PPPoE Disconnection frequently.

[Mohammed_Yasin]

Facing PPPoE session disconnection issue. 
As per ISP, this is a Firewall issue as from Laptop or Computer (directly connected to ISP Router) no disconnection being observed.

Palo Alto PA-3020

Following logs and capture packet are below 

2021-07-15 11:27:25.969 +0400 debug: log_write(ppp/utils.c:678): No response to 5 echo-requests
2021-07-15 11:27:25.969 +0400 debug: log_write(ppp/utils.c:678): Serial link appears to be disconnected.
2021-07-15 11:27:25.969 +0400 debug: log_write(ppp/utils.c:678): ipcp: down
2021-07-15 11:27:25.969 +0400 debug: log_write(ppp/utils.c:678): [0x7f59d407cec0/17][1] PPP SENT: [LCP TermReq id=0x3 "Peer not responding"]
2021-07-15 11:27:25.969 +0400 debug: pan_pppoe_output(pan_pppoe_thread.c:1016): [0x7f59d407cec0/17][1] Sent 53 (45 on wire) bytes of PPPoE pkt to DP on socket 6
2021-07-15 11:27:29.969 +0400 debug: log_write(ppp/utils.c:678): [0x7f59d407cec0/17][1] PPP SENT: [LCP TermReq id=0x4 "Peer not responding"]
2021-07-15 11:27:29.969 +0400 debug: pan_pppoe_output(pan_pppoe_thread.c:1016): [0x7f59d407cec0/17][1] Sent 53 (45 on wire) bytes of PPPoE pkt to DP on socket 6
2021-07-15 11:27:33.968 +0400 debug: pan_pppoe_ok_to_send(pan_pppoe_fsm.c:352): [0x7f59d407cec0/17][1] Ok to send, ha_state:5 (fsm state is:4) for ethernet1/2
2021-07-15 11:27:33.968 +0400 debug: pan_pppoe_send_padt(pan_pppoe_fsm.c:931): [0x7f59d407cec0/17][1] Sending PADT on ethernet1/2
2021-07-15 11:27:33.968 +0400 debug: pan_pppoe_output(pan_pppoe_thread.c:1016): [0x7f59d407cec0/17][1] Sent 28 (20 on wire) bytes of PPPoE pkt to DP on socket 6
2021-07-15 11:27:33.968 +0400 debug: pan_pppoed_sysd_update_interface(pan_pppoed_sysd.c:439): Updating pppoe runtime info for interface ethernet1/2.

2021-07-15 11:18:35.138 +0400 Error: pan_ppp_fsm_run(pan_ppp_fsm.c:588): [0x7f59d407cec0/17][1] Unsupported protocol: 'IPv6 Control Protovol' (0x8057) received
2021-07-15 11:18:37.114 +0400 Error: pan_pppoe_fsm_run(pan_pppoe_fsm.c:1203): [0x7f59d407cec0/17][1] Drop PPPoE PADT pkt, sess_id received:4476 does not match pppoe_fsm sess id:0
2021-07-15 11:18:37.114 +0400 Error: pan_pppoe_fsm_run(pan_pppoe_fsm.c:1204):
2021-07-15 11:18:38.166 +0400 Error: pan_ppp_fsm_run(pan_ppp_fsm.c:588): [0x7f59d407cec0/17][1] Unsupported protocol: 'IPv6 Control Protovol' (0x8057) received
2021-07-15 11:19:22.119 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1322): [0x7f59d407cec0/17][1] Drop PPP Sess pkt, sess_id received:14663 does not match pppoe_fsm sess id:0
2021-07-15 11:19:22.119 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1323):
2021-07-15 11:19:25.117 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1322): [0x7f59d407cec0/17][1] Drop PPP Sess pkt, sess_id received:14663 does not match pppoe_fsm sess id:0
2021-07-15 11:19:25.117 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1323):
2021-07-15 11:19:28.117 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1322): [0x7f59d407cec0/17][1] Drop PPP Sess pkt, sess_id received:14663 does not match pppoe_fsm sess id:0
2021-07-15 11:19:28.117 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1323):
2021-07-15 11:19:29.215 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1322): [0x7f59d407cec0/17][1] Drop PPP Sess pkt, sess_id received:14663 does not match pppoe_fsm sess id:0
2021-07-15 11:19:29.215 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1323):
2021-07-15 11:19:31.117 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1322): [0x7f59d407cec0/17][1] Drop PPP Sess pkt, sess_id received:14663 does not match pppoe_fsm sess id:0
2021-07-15 11:19:31.117 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1323):
2021-07-15 11:19:37.118 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1322): [0x7f59d407cec0/17][1] Drop PPP Sess pkt, sess_id received:14663 does not match pppoe_fsm sess id:0
2021-07-15 11:19:37.118 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1323):
2021-07-15 11:19:40.117 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1322): [0x7f59d407cec0/17][1] Drop PPP Sess pkt, sess_id received:14663 does not match pppoe_fsm sess id:0
2021-07-15 11:19:40.117 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1323):
2021-07-15 11:19:41.215 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1322): [0x7f59d407cec0/17][1] Drop PPP Sess pkt, sess_id received:14663 does not match pppoe_fsm sess id:0
2021-07-15 11:19:41.215 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1323):
2021-07-15 11:19:43.117 +0400 Error: pan_pppoe_recv_pkt(pan_pppoe_fsm.c:1322): [0x7f59d407cec0/17][1] Drop PPP Sess pkt, sess_id received:14663 does not match pppoe_fsm sess id:0

noticed, the following messages on the system logs

PPPoE session failed to connect for user:**bleep**@ABCDEF.Com on interface:ethernet1/2. Reason: No PPPoE Offer received

PPPoE session failed to connect for user:NIP4@ABCDEF.Com on interface:ethernet1/2. Reason: Timeout, LCP down

PPPoE session failed to connect for user:NIP4@ABCDEF.Com on interface:ethernet1/2. Reason: No PPPoE Confirm received

PPPoE session failed to connect for user:NIP4@ABCDEF.Com on interface:ethernet1/2. Reason: Peer not responding, LCP down

On Packet Capture..

in package capture, I noticed that a PPP LCP sent a Termination request to the Palo alto interface. And other codes such as 0xa7 – PPPoE Active Discovery Terminate (PADT) that may be initiated from a server or client.

And some Reject configuration& Protocol packet of PPP – IPCP / LCP

[BPry]

@Mohammed_Yasin,

From the logs the firewall is the one sending the PADT, so at least what the ISP is telling you appears correct. There's however the matter of the unsupported protocol alert that is present:
2021-07-15 11:18:38.166 +0400 Error: pan_ppp_fsm_run(pan_ppp_fsm.c:588): [0x7f59d407cec0/17][1] Unsupported protocol: 'IPv6 Control Protovol' (0x8057) received

Outside of there apparently being a typo in the log message which is awesome, it appears the ISP is attempting to send control traffic over IPv6. Last I checked (which was awhile ago since the US doesn't deal with PPPoE that much) this wasn't supported by PAN.