My first answer is always to try a more recent version of POX (carp or dart) and see if things are just magically better.
-- Murphy On Jun 15, 2014, at 11:16 PM, Farzaneh Pakzad <f.pak...@uq.edu.au> wrote: > Hi all, > > I have been experiencing unexpected loss of LLDP packets when running > discovery.py in POX, for different tree topologies in Mininet. > The loss only starts to occur for a network size of more than ~20 switches, > and seems to happen between a pair of switches. > There is no other traffic on the network, and no other application running in > POX. > > Below are some more details. > > I have made a tree topology with depth 5 and fanout 2 which means that we > have 31 switches and 32 host. As I understand, in discovery.py the controller > sends packet_out messages to all switches, instructing them to send a LLDP > packet via each of its ports. When an LLDP packet is received by a switch at > the other end of the link, the switch sends a packet_in message to the > controller, and the controller can detect a link between these two > switches/ports. > > Based on this, the controller should receive 2 packet_in messages for each > link in the network, one for each direction. > In my experiments, this works fine for small networks of < 20 switches. > However, for larger networks, I’m starting to see a lower than expected > number of packet_in messages received at the controller. > For example in our example tree topology, the controller should receive 60 > packet_in messages during a single topology discovery round, but consistently > only gets 55-58. > > I’ve used wireshark to investigate where the packet loss occurs, and it looks > like some LLDP packets are lost in transit between switches. > > An example is shown below. The first example shows a case without packet > loss, i.e. we see the packet_out message, the corresponding LLDP packet at > the sender side and at the receiver side, and the corresponding packet_in > message. > > The case with both packet_out and In: > OFP+LLDP 133 Packet Out (CSM) (67B) => Chassis Id = dpid:19 Port Id = > 1 TTL = 120 > LLDP 43 Chassis Id = dpid:19 Port Id = 2 TTL = 120 (sender side) > LLDP 43 Chassis Id = dpid:19 Port Id = 2 TTL = 120 (reciever side) > OFP+LLDP 127 Packet In (AM) (61B) => Chassis Id = dpid:19 Port Id = 2 > TTL = 120 > > The following example shows the same thing, with the difference that the LLDP > packet is sent but not received: > > The case that packet_In lost: > OFP+LLDP 133 Packet Out (CSM) (67B) => Chassis Id = dpid:19 Port Id = 1 > TTL = 120 > LLDP 43 Chassis Id = dpid:19 Port Id = 2 TTL = 120 (sender side) > > As mentioned, there is no other traffic, and the load on each link is only 2 > LLDP packets, one in each direction, and links are configured to be reliable, > so as far as I understand, there should be no packet loss. > > I’m using the following software: > > Mininet version 2.0 > POX version betta > > My questions is: Has anybody experienced similar problems, or does anybody > have an idea of what the problem could be? > Any help would be greatly appreciated. > > > Best regards, > Farzaneh
