[systemd-devel] systemd-network and loopback

[Mantas Mikulėnas]

On Fri, Sep 9, 2022 at 11:36 PM Andrea Pappacoda <andrea at pappacoda.it>
wrote:

> Il giorno ven 9 set 2022 alle 12:17:42 -05:00:00, Greg Oliver
> <oliver.greg at gmail.com> ha scritto:
> > Well, easiest to explain is user apps that use tcp or udp sockets to
> > communicate.  If they are on the same host, then huge gains can be
> > achieved by using the loopback adapter (especially TCP comms).
>
> Thanks, but again, is this related to systemd-network in any way? My
> question is whether letting systemd-network manage the loopback
> interface is useful or not, not what the loopback interface is used for
> in general.
>
> As far as I understand, systemd itself brings up the loopback interface
> on its own during the early boot stage, and systemd-network(d) is
> launched much later. But is writing something like this in
> /etc/systemd/network/foo.conf ever useful?
>
>     $ cat /etc/systemd/network/foo.conf
>     [Match]
>     Name=*
>     Type=loopback
>

It's useful when you want the `lo` interface to have a custom [Address] or
two.

Routers often have an address assigned that's supposed to be independent
from any "physical" interface – on Linux it could be assigned to a
Type=dummy interface or to an empty bridge, but just as frequently it's
assigned to `lo`. (It's even called a "loopback address".)

-- 
Mantas Mikulėnas
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