[Techtalk] 2nd networking question

coldfire rolick571 at duq.edu
Fri Aug 30 15:49:12 EST 2002

> > Yeah I understand that I can ping with 1474 but not 1475 as the
> > argument and I know that this goes over the 1500 mark. But is this the
> > MTU setting which is limiting this?
> In general, if you do not set the MTU lower, this won't cause many
> problems, since every time you send a packet that is too big to pass over
> the PPPoE tunnel an ICMP packet will be sent back to your machine telling
> it that it must fragment the packet.  All this will do is reduce the
> performance slightly.
> However in some cases these packet too big messages won't be sent, and the
> packet that is too large will be silently dropped.  To complicate things
> further there are many sites on the internet at large who block these
> ICMP_MUST_FRAGMENT packets.  So when they send a 1500 byte packet towards
> you, the other end of the tunnel sends back the message that it's too big,
> which is discarded, and the other site never knows it sent a packet that
> was too big and sits there waiting

which is why pppoe is evil.

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