# iftop shows no traffic, tcpdump shows lots of traffic



## darkpixel (Feb 26, 2020)

I have a FreeBSD box with interface ix1 plugged into a SPAN port on our switch.
If I run `tcpdump -i ix1 -v` I get a flood of output.  There's several hundred mbit of traffic running past that interface every second.
If I run `iftop -i ix1` the screen shows nothing. 0 bytes for transmit, receive, and total.
I also tried `iftop -p -i ix1` with the same results.

The interface is up and in promiscuous mode.

I have a very similar box with slightly different network cards and plugging it in and running `iftop -i igb1` shows what I would expect.

Am I missing something?


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