Re: Setting MTU size for ppp0
Hi Sven
On Sun, 2005-02-27 at 02:23 +0100, Sven Nielsen wrote:
> PROBLEM IS: my attempts to limit MTU to 1412 are ignored.
> tried adding "mtu 1412" to
> /etc/ppp/peers/dsl-provider
> /etc/ppp/options
>
> still, after reboot or after poff -> ifdown -> ifup -> pon dsl-provider, ifconfig always reports ppp0 with
> MTU: 1492. Also tried #pppd noauth mtu 1412 while ppp0 is already active, no effect.
I found a similar thing happening. I did find that doing
ifconfig ppp0 mtu xxx
seemed to work. Set it to 576 or something really low when your testing
just to see :) Anyway, I'm not 100% sure this works as advertised (it
does change the MTU as reported by pppd), but it seemed to work for me.
Digging a little deeper, I found that, by default, pppoeconf sets up the
kernel-mode pppoe driver, using the roaring penguin pppd plugin. Under
this setup it seems to resist listening to any pppd specified MRU/MTU
values.
If, in /etc/ppp/peers/dsl-provider, you comment out the "plugin
rp-pppoe.os eth0" line like so:
#plugin rp-pppoe.so eth0
and uncomment
pty "/usr/sbin/pppoe -I eth0 -T 80 -m 1412"
which should be near the top of the file, pppd uses the user-space pppoe
driver instead. And then I find that setting the MRU/MTU in is honoured,
though I don't think there is a good reason to set it to anything other
than 1412, since the pppoe driver will be clamping it to 1412 anyway.
Actually, the config is very confusing. All the documentation I found
seemed to imply that the user space deamon will be used by default,
while it is definitely not the case!
> Is some other script overriding my attempts ?
> Anybody any clue why setting MTU is ignored ??
See above :)
> Thanks for the help !
Hope this helps!
> wunderful linux :-) . BTW, using Ubuntu AMD64 (in native 64bit-mode) with self-compiled 2.6.x kernel.
I'm jealous haha. I actually do computational stuff for a "living" (as a
PhD student), and multi-gig memory using simulations aren't all that
uncommon... 64 bits would be sweet.
Cheers
Neilen
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