"unreachable" routes

[Robert Vogelgesang <vogel folz de>]

Hello @all,

currently I'm trying to update an old server running CentOS 6, which
doesn't use NetworkManager, to a system with Networkmanager 1.26.0.
I'm strugging to find the correct syntax to define "unreachable" routes.

In CentOS 6 this could be done by creating a file, e. g.
/etc/sysconfig/network-scripts/route-eth0, with the content:

unreachable 192.0.2.0/24 metric 3

If I read
https://gitlab.freedesktop.org/NetworkManager/NetworkManager/-/blob/nm-1-26/src/settings/plugins/ifcfg-rh/nms-ifcfg-rh-reader.c
correctly, NM 1.26.0 should still support this syntax, but when I try
it, reading the interface configration fails, without any error message.

The nmcli man page doesn't mention "unreachable" or "blackhole" routes.
nmcli does not accept this syntax when I try to set the ipv4.routes
property of a connection.

Any hints?

Best,

Robert