IPv6 issues Ubuntu 20.04 server

Alex Smith

1/19/24, 12:56 PM

I have a server running the following software:
Ubuntu 20.04
cPanel 106.0.13
PHP 8.1
MySQL 8
Litespeed Web Server
Elasticsearch 7.17
Redis 7

I am running a magento 2.4.5 store on this server which connects to a remote FTP each day to update products, stock and pricing. My problem is that connecting to this FTP over IPv6 doesnt always work and it doesnt fall back to IPv4, so i have tried disabling IPv6 by adding the following 2 lines to sysctl.conf

net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1

This allows me to connect to the FTP and everything works fine for around 40ish hours at which point the network seems to crash and i lose access to my server. The only way i can get everything running again is to reboot the server from the host control panel.

The host deny IPv6 is running by default and wont help me diagnose/solve the issue.

looking through syslog i can see the lines a couple minutes before the network dies (at least before i get alerted)

systemd-networkd-wait-online[123796]: Event loop failed: Connection timed out
apt-helper[123794]: E: Sub-process /lib/systemd/systemd-networkd-wait-online returned an error code (1)
apt-helper[123794]: E: Sub-process nm-online returned an error code (1)

How can i further diagnose this and fully disable ipv6 without issue?

EDIT: Below is my netplan config. I have not edited this file. It has many routes define under "routes:"

network:
    version: 2
    ethernets:
        enp3s0f0:
            accept-ra: false
            addresses:
            - 2001:41d0:800:354d::/56
            dhcp4: true
            gateway6: 2001:41d0:800:35ff:ff:ff:ff:ff
            match:
                macaddress: fc:34:97:b0:54:57
            nameservers:
                addresses:
                - 2001:41d0:3:163::1
            routes:
            <lots of routes are here>
            set-name: enp3s0f0

232

0 + 2

server

ipv6

networking

20.04

matigo

1/19/24, 1:11 PM

The `systemd-networkd-wait-online` service requires IPv6 in order to run. Disabling that network stack is why it times out and crashes. Are you defining `IPv6AcceptRA` in your netplan config?

Alex Smith

1/19/24, 1:29 PM

I've added my netplan config. accept-ra is set to false. When testing a few things i also tried putting `net.ipv6.conf.all.autoconf=0` and `net.ipv6.conf.all.accept_ra=0` in sysctl.conf which didnt help

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