CentOS - Jan 2021 - How to do virtual IP on NetworkManager

On Mon, Jan 18, 2021 at 2:56 PM Jerry Geis <jerry.geis at gmail.com>
wrote:
> Hi All,
>
> I use virtual IP from time to time on CentOS 7. just take something like
> eth0 and make eth0:1 put in there the IP and subnet and bring up the new IP
> and it works.
>
> How do I do that with NetworkManager on the command line (assuming all
> static IP information)
> I do something like this from nmcli to set the static address:
> nmcli connection modify eth0 ipv4.method manual ipv6.method ignore
> autoconnect yes ipv4.addr 192.168.1.8/24 gw4 192.168.1.1 ipv4.dns 8.8.8.8
>
> How then do I add a virtual IP?
>
> Thanks
>
> Jerry

With nmcli you should use:
nmcli con mod eth0 +ipv4.addresses 192.168.1.X/24

This would modify your existing ifcfg-eth0 adding the lines:

IPADDR1=192.168.1.X
PREFIX1=24

To have the new setting applied and your new ip alias up and running you
can then use

nmcli dev reapply eth0
(supposing the device name bound to the connection is eth0)

You can also manually modify the file adding the two lines above and then
run:
nmcli con reload
nmcli dev reapply eth0

I think you should not lose your connection, but always test on a non
production machine with the same os version... just for safety
HIH,
Gianluca

> On Mon, Jan 18, 2021 at 2:56 PM Jerry Geis <jerry.geis at gmail.com>
wrote:
>
>> Hi All,
>>
>> I use virtual IP from time to time on CentOS 7. just take something
like
>> eth0 and make eth0:1 put in there the IP and subnet and bring up the
new
>> IP
>> and it works.
>>
>> How do I do that with NetworkManager on the command line (assuming all
>> static IP information)
>> I do something like this from nmcli to set the static address:
>> nmcli connection modify eth0 ipv4.method manual ipv6.method ignore
>> autoconnect yes ipv4.addr 192.168.1.8/24 gw4 192.168.1.1 ipv4.dns
>> 8.8.8.8
>>
>> How then do I add a virtual IP?
>>
>> Thanks
>>
>> Jerry
>
>
> With nmcli you should use:
> nmcli con mod eth0 +ipv4.addresses 192.168.1.X/24
>
> This would modify your existing ifcfg-eth0 adding the lines:
>
> IPADDR1=192.168.1.X
> PREFIX1=24
>
> To have the new setting applied and your new ip alias up and running you
> can then use
>
> nmcli dev reapply eth0
> (supposing the device name bound to the connection is eth0)
>
> You can also manually modify the file adding the two lines above and then
> run:
> nmcli con reload
> nmcli dev reapply eth0
>
> I think you should not lose your connection, but always test on a non
> production machine with the same os version... just for safety
> HIH,
> Gianluca
Hi Gianluca,

Am I right that what you describe doesn't add an alias device like eth0:1
but adds the additional IP address to the eth0 device?

Apart from that, when running with NetworkManager, can one still add a
temporary eth0:1 alias (with ifconfig/ip), use it and remove it again, or
does NM somehow prevent this?

Regards,
Simon