hardware loop and frame length increase

[Martin T <m4rtntns () gmail com>]

I made a RJ45 hardware loopback connector(connected Tx- with Rx+ and
Tx+ with Rx-), connected this to my eth2 port, configured
192.168.88.0/24 to eth2 and executed:

"ping -i0.1 -c3 192.168.88.88"

..while running tcpdump like this:

root@martin-desktop:~# tcpdump -n -i eth2 -e -v -XX
tcpdump: listening on eth2, link-type EN10MB (Ethernet), capture size 96 bytes
01:54:06.148476 00:15:17:26:7c:ca > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 42: Ethernet (len 6), IPv4 (len 4), Request who-has
192.168.88.88 tell 192.168.88.0, length 28
        0x0000:  ffff ffff ffff 0015 1726 7cca 0806 0001  .........&|.....
        0x0010:  0800 0604 0001 0015 1726 7cca c0a8 5800  .........&|...X.
        0x0020:  0000 0000 0000 c0a8 5858                 ........XX
01:54:06.148745 00:15:17:26:7c:ca > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Request who-has
192.168.88.88 tell 192.168.88.0, length 46
        0x0000:  ffff ffff ffff 0015 1726 7cca 0806 0001  .........&|.....
        0x0010:  0800 0604 0001 0015 1726 7cca c0a8 5800  .........&|...X.
        0x0020:  0000 0000 0000 c0a8 5858 0000 0000 0000  ........XX......
        0x0030:  0000 0000 0000 0000 0000 0000            ............
01:54:07.148479 00:15:17:26:7c:ca > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 42: Ethernet (len 6), IPv4 (len 4), Request who-has
192.168.88.88 tell 192.168.88.0, length 28
        0x0000:  ffff ffff ffff 0015 1726 7cca 0806 0001  .........&|.....
        0x0010:  0800 0604 0001 0015 1726 7cca c0a8 5800  .........&|...X.
        0x0020:  0000 0000 0000 c0a8 5858                 ........XX
01:54:07.148740 00:15:17:26:7c:ca > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Request who-has
192.168.88.88 tell 192.168.88.0, length 46
        0x0000:  ffff ffff ffff 0015 1726 7cca 0806 0001  .........&|.....
        0x0010:  0800 0604 0001 0015 1726 7cca c0a8 5800  .........&|...X.
        0x0020:  0000 0000 0000 c0a8 5858 0000 0000 0000  ........XX......
        0x0030:  0000 0000 0000 0000 0000 0000            ............
01:54:08.148482 00:15:17:26:7c:ca > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 42: Ethernet (len 6), IPv4 (len 4), Request who-has
192.168.88.88 tell 192.168.88.0, length 28
        0x0000:  ffff ffff ffff 0015 1726 7cca 0806 0001  .........&|.....
        0x0010:  0800 0604 0001 0015 1726 7cca c0a8 5800  .........&|...X.
        0x0020:  0000 0000 0000 c0a8 5858                 ........XX
01:54:08.148738 00:15:17:26:7c:ca > ff:ff:ff:ff:ff:ff, ethertype ARP
(0x0806), length 60: Ethernet (len 6), IPv4 (len 4), Request who-has
192.168.88.88 tell 192.168.88.0, length 46
        0x0000:  ffff ffff ffff 0015 1726 7cca 0806 0001  .........&|.....
        0x0010:  0800 0604 0001 0015 1726 7cca c0a8 5800  .........&|...X.
        0x0020:  0000 0000 0000 c0a8 5858 0000 0000 0000  ........XX......
        0x0030:  0000 0000 0000 0000 0000 0000            ............
^C
6 packets captured
6 packets received by filter
0 packets dropped by kernel
root@martin-desktop:~#

As you can see, every second I sent and received one frame. The
question is, why is the frame, which I receive, 18 bytes longer than
the one I sent? I mean what are those 144 0-bits at the end of the
each frame back from the hardware loop?

PS hopefully it's the correct mailing list to post such questions =)

regards,
martin
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