IPv6 gets disabled on server reboot if DHCP is enabled

Created:

2017-04-20 17:37:13 UTC

Modified:

2017-08-08 13:28:21 UTC

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IPv6 gets disabled on server reboot if DHCP is enabled

Applicable to:

  • Plesk for Linux

Symptoms

After the server reboot, IPv6 addresses are absent from network interface.

IPv6 is disabled on server:

# cat /proc/sys/net/ipv6/conf/all/disable_ipv6
1

 

# cat /proc/sys/net/ipv6/conf/default/disable_ipv6
1

Settings in /etc/sysctl.conf does not resolve the issue: 

# cat /etc/sysctl.conf | grep ipv6  

net.ipv6.conf.all.disable_ipv6=0
net.ipv6.conf.default.disable_ipv6=0

DHCP server is enabled in interface settings:

# cat /etc/sysconfig/network-scripts/ifcfg-eth0 | grep dhcp  

BOOTPROTO=dhcp

Following lines can be found in the /var/log/messages file:

Apr 21 12:02:47 servername dhclient[963]: bound to 203.0.113.2 -- renewal in 42257 seconds.
Apr 21 12:02:47 servername network: Determining IP information for eth0... done.
Apr 21 12:02:47 servername network: INFO    : [ipv6_wait_tentative] Waiting for interface eth0 IPv6 address(es) to leave the "tentative" state
Apr 21 12:02:47 servername ipv6_wait_tentative: Waiting for interface eth0 IPv6 address(es) to leave the "tentative" state
Apr 21 12:02:48 servername network: INFO    : [ipv6_wait_tentative] Waiting for interface eth0 IPv6 address(es) to leave the "tentative" state
Apr 21 12:02:48 servername ipv6_wait_tentative: Waiting for interface eth0 IPv6 address(es) to leave the "tentative" state

Cause

DHCP server misconfiguration. IPv6 address is removed from the network interface after IPv4 address is assigned by DHCP server.

Resolution

Contact the network administrator in order to resolve the issue.

As a workaround, IPv6 can be enabled manually via the following commands:

# echo 0 > /proc/sys/net/ipv6/conf/all/disable_ipv6


# echo 0 > /proc/sys/net/ipv6/conf/default/disable_ipv6
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