#14148: Custom MTU for PPPoE connection is set for Ethernet adapter too
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Reporter: alexatkinuk | Owner: developers
Type: defect | Status: new
Priority: normal | Milestone: Barrier Breaker 14.07
Component: packages | Version: Trunk
Resolution: | Keywords: pppoe mtu
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Comment (by Vortify12):
I can't believe that this ticket is a year old and still has not been
fixed. the MTU setting in /etc/config/network , affects the interface
itself rather than only applying to pppoe. then the script in
/lib/netifd/proto/ppp.sh , reads the value and set it for both MTU and MRU
of the pppoe connection. this is very wrong and problematic. for starters,
the applied MTU to the pppoe interface, is always 8 bytes lower that whats
been set(luckily the pppd daemon is smart enough to figure that out), also
there is absolutely no guarantee that MRU value is always the same as MTU.
there also could be different pppoe instances on a same interface which
you would have no way of separating MTU/MRU for each of them. not only
that, why would i want to limit my ethernet interface throughout just
because i have to limit my MTU/MRU of a pppoe interface on that link? i
could be using that interface for other purposes as well.
In conclusion, we indeed need separate set of settings for pppoe MTU/MRU
values.
Even pppd engine is not happy when you directly change your ethernet MTU
as can be observed in the log:
{{{
daemon.err pppd[3744]: Interface eth0.2 has MTU of 1488 -- should be at
least 1500.
daemon.err pppd[3744]: This may cause serious connection problems
}}}
also, default values for MTU/MRU for pppoe, should be set to 1480 (this
does not include the pppoe overhead obviously)
--
Ticket URL: <https://dev.openwrt.org/ticket/14148#comment:3>
OpenWrt <http://openwrt.org>
Opensource Wireless Router Technology
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