enabling ipv4 forwarding on docker server

Common errors when the ipv4 forwarding is not enabled on the linux host leading to unidentifiable issues. here is one such rare log from the system logs

level=warning msg="IPv4 forwarding is disabled. N...t work."

Its good to check the current ipv4.forwarding rules as follows:

[root@LinuxCent ~]# sysctl net.ipv4.conf.all.forwarding
net.ipv4.conf.all.forwarding = 0

 

You can also enable the changes for the current session using the -w option

sysctl -w net.ipv4.conf.all.forwarding=1

To make the changes persistent we need to write to a config file and enforce the system to read it.

[root@LinuxCent ~]# vi /etc/sysctl.d/01-rules.conf
net.ipv4.conf.all.forwarding=1

Then apply the changes to the system on the fly with the sysctl command to load the changes from systemwide config files.

# sysctl –system
--system : tells the sysctl to read all the configuration file system wide

 

[root@Linux1 ~]# sysctl --system
* Applying /usr/lib/sysctl.d/00-system.conf ...
net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0
* Applying /etc/sysctl.d/01-rules.conf ...
net.ipv4.conf.all.forwarding = 1
* Applying /usr/lib/sysctl.d/10-default-yama-scope.conf ...
kernel.yama.ptrace_scope = 0
* Applying /usr/lib/sysctl.d/50-default.conf ...
kernel.sysrq = 16
kernel.core_uses_pid = 1
net.ipv4.conf.default.rp_filter = 1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.default.accept_source_route = 0
net.ipv4.conf.all.accept_source_route = 0
net.ipv4.conf.default.promote_secondaries = 1
net.ipv4.conf.all.promote_secondaries = 1
fs.protected_hardlinks = 1
fs.protected_symlinks = 1
* Applying /etc/sysctl.d/99-sysctl.conf ...
* Applying /etc/sysctl.conf ...
[root@Linux1 ~]# sysctl net.ipv4.conf.all.forwarding
net.ipv4.conf.all.forwarding = 1

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