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[mininet-discuss] ovs-vswitchd support?

Parantapa Bhattacharya parantapa at
Thu Oct 27 00:46:05 PDT 2011

On Thu, Oct 27, 2011 at 1:37 AM, Bob Lantz <rlantz at> wrote:
> Hmm, I like it!
> Good things it preserves from mininet:
> - use of python as configuration language (this is key)
> - hosts as shells in network namespaces
> Good things it adds:
> - built-in native interfaces
> - namespace support in pure-ish python (crafty! though I wonder how you pick the library)
> - vswitchd support
> - actual class for links

Thanks :)

> Using the multiprocessing module is interesting. I didn't use call() since it fails with large numbers of file descriptors.

Did you try close_fds parameter for call? Anyway i didn't hit the
limit so it didn't bother me.

> One thing I'm puzzled by though: if you want to make it small, why use the Linux bridge at all? Open vSwitch replaces it, particularly with its bridge compatibility module.

Mininet uses mnexec to call unshare, and execs bash for the shell. In
python you can call native c libraries (shared not static) using
ctypes module. So i just called unshare from my python shell using
ctypes module.

> It reminds me of my original implementation(s) of Mininet, which just had the basic functionality in about 200 lines of code. Perhaps we (Mininet devs) can think a bit about reorganizing ("refactoring") the code to make it more modular so that a minimal core of code can be used standalone (this is almost true at the moment because of the different API layers, but the code is intermixed in the actual files.)

It would really be appreciated. It would make submitting patches to
mininet so much easier.

> Heheh, I agree the screen hack isn't ideal. If you can create an elegant replacement, I'd be interested. In theory, one should be able to simply use a unix domain socket, but I wasn't able to get that to work immediately when I tried it a while back.

I had actually two solutions. But both had some problems. First,
inside the network namespace  you create a custom pty pair and attach
its master to a shell. On the root namespace you create a dummy
terminal and attach the slave side of the pty pair to it (in xterm you
can use -Sccn, on urxvt you can use -pty-fd, i didn't find options in
other terminals). This works real well and there is no overhead of
sockets or anything. But the again the terminal cannot know when the
shell exits and the shell cannot know if the terminal exits. So if you
accidentally close one you have to manually close the other which is
quite irritating. The solution is to monitor both processes (across
the namespaces) and close one if other exits. But i was to lazy to
write that part :P

The other solution is to use X forwarding. It is easy to have it if
the network is properly set up. But that's mostly difficult to have in
the mininet scenario. Since network access to root namespace is cut
off we have to use other methods of IPC. I find named pipes very
useful for this. Basically one needs couple of named pipes and two
processes (i used socat) for forwarding on either side per X using
program. On the plus side this allows any X using program to be run.
So one can use gnome-terminal or xfce4-terminal and even firefox or
wireshark. But has a very high overhead. It also has the same problem
of cross namespace process monitoring.

> I think we can improve the topology support in mininet; currently we have a couple of mechanisms to do the same thing, which may not be optimal.

I feel generating a topology is extremely easy since python is the
configuration language and should be left to the users. Any fixed
number of topologies is good for a fixed number of purpose. But it
only increases code size and people complain when their required
topology is not there. I was working with a few who were also working
on mininet. And they were already writing their custom topologies. I
think mininet is best for managing programmable network namespaces and
it should stick to that.

> -Bob
> On Oct 25, 2011, at 10:28 PM, Parantapa Bhattacharya wrote:
>> Hi
>> I had tried to include ovs-vswitchd support in OVS some time back. But
>> i found somthings in mininte that i disliked. So i cooked up a little
>> version of my own which i called Piconet. Please check it if you like.
>> --
>> Parantapa Bhattacharya
>> _______________________________________________
>> mininet-discuss mailing list
>> mininet-discuss at

Parantapa Bhattacharya

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