The "ipv6 disable=1" option does not seem to work on Red Hat Enterprise Linux 6 system

Solution Verified - Updated

Environment

  • Red Hat Enterprise Linux 6
  • dracut-network plugin

Issue

  • Using instruction mentioned on this kbase : https://access.redhat.com/kb/docs/DOC-8709 the following entry has been made in /etc/modprobe.d/ipv6.conf file :
options ipv6 disable=1
  • But this does not disable ipv6

Resolution

  • There are two options to resolve this.

    • Remove the dracut-network package, and then rebuild the initramfs , as the modules pulled by darcut-network will still be available in the initramfs file.
    • Just rebuild the initramfs file. The ipv6.conf file will be pulled into the initramfs file, and applied at the initramfs stage.

  • The problem only arises if all these conditions are met :

    • The dracut-network plug-in is installed
    • No ipv6.conf file is present, and
    • No initramfs is built.

  • So, creating the ipv6.conf file immediately after the system install, should reduce the probability of this problem occuring.

Root Cause

  • The root cause of the issue is the dracut-network plug-in
  • This plugin (used for network booting) pulls in ipv6 dependency at the initramfs stage itself, and thus when the system completely boots up, any modprobe.conf option for ipv6 is not applied (as the module has been already loaded during the initramfs stage).
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