Debian one interfaces gets two ip addresses

Question

I've just installed the new debian 10.4.0-amd64-standard.

I configured the network interface ip to static (eth0):

iface eth0 inet static
address 10.1.1.41/24
gateway 10.1.1.1
dns-nameservers 10.1.1.20

But when I type ip addr I get two ip addresses on the same interface.

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 mq state UP group default qlen 1000
    link/ether 00:15:5d:01:0a:09 brd ff:ff:ff:ff:ff:ff
    inet 10.1.1.103/24 brd 10.1.1.255 scope global dynamic eth0
       valid_lft 549236sec preferred_lft 549236sec
    inet 10.1.1.41/24 brd 10.1.1.255 scope global secondary eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::215:5dff:fe01:a09/64 scope link
       valid_lft forever preferred_lft forever

What do I have to do to get rid of the DHCP IP "10.1.1.103"?

As requested output of ps aux | grep dhcp:

root        381  0.0  0.2   9488  5736 ?        Ss   Aug12   0:00 /sbin/dhclient -4 -v -i -pf /run/dhclient.eth0.pid -lf /var/lib/dhcp/dhclient.eth0.leases -I -df /var/lib/dhcp/dhclient6.eth0.leases eth0
root      12551  0.0  0.0   6076   828 pts/0    S+   07:43   0:00 grep dhcp

After disabling the dhcp service. This shows up when I type ifup eth0:

sudo ifup eth0
Internet Systems Consortium DHCP Client 4.4.1
Copyright 2004-2018 Internet Systems Consortium.
All rights reserved.
For info, please visit https://www.isc.org/software/dhcp/

Listening on LPF/eth0/00:15:5d:01:0a:09
Sending on   LPF/eth0/00:15:5d:01:0a:09
Sending on   Socket/fallback
DHCPDISCOVER on eth0 to 255.255.255.255 port 67 interval 3
DHCPOFFER of 10.1.1.103 from 10.1.1.20
DHCPREQUEST for 10.1.1.103 on eth0 to 255.255.255.255 port 67
DHCPACK of 10.1.1.103 from 10.1.1.20
bound to 10.1.1.103 -- renewal in 1523 seconds.

Looks like it is still requesting the dhcp for an ip.

Answer 1

I just ran into this as well on a fresh install of Debian 11 on 5 Mac Minis and wanted to share what I found. Digging into /var/log/syslog, I noticed that connmand was bringing up my Ethernet and requesting DHCP. Then about 5 seconds later, dhclient was doing the same.

This resulted in two IP addresses being assigned to my machines. I removed connman package, rebooted, and everything is happy now only pulling a single DHCP request.

Answer 2

Most likely, you have Network Manager still running: the extra ip address your eth0 interface gets can only come from a DHCP request (as shown also by the presence of dhclient in the output of ps aux).

Just disable it,

sudo systemctl disable network-manager

and reboot to check that now you are indeed getting a single IP address.

Answer 3

Got the same issue recently:

You can resolve it in systemd like this:

You do not need to add/modify file /etc/network/interfaces to setup an IP

mv /etc/systemd/network/99-dhcp.network   /etc/systemd/network/99-static.network

edit the renamed file:

Inside replace [network] part from DHCP to:

[NETWORK]

Address=xxx.xxx.xxx.xxx/yy

Gateway=xxx.xxx.xxx.xxx

DNS=xxx.xxx.xxx.xxx.xxx

(Just in case check the [MATCH] section has a correct expression to match your iface name like: Name=e* )

Then reboot

Answer 4

For me, I installed a new Debian 11 (console only) and then added my xfce4, xorg etc... so as to avoid all the un-needed add on packages. I could not get a Network Icon to work on my xfce4 panel without adding network-manager and putting it in control. Once I did that, I could get my Icon back but then ended up with two IP addresses (just as this OP described).

It stayed that way until I removed isc-dhcp-client. Once that was done things worked as expected - seems that if the two network manager packages will run on top of each other - that installing one might remove the other? Anyway that seemed to work for me.

Answer 5

I just figured out a solution and will share a theory about what I think was happening.

On my system, at least, it looks like the interface is assigned connections from NetworkManager and /etc/network/interfaces. I was digging around the NetworkManager man pages and in NetworkManager.conf(5), in section IFUPDOWN SECTION, it says that if the managed variable is set to false, "any interface listed in /etc/network/interfaces will be ignored by NetworkManager."

When I set managed to true, the first of the two connections went away (after restarting networking), leaving the only defined connection the one I defined in /etc/network/interfaces.

I hesitate to speculate further because I often misinterpret what I think are clues, but I can't help myself.

My objective was to have a static IP address, which I defined in /etc/network/interfaces, but calling ip address always showed a DHCP-defined address. I installed isc-dhcp-client and kept trying to get a static address until I noticed that (for who knows how long) multiple IP addresses were listed, one of which was the one I defined in /etc/network/interfaces. This contradicts NetworkManager.conf(5), which says that it should have been ignored if managed is set to false. Perhaps installing the DHCP client overrode NetworkManager.