Apple Mac MTU change
The following applies to iBurst, but I am sure if you substitute the correct MTU size for Wimax, it should work (never tried this):
Setting MTU’s on an Apple OS.
These instructions assume you already have your iBurst modem set up and connected directly to your Mac with USB or Ethernet and have also connected to the Internet.
Temporary MTU Setting
If you experience poor download speed, websites that don't load, can't check email or any similar problem, try typing this into a Terminal window and press return:
sudo ifconfig ppp0 mtu 1352
You can find the Terminal application in the Utilities folder inside the Applications folder. You'll need an administrator password handy (probably the password you use to login to your Mac).
The iBurst documentation details how to change the MTU via System Preferences, which only allows changing the Ethernet interface (which will be something like en0 if you connect your iBurst modem by Ethernet cable, or en2 for USB cable). Instead you need to change the MTU for the PPPoE client AFTER you have connected to the Internet:
sudo ifconfig ppp0 mtu 1352
The default value of 1460 doesn't seem to work very well, however 1352 worked best for me. This command is not permanent. The MTU will change back to 1460 on restart.
If you connect the iBurst modem to a wireless router, you'll need to change the MTU settings on the router. For Apple AirPort Extreme/Express base stations this does not seem to be a problem (ie. it just works).
Where to change MTU in Apple's Airport Extreme configurator?
You can't. And as I mentioned you don't need to, it seems to work with iBurst anyway.
The best you can do is change the MTU for your Airport card which may or may not follow through to the base station's PPPoE client. The name of the Airport interface is probably en1, so you would type:
sudo ifconfig en1 mtu 1352
Mac OS 10.1.5 I. You can set the MTU manually/permanently in the terminal by typing:
Log in as root and launch the terminal. I used pico. Open the network file located at ...
/System -> Library -> Startup Items -> Network -> Network
and find the references to setting up your network interface.
Add a line and enter ifconfig en1 MTU 1352 for airport or ifconfig en0 MTU 1352 for Ethernet.
This needs to be done on ALL computers connected to the internet and sending email using iBurst. Restart your computer and you should now automatically be setup with an MTU of 1352 and emails should send correctly.
Mac OS X 10.2: How to Set the MTU Value during Startup
Use the procedure below to create a startup item script that sets the maximum transmission unit (MTU) value for your network interface(s). This may be required when using certain Internet service providers.
Note: This document applies to Mac OS X 10.2 through 10.2.8.
Important:
§ This document discusses an advanced procedure. If you are not familiar with command line interface and manual configuration in general, you should seek assistance. If you do not follow these steps precisely, the script may not work, which could prevent the computer from starting up normally.
Follow these steps to create a script that sets the MTU each time the computer restarts:
1. Open Terminal (/Applications/Utilities/).
2. Type: cd /Library
3. Press Return.
4. Type: mkdir StartupItems
5. Press Return. (If you encounter an error, continue to step 6.)
6. Type: cd StartupItems
7. Press Return.
8. Type: mkdir MTU
9. Press Return.
10. Type: cd MTU
11. Press Return.
12. Type: pico MTU
13. Press Return.
14. In the pico editor, paste in the following text.
Begin copying below this line.
--------------------------------------------------------------------------------
#!/bin/sh
. /etc/rc.common
##
# Configure a network interface MTU setting
##
#
# This script will set the MTU setting for the specified interface(s)
#
# The name of the interface (ex. en0) must be edited to match the interface
# to which the MTU setting should be applied
#
##
StartService ()
{
ConsoleMessage "Configuring MTU"
### uncomment lines and change the value following 'mtu' as appropriate
if [ "${MTU:=-NO-}" = "-YES-" ]; then
# /sbin/ifconfig en0 mtu 1352
# /sbin/ifconfig en1 mtu 1352
fi
}
StopService ()
{
return 0
}
RestartService ()
{
return 0
}
RunService "$1"
--------------------------------------------------------------------------------
End copying above this line.
15. Uncomment the /sbin/ifconfig line(s) to set the MTU for a particular interface.
Note: Removing the number sign (#) from the beginning of a line uncomments it. Typically, en0 is the interface name for the Built-in Ethernet port and en1 is interface name for the AirPort Card. This is not always the case, though. To confirm that a network port is associated with a particular interface name, open the Network Utility (/Applications/Utilities/), and click the Info tab.
16. When you have finished customizing the file, save it (press Control-O), press Return, and exit pico (press Control-X).
17. Type: chmod 755 MTU
18. Press Return.
19. Type: pico StartupParameters.plist
20. Press Return.
21. In the pico editor paste in the following text.
Begin copying below this line.
--------------------------------------------------------------------------------
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>Description</key>
<string>Can set MTU</string>
<key>OrderPreference</key>
<string>None</string>
<key>Provides</key>
<array>
<string>MTU</string>
</array>
<key>Requires</key>
<array>
<string>Network Configuration</string>
</array>
</dict>
</plist>
--------------------------------------------------------------------------------
End copying above this line.
22. When you have finished customizing the file, save it (Control-O), press Return, and exit pico (Control-X).
23. Type: chmod 755 StartupParameters.plist
24. Press Return.
25. Type: sudo pico /etc/hostconfig
26. When prompted, enter your password.
27. Press Return.
28. In the pico editor, add this line at the bottom:
MTU=-YES-
29. Save it (Control-O), press Return, and exit pico (Control-X).
When you restart the computer, MTU is set for the interface that you specified.
Notes
1. The MTU will be reset after changing a Location, waking the computer from sleep, or changing the state of the network interface. To use the script again without having to restart, enter the following command:
sudo SystemStarter start MTU
2. If you experience any issues or wish to not set MTU during startup, you can turn off the new script by changing the MTU line in /etc/hostconfig to:
MTU=-NO-
