Re: "unreachable" routes

Hi Thomas,

think of this system as a VPN Access Concentrator.  "unreachable" routes
are used to avoid "ping-pong-storms" between this system and the gateway
for networks that currently aren't connected.  That's a simpler solution
than to use a dynamic routing protocol.

I think we'll go with "network-script", again for simplicity.

Thank you for your feedback.



On Mon, Feb 22, 2021 at 05:42:15PM +0100, Thomas Haller via networkmanager-list wrote:
On Thu, 2021-02-18 at 12:28 +0100, Robert Vogelgesang wrote:
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"

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

unreachable metric 3

If I read
correctly, NM 1.26.0 should still support this syntax, but when I try
it, reading the interface configration fails, without any error

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

Any hints?


Currenlty, NetworkManager only supports "type=unicast" and "type=local"
routes. It would be nice to add support for other route types.

Anyway, as it is, the options are:

(1) not use NetworkManager but a script/tool of your choice that works
for you (like "network-script" from "initscripts" package).

(2) use a dispatcher script, that would call `ip route add`. See `man

(3) use "NetworkManager-dispatcher-routing-rules". That is basically a
dispatcher script ([1]) which does what "network-scripts" do. You would
configure the routes and rules in /etc/sysconfig/network-
scripts/{rule,route}. I don't think this is the best solution. If you
go with the dispatcher script way, then (2) is simple enough without
requiring you to configure routes in ifcfg format.

I would get inspired by (3) (see the script at [1]) and write a simple
dispatcher script that works for you (2).


Can you elaborate why you use "unreachable" routes? It's the first time
I encounter somebody actually using this. Seems you hav specific
requirements, and while NetworkManager should support them, I think it
may be warranted that for now you roll your own special solution (that
is, a script).


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