Non riesco a modificare l'MTU !

TCP options string = 020405980103030201010402
MTU = 1472
MTU is not fully optimized for broadband. Consider increasing your MTU to 1500 for better throughput.
MSS = 1432
MSS is not fully optimized for broadband (although it might work well for slower connections). Consider increasing your MTU value.

Default Receive Window (RWIN) = 256960
RWIN Scaling (RFC1323) = 2 bits (scale factor of 4)
Unscaled Receive Window = 64240

For optimum performance, consider changing RWIN to a multiple of MSS.
Other values for RWIN that might work well with your current MTU/MSS:
504064 (MSS x 44 * scale factor of 8)
252032 (MSS x 44 * scale factor of 4)
126016 (MSS x 44 * scale factor of 2)
63008 (MSS x 44)
bandwidth * delay product:

Your RcvWindow limits you to: 10278.4 kbps (1284.8 KBytes/s) @ 200ms
Your RcvWindow limits you to: 4111.36 kbps (513.92 KBytes/s) @ 500ms
MTU Discovery (RFC1191) = ON
Time to live left = 58 hops

TTL value is ok.
Timestamps (RFC1323) = OFF
Selective Acknowledgements (RFC2018) = ON
IP type of service field (RFC1349) = 00000000