[plug] ADSL - was: *NOTHING*

[Craig Ringer]

> The "modem" is an Alcatel Speed Touch "Home". I don't know whether it is a router or not.

It is not. Your machine must understand PPPoE or you won't get a connection.

> The MAC software we have talking to it at the moment uses the static ip address and the gateway ip address supplied by our isp.

... different. Are you sure its not setting up a PPPoE connection and 
acquiring those addresses during PPP negotiation with the ISP?

> I also know they have a broadast address. all of these addresss must be used somewhere, but perhaps it's not as hard as I think and I should just set a default route. What do you reckon?

If you have a SpeedTouch home, that's unlikely.

Its possibe you have a "Layer 3" DSL service if its very old - in that 
case setting a default route + the correct IP and netmask will make it 
work fine. This is unlikely though, I think telstra forced all layer 3 
customers to layer 2 DSL a while back anyway. I jumped ship before that 
so I'm not sure.

More likely, you have a "Layer 2" DSL service and must use PPPoE to 
tunnel your connection through Telstra to your ISPs servers.

If you have a Debian box, all you should need to do is
	apt-get install pppoe pppoeconf
enter the config, and "pon dsl-provider". Run "tail -f /var/log/syslog" 
to make sure its connecting, but if all is well an interface called 
"ppp0" will appear and get an IP. If so ... you're all set.

If you're using RH etc... well, all my firewalls and such are Debian 
based, but I have set up vanilla rp-pppoe once. It looks like RH9 at 
least has a package called "rp-pppoe" which you should rpm -i if you 
don't already have it installed. After that its really not difficult to 
configure PPPoE and if you get it right, "it just works".

Important pitfall to be aware of: you must not set an IP address on the 
interface connected to your DSL modem. "ifconfig ethX 0.0.0.0" to make 
sure (where ethX is your DSL ethernet iface, conventionally eth1 but 
depends on how you've connected things up).

If you're still having trouble after a try at setting up PPPoE, try a 
tcpdump on the PPPoE interface while trying to start a session. DO NOT 
SEND THIS TO THE LIST as it will contain your unencrypted username and 
password.

A suitable command is:
	# tcpdump -i ethX -s 0 -w /tmp/dump
then analyse with ethereal,
	# chown yourusername.yourgroup /tmp/dump
	$ ethereal /tmp/dump
Don't run ethereal as root. Tcpdump and ethereal are on most distro CDs 
if you don't have them installed.

[warning: rest from memory of previous troubleshooting, including being 
customer-on-the-spot for iiNet during the Subi exchange failures. I'm no 
  expert here.]

The output will be weird, but what you want to watch out for is a PADI 
packet going out (requesting a session). After that, if anything at all 
is working, there should be a PADO packet in reply (offering a connection).

If you don't even see a PADI packet, make sure you're dumping the same 
interface that your DSL modem is connected to and pppoe is configured to 
use. Also make sure your DSL modem is in fact connected to the interface 
PPPoE is configured to use.

If you see an outgoing PADI but don't see a PADO packet, check you have 
your DSL modem connected to the right phone line and powered on, the DSL 
modem has line sync, the ethernet link between the DSL modem and the PCs 
NIC is up (link light on), and Telstra hasn't broken the DSL network 
(again).

If it still doesn't work, post a syslog snippet to the list after making 
SURE your password isn't shown in it.

Craig Ringer