OpenVSwitch or OVS can run in two modes
1. NORMAL mode
2. Flow mode
In NORMAL mode, OVS works like any other L2 layer switch operating on MAC-Port mapping.
To use an OVS in NORMAL mode, simple create an OVS bridge and add the below flow entry
ovs-vsctl add-br br0
ovs-vsctl add-port eth0
ovs-ofctl add-flow br0 action=NORMAL
For flows hitting this entry, the MAC table maintained by OVS would be referred for forwarding decision.
In Flow mode, the regular OpenFlow pipeline is hit and OVS works on the basis of flows installed.
In my experiment, I would explain how the NORMAL mode works standalone and also how it works in conjunction with flow mode.
I have only used mininet and OVS for this experiment on Ubuntu 14.04 LTS.
Step 1: Create a simple topology with one switch and three hosts.
$ sudo mn --topo=single,3 --controller=none --mac
*** Creating network
*** Adding controller
*** Adding hosts:
h1 h2 h3
*** Adding switches:
s1
*** Adding links:
(h1, s1) (h2, s1) (h3, s1)
*** Configuring hosts
h1 h2 h3
*** Starting controller
*** Starting 1 switches
s1
*** Starting CLI:
Step 2: Execute ovs-appctl command. This command displays the MAC table created by OVS. Since we have not done any ping, the table doesn't has the MAC entries for h1,h2 and h3.
mininet> sh ovs-appctl fdb/show s1
port VLAN MAC Age
LOCAL 0 b2:c9:fc:3c:1a:41 8
mininet>
Step 3: We do not have any flows installed on OVS. If you try to ping between hosts, nothing would happen.
mininet> sh ovs-ofctl dump-flows s1
NXST_FLOW reply (xid=0x4):
mininet>
Step 4: Now, lets add a NORMAL action flow entry on OVS and see what happens.
mininet> sh ovs-ofctl add-flow s1 action=normal
mininet> sh ovs-ofctl dump-flows s1
NXST_FLOW reply (xid=0x4):
cookie=0x0, duration=12.023s, table=0, n_packets=0, n_bytes=0, idle_age=12, actions=NORMAL
mininet>
The MAC table is still blank as in step 2.
mininet> sh ovs-appctl fdb/show s1
port VLAN MAC Age
LOCAL 0 b2:c9:fc:3c:1a:41 56
mininet>
Step 5: Lets ping
mininet> h1 ping h2
PING 10.0.0.2 (10.0.0.2) 56(84) bytes of data.
64 bytes from 10.0.0.2: icmp_seq=1 ttl=64 time=0.587 ms
64 bytes from 10.0.0.2: icmp_seq=2 ttl=64 time=0.085 ms
^C
--- 10.0.0.2 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1001ms
rtt min/avg/max/mdev = 0.085/0.336/0.587/0.251 ms
The ping is successful because of NORMAL flow entry. The MAC addresses of the hosts h1 and h2 are learnt. h3 is still not learnt as there has been no ping to/from h3.
mininet> sh ovs-appctl fdb/show s1
port VLAN MAC Age
LOCAL 0 b2:c9:fc:3c:1a:41 63
2 0 00:00:00:00:00:02 1
1 0 00:00:00:00:00:01 1
mininet>
The above steps show the OVS operation in NORMAL mode.
Step 6 onwards, I would explain how NORMAL and FLOW mode work in conjunction,
Step 6: Now, lets add a flow for MAC address and port of h3 with a higher priority.
mininet> sh ovs-ofctl add-flow s1 priority=60000,dl_dst=00:00:00:00:00:03,actions=output:3
mininet> sh ovs-ofctl dump-flows s1
NXST_FLOW reply (xid=0x4):
cookie=0x0, duration=4.242s, table=0, n_packets=0, n_bytes=0, idle_age=4, priority=60000,dl_dst=00:00:00:00:00:03 actions=output:3
cookie=0x0, duration=71.223s, table=0, n_packets=8, n_bytes=560, idle_age=43, actions=NORMAL
mininet>
Step 7: Lets ping and notice n_packets/n_bytes of flow entries.
mininet> h1 ping h3
PING 10.0.0.3 (10.0.0.3) 56(84) bytes of data.
64 bytes from 10.0.0.3: icmp_seq=1 ttl=64 time=0.558 ms
64 bytes from 10.0.0.3: icmp_seq=2 ttl=64 time=0.090 ms
^C
--- 10.0.0.3 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 999ms
rtt min/avg/max/mdev = 0.090/0.324/0.558/0.234 ms
mininet> sh ovs-ofctl dump-flows s1
NXST_FLOW reply (xid=0x4):
cookie=0x0, duration=13.124s, table=0, n_packets=2, n_bytes=196, idle_age=2, priority=60000,dl_dst=00:00:00:00:00:03 actions=output:3 --> Flow1
cookie=0x0, duration=80.105s, table=0, n_packets=12, n_bytes=840, idle_age=2, actions=NORMAL ---> Flow2
mininet>
Notice that the packets/bytes increase for both the entries. This is because when h1 ping is sent to h3, Flow 1 is hit and for the ping reply, Flow 2 gets hit.
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