wiki:HowTo/ConfigureOVSStaticRouteMirroringNoController

Version 20 (modified by lnevers@bbn.com, 7 years ago) (diff)

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How to set up static flows in OVS

This page demonstrates how to set up static IP traffic flows between two hosts connected to an OVS switch without running a separate OpenFlow controller and by using custom OpenFlow table rules.

The following RSpec is used: https://raw.githubusercontent.com/GENI-NSF/geni-tutorials/master/OVSRyu/openflowovs-all-xen.rspec.xml

This RSpec requests a network topology with 3 nodes (host1, host2, host3) connected to an OVS switch (OVS). The figure below details the connections.


First we will establish rules for allowing IP traffic to flow between host1 and host2. Later in the howto we will discuss how to setup the OVS switch to allow for host3 to observe the traffic between host1 and host2 using OpenFlow table rules. An alternative method using the Mirror feature of the OVS switch is also presented if only mirroring is required. These setups maybe be used for network monitoring.

Setting up the static IP traffic

Configure OVS Switch

  1. Login to the OVS host
  2. Download the script geniovs.sh, which will create an OVS bridge and add all the dataplane interfaces to the bridge:
    wget https://raw.githubusercontent.com/GENI-NSF/geni-support/master/Utilities/geniovs.sh
    bash ./geniovs.sh
    
  3. Verify the dataplane ports have been assigned to bridge:
    sudo ovs-vsctl list-ports br0
    
  4. We want our switch to act without a separate controller thus setting it to operate as standalone.
    sudo ovs-vsctl set-fail-mode br0 standalone
    
  5. Verify all OVS settings by issuing the following:
    sudo ovs-vsctl show
    

Testing the connectivity between host1, host2 and host3

Initially the OVS switch is setup to act like an L2 learning switch. We want to disable this behavior except for specific IP addresses.

On the host OVS:

sudo ovs-ofctl del-flows br0

Next we will test the connectivity of our hosts to each other using the ping command.

From host1

ping -c 10 host2

From host2

ping -c 10 host1

From host3

ping -c 10 host2

Each of these should be unreachable.

Setting up the static IP flows

We can now setup routing between host1 and host2 on the OVS switch. First we will add rules to allow the OVS switch to behave like a normal switch for IP traffic between the two hosts.

On the OVS switch:

sudo ovs-ofctl add-flow br0 ip,nw_src=10.10.1.1,nw_dst=10.10.1.2,actions=normal
sudo ovs-ofctl add-flow br0 ip,nw_src=10.10.1.2,nw_dst=10.10.1.1,actions=normal

ARP traffic will also need to be able to flow in order for the routes to each host to be learned.

On the OVS switch:

sudo ovs-ofctl add-flow br0 "arp,nw_dst=10.10.1.1 actions=normal"
sudo ovs-ofctl add-flow br0 "arp,nw_dst=10.10.1.2 actions=normal"

Test connectivity with the above flows in place:

From host1:

ping -c 10 host2

From host2:

ping -c 10 host1

From host3:

ping -c 10 host2

Pings between host1 and host2 should succeed whereas pings from host3 will fail.

Setting up mirroring behavior

There are two possible ways in which port mirroring can be setup using an OVS switch. The first method presented uses OpenFlow table rules. An alternative method is presented that does not use OpenFlow at all.

Setting up mirroring of traffic from host1 and host2 to host3 (using ovs-ofctl)

Mirroring can be setup by adding flows to the OpenFlow table that take for in_port the port we want monitored, and by specifying the output port in which we want the monitoring traffic to be sent to. This is done using actions=output:#.

For example if we want ports 1 and 2 to be monitored by port 3, the following flows need to be added.

On the OVS switch:

sudo ovs-ofctl add-flow br0 in_port=1,actions=normal,output:3
sudo ovs-ofctl add-flow br0 in_port=2,actions=normal,output:3

Port numbers are assigned based on the order that the ports were added to the bridge as presented in Configure OVS Switch

Setting up mirroring of traffic from host1 and host2 to host3 (using ovs-vctl)

It is possible to setup mirroring without ever adding any flows to the OpenFlow table. It can be done independently of setting up the static IP flows. This is done with a single command to ovs-vsctl.

On the OVS switch:

sudo ovs-vsctl -- set Bridge br0 mirrors=@m \
              -- --id=@ethX get Port ethX \
              -- --id=@ethY get Port ethY \
              -- --id=@ethZ get Port ethZ \
              -- --id=@m create Mirror name=mymirror select-dst-port=@ethX,@ethY select-src-port=@ethX,@ethY output-port=@ethZ

A file /tmp/InterfacesInfo was created on the OVS switch that includes all interface information before the IP was shutdown. From the file /tmp/InterfacesInfo determine ethX and ethY are the names of the interfaces connected to host1 and host2 on the OVS node. The interface ethZ is the interface on the OVS switch that connects to host3.

Verifying mirroring behavior

Using either mirroring method it is useful to verify the behavior. We will use netcat to pass along messages. To observe the mirroring behavior, three terminal windows will need to be opened.

In one terminal ssh into host1 and execute

nc -ul 24565

In one terminal ssh into host2 and execute

nc -u host1 24565

In one terminal ssh into host3 and execute

sudo tcpdump -i eth1 -vv -X

In the terminal with host2 type a message and hit return

A message

Observe that the message is received on host1. On host3 the packet was also received and we can observe the message "A message" inside of the packet.

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