[USRP-users] USRP x310 does not reply to IP packets of odd length?

Hrishikesh Shelar hshelar at umich.edu
Wed Oct 8 14:45:37 EDT 2014


Hey all,

I was observing some weird behavior while testing out transfer of IP
packets to and from the USRP. It seems as though the USRP can't correctly
parse packets that are odd in length. I was seeing odd length packets leave
my machine (using wireshark) but failed to see my custom USRP logic react
accordingly. Everything works if packets are even in length. At first I
thought it was a problem with my logic but I ran extensive testbenches and
couldn't pinpoint the error. So I decided to the USRP itself without my
logic in it and observed the same behavior. Using wireshark to sniff the
packets here is what I observed: (my USRP IP is 192.168.1.3)

>From a Windows terminal

ping 192.168.1.3 works
ping -l 512 192.168.1.3 works; reply packets are also 512 bytes long
ping -l 513 192.168.1.3 doesn't work: wireshark reports reply packets are
60 bytes long
ping -l 5 192.168.1.3 doesn't work: wireshark reports reply packets are 60
bytes long

Any odd length doesn't work.

>From a Linux terminal

ping 192.168.1.3 works
ping -s 512 192.168.1.3 works: reply packets are 520 bytes long
ping -s 513 192.168.1.3 doesn't work: wireshark reports reply packets are
60 bytes long
ping -s 5 192.168.1.3 works; reply packets are 60 bytes long

Any odd length above 17 doesn't work.

Any clue as to why this is happening? Also it seems as though the USRP
nominally uses packets that are even in length so this error wouldn't have
come up before?

Thanks,
Hrishikesh Shelar
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