hping, fragmented packet

[np2k]

Hi all! I've a question.

if i digit this:

hping -m 32 --data 140 -c 1 localhost

(with an mtu = 32byte) i have, this output

HPING localhost (lo 127.0.0.1): NO FLAGS are set, 40 headers + 140 data bytes
len=40 ip=127.0.0.1 ttl=64 DF id=0 sport=0 flags=RA seq=0 win=0 rtt=0.3 ms

--- localhost hping statistic ---
1 packets tramitted, 1 packets received, 0% packet loss
round-trip min/avg/max = 0.3/0.3/0.3 ms

I RECEIVED the response packet!

but if i digit:

hping -m 30 --data 140 -c 1 localhost

(an mtu = 30)

the output is:

HPING localhost (lo 127.0.0.1): NO FLAGS are set, 40 headers + 140 data bytes

--- localhost hping statistic ---
1 packets tramitted, 0 packets received, 100% packet loss
round-trip min/avg/max = 0.0/0.0/0.0 ms

i.e: I don't receive packet....WHY? WHY? WHY?

[Kloschüssel]

Do you know what MTU is and how routers behave if it is set to values so small that the packet header can't be sent in one transmission unit but becomes sliced and the router drops the packet cause it is no longer valid for him?

Normal MTU values nowadays are somewhere around 1500 to 9000 depending on your network hardware (ethernet, gigabit ethernet, ..) but surely not 30 bytes. You would produce more header traffic than packet payload.