Re: [LARTC] Patch to allow for the ATM "cell tax"

[Andy Furniss <andy.furniss@dsl.pipex.com>]

gentoo@databit7.com wrote:
> 
> On netBSD setting the MTU also seems to set the MRU, is this the case 
> here to? should people have thier DSLAMs configured for the same MTU?

It doesn't set MRU - you can still receive a larger than MTU packet.

I guess what you mean is MSS, if so yes Linux and Windows TCP also 
choose what tcp MSS to advertise by looking at the MTU on the interface. 
This means you get the tweak both ways. If you can't change each LAN PC 
then you can do it with Linux iptables set mss, you can make it 
aysymmetric and have min limits this way aswell.

The DSLAM is at the exchange. Doing it on the router by setting MTUs can 
cause problems and isn't as good as doing each client/clamping. If you 
set the LAN facing interface of the router to less than the clients all 
the websites/networks that set DF and don't respond to ICMP frag needed 
  will expose their brokenness.

FWIW the only time I see MRU is when I log on (pppoa) to my dsl 
connection. The other end asks for 32725 so the MTU on my ppp0 gets set 
to 32725 - it's lucky I can't really use it and tc doesn't pick up on 
it, though the mtu bit of the atm/dsl hack I use hardcodes it.

Andy.
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