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(?) pppd problem

From pclouds

Answered By Mike "Iron" Orr, Mike Ellis

Hi people

I try to connect to my isp using pppd:

pppd /dev/ttyS4 connect "chat -V " ATZ OK ATM0 OK ATDT1260 CONNECT" modem
defaultroute crtscts -detach

It saids:

CONNECTSerial connection established.
Using interface ppp0
Connect: ppp0 <--> /dev/ttyS4
Serial line is looped back.
Connection terminated.

I use modem Motorola SM56. /dev/ttyS4 is a symbolic link to /dev/sm56 (created by the modem). I can connect to that isp using rp3 with no problem. What is "Serial line is looped back"? Help me!

Thanks very much.

(!) [Iron] It means it tried to contact the remote server, but ended up contacting itself instead. I haven't used ppp for years, so I don't remember the solution. Either there's a line crossed in your serial cable (unlikely), or there's some option you add or remove in the config fie. Check the docs for "looped back", "server" and "master".
Maybe one of the other Answer Gang members can reply better.
(!) [Mike E] Good morning!
My guess is that you're seeing the login sequence of your ISP, some of which echo your username back to you. When the PPP daemon starts, it sends some strange characters to your ISP, which dutifully echos them back to you confusing pppd into thinking that it's talking to itself.
The command you quoted will get 'chat' to do the actual dialing, but as soon as your modem has connected to the remote modem, 'chat' will exit and the pppd will expect a PPP connection to be in place. What you need to do is get chat to do a little more work to log you in to your ISP: I'd suggest you try starting pppd using a modified command line, for example:
pppd /dev/ttyS4 connect "chat -V " ATZ OK ATM0 OK ATDT1260 CONNECT ogin
<yourlogin> assword <yourpassword>" modem defaultroute crtscts -detach
(I probably don't need to say this, but just in case, substitute your ISP account name for <yourlogin> and your password for <yourpassword>...)
Notice that I've deliberately used "ogin" and "assword" since it's not certain whether you will see "login" or "Login" and 'chat' is case-sensitive.
It is definitely worth checking with your ISP for their exact login sequence: the one I've shown is a very general one and may well not work exactly as given. I use Demon in the UK and they have an excellent on-line helpdesk - have a look at http://www.demon.net/helpdesk/general/connscp.shtml for an excellent example of how their login sequence works - Demon support protocols other than PPP, so have to query the protocol to use too. Although Demon don't give detailed help for Linux setup, they do provide all the information you need and several newsgroups to help users too. Hopefully your ISP will be similarly helpful...
Incidentally, more and more ISPs are now moving away from "scripted clear text password login" to CHAP or PAP based login sequences. These don't send your password in cleartext, and also re-validate your credentials periodically. However, I have no first-hand experience of these, so over to another Gang member...

(?) Thanks for your help. I have resolved this problem. Because i missed user & remotename options, so the PAP authentication was not completed. I guess that ppp on the isp was terminated then, and all messages sent by my pppd was sent back.

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