'''Execute Experiment:'''
After your slice is ready, you will be able to interact with your nodes. Even though your OVS nodes are now visible to the controller, their tables are empty and therefore they will not forward any packet. 

 1. '''Login to hosts'''
  To start our experiment we need to ssh our hosts, '''h1''' and '''h2''', you may use any SSH client or the GENI Dekstop's SSH module to access the hosts from the browser.XXXX link 

  In the terminal of '''h1''', ping '''h2'''. This should timeout, since there are no rules installed at the switches. 
  {{{
user@h1:~$ ping h2
PING h2-link-4 (10.10.5.2) 56(84) bytes of data.
From h1-link-0 (10.10.1.1) icmp_seq=1 Destination Host Unreachable
From h1-link-0 (10.10.1.1) icmp_seq=2 Destination Host Unreachable
From h1-link-0 (10.10.1.1) icmp_seq=3 Destination Host Unreachable
  }}}
 2. '''Setup Shortest Path Flows'''
  Now we want to make h1 and h2 able to communicate using shortest paths. To do so, you have to load the Flow Install module from the list of modules on the left hand side of your screen. 

  [[Image(finstall.png)]]

  The first section tells you the public IP address where the controller is running, and what controller did you choose when creating the slice. 

  The second section allows you compute shortest paths between all hosts and automatically install the corresponding flow entries at every switch in the path. We need to handle ARP processing as well in order to be able to communicate between hosts. The controller images loaded in the AAG features include ARP processing modules. Therefore, by checking the ARP processing box we will let the controller handle all ARP requests/responses. Then, click on the Initialize button. 

  The output message should be: 
  {{{
ARP flow entries successfully installed.
Shortest paths successfully installed.
  }}}


  Now, if we try to ping h2 from h1 we can see that communication is successful. 
 {{{
user@h1:~$ ping h2
PING h2-link-4 (10.10.5.2) 56(84) bytes of data.
64 bytes from h2-link-4 (10.10.5.2): icmp_seq=1 ttl=64 time=7.40 ms
64 bytes from h2-link-4 (10.10.5.2): icmp_seq=2 ttl=64 time=1.74 ms
64 bytes from h2-link-4 (10.10.5.2): icmp_seq=3 ttl=64 time=1.69 ms
 }}}

 3. '''Install Alternate Paths'''
    1. List Flows


      The Flow Install module allows you to list existing end-to-end flows (Refresh List button) you have added using the GENI Desktop as well as individual flow entries (possibly) installed using other tools that interact with the controller REST API. 

      Note that end-to-end flows display the path a flow follows from one host to another instead of displaying low-level details. For individual flow entries, information about the match fields is shown (e.g. ARP flows). 
      [[Image(flowlist.png)]]

    2. Delete a Flow
      With the flows listed, it is straightforward to remove an existing path. For this tutorial we will leave the communication from h1 to h2 intact (i.e. shortest path), but you will select and remove the flow that goes from h2 to h1. 

    3. Defining an Alternate Path

      Defining an Alternate Path


      Using the topology view, you will select all the elements (links and nodes) across an alternate path that communicate h2 with h1. In the flow definition section, select h2 as source node and define the path as a one-way flow. Leave the information about ports blank and install the new flow. 


      [[Image(altflow.png)]]

      '''Tip''': Select multiple elements by holding the CTRL key and clicking on the desired element. 

      Output 
      {{{
End-to-End flow(s) installed successfully.
      }}}

    4. Testing New Path

      With the new path installed, you should be able to ping again from h1 to h2. 
      {{{
user@h1:~$ ping h2
PING h2-link-4 (10.10.5.2) 56(84) bytes of data.
64 bytes from h2-link-4 (10.10.5.2): icmp_seq=1 ttl=64 time=2.64 ms
64 bytes from h2-link-4 (10.10.5.2): icmp_seq=2 ttl=64 time=2.16 ms
      }}}

      Notice the extra delay added to the communication because we are using a longer path.


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