/etc/logcheck/ignore.d.server/isdnutils is in logcheck-database 1.3.16.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 13 | ^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: isdn_tty: call from .* -> .* ignored$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: isdn_net: Incoming call without CPN, assuming '0'$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: isdn_tty: Incoming call without CPN, assuming '0'$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: isdn_net: Incoming call without OAD, assuming '0'$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: isdn_tty: Incoming call without OAD, assuming '0'$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: (ippp.|isdn.): dialing$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: (ippp.|isdn.): Chargesum is$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: isdn_net: chargetime of (ippp.|isdn.) now$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: isdn_net: (ippp.|isdn.) connected$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: isdn_net: local hangup (ippp.|isdn.)$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: (ippp.|isdn.): remote hangup$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: ippp_ccp:$
^\w{3} [ :0-9]{11} [._[:alnum:]-]+ kernel: ippp, open, slot: .*, minor: .*, state:$
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