/etc/ppp/ip-down.d/000resolvconf is in openresolv 3.8.0-1.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 | #!/bin/sh
# ppp.ip-down hook script for resolvconf
# Written by Roy Marples <roy@marples.name> under the BSD-2 license
[ -x /sbin/resolvconf ] || exit 0
/sbin/resolvconf -f -d "$PPP_IFACE"
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