Are you authenticating with PPPoE? If so, it has a maximum MTU size of 1492 due to the encapsulation overhead. --- Tom Pipes T6 Broadband/ Essex Telcom Inc tom.pipes@t6mail.com ----- Original Message ----- From: "William Herrin" <bill@herrin.us> To: "Deric Kwok" <deric.kwok2000@gmail.com> Cc: "nanog list" <nanog@nanog.org> Sent: Thursday, June 17, 2010 8:36:00 AM Subject: Re: pls help about mtu setting On Thu, Jun 17, 2010 at 8:19 AM, Deric Kwok <deric.kwok2000@gmail.com> wrote:
My DSL company asks me to set the modem 146 2 and my old company used 14 92 Why it is not standard 1 500?
Because they're wrapping your packet inside another packet that they then transmit on a line with a 1500 byte MTU. The header on their packet needs a few bytes, so you can't have them. Regards, Bill Herrin -- William D. Herrin ................ herrin@dirtside.com bill@herrin.us 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004