Why do iptables rules disappear when restarting my Debian system?

I add this rule:

sudo iptables -t nat -A OUTPUT -d a.b.c.d -p tcp 
       --dport 1723 -j DNAT --to-destination a.b.c.d:10000

1. When restart computer rules are deleted. Why?
2. What I can do to make the rules persist?

Answers:

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Method 1

On Debian, install iptables-persistent:

sudo apt-get install iptables-persistent

The package will automatically load /etc/iptables/rules for you during boot.

Any time you modify your rules, run /sbin/iptables-save > /etc/iptables/rules to save them. You can also add that to the shutdown sequence if you like.

Method 2

There is no option in iptables which will make your rules permanent. But you can use iptables-save and iptables-restore to fulfill your task.

First add the iptable rule using the command you gave.

Then save iptables rules to some file like /etc/iptables.conf using following command:

$  iptables-save > /etc/iptables.conf

Add the following command in /etc/rc.local to reload the rules in every reboot.

$  iptables-restore < /etc/iptables.conf

Method 3

After installing iptables-persistent above you can also save rules with the following shorter command on Ubuntu 16.04+:
sudo netfilter-persistent save

And they can also be restored back to how they were last time you saved them with:
sudo netfilter-persistent reload

Method 4

Because you did not save the iptables rules.

You can do that by using sudo iptables-save

Method 5

1. Install iptables-persistent package
2. Whenever you change the rules of iptables, you should save the backup into following file using following command:

iptables-save -f /etc/iptables/rules.v4 (for iptables)

iptables-save -f /etc/iptables/rules.v6 (for ip6tables)

Method 6

First install the persist iptables (ubunut or debian)

   apt install iptables-persistent

Run your statement:

   iptables -A INPUT -s 0/0 -p tcp --dport 5433 -j ACCEPT

Then save the settings

   iptables-save

Finally restart the machine to verify

reboot

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0