I am confused about the length of TX_ACK messages


(Traberry) #1

I captured some messages using Wireshark in network server. I found something strange in the length of TX_ACK message showed in the Wireshark.


There are lots of “0” added in the payload. However, the payload data should only be “02 f3 58 05 aa 55 5a 00 00 00 00 00” as source code.

Forgive the red and ugly handwrriting. :joy:


(Dion Dokter) #2

Some versions of the Ethernet protocol require network packets to be padded so they are at least 64 bytes.


(Traberry) #4

Thanks for your attention.
The minimum Ethernet frame length is 64 bytes, 10 bytes of ‘0’ added is enough for this message. However, it adds 46 bytes of ‘0’ in which I am confused.


(Arjan) #5

Why?

You’re saying "the payload data should only be “02 f3 58 05 aa 55 5a 00 00 00 00 00 as source code”, being 12 bytes. How would only adding 10 bytes yield 64 bytes then? And what does “as source code” mean?

Also, the screenshot doesn’t even show these bytes that you mention.

In short: confusing question.


#6

Guess this means that topic starter took a look at packet forwarder source code.

Yea, and the “length” field of UDP header is set to 72 (0x48) - 8 bytes for header and 64 for data.
What version of packet forwarder do you use?