When running a lab VM, IPv6 is often not needed. Keeping things simple helps avoid unexpected issues.

Check Current IPv6 Usage

sudo lsof -n | grep -i tcp
sshd       456    root    3u     IPv4    14117    0t0    TCP *:ssh (LISTEN)
sshd       456    root    4u     IPv6    14140    0t0    TCP *:ssh (LISTEN)
nginx     5536    root    6u     IPv4    23900    0t0    TCP *:http (LISTEN)
nginx     5536    root    7u     IPv6    23901    0t0    TCP *:http (LISTEN)

# Edit /etc/sysctl.conf
sudo vi /etc/sysctl.conf

# Add these lines at the bottom
net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.default.disable_ipv6=1
net.ipv6.conf.lo.disable_ipv6=1

# Apply changes
sudo sysctl -p

Method 2: GRUB

# Edit /etc/default/grub
sudo vi /etc/default/grub

# Change these lines
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash ipv6.disable=1"
GRUB_CMDLINE_LINUX="ipv6.disable=1"

# Update GRUB and reboot
sudo update-grub
sudo reboot

Source: BLOG-D

Fixing Nginx After Disabling IPv6

After disabling IPv6, nginx may fail to start:

nginx: [emerg] socket() [::]:80 failed (97: Address family not supported by protocol)

Solution: Edit nginx config to listen on IPv4 only:

# Edit nginx config
sudo vim /etc/nginx/sites-enabled/default

# Comment out this line:
# listen [::]:80 default_server;

# Restart nginx
sudo systemctl restart nginx

After the fix:

sudo lsof -n | grep -i tcp
sshd      460    root    3u     IPv4    13874    0t0    TCP *:ssh (LISTEN)
nginx     589    root    6u     IPv4    16525    0t0    TCP *:http (LISTEN)

Source: techglimpse.com