To be precise, what I want to do is iterate over all of the ports and send a
packet out of each of them, NOT broadcast - I understand that that wouldn't
work if I wanted to get specific port information. My reading of
discovery.py (which might not be right, again, I'm new to python) seems to
indicate that it has a delay between scans. I'm implementing a system that
only scans reactively on events - for example, when a switch comes online
I'd like to scan all of its ports (individually, but those packets would all
be on the network at once, on different wires).
Since this is only at most two packets per link on the network (assuming I
don't scan the entire network very frequently), I don't see how this is a
threat to overloading the switches if the lldp packets don't get forwarded.
I don't think this would be a problem, but since discovery.py implements
this delay, I'm afraid I'm missing something. The crux of the issue is
this:
Would there be a problem with having multiple lldp packets on different
wires in the same network?
On Sun, Nov 14, 2010 at 5:27 PM, Ali Reza Sharafat
<ali.shara...@gmail.com>wrote:
> Well, there are two things to consider:
> 1. If by "scanning the network simultaneously" you mean doing a
> broadcast at every switch, then you will be a bit handicapped. That's
> because when you do a broadcast, you have to send the same packet out
> of every port and so your packet cannot carry the "originating port"
> data with it.
> 2. Now, if you want to just send all packets at once from all
> switches, then you are risking both a flood on the network and/or
> overloading the switches' cpu.
>
> Hope that helps.
>
> On Sun, Nov 14, 2010 at 2:14 PM, Alec Story <av...@cornell.edu> wrote:
> > But you know (from the lldp packet) where the packet originated, and you
> > know from the dpid and inport argument to your packet handler where the
> > packet ended up, so, as far as I can tell, you can differentiate between
> > multiple packets just fine.
> >
> > On Sun, Nov 14, 2010 at 4:57 PM, Macapuna, Carlos A. B.
> > <carlosmacap...@gmail.com> wrote:
> >>
> >> Because do you have only one controller and the controller have that
> send
> >> and receive the LLDP packets for all (ports) OpenFlow switches. Do you
> can
> >> to implement Python threads or multiple controller. But do you will have
> >> many LLDP packets for treat at the some time. Was that?
> >>
> >> Greetings,
> >>
> >> ----
> >> Carlos Macapuna
> >> www.macapuna.com.br
> >>
> >>
> >>
> >>
> >> On Sun, Nov 14, 2010 at 7:03 PM, Alec Story <av...@cornell.edu> wrote:
> >>>
> >>> I'm trying to understand discovery.py's use of lldp scanning. I'm
> >>> relatively new to python, but it looks like it only sends one lldp
> packet on
> >>> the network at a time (lines 315-350), but I can't figure out why this
> would
> >>> be. Since the lldp packets have no rule for forwarding, they should
> only
> >>> travel over one network edge, and have no chance of being received by
> some
> >>> switch other than the one on the other end of that pipe - why only send
> one
> >>> out at a time, rather than scanning the whole network simultaneously?
> >>>
> >>> The code in question, for convenience:
> >>>>
> >>>> def start_lldp_timer_thread(self):
> >>>>
> >>>>
> >>>>
> #----------------------------------------------------------------------
> >>>> # Generator which iterates over a set of dp's and sends an
> LLDP
> >>>> packet
> >>>> # out of each port.
> >>>>
> >>>>
> #----------------------------------------------------------------------
> >>>>
> >>>> def send_lldp (packets):
> >>>> for dp in packets:
> >>>> # if they've left, ignore
> >>>> if not dp in self.dps:
> >>>> continue
> >>>> try:
> >>>> for port in packets[dp]:
> >>>> #print 'Sending packet out of
> >>>> ',longlong_to_octstr(dp), ' port ',str(port)
> >>>> self.send_openflow_packet(dp,
> >>>> packets[dp][port].tostring(), port)
> >>>> yield dp
> >>>> except Exception, e:
> >>>> # catch exception while yielding
> >>>> lg.error('Caught exception while yielding'+str(e))
> >>>>
> >>>> def build_lldp_generator():
> >>>>
> >>>> def g():
> >>>> try:
> >>>> g.sendfunc.next()
> >>>> except StopIteration, e:
> >>>> g.sendfunc =
> >>>> send_lldp(copy.deepcopy(self.lldp_packets))
> >>>> except Exception, e:
> >>>> lg.error('Caught exception from generator
> '+str(e))
> >>>> g.sendfunc =
> >>>> send_lldp(copy.deepcopy(self.lldp_packets))
> >>>> self.post_callback(self.lldp_send_period, g)
> >>>> g.sendfunc = send_lldp(copy.deepcopy(self.lldp_packets))
> >>>> return g
> >>>>
> >>>> self.post_callback(self.lldp_send_period,
> >>>> build_lldp_generator())
> >>>> self.post_callback(TIMEOUT_CHECK_PERIOD, lambda :
> >>>> discovery.timeout_links(self)
> >>>
> >>> --
> >>> Alec Story
> >>> Cornell University
> >>> Biological Sciences, Computer Science 2012
> >>>
> >>> _______________________________________________
> >>> nox-dev mailing list
> >>> nox-dev@noxrepo.org
> >>> http://noxrepo.org/mailman/listinfo/nox-dev_noxrepo.org
> >>>
> >>
> >
> >
> >
> > --
> > Alec Story
> > Cornell University
> > Biological Sciences, Computer Science 2012
> >
> > _______________________________________________
> > nox-dev mailing list
> > nox-dev@noxrepo.org
> > http://noxrepo.org/mailman/listinfo/nox-dev_noxrepo.org
> >
> >
>
--
Alec Story
Cornell University
Biological Sciences, Computer Science 2012
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