Installing and Administering PPP

Chapter 6 139

Troubleshooting pppd

An LQM failure one minute after connection startup, particularly during

successful user data transfers, indicates that the peer neither properly

Conﬁgure-Rejected LQM during LCP negotiations, nor properly

Protocol-Rejected HP-UX PPP’s ﬁrst LQR.

Scenario: When the modem abruptly gets hung up, pppd does not notice.

Solution: Make sure that the modem drops the Carrier Detect (CD), also called

Data Carrier Detect (DCD), signal when the carrier is lost. On a Telebit

T1600, set ’&C1."

Make sure that the cable properly connects CD (RS-232 pin 8) from the

modem to the serial port, and that the pppd command line does not

include the ignore-cd option.

Scenario: Shortly after the Systems chat script completes, the log ﬁle records a

SIGHUP and the connection drops. But the remote modem did not

actually hang up the connection and tip works correctly.

Solution: Make sure that the modem asserts Carrier Detect (CD), also called Data

Carrier Detect (DCD), signal when it is actually talking to a remote

modem. On a Telebit T1600, set ’&C1."

Make sure that the cable properly connects CD (RS-232 pin 8) from the

modem through to the serial port. pppd does not check the state of DCD

until after the Systems chat script completes, about the time that PPP

negotiations begin. If the modem is not asserting DCD, or if the cable is

not delivering the signal to the serial port, pppd will not be able to tell

that the modem is connected. To test this, or to work around a defective

cable, start pppd with the ignore-cd option.

Scenario: pppd will not hang up the phone, even though it was started with idle

300.

Solution: Increase pppd’s debugging level to 6 (IP frame summary) and watch for

logged frames that do not say ‘!keepup.’ If you do not want those

messages to keep your line active, put them in the ‘keepup’ ﬁlter in the

Filter ﬁle ($PPPHOME/Filter by default).

Scenario: pppd dies with a ‘Fatal error: ...’ or ‘Fatal system error: ...’ message.

Solution: Contact your HP support representative.