If a packet from Host 1 is forwarded across four switches, how do you know
which one was the first one where Host 1 is actually attached and not just some
non-first switch?
There may not be a super easy answer to this question. POX's host_tracker
component attempts one possible solution to this issue. A simple possibility
is to use openflow.discovery to figure out which ports are "edge" ports and
which ports connect switches to other switches. Only "learn" a host position
at an edge port.
-- Murphy
On Jul 8, 2013, at 2:50 PM, nibble nibble wrote:
>
> I am creating a topology with two switches and each switch has 4 hosts(the
> code for creating the topology is included). Then I have a script for pox
> learning which process each received packet and try to figure out each host
> is connected to which one of the switches(the code is included).
>
> When I ping two hosts inside the same switch, the code is working perfectly,
> but if I do "n1 ping n6 -c1"
> it does not return the correct switches. For example this is the result:(I
> can also include the complete code)
>
>
>
> host 1
> switch 1
> [ 1. 0. 0. 0. 0. 0. 0. 0.]
>
> host 1
> switch 2
> [ 2. 0. 0. 0. 0. 0. 0. 0.]
>
> host 6
> switch 2
> [ 2. 0. 0. 0. 0. 2. 0. 0.]
>
> host 6
> switch 1
> [ 2. 0. 0. 0. 0. 1. 0. 0.]
>
>
>
>
>
>
>
> Creating topology:
>
> Class MyTopo(Topo):
> def __init__(self, enable_all = True):
> setLogLevel('info')
> super(MyTopo, self).__init__()
>
> self.switch1 = self.addSwitch('s1')
> self.switch2 = self.addSwitch('s2')
> n = 0
> for h in range(4):
> n += 1
> host = self.addHost('n%s' % (n))
> self.addLink(host, self.switch1)
> for h in range(4):
> n += 1
> host = self.addHost('n%s' % (n))
> self.addLink(host, self.switch2)
> self.addLink(self.switch1, self.switch2)
>
>
>
> Processing packets:
>
> packet = event.parsed
> ip = packet.find('ipv4')
> if ip is not None:
> parts = (str(ip.srcip)).split(".")
> lp = parts[3]
> log.info("host %s" % lp)
> log.info("switch %s" % event.dpid)
> hosts[int(lp) - 1] = event.dpid
>
>
>
