  • OVN ports are logical entities that reside somewhere on a network, not physical ports on a single switch.
  • OVN gives each table in the pipeline a name in addition to its number. The name describes the purpose of that stage in the pipeline.
  • The OVN match syntax supports complex Boolean expressions.
  • The actions supported in OVN logical flows extend beyond those of OpenFlow. You can implement higher level features, such as DHCP, in the OVN logical flow syntax.

ovn-trace

The ovn-trace command can simulate how a packet travels through the OVN logical flows, or help you determine why a packet is dropped. Provide the ovn-trace command with the following parameters:

DATAPATH
The logical switch or logical router where the simulated packet starts.
MICROFLOW
The simulated packet, in the syntax used by the ovn-sb database.

This example displays the --minimal output option on a simulated packet and shows that the packet reaches its destination:

$ ovn-trace --minimal sw0 'inport == "sw0-port1" && eth.src == 00:00:00:00:00:01 && eth.dst == 00:00:00:00:00:02'
    # reg14=0x1,vlan_tci=0x0000,dl_src=00:00:00:00:00:01,dl_dst=00:00:00:00:00:02,dl_type=0x0000
    output("sw0-port2");

In more detail, the --summary output for this same simulated packet shows the full execution pipeline:

$ ovn-trace --summary sw0 'inport == "sw0-port1" && eth.src == 00:00:00:00:00:01 && eth.dst == 00:00:00:00:00:02'
# reg14=0x1,vlan_tci=0x0000,dl_src=00:00:00:00:00:01,dl_dst=00:00:00:00:00:02,dl_type=0x0000
ingress(dp="sw0", inport="sw0-port1") {
    outport = "sw0-port2";
    output;
    egress(dp="sw0", inport="sw0-port1", outport="sw0-port2") {
        output;
        /* output to "sw0-port2", type "" */;
    };
};

The example output shows:

  • The packet enters the sw0 network from the sw0-port1 port and runs the ingress pipeline.
  • The outport variable is set to sw0-port2 indicating that the intended destination for this packet is sw0-port2.
  • The packet is output from the ingress pipeline, which brings it to the egress pipeline for sw0 with the outport variable set to sw0-port2.
  • The output action is executed in the egress pipeline, which outputs the packet to the current value of the outport variable, which is sw0-port2.

See the ovn-trace man page for complete details.

4.2. Monitoring OpenFlows

You can use ovs-ofctl dump-flows command to monitor the OpenFlow flows on a logical switch in your network.

$ ovs-ofctl dump-flows br-int
NXST_FLOW reply (xid=0x4):
 cookie=0x0, duration=72.132s, table=0, n_packets=0, n_bytes=0, idle_age=72, priority=10,in_port=1,dl_src=00:00:00:00:00:01 actions=resubmit(,1)
 cookie=0x0, duration=60.565s, table=0, n_packets=0, n_bytes=0, idle_age=60, priority=10,in_port=2,dl_src=00:00:00:00:00:02 actions=resubmit(,1)
 cookie=0x0, duration=28.127s, table=0, n_packets=0, n_bytes=0, idle_age=28, priority=0 actions=drop
 cookie=0x0, duration=13.887s, table=1, n_packets=0, n_bytes=0, idle_age=13, priority=0,in_port=1 actions=output:2
 cookie=0x0, duration=4.023s, table=1, n_packets=0, n_bytes=0, idle_age=4, priority=0,in_port=2 actions=output:1