MTU settings.

[Sten Daniel Soersdal]

eternityos at free.fr wrote:
> 
> Hi everyone :)
> 
> Recently, we changed our internet connection to a ppp based (2Mbps).
> So naturaly, I thought about changing the MTU of my interfaces on the FreeBSD
> NAT router.
> So I set it to 576 instead of the default, 1500 on the two interfaces, LAN and
> WAN.
> In what I have seen, 576 is the natural mtu for a ppp connection.

1500 is the natural mtu for ppp (lesser mtu sizes are the exception).
You also contract a wide range of hard to diagnose problems, if you are
not familiar with diagnosing mtu problems.

> 
> Right away after this change, the internet connection blocked. I only got it
> back setting the mtu back at 1500.
> 
> Why did this block ?
> Between the modem and the NAT router, we have a cisco router, I didn't change
> it's mtu yet, would it be the cause ?

It has to be negotiated during connection. ppp is a protocol which
preferres the same settings on both ends of the ppp connection. Or
atleast compatible ones.


-- 
Sten Daniel Soersdal