good evening gentlemen!

i'm doing a presentation about wireless security for my study. right now i'm trying to crack my WPA-PSK secured WLAN. i'm capturing the eapol handshake with wireshark with a filter for eapol. in the tutorials if read people talk about 4 frames. but i get six eapol frames.

when i start aircrack with the file i get the following:
$ sudo aircrack-ng -a 2 -w words.txt eap4.cap 
Opening eap4.cap
This file is not a regular 802.11 (wireless) capture.
Read 0 packets.

No networks found, exiting.
i found out that the first 4 are for the pairwise master key and the other two for the group key. i tried with the first 4 but got the same error.

Does anyone know how the format of the handshake file has to be for aircrack?

i know there are other ways to get the handshake (airodump) but i want to do it that way