Second IP via DHCP. Why?

Question

I have a secondary IP on my ens160 interface and I don't know why :) System is Ubuntu 17.10. Any hints where to dig here?

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: ens160: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group default qlen 1000
    link/ether 00:0c:29:07:bd:e3 brd ff:ff:ff:ff:ff:ff
    inet 192.168.0.5/24 brd 192.168.0.255 scope global ens160
       valid_lft forever preferred_lft forever
    inet 192.168.0.165/24 brd 192.168.0.255 scope global secondary ens160
       valid_lft forever preferred_lft forever
    inet6 fe80::20c:29ff:fe07:bde3/64 scope link
       valid_lft forever preferred_lft forever

192.168.0.5 is my static ip, configured via netplan:

network:
  version: 2
  renderer: networkd
  ethernets:
    ens160:
      dhcp4: no
      dhcp6: no
      addresses: [192.168.0.5/24]
      gateway4: 192.168.0.254
      nameservers:
        addresses: [8.8.8.8,1.1.1.1]

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

...then reboot.

sudo shutdown -r

This kills the secondary IP.

Comments

[Admin]

I think the secondary address is configured statically somewhere. A DHCP assigned address seem to contain the keyword dynamic (ie. inet 192.168.0.165/24 brd 192.168.0.255 scope global dynamic secondary ens160). Your output of the command ip addr doesn't.

[Admin]

Check out these locations for configurations files that might cause your problem: /run/netplan/*.yaml, /etc/netplan/*.yaml and /lib/netplan/*.yaml.

[Conti]

I will check these files. But its clearly DHCP, because I see the lease in my DHCP server. And, maybe thats the trick, I added a denyinterfaces ens160 to the /etc/dhcpcd.conf file. But why is this file triggered and where?

[Admin]

Can you see in the DHCP log that 192.168.0.165 is leased to the MAC address 00:0c:29:07:bd:e3?

[Conti]

May 02 10:39:15 pihole systemd[1]: Starting LSB: IPv4 DHCP client with IPv4LL support... May 02 10:39:16 pihole dhcpcd[1310]: ens160: soliciting a DHCP lease May 02 10:39:17 pihole dhcpcd[1310]: ens160: offered 192.168.0.165 from 192.168.0.254 May 02 10:39:17 pihole dhcpcd[1310]: ens160: probing address 192.168.0.165/24 May 02 10:39:23 pihole dhcpcd[1310]: ens160: leased 192.168.0.165 for 3600 seconds May 02 10:39:23 pihole dhcpcd[1310]: ens160: adding route to 192.168.0.0/24