The server ppp-server works ONLY ONCE before appearing to go mute. To restore operation, I have to either:
- reboot the server device, or
- disable ppp-server, set USB serial "port" to its existing baud rate again, and then enable the ppp-server again
As a further aggravation, the ppp-server is always disabled after a reboot, forcing the user to log into the webfig or CLI to manually enable the ppp-server.
The test setup consists of two Mikrotik devices (they happen to be hAP ac^2 in my testing) running RouterOS v7.20 (stable).
The two devices have a null-modem USB serial interconnect between the two. (I've tried both USB serial chips Prolific PL2303 and FTDI FT232R, if it matters.)
The "server" device has this configuration:
/interface ppp-server add disabled=no name=ppp-in1 null-modem=yes port=usb1 /ppp secret add name=user password="123"
The "client" device has this configuration:
/interface ppp-client add dial-on-demand=no disabled=no name=ppp-out1 null-modem=yes port=usb1 user=user password="123"
If for whatever reason the ppp-server is disabled (even temporarily, as can happen when a setting is being reconfigured), the ppp-server stops responding to the ppp-client.
From that point on, seemingly the only way to make the ppp-server to work again is to either reboot the server device (and once again manually enable the ppp-server), or needlessly reconfigure the USB serial "port" (and then re-enable the ppp-server).
To further diagnose the problem, I wrote code to sniff the UART traffic between the two devices.
The client repeats the following non-PPP text over and over again every ~4 seconds:
/AutoPPP/x0D/x0ACLIENT
(the "/x0D/x0A" is intended to accurately represent a CRLF)
When the ppp-server is manually enabled on the server, it sees the non-PPP traffic from the client, sends HDLC frames (actually expected for PPP) and the client responses with HDLC frames (again, actually expected traffic for PPP).
When the ppp-server gets disabled, there is a HDLC frame with some human-readable text ("administrator request") embedded in the frame (presumably a reason for the disconnect), and the ppp-client responds with a final HDLC frame.
Within a second, the ppp-client starts spewing its AutoPPP CLIENT text, and repeats it every ~4 seconds again.
When the ppp-server is enabled again, it appears to output ABSOLUTELY NOTHING; it has gone completely mute. One possibility is that RouterOS has reconfigured it to a wrong mystery baud rate.
The only way to restore the PPP connection is to reboot the server or do the port reconfigure whilst the ppp-server is disabled.
From my perspective, this mute behavior feels like a bug. Having to manually enable the ppp-server each time the device boots (behavior that is unlike ppp-client) just adds to the aggravation.