detect tcp fragmented packets

Good morning.

does iptables' option "-f" reveal ip fragments or also tcp fragments?

My network does not work very well and i would like to discover if it is due
to
fragmentation in tcp header.

How can i detect tcp fragmented arriving packets to my machine?

If the problem was this, how could i find an example in linux kernel where
reassembling of fragments takes place?

Thanks a lot!
Giacomo