Ubuntu 18.04 minimal server has two IP addresses!

Question

I'm seeing two different IP addresses on my Odroid XU4. I only noticed after I set up a Unifi controller on the box, but then tried to ssh into both of the addresses with success. I only want 192.168.2.3, and no IPv6.

mike@odroid:~$ ip addr show
1: lo:  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:  mtu 1500 qdisc fq_codel state UP group default qlen 1000
    link/ether 00:1e:06:30:1e:f5 brd ff:ff:ff:ff:ff:ff
    inet 192.168.2.3/24 brd 192.168.2.255 scope global dynamic noprefixroute eth0
       valid_lft 3069558340sec preferred_lft 3069558340sec
    inet 192.168.2.9/24 brd 192.168.2.255 scope global secondary eth0
       valid_lft forever preferred_lft forever

mike@odroid:~$ ifconfig
eth0: flags=4163  mtu 1500
        inet 192.168.2.3  netmask 255.255.255.0  broadcast 192.168.2.255
        ether 00:1e:06:30:1e:f5  txqueuelen 1000  (Ethernet)
        RX packets 12821  bytes 2393432 (2.3 MB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 13336  bytes 9323830 (9.3 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73  mtu 65536
        inet 127.0.0.1  netmask 255.0.0.0
        inet6 ::1  prefixlen 128  scopeid 0x10
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 10593  bytes 4855090 (4.8 MB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 10593  bytes 4855090 (4.8 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

As we can see here eth0 has two IP address and is only shown by ip command and not by ifconfig. I am unable to understand where this is coming from or how to disable the 2nd IP permanently. I would like to get rid of the 2nd IP address permanently.

mike@odroid:~$ cat /etc/network/interfaces
# interfaces(5) file used by ifup(8) and ifdown(8)
# Include files from /etc/network/interfaces.d:
source-directory /etc/network/interfaces.d

mike@odroid:~$ cat /etc/netplan/*.yaml
cat: '/etc/netplan/*.yaml': No such file or directory

Solution

I have struggled with this exact same problem and every search comes up with several others experiencing the same issue with no resolution.

FINALLY, here is what solved it for me:

ip addr flush dev <your_adapter_id>

for me it was

ip addr flush dev enp0s4

This kills the secondary IP.

Comments

[chili555]

eth0 seems unusual for an interface in 18.04. Please edit your question to add the result of the terminal commands: cat /etc/network/interfaces and also: cat /etc/netplan/*.yaml Welcome to Ask Ubuntu.

[Mike Tarbox]

mike@odroid:~$ cat /etc/network/interfaces # interfaces(5) file used by ifup(8) and ifdown(8) # Include files from /etc/network/interfaces.d: source-directory /etc/network/interfaces.d

[Mike Tarbox]

mike@odroid:~$ cat /etc/netplan/*.yaml cat: '/etc/netplan/*.yaml': No such file or directory

[Thomas Ward]

Are you 100% certain this is Ubuntu 18.04? What's the output of lsb_release -a (to confirm the version of Ubuntu you're using)? Have you checked /etc/network/interfaces.d/ for any configuration items there that might be the network config?

[Mike Tarbox]

mike@odroid:~$ lsb_release -a No LSB modules are available. Distributor ID: Ubuntu Description: Ubuntu 18.04.1 LTS Release: 18.04 Codename: bionic

[Mike Tarbox]

And /etc/network/interfaces.d doesn't exist. mike@odroid:/etc/network$ ls if-down.d if-post-down.d if-pre-up.d if-up.d interfaces

[chili555]

I'm not sure how this even connects! Do you have to issue a terminal command or what? If so, what is it?

[Mike Tarbox]

It's connected. I am ssh'd into it as I type. After every reboot I do have to go in and disable ipv6 and add the DNS servers. I use webmin as my cli is almost nonexistent.

[Mike Tarbox]

I should also note that this was a fresh install and not an upgrade from 16.04. Is it possible that the builders of the distro have messed up? This is for an Odroid XU4, downloaded directly from hardkernel.

[Sergiy Kolodyazhnyy]

This seems to be a form of a bug where old IP address is not being released (potentially a DHCP bug, though I've not done much digging on the subject). Please VTC askubuntu.com/q/1082605/295286 and askubuntu.com/q/1030957/295286 as duplicates of this post

[Sergiy Kolodyazhnyy]

I suspect this issue may be due to previous failed dhcp lease not being released by the system, hence why flushing config works. Since this post is unlikely to be revisited by OP to confirm +1ed this post for effort to resolve and for providing what appears to be appropriate solution

[Mike Tarbox]

Actually I did log in to see the response. I ended up switching over to 16.04. I was using the odroid to run pi-hole, or at least attempting to. I ended up using the odroid to run my unifi controller instead.