Nothing is ever easy, but if it is difficult you must be doing it wrong.
I am still confused how come netplan didn't create any configuration on install. Possible arp remains in the switches are valid point but I do not think it is the issue. They should be cleared after a while anyway otherwise IP changes in a network would be impossible.
I know it is difficult to play around with production servers, but because all of this is very confusing, I would try commenting out the .139 setup you did in /etc/network/interfaces and reboot. If the server starts responding only to .190 that would prove the theory that it is somewhere configured (although we can't figure out where ).
If that is the case, I would even try using the command line and 'ip' command to try replacing the IP like that, and to continue the investigation... Basically that command could show a lot (with correct parameters) although I have never needed to use it because I have always worked with /etc/network/interfaces and I still haven't installed my first 18.04 to start using netplan.
Darko.
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Ubuntu 18.04 LTS 64bit
As .190 doesn't show in ifconfig, maybe it's not an assigned address. Does it show up in the output of command "ip address list"?
I wonder if it's a NAT redirect entry somewhere. See if this command outputs anything: "sudo iptables-save | grep 190".
I might be able to try this tonight; if so I'll report back with the findings.
Code: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:d7:a8:20 brd ff:ff:ff:ff:ff:ff inet 172.16.249.139/24 brd 172.16.249.255 scope global ens160 valid_lft forever preferred_lft forever inet 172.16.249.190/24 brd 172.16.249.255 scope global secondary ens160 valid_lft forever preferred_lft forever inet6 fe80::20c:29ff:fed7:a820/64 scope link valid_lft forever preferred_lft forever
"sudo iptables-save | grep 190" doesn't output anything after entering in my admin password.
Booted up off a linux live disc. Could not ping .139 or .190. Live OS only showed one NIC in the system.I know you don't want down time, but you can prove if there is an arp issue
if you boot a live "CD/USB" and see if those addresses are still pingable.
If they are, you can rule out config on the server.
https://imgur.com/a/bfgsH5w
Well the output in post #15 shows both IPs as configured on that single interface. The harder part seems to be to find how and where... The 'ip' command should also have options to delete an IP, in this case the .190. I just haven't used it before and I'm little busy to google right now. I'll try later if you don't resolve it...
Darko.
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Ubuntu 18.04 LTS 64bit
I'll google and report back...
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