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GENI is a nationwide testbed for developing and conducting network or distributed experiments. There are many GENI racks with compute and networking resources scattered around the country, where we can reserve virtual machines (VMs), entire servers, programmable network switches, and layer 2/layer 3 links to interconnect our resources. Due to the distributed nature of GENI, resources can be reserved in strategic locations given a desired bandwidth or latency.
Clemson is a member of the GENI testbed with two GENI racks and a wireless testbed for conducting WiMAX, LTE, and WiFi experiments. GENI is programmable from the application layer where your programs run all the way down into the link layer where switches forward packets. As such, it is a very powerful and flexible testbed, especially for network experimenters and those interested in software defined networking research (as our research group is).
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To access GENI, navigate in your favorite browser to http://portal.geni.net. From here, select Clemson University from the list of or click the Clemson logo if you see it present already. Then, enter your Clemson username (omitting @clemson.edu) and password. You should be granted access to the GENI portal.
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The route command allows you to see the current routes configured on the system, as well as add and remove existing routes.
View Routes
The -n flag tells the kernel to not resolve host names, which IMHO is easier to reason with when working with IP networks.
Add a Route
The gw <IP-of-gateway> parameter can be omitted if the route does not have a next hop gateway.
Remove a Route
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When removing a route, simply use the exact same syntax used when adding the route, but change the "add" to a "del".
tcpdump
tcpdump is a stripped down version of Wireshark that allows us to view packets that are actively entering or exiting the network interfaces of a machine. There are countless tcpdump filters to get the output to show only what we're interested in. Here's a basic example that will show all ARP and ICMP packets on interface eth1. The trailing -e flag is to show Ethernet headers (MAC addresses), and the -vv is to increase the verbosity.
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To undo any of the above OVS operations, replace "add" in the command with "del", e.g. "add-br" becomes "del-br" and "add-port" becomes "del-port". There are many other OVS commands we won't discuss here (or yet, rather) that follow the same convention.
Lastly, to To view all running switch configurations:
Here is a presentation that covers other useful OVS commands, many of which are beyond the scope of this tutorial but might still be useful. Topics covered include bridge configuration, OpenFlow, and spanning tree to name a few.