Package: ifupdown Version: 0.8.14 Running "ifdown <interface>" prints the warning "Missing required variable: vlan_id1" at the end, which is apparently coming from ifdown itself (see execute.c in the source code).
Downgrading ifupdown to 0.8.13 fixes this. -- System Information: Debian Release: stretch/sid APT prefers unstable APT policy: (500, 'unstable'), (101, 'experimental') Architecture: i386 (x86_64) Kernel: Linux 4.7.4-nouveau (SMP w/2 CPU cores) Locale: LANG=de_DE.UTF-8, LC_CTYPE=de_DE.UTF-8 (charmap=UTF-8) Shell: /bin/sh linked to /bin/dash Init: systemd (via /run/systemd/system) Versions of packages ifupdown depends on: ii adduser 3.115 ii init-system-helpers 1.44 ii iproute2 4.6.0-4 ii libc6 2.24-3 ii lsb-base 9.20160629 Versions of packages ifupdown recommends: ii isc-dhcp-client [dhcp-client] 4.3.5~b1-1 Versions of packages ifupdown suggests: pn ppp <none> pn rdnssd <none> -- no debconf information
