Massimo Senna, asked about the matter, reports: "I tried disconnecting the router and network to make a direct connection with the modem provided by TIN and I have no problem: the PPPoE automatically switches the MTU to 1492, probably the tin server correctly send this information and others not. The MTU in practice the maximum size of the TCP / IP packets, normally with PPPoE the value 1492 is used, while on the ethernet 10/100 the standard value 1500. If I am not mistaken the choice of this value is also part of the data that changes PPPoE clients and servers when logging in … usually.
sudo ifconfig ppp0 mtu 1492
does nothing but force the MTU value to 1492
To find out the active MTU value, AFTER activating the basic connection, enter from the terminal:
such a result should be obtained (this derives from the connection to TIN, the mtu 1492 without needing any other command):
if the MTU not 1492 can be forced with:
sudo ifconfig ppp0 mtu 1492
But, you should actually type it after each connection.
Since, if I'm not mistaken, the PPPoE client is part of Darwin (= open source) you could check the source to understand what happens and if possible always force the right value, without automatic selection)
We invite our readers to experiment with the various providers and see who MacOSX uses the wrong MTU value for.
Anyway, to summarize:
– do not change anything and set PPPoE normally – activate the connection and wait for it to be active – open the terminal – type:
– if the answer contains' mtu 1492 'then all is well, there is nothing to change – if the answer contains' mtu 1500' '_E_ the connection speed seems low, then you can try typing:
sudo ifconfig ppp0 mtu 1492– at this point if the performances improve then this modification is necessary, if they remain as they are and useless.
Unfortunately, too many tips of this type are circulating and there are people who 'type' everything without knowing what they are doing.I would add a tip: if you are not 100% sure of the source, NEVER give any terminal containing 'sudo' from the terminal. "
Taking advantage of the latter advice, however, we would like to point out a script, created by our reader Pierpaolo Fantauzzi that avoids, in case you need to enter the command on MTU to avoid problems with attachments by mail via Airport, to do it from the terminal. :
"I am writing to inform you of a small problem under Mac OS X 10.2, I believe it has already been dealt with, that is, the impossibility with an Air port commission to send attachments via email … the solution is to type a small command from the Terminal sudo ifconfig en1 mtu 1492v or if you prefer a small, but really small utility it does it for you without too many pretensions … made for a friend of mine who had submitted the problem. You can download it from the sharing section of this page. "