1472 is the maximum ICMP payload size for standard Ethernet. 1480 fails because, well, it is > 1472.
-- () ascii ribbon campaign against html e-mail /\ www.asciiribbon.org >-----Original Message----- >From: Deric Kwok [mailto:deric.kwok2...@gmail.com] >Sent: Wednesday, 23 June, 2010 12:53 >To: nanog list >Subject: pls help about mtu setting again > >Hi > >Thank you for your reply about DSL mtu > >Now I have question about internet cable connection. ls it same as DSL? > >I tested it in my friend cable connection. > >1470 is fine but 1480 is problem. Why it needs header in cable connection >also? > >C:\Documents and Settings\deric>ping yahoo.com -f -l 1470 > >Pinging yahoo.com [98.137.149.56] with 1470 bytes of data: > >Reply from 98.137.149.56: bytes=1470 time=96ms TTL=50 >Reply from 98.137.149.56: bytes=1470 time=91ms TTL=50 >Reply from 98.137.149.56: bytes=1470 time=92ms TTL=50 >Reply from 98.137.149.56: bytes=1470 time=89ms TTL=50 > >Ping statistics for 98.137.149.56: > Packets: Sent = 4, Received = 4, Lost = 0 (0% loss), >Approximate round trip times in milli-seconds: > Minimum = 89ms, Maximum = 96ms, Average = 92ms > >C:\Documents and Settings\deric>ping yahoo.com -f -l 1480 > >Pinging yahoo.com [98.137.149.56] with 1480 bytes of data: > >Packet needs to be fragmented but DF set. >Packet needs to be fragmented but DF set. >Packet needs to be fragmented but DF set. >Packet needs to be fragmented but DF set. > >Ping statistics for 98.137.149.56: > Packets: Sent = 4, Received = 0, Lost = 4 (100% loss), > >Thank you for your help
