Installing and Administering PPP

74 Chapter 4
Common pppd Options
Link Quality Monitoring
Peer Refusal to Comply with LQM Request
If, during LCP option negotiation, the peer refuses to send Link Quality
Reports, pppd instead begins sending LCP Echo-Request messages at
the requested lqrinterval and use the arriving LCP Echo-Response
messages to make the link quality decision. If the peer does not correctly
use a LCP Configure-Reject message to tell PPP to switch to LCP
Echo-Requests, PPP can be given either the echolqm argument, to
dispense with the negotiation phase and begin directly with
Echo-Requests, or the nolqm argument, to disable link quality
monitoring completely. At pppd’s debugging verbosity level 4, the log file
receives summary messages like this:
5/7-13:45:27-1514 LQM: Pkt: 1/1 Oct: 53/53 LQRs: 5/5
This means that, during the last testing interval, this system
transmitted one packet and received one packet. Fifty-three octets
crossed the link in each direction. And this system has received
responses to all five of the most recent five Link Quality Reports it sent.
The LQR packet is 36 octets long, and the default lqrinterval of ten
seconds will cause the additional traffic to be unnoticed on most
connections. However, if the application is very sensitive to speed and
requires absolutely every bit of available line bandwidth, use the nolqm
argument to disable LQM.