openwrt
LCP echo failure threshold 0 does not behave as described in LuCI
For BT Home Hub 5A configured to use PPPoE or PPPoA protocol for example.
In LuCI→Network→Interfaces→WAN→Advanced Settings, there are two default settings displayed:
LCP echo failure threshold 0 LCP echo interval 5
On the page, the 'default' setting LCP echo failure threshold to Zero, implies all LCP echo failures would be ignored. (see attached image) But I found this to be incorrect/misleading.
There is no keepalive option found in the WAN interface section of /etc/config/network on Home Hub 5A when selecting PPPoE or PPPOA protocols. But there appears to be a fixed timeout (possibly 5 seconds) on the Home Hub 5A when I use PPPoE on VDSL connection. ie. not infinite as quoted in LuCI.
I don't know if this is the same behaviour for all devices.
If LCP echo failure threshold is set to a non-Zero value, then keepalive option is CREATED in the WAN interface within /e/c/network file.
The description displayed in LuCI for LEDE and OpenWRT 18:
'Presume peer to be dead after a given amount of LCP echo failures, use 0 to ignore failures'
perhaps needs to be changed?
eg. perhaps simplest solution is to remove the phrase 'use 0 to ignore failures' ?
This closed ticket may be of interest (I added my observations affecting HH5A running LEDE 17 to end of the closed ticket) https://bugs.openwrt.org/index.php?do=details&task_id=1259
Would it be possible to add 'keepalive_adaptive' setting into LuCI mentioned in above ticket in the future?
Another ticket on same subject https://bugs.openwrt.org/index.php?do=details&task_id=854
From ppp.sh:
local lcp_failure="${keepalive%%[, ]*}"
local lcp_interval="${keepalive##*[, ]}"
...
[ "${lcp_failure:-0}" -lt 1 ] && lcp_failure=""
...
proto_run_command "$config" /usr/sbin/pppd \
${lcp_failure:+lcp-echo-interval $lcp_interval lcp-echo-failure $lcp_failure $lcp_adaptive} \
Means if you set it to 0 in LuCI, option keepalive will be deleted. When no option keepalive is present, $lcp_failure will end up being empty which means that no lcp-echo-interval and no lcp-echo-failure is passed to pppd.
Default values in pppd lcp.c:
int lcp_echo_interval = 0; /* Interval between LCP echo-requests */
int lcp_echo_fails = 0; /* Tolerance to unanswered echo-requests */
So I am confused. The option seems to behave as intended?
To be perfectly clear: 0 is supposed to disable LCP stuff. If that does not work it is a bug that has to be fixed in OpenWrt.
Turns out the OpenWrt implementation is completely flawed and cannot be fixed in a way where omitting option keepalive would yield the expected behaviour without breaking the majority of existing setups.
Will change LuCI to emit an explicit option keepalive 0 but that'll still need fixes on the OpenWrt side.
from master ppp.sh:
[ -n "$keepalive" ] || keepalive="5 1"
local lcp_failure="${keepalive%%[, ]*}"
local lcp_interval="${keepalive##*[, ]}"
local lcp_adaptive="lcp-echo-adaptive"
In the LuCI setting, the default value is to leave blank, so $keepalive is null. At this time, lcp-failure=5, lcp-interval=1, this is inconsistent with the description of LuCI. And if you fill in 0/5 in LuCI, you can't save it, because the value hasn't changed and doesn't need to be saved, then $keepalive will always be null, which means that you can't set lcp-echo-failure = 0 through LuCI.
