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 From:  Vincent Fleuranceau <vincent at bikost dot com>
 To:  m0n0wall at lists dot m0n0 dot ch
 Subject:  Re: [m0n0wall] R: [m0n0wall] VNC Problem
 Date:  Thu, 07 Oct 2004 14:22:47 +0200
-------- Original Message --------

> You need to change the MTU on the WAN side of your m0n0wall. The
> initiating computers should negotiate the MTU with the next hop.
> 
> Axel
> 

The question is: do Windows machines take this info into account? If I 
change the MTU for my PPPoE connection, on what interface will I notice 
the change on the status page?

Without changing the MTU, I have:

ng0: flags=88d1<UP,POINTOPOINT,RUNNING,NOARP,SIMPLEX,MULTICAST> mtu 1492
	inet A.B.C.D --> E.F.G.H netmask 0xffffffff

If I set it to a different (lower) value, I can see no change :-(

So, where can I look to see if the MTU has really changed?

More, in filter.inc:

	/* set up MSS clamping */
	$wanif = get_real_wan_interface();
	
	if ($config['interfaces']['wan']['mtu'])
		$mssclamp = $config['interfaces']['wan']['mtu'] - 40;
	else if ($config['interfaces']['wan']['ipaddr'] == "pppoe")
		$mssclamp = 1452;
	else
		$mssclamp = 0;
	
	mwexec("/sbin/sysctl net.inet.ipf.fr_mssif={$wanif}");
	mwexec("/sbin/sysctl net.inet.ipf.fr_mssclamp={$mssclamp}");


Does this portion of code concern NATed connections only or does it 
apply to every packet (including ESP trafic) passing through the WAN 
interface?

(see 
http://m0n0.ch/wall/list-dev/?action=show_msg&actionargs%5B%5D=0&actionargs%5B%5D=50)

Could someone explain?

-- Vincent