PPPoE crash: Fatal signal 4

[Filippo Carletti]

Hello,

> Could you please share the pacp which triggers this problem.

The attached "replay.pcap" contains only the packets sent from the ISP
captured on the ethernet interface. It's the file I used to "crash"
pppd.

pppd_log.txt is a connection log with debug enabled in /etc/ppp/options.

A clarification: I "manage" many routers and most of the PPPoE
connections to this ISP work well. Over time, as of today, I found the
error in 4 different sites: two resolved after a few days, but I
wasn't able to capture the traffic from the ISP.
One site has worked for months, but exhibited the problem after a
downtime from the ISP.

-- 
Filippo
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Sun Jan 18 15:09:02 2026 daemon.notice netifd: Interface 'eolo' is setting up now
Sun Jan 18 15:09:02 2026 daemon.info pppd[23742]: Plugin pppoe.so loaded.
Sun Jan 18 15:09:02 2026 daemon.info pppd[23742]: PPPoE plugin from pppd 2.5.2
Sun Jan 18 15:09:02 2026 daemon.notice pppd[23742]: pppd 2.5.2 started by root, uid 0
Sun Jan 18 15:09:02 2026 daemon.debug pppd[23742]: Send PPPOE Discovery V1T1 PADI session 0x0 length 12
Sun Jan 18 15:09:02 2026 daemon.debug pppd[23742]:  dst ff:ff:ff:ff:ff:ff  src 52:54:00:cd:6b:1a
Sun Jan 18 15:09:02 2026 daemon.debug pppd[23742]:  [service-name] [host-uniq be 5c 00 00]
Sun Jan 18 15:09:02 2026 daemon.debug pppd[23742]: Recv PPPOE Discovery V1T1 PADO session 0x0 length 59
Sun Jan 18 15:09:02 2026 daemon.debug pppd[23742]:  dst 52:54:00:cd:6b:1a  src 52:54:00:93:dc:01
Sun Jan 18 15:09:02 2026 daemon.debug pppd[23742]:  [AC-name lac-vpdn] [service-name lac] [service-name] [AC-cookie c7 27 26 96 7b 00 63 5d 7a 78 0a 2a 5f e1 b0 1c b8 74 fa ca b4 e4 26 a7] [host-uniq be 5c 00 00]
Sun Jan 18 15:09:02 2026 daemon.debug pppd[23742]: Send PPPOE Discovery V1T1 PADR session 0x0 length 40
Sun Jan 18 15:09:02 2026 daemon.debug pppd[23742]:  dst 52:54:00:93:dc:01  src 52:54:00:cd:6b:1a
Sun Jan 18 15:09:02 2026 daemon.debug pppd[23742]:  [service-name] [host-uniq be 5c 00 00] [AC-cookie c7 27 26 96 7b 00 63 5d 7a 78 0a 2a 5f e1 b0 1c b8 74 fa ca b4 e4 26 a7]
Sun Jan 18 15:09:03 2026 daemon.debug pppd[23742]: Recv PPPOE Discovery V1T1 PADS session 0xdac0 length 24
Sun Jan 18 15:09:03 2026 daemon.debug pppd[23742]:  dst 52:54:00:cd:6b:1a  src 52:54:00:93:dc:01
Sun Jan 18 15:09:03 2026 daemon.debug pppd[23742]:  [AC-name lac-vpdn] [service-name] [host-uniq be 5c 00 00]
Sun Jan 18 15:09:03 2026 daemon.info pppd[23742]: PPP session is 56000
Sun Jan 18 15:09:03 2026 daemon.warn pppd[23742]: Connected to 52:54:00:93:DC:01 via interface eth2
Sun Jan 18 15:09:03 2026 daemon.debug pppd[23742]: using channel 169
Sun Jan 18 15:09:03 2026 daemon.info pppd[23742]: Using interface pppoe-eolo
Sun Jan 18 15:09:03 2026 daemon.notice pppd[23742]: Connect: pppoe-eolo <--> eth2
Sun Jan 18 15:09:03 2026 daemon.debug pppd[23742]: sent [LCP ConfReq id=0x1 <mru 1492> <magic 0x32db8a44>]
Sun Jan 18 15:09:03 2026 daemon.info ModemManager[23758]: hotplug: add network interface pppoe-eolo: event processed
Sun Jan 18 15:09:03 2026 daemon.debug pppd[23742]: rcvd [LCP ConfReq id=0x1 <mru 1492> <asyncmap 0xa0000> <auth pap> <magic 0x51727743> <pcomp> <accomp>]
Sun Jan 18 15:09:03 2026 daemon.err pppd[23742]: Fatal signal 4
Sun Jan 18 15:09:03 2026 daemon.info ModemManager[23783]: hotplug: remove network interface pppoe-eolo: event processed
Sun Jan 18 15:09:03 2026 daemon.info pppd[23742]: Exit.
Sun Jan 18 15:09:03 2026 daemon.notice netifd: Interface 'eolo' is now down
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