How to change the MTU on a Zyxel 600 series modem with PPPoE ?
Prestige 600 series DSL modems, when using PPPoE, seem to have the MTU set to 1440 by default ! It can be edited using the following steps:
Telnet into the Prestige 645 and go to Telnet Menu 24, option 8. To verify what the LAN & WAN MTU is currently set at, type "ip ifconfig" and press [Enter].
To change the MTU and save it to the autoexec.net file:
1. Go to Telnet Menu 24, option 8, and type, "sys edit autoexec.net", and press [Enter];
2. Next, type, ‘I’ and press [Enter];
3. Type "ip ifconfig enif0 / mtu
4. Finally, type ‘x’ to save and exit, and press [Enter].