Subject: Re: Networking question MTU on non-local nets
To: None <port-macppc@netbsd.org>
From: Don Lee <MacPPC@caution.icompute.com>
List: port-macppc
Date: 06/16/2003 17:54:22
At 4:19 PM -0400 6/16/03, gabriel rosenkoetter wrote:
>On Sat, Jun 14, 2003 at 10:59:28AM -0500, Donald Lee wrote:
>> If you hit a small packet router (i.e. PPPoE, VPN, etc) the fragmented
>> or oversized packets effectively get silently dropped.  This behavior has to be
>> MI, and it's hard to believe that no one has run into this.
>
>If the ICMP responses to your DF bit are getting dropped, there's a
>firewall in violation of RFC 2979 between you and the host you're
>trying to reach.

I jumped the gun on this.  "The Problem" actually has to be a
combination of such a "small MTU" link *and* something busted,
as you point out.

It turns out that RFCs 1122 and 1191 strongly imply that the MTU
on a non-local connection should be reduced to the neighborhood
of 576 bytes, which NetBSD 1.6.1 does, and 1.5.2 does not.


For the record, my Japanese friend can now access my server, now
that I'm using PMTU-D.  All is well.

Again, thank you all for your help.

-dgl-