Subject: Re: NetBSD vs. PPPoA (with native IPv6)
To: None <>
From: Matthias Scheler <>
List: regional-london
Date: 09/14/2006 21:53:46
On Wed, May 03, 2006 at 03:29:18PM +0100, Matthias Scheler wrote:
> ... and allows me to use AAISP's support for native
> IPv6 over DSL connections (without any tunneling).

I found a problem with native IPv6 over PPPoA today:
The MTU is for some reason not properly set on the bridged PPPoE/PPPoA
connection. One usually doesn't notice that with IPv6 because a lot
of the network uses tunnel with MTUs smaller than ethernet.

When I however tried to download a test file from one of AAISP's
server with "wget -6" today the connection hung. Because there is
apparently only ethernet and PPPoA between my router and that system
it was sending full ethernet MTU sized IPv6 packets. But those packets
never made it over my DSL link. And the ADSL2MUE cannot send ICMP
packets (besides not understanding IPv6 it doesn't have a public IP
address assigned) back to tell the sender to reduce its TCP maximum
segment size.

The fix was to use more severes MSS clamping. My router now clamps
the MSS of TCP connection to 1420 bytes and both IPv4 and IPv6
TCP connections work fine.

	Kind regards

Matthias Scheler