Why different port number is mapped on ipv4 and ipv6 address for same expose port?

Docker Engine General
1

With docker version 20.10.6, build 370c289. observed that different port is assigned for same exposed port on ipv4 and ipv6 addresses. Why?

$ docker ps --format "{{.Ports}}"
0.0.0.0:49338->9999/tcp, :::49337->9999/tcp
0.0.0.0:49339->6379/tcp, :::49338->6379/tcp
0.0.0.0:49319->6379/tcp, :::49318->6379/tcp
3

I have the very same problem. In my case only installing the version 20.10.1 fixed the issue - because it does not assign IPv6 ports by default.

I have not found out any other way to disable IPv6 port assignment yet. My case is, that I require IPv6 available in the container itself, but the port being bound to only IPv4. Since I’m using Jenkins I can not use the syntax 0.0.0.0:80:80 for that, because I need the port bound to an arbitrary host port.

The problem accumulates due to using the classic swarm which maps the IPv6 ports to IPv4 ports, resulting in port overlaps.

4

Running Docker version 20.10.8, build 3967b7d on Debian 10 does not show the mentioned problem - all ports are available for IPv4 + IPv6 the way I expected it

~$ docker ps --format '{{.Ports}}' | grep '\->'
0.0.0.0:2180->80/tcp, :::2180->80/tcp
0.0.0.0:2080->80/tcp, :::2080->80/tcp, 0.0.0.0:2443->443/tcp, :::2443->443/tcp
80/tcp, 0.0.0.0:3443->443/tcp, :::3443->443/tcp
0.0.0.0:7080->80/tcp, :::7080->80/tcp, 0.0.0.0:7443->443/tcp, :::7443->443/tcp
0.0.0.0:1883-1884->1883-1884/tcp, :::1883-1884->1883-1884/tcp, 0.0.0.0:9001->9001/tcp, :::9001->9001/tcp

That means the bug (?) is gone/fixed with newer versions :slight_smile:

5

I had a short exchange over at Vendor in Libnetwork changes by arkodg · Pull Request #41805 · moby/moby · GitHub - I did check the version 20.10.7 since that is the must recent one on Ubuntu when I installed a few days ago.

There is also the issue Different port number are getting mapped on ipv4 and ipv6 for same expose port · Issue #42442 · moby/moby · GitHub which is not yet fixed.

The issue may not show from the start, it looks more like something coming after a while.