Hi Guanyao-- For (1), I expect that the CRC is counted in the stats on the switch, but not by pcap. It is a 4 byte "checksum" (actually, cyclical redundancy check) attached at the L2 layer. This is a frequent problem with counting bytes on Ethernet switches.
I'm not sure about (2). Flows expire and it can sometimes be hard to know what's there when a packet hits the switch. It could also be something particular about your hardware setup. What hardware are you using? -Dan On 1/26/10 1:09 PM, Guanyao Huang wrote:
Hi I am running on my own nox module on a topology of 5 switches. I find two phenomena: 1, The byte number of every packet read from statistics is always 4 bytes larger than the real size. If pcap shows the packet is of size N, ./dpctl dump-flows will show a size of N+4. So, if we query statistics, it is also N+4. I want to know why there is a difference of 4? 2, I found that sometimes packets can also get redirected without an entry in flow table, or, the switch has a bug to show the correct flow table. When I tcpreplay from one host to another one, packets get redirected (tcpdump shows so), but ./dpctl dump-flows shows no entry. Even if the flow is so short to get counted as 0 size (first packet get lost), an entry should still exist. However, if I ping between these two hosts and then tcpreplay, the entries will show correctly. Is there any possible reason why flows get redirected but an entry is not there? Many thanks. _______________________________________________ openflow-discuss mailing list [email protected] https://mailman.stanford.edu/mailman/listinfo/openflow-discuss
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