Suricata and ppp: restart of suricata needed after ppp down/up / 2020-01-21

Suricata is running and detecting attacks, but it was causing a 100% cpu load after a restart of the ppp connection (the DSL here uses PPP over Ethernet).

The errors point at the problem starting when the ppp connection restarts:

21/1/2020 -- 00:59:36 - <Error> - [ERRCODE: SC_ERR_AFP_READ(191)] - Error reading data from iface 'ppp0': (100u) Network is down
21/1/2020 -- 00:59:37 - <Error> - [ERRCODE: SC_ERR_AFP_CREATE(190)] - Couldn't set fanout mode, error Invalid argument

Which also starts to fill the system log with:

Jan 21 00:59:42 xxxxxxxx kernel: [11347441.726755] device ppp0 left promiscuous mode
Jan 21 01:00:13 xxxxxxxx kernel: [11347472.055712] device ppp0 entered promiscuous mode
Jan 21 01:00:13 xxxxxxxx kernel: [11347472.071533] device ppp0 left promiscuous mode
Jan 21 01:00:13 xxxxxxxx kernel: [11347472.091653] device ppp0 entered promiscuous mode

The interesting part is that this causes higher power usage about five and a half hours later.

Solution: restart suricata in an /etc/ppp/ip-up.d/ script.