pppd: No response to 4 echo-requests

Problem

This error is typical of a Linux dial-up modem Internet connection that lasts only 2 or 3 minutes. The connection ends suddenly and the following lines appear in /var/log/messages, regardless of which dialler front end (diald, wvdial, kppp, rp3...) is used to make the connection:

pppd: No response to 4 echo-requests
pppd: Serial link appears to be disconnected.
pppd: Connection terminated. 
pppd: Terminating on signal 15.

Meaning

The computer is sending Link Control Protocol (LCP) echo requests to the Internet Service Provider (ISP), but the ISP does not support LCP echo.

Solution

Turn off LCP echo on your Linux computer. Edit the configuration file /etc/ppp/options and add the following option, or change the following line if it already exists:

lcp-echo-failure 0

Discussion

The Link Control Protocol echo function is like an "Are you there?" message. It is there because early dial-up modems could not tell if the phone line was up or not during the call. Practically all dial-up modems have hardware modem control these days and that makes LCP echo somewhat unnecessary.

Some ISPs turn off LCP echo, because Microsoft Windows doesn't use it, I assume. They should leave it on for the sake of correctness (and for the convenience of Linux users). By default, the Linux Point to Point Protocol (PPP) manager "pppd" sends LCP echo requests every 30 seconds and disconnects after 4 no-replies. The result is a connection that lasts no more than between 2 and 3 minutes. Turning off LCP echo solves the problem at the expense of disabling this (possibly useful?) dial-up-modem-independent connection status monitoring function.

Phil Jones, August 2005. Email: philjones1 {at} blueyonder.co.uk. Remove {at} to email.