mesh.cc PCAP shows no UDP traffic

[JTL]

Hi folks,

I noticed a bizarre behavior when I ran the mesh.cc as it is with pcap trace on.  There is no UDP traffic from Node 9 to 0 (as it should be according to the configuration).

Wha't weird is when I set the UDP client to anything from node 1 to node 8, the UDP traffic was captured as expected.

I am using release 3.25.

I have attached the PCAP files here: 

• mp-9--8-1.pcap has UDP echo client on Node9 and server on 0
  
• mp--8-1.pcap has UDP echo client on Node8 and server on 0

Is this a bug? or am I missing something?

Thanks

JT

[JTL]

Sorry, I meant node 8 when I said node 9... mesh.cc creates a 3x3 mesh... node # from 0 to 8. Mac from 01-09. with 0 being UDP echo server and 8 being UDP echo client

[Tommaso Pecorella]

Hi,

I strongly suspect that Wireshark isn't able to decode properly the mesh headers.

It could be a bug in Wireshark OR in ns-3. Feel free to investigate, and in case one a bug on our bugzilla.

Thanks,

T.

[Jung-Tao Liu]

Hi T,

Thanks for the inputs. 

I tried replacing EchoServer-Client app with the PING application, the outcome is the same. 

One observation: For the PCAPs with Client installed on Node8, you can see periodic ARP packets from Node 0 to find route to Node 8, for example at time 164.989813.  A check on the PCAP files from neighboring nodes, reveal no such ARP packets being captured. While for the node 7 case, the ARP are received and passed-on by the neighbors.

PCAPs for all 9 nodes are included in two tar files attached, one with client on last mesh node (node8), the other with client on 2nd to the last mesh node (node7). 

Regarding the Wireshark not able to decode: shouldn't we expect the UDP message captured in PCAP the same across all nodes in NS3? 

The point being this:

The UDP is captured on all nodes (1-7) except node 8 (last node in the mesh grid) - Node 0 doesn’t count since it is the UDP Echo server. If it is the Wireshark decoding issue, the problem should probably be consistent no matter which node the UDP Echo client is installed.

Again, I may be missing something important here. Please let me know what you think. 

Thanks

JT

[Tommaso Pecorella]

Hi,

I didn't check the PCAPs, but if Wireshark is not decoding them right, then you should NOT trust them.

Use an ascii log and see what's being sent and received, then compare it with the PCAPs.

Cheers,

T.