What determines whether I have an IPv4 or IPv6 address to the outside?

RouterOS Beginner Basics
1

Hi,

I have a Mikrotik Router with RouterOS v6.29.1.
When I ask Google what is my ip address, most of the time I get an IPv6 address. But sometimes I get an IPv4 address.
This is on my Dell laptop with Ubuntu. I also have a new Odroid XU4 SoC (also with Ubuntu) and so far it has only had an IPv4 address to the outside.
What determines this and how can I change it?

When I run ifconfig on either of my Ubuntu computers, it shows both an IPv4 and IPv6 address, but the IPv6 address only seems to be accessible from outside my network when it is also the IP address that Google tells me I have.

Thanks,
David

2

It depends on clients application. In most cases ipv6 is preferred, if it fails ipv4 is used.

3

Thanks.
But that doesn’t explain why on one compute when I connect with Firefox to Google I get an IPv6 address and on the other computer when I again connect with Firefox to Google I get on IPv4 address.
And it also doesn’t explain why (when I open the firewall) I can connect to one device (from outside my network) through its IPv6 address but to the other device only though NAT and my external IPv4 address.

Could you suggest a client application that should always connect through IPv6 and some way I could test this hypothesis?

4

Do both PCs have an IPv6 address?
Linux: ifconfig
Windows command prompt: ipconfig

5

My laptop has 3 IPv6 addresses. Two that start with 2a02 and one that starts with fe80.
My server has 2 IPv6 addresses. One that starts with 2a02 and one that starts with fe80.

When on my laptop I ask google my ip address I get one of the addresses that start with 2a02.
When I do the same on my server, I get an IPv4 address starting with 85.