Problem of MTU of eth0 when connected to ADSL modem

[pubo]

I encountered problem in Knoppix 5.0.1, when trying to config pppoe. The script reports that the eh0 has a MTU of 64.

Here is my configration: eth0 (Intel Pro 10/100 network card) -> ADSL modem (prolink hurricane 9000/B) -> phone line.

After boot up, even before I start the pppoe script, I did a ifconfig and found that the eth0 is really configured with MTU 64. With this MTU of 64, I can not start pppoe properly. I have to do this before I can get the pppoe script to work:
1. ifconfig eth0 down
2. ifconfig eth0 mtu 1500
3. start the pppoe script with eth0 still in down state (otherwise the pppoe can not find the concentrator).

With the exactly the same hardware, I don't have this issue in knoppix 4.0.2.

Any clue why 5.0.1 configures my eth0 wrongly? How to fix it?

Thanks,

pubo

[Harry Kuhman]

.... How to fix it?

I do not have any idea why it is doing that. Would you consider for the fix looking at answer #4,an appraoch that does not need pppoe at all, and has many other advantages as well.

[pubo]

Thanks. But I am using ADSL JetPack package, the connection time is limited per month (13 hours/month). Thus I need to controll the on/off of the DSL connection closely.

Not sure if the router can do that?

[Harry Kuhman]

Not sure if the router can do that?

You might want to shop around a little, most routers have a setting in them that will do the shutdown automatically after x minutes of no activity, some others might not. This feature might show up in the WAN setup secton as something like "Maximum idle time", setting this to zero usually tells the router to stay connected, setting it to a number gives the minutes to stay connected with no activity before automatically disconnecting from the ISP. All routers that I've used have a web interface page that will let you manually break the connection, should be at least as easy as starting and stopping PPPoE. the problem is that lots of things might generate extra traffic and cause the router to think that you want the connection restarted, such as a mail program left running checking it's mailbox, so you also want to look for a setting like auto reconnect/manual and be sure that it's on manual so that the router does not reconnect when you don't want it to (you could leave it on auto-reconnect if you were extremely sure that nothing would generate stray traffic, but then ever spyware in some package that you didn't expect might start phoning home and burning your limited time). So the answer is that many routers can do that, but as router features vary greatly between brands and even models from the same brand, it would be best to read the manuals for the devices that you are considering and confirm that the router you select will do what you want.