CONFIG_MPTCP_IPV6 should be enabled

[bjacke]

Describe the bug

ip mptcp endpoint can't add IPv6 addresses.

Steps to reproduce the behaviour

The reason is that CONFIG_MPTCP_IPV6 isn't enabled for the kernel compile configuration.

Device (s)

Raspberry Pi 5

System

Kernel: 6.6.62+rpt-rpi-2712 #1 SMP PREEMPT Debian 1:6.6.62-1+rpt1 (2024-11-25) aarch64 GNU/Linux

Logs

No response

Additional context

No response

[pelwell]

This is effectively a duplicate of #5487, which was rejected. The fundamental facts haven't changed in the last 18 months - MPTCP_IPV6 still requires that IPV6 is built-in (CONFIG_IPV6=y). Last time I checked, this caused a kernel size increase of ~500kB, which is quite a punishment for the majority of people who don't use IPV6 - it's worst on small-memory platforms like Pi Zero 2.

[matttbe]

Hi @pelwell

Thank you for your reply!

@bjacke just pinged me about this ticket.

The fundamental facts haven't changed in the last 18 months - MPTCP_IPV6 still requires that IPV6 is built-in (CONFIG_IPV6=y). Last time I checked, this caused a kernel size increase of ~500kB, which is quite a punishment for the majority of people who don't use IPV6 - it's worst on small-memory platforms like Pi Zero 2.

Being able to support MPTCP as a module means quite a lot of development, for a very low benefit. Not being able to use MPTCP with IPv6 is quite blocking for some users. As a compromise, would it be eventually possible to have IPV6 (+ MPTCP_IPV6) built-in on all platforms except the RPi Zero and the RPI 1? So not on BCM2835 and BCM2710?

Please note that having IPV6 as a module instead of built-in also has a small extra cost for all deployments with a network connection, including the ones with just a loopback interface having assigned the ::1/128 IPv6 address. Likely most deployments? (Or at least the majority of the ones still getting updates :) )