Inspired by some PMs with
snadge about getting full 1500 MTU on these devices when used as a router I have found a few things out after putting an 8324 on my line as a full router with stock firmware.
The commands required with unmodified firmware are as follows:
ifconfig ptm0 mtu 1508
ifconfig ptm0.1 mtu 1508
This will cause the ppp session to break, timeout and reconnect. The process takes 2.5 – 3 minutes and you will lose internet connectivity but
not sync.
After the new ppp session is created it must be changed:
ifconfig ppp2.1 mtu 1500
At least with my testing (many times) this always resulted in successful 1500 byte pings. One caveat is that when quickly changing between them it is sometimes required to disable and re-enable your networking adapter to get accurate results with the ping test (on linux at least).
This leads me to the conclusion that even if using the devices as routers the modified firmware is desirable as no drop and wait for reconnect of the ppp session is required. Of the two modifications one is to bring up all the ptm interfaces with 1508 MTU by default, so only the instant “ifconfig ppp2.1 mtu 1500” is required, which is what I believe
spring was talking about all along.
Given this single command that causes no loss of session or sync is all thats required with the baby jumbo frames patches applied I thought I would make a firmware with the most basic of scripts to check the current MTU and change if required:
#!/bin/bash
waitTime=60
interface="/sys/devices/virtual/net/ppp2.1/mtu"
sleep 50
while [ 1 ]
do
if [ -f $interface ]
then
currentMtu=`cat $interface`
if [ $currentMtu -eq 1492 ]
then
echo 1500 > $interface
fi
fi
sleep $waitTime
done
Just tests the if the interface exists and if so checks for 1492 and changes to 1500. Couldnt be simpler.
I would have liked to change the ppp negotiation so it comes up at 1500 be default but after a decent amount of trying could not. I tried changing the GUI so 1500 was accepted and changing all references to the 1492 limit in the pppd program to no avail. I suspect (as always) that one of the closed source binarys supplied that takes the value from the web interface and supplies it to the pppd program/commits it to config has its own checks that default to 1492.
So, for anyone running an 8924/8324 as a full router (can make one for 1312s but doubt people are using them in this way) this firmware has the jumbo frames patches and the script above running from boot:
https://www.dropbox.com/s/b7b5gwzwteysk9t/8924-B10A-AAKL24-router1500.bin?dl=0Have flashed to my 8324, connected to a line and it works as intended, but as always you are flashing at your own risk.
Any questions please ask!