netplan breaks route_localnet set in /proc/sys/net/ipv4/conf after apply/try

[Fero Tapeta]

Hello,

VERSION: 0.106-2+deb12u1

Our server provider uses netplan so I've tried to migrate our configuration to netplan. We use internally developed transparent proxy similar to https://github.com/cloudflare/mmproxy/. For the proper functionality route_localnet must be enabled on the interface - echo 1 > /proc/sys/net/ipv4/conf/ens3/route_localnet

After restarting network using 'netplan apply' or 'netplan try' the setting resets back to 0 and routing become broken.

I've tried using networkd-dispatcher and putting script to routable.d and seems it executes BEFORE netplan reset to setting back to 0 so the result is not as intended - interface will keep set at 0 at the end.

Therefore, We had to go back to ifupdown and use post-up/post-down scripts to setup everything properly.