IPv6 support

[rhc54]

Background information

What version of Open MPI are you using? (e.g., v1.10.3, v2.1.0, git branch name and hash, etc.)

3.1.3 and 4.0.1

Describe how Open MPI was installed (e.g., from a source/distribution tarball, from a git clone, from an operating system distribution package, etc.)

from a source tarball

Please describe the system on which you are running

Operating system/version: Linux CentOS 7
Computer hardware: Intel Xeon
Network type: Different
Details of the problem

Hi everyone,

We are experiencing issues with Open MPI on systems with various IPv4/IPv6 configurations and I'd like to dispel some confusion here. It seems like we need --enable-ipv6 to use Open MPI on IPv6-only systems. It also seems like this will still make Open MPI usable on mixed IPv4/IPv6 systems (network interfaces having both IPv4 and an IPv6 addresses). However, we are seeing problems with this configuration flags on IPv4-only systems, where our runs abort with

[epb234:369271] [[47204,0],0] ORTE_ERROR_LOG: Address family not supported by protocol in file oob_tcp_listener.c at line 123
[epb234:369271] [[47204,0],0] ORTE_ERROR_LOG: Address family not supported by protocol in file oob_tcp_component.c at line 700
I got a couple of questions:

Is it true that --enable-ipv6 is required to make Open MPI usable on IPv6-only systems?
Is it true that we must not specify --enable-ipv6 to make Open MPI usable on IPv4-only systems?
If the answer is 2x yes, is it true that there is no way to get a single Open MPI build which supports all three configurations (IPv4-only, mixed IPv4/IPv6, and IPv6-only)?
Thanks a lot for your help,
Moritz

Cross-reference: open-mpi/ompi#6960

[rhc54]

Note that it may well be a higher priority for some community members where IPv6 support is considered important.