NetworkManager shows connection to "lo"

English Network/Internet
#1

After I updated my openSUSE Tumbleweed system to snapshot 20230214 NetworkManager automatically “creates” a connection to “lo” (127.0.0.1).

The plasma5-nm-applet does not give any details on that connection nor will it allow me to terminate that connection permanently (it will be re-established within a second) or delete it (there is no connection profile in /etc/NetworkManager/system-connections).

All this happens although I have set no-auto-default=*.

Does anyone else see this?

What creates this connection and what is it used for? Can/should I get rid of it (and when yes, how)?

Any feedback is welcome.

My system:

Operating System: openSUSE Tumbleweed 20230214
KDE Plasma Version: 5.27.0
KDE Frameworks Version: 5.103.0
Qt Version: 5.15.8
Kernel Version: 6.1.10-1-default (64-bit)
Graphics Platform: X11
Graphics Processor: Mesa Intel® HD Graphics 630
#2

I forgot to mention:

I saw the change log which says

  • Connections can now be activated on a loopback interface.

But that does not explain why it is activated automatically, nor why it can’t be canceled.

#3

I am not running Tumbleweed and also not NM, but here

boven:~ # ip addr
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether ec:8e:b5:da:0d:0d brd ff:ff:ff:ff:ff:ff
    altname enp1s0
    inet 10.0.0.154/24 brd 10.0.0.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 2a02:a465:d34e:1:ee8e:b5ff:feda:d0d/64 scope global dynamic mngtmpaddr noprefixroute 
       valid_lft 7048sec preferred_lft 3448sec
    inet6 fe80::ee8e:b5ff:feda:d0d/64 scope link 
       valid_lft forever preferred_lft forever
boven:~ #

And as long as I can remember (and that is far before the word Linux even existed), the local loopback device lo is always up whenever anything network like is functioning.

1 Like
#4

@susejunky it’s for the host system, the loopback (127.0.0.x) is a virtual network that your computer uses to communicate with itself.

Have a look with the likes of tcpview, I submitted it to Show network:utilities / tcpview - openSUSE Build Service

Screenshot from 2023-02-16 09-51-37
Screenshot from 2023-02-16 09-51-371685×199 55.7 KB

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#5

@hcvv , @malcolmlewis Thank you very much for your immediate feedback.

I know about the loopback interface (I use it to run a local apache/dokuwiki instance). However I can not see any use of having it presented in NetworkManager.

What sort of management can I apply to “lo” via NetworkManager?

#6

There is a bugreport…
https://bugzilla.opensuse.org/show_bug.cgi?id=1208369

#7

I am not sure what NetworkManager is supposed to do. I assume that it was originally designed to enable users on “carry around” computers (like laptops) to choose which network to use on the place they happen to be without need for help from the system manager (root). In that case, I can understand that lo is hidden from the end-user (although still functioning of course) as being of no importance to him.

But it seems that NM is nowadays also used for network management on computers that are always on the same spot and always use the same network connections (with the same IP addresses, etc.). Situations that were earlier covered by Wicked and it’s predecessors. As such NM is now a tool for the system manager and I can understand that as such it will show the complete picture. Like my ip addr above does.

#8

@hui Thank you for the link. I will keep an eye on it.

#9

From my point of view it is more irritating than helpful to show the “lo”-connections in NetworkManager. Especially as they behave very different to all other NM-connections (no way to stop them, no connection profile, nothing to be managed, …).

But if that is the way it is supposed to be then I will not worry any longer. Just another feature hard to explain to all those “plain users” …

#10

As I said, I can fully understand that NM, in the guise of the client application on a end-users desktop, should not show lo as the end-user has nothing to do with it.
And I see from the bug report that more end-users are confused by it now showing.

But I probably did not interpret your first post correct. I know you as someone with system manager capacity and was really wondering why you never heard before of the lo network device.

1 Like
#11

And scroll to Managing the loopback interface.

#12

Sorry! My fault.

My English is not that good (I’m no native English speaker). It’s difficult for me to give a problem description which can be understood easily.

#13

Thank you very much for that link.

I looked at the chance log in YaST and scanned through the NetworkManager site but I missed this peace of important information.

Nevertheless I have difficulties to imagine any use cases for this change but I will give it a closer look.

#14

Yes, for ordinary users, no manual configuration should be required, but sometimes being able to add an additional IP address may be useful. For example, you may have a service that binds a port on an interface, and want to run a different service on the same port and network.

#15

Thank you very much for the explanation.

I have to admit: Such use cases are far from what I did with networks so far. But who knows …

For the time beeing I created a file /etc/NetworkManager/conf.d/19-unmanaged-interfaces.conf with

[keyfile]
# Specify interfaces not to be managed by NetworkManager.
unmanaged-devices=interface-name:lo

as described here and now “lo” is no longer shown by plasma5-nm.

1 Like
#16

And what exact problem did it solve?

#17

I found a way to hide “lo” in NetworkManager on all those installations I care for which are used by “plain users” (some of them 80+ of age) who become quite nervous about sudden changes in their systems.

#18

The faint of heart may prefer a more radical solution: Never show NetworkManager in the system tray. An icon which is not needed may amount to a big annoyance for some users.

#19

I think I fully understand where susejunky is after. Do not bother end-users with information that is none of their business.

That is the same reason why I haven’t NM installed at all. My systems are no “carry around” systems and thus network is configured using Wicked (and predecessors and nowadays systemd-network), thus I do not want an useless NM applet shown to my users.

#20

Exactly !!!

Most of the people I support do use laptops. And when they travel (to visit friends, children, grand-children, …) they want to take those laptops with them. They have to be able to switch to different wifi-networks in an easy way. NetworkManager is the way they are familiar with. I cannot simply “remove” it from their UI.