[FS#854] Unstable Internet caused by frequent PPPoE reconnect, network.wan.keepalive=0 has no effect

[LEDE Bugs]

A new Flyspray task has been opened.  Details are below. 

User who did this - ppuzr (ppuzr) 

Attached to Project - LEDE Project
Summary - Unstable Internet caused by frequent PPPoE reconnect, network.wan.keepalive=0 has no effect
Task Type - Bug Report
Category - Base system
Status - Unconfirmed
Assigned To - 
Operating System - All
Severity - Very Low
Priority - Very Low
Reported Version - lede-17.01
Due in Version - Undecided
Due Date - Undecided
Details -   * Problem occurs on EE Brightbox 1 (Arcadyan AR7516)
  * Software version is lede 17.01.1, r3316-7eb58cf109 (https://downloads.lede-project.org/releases/17.01.1/targets/brcm63xx/generic/lede-17.01.1-brcm63xx-generic-A4001N-squashfs-cfe.bin)
  * Steps to reproduce: after a PPPoE session has been established for a while, it reconnects and the following messages appear in the log

daemon.info pppd[7738]: No response to 5 echo-requests
daemon.notice pppd[7738]: Serial link appears to be disconnected.
daemon.info pppd[7738]: Connect time 1.0 minutes.
daemon.info pppd[7738]: Sent 28006 bytes, received 46170 bytes.
daemon.notice pppd[7738]: Connection terminated.
daemon.info pppd[7738]: Connect time 1.0 minutes.
daemon.info pppd[7738]: Sent 28006 bytes, received 46170 bytes.
daemon.info pppd[7738]: Sent PADT
daemon.info pppd[7738]: Exit.


network.wan.keepalive is not set, and on luci "LCP echo failure threshold" shows a grey 0 and the description below it says "Presume peer to be dead after given amount of LCP echo failures, use 0 to ignore failures", but this description is not consistent with the behaviour.

After running the commands below, the grey 0 becomes darker, but the problem persists.

root at LEDE:~# uci set network.wan.keepalive=0
root at LEDE:~# /etc/init.d/network restart


The value of network.wan.keepalive when set using luci has two numbers separated by a space (which appears to be in the format of '[threshold] [interval]'), but it should be a number according to the wiki [[https://lede-project.org/docs/user-guide/wan_interface_protocols?s[]=pppoe#protocol_pppoe_ppp_over_ethernet]]

I then tried the following commands, and there're no reconnects after one hour.

root at LEDE:~# uci set network.wan.keepalive='0 1'
root at LEDE:~# /etc/init.d/network restart


Is it better to have a default of 0 (default=undefined network.wan.keepalive) instead of seemingly 5 which would also be consistent with luci?

More information can be found at the following URL:
https://bugs.lede-project.org/index.php?do=details&task_id=854