Why is 'ip_forward' enabled by default upon boot in Red Hat Enterprise Linux?

Solution Verified - Updated -

Issue

  • Upon boot, the output of /proc/sys/net/ipv4/ip_forward as well as sysctl net.ipv4.ip_forward shows ip_forward as enabled:
$ cat /proc/sys/net/ipv4/ip_forward 
1
$ sysctl net.ipv4.ip_forward
net.ipv4.ip_forward = 1
$ 

However, /etc/sysctl.conf has the parameter disabled by default:

$ grep ip_forward /etc/sysctl.conf 
net.ipv4.ip_forward = 0
$ 
  • Why can't the kernel parameter net.ipv4.ip_forward = 0 be disabled permanently?
  • Even if net.ipv4.ip_forward = 0 is set in /etc/sysctl.conf, ip forwarding does not get disabled after reboot

Environment

  • Red Hat Enterprise Linux 5
  • Red Hat Enterprise Linux 6
  • Red Hat Enterprise Linux 7

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