Step 1 – List iptables postrouting rules on Linux

The syntax is as follows:
iptables -t nat -v -L POSTROUTING -n --line-number
OR
iptables -t nat -v -L -n --line-number
Sample outputs:

1. -t nat : Select nat table.
2. -v : Verbose output.
3. -L : List all rules in the selected chain i.e show all rules in nat table.
4. -L POSTROUTING : List all rules in the POSTROUTING chain only.
5. -n : Numeric output. In other words, IP addresses and port numbers will be printed in numeric format instead of DNS names. This will speed up listing rules.
6. --line-number : When listing rules, add line numbers to the beginning of each rule, corresponding to that rule’s position in the chain. You need to use line numbers to delete nat rules from POSTROUTING chain.

Step 2 – Linux iptables delete postrouting nat rule (version 1)

The syntax is:
iptables -t nat -D POSTROUTING {number-here}
To delete rule # 5 i.e. the following rule:

5       40  3360 SNAT       all  --  *      *       10.8.0.0/24          0.0.0.0/0            to:202.54.1.5

Type the following command:
iptables -t nat -D POSTROUTING 5
OR
iptables -t nat --delete POSTROUTING 5
Verify it, enter:
iptables -t nat -v -L POSTROUTING -n --line-number
Sample outputs:

Chain POSTROUTING (policy ACCEPT 94 packets, 6392 bytes)
num   pkts bytes target     prot opt in     out     source               destination         
1       10   762 MASQUERADE  all  --  *      eth1    10.8.0.0/24          0.0.0.0/0           
2        0     0 MASQUERADE  all  --  *      eth1    10.8.0.0/24          0.0.0.0/0           
3        0     0 MASQUERADE  all  --  *      eth1    10.0.0.0/8           0.0.0.0/0           
4        0     0 MASQUERADE  all  --  *      eth1    10.0.0.0/8           0.0.0.0/0

Another syntax to remove specific postrouting rules from iptables (version 2)

Say, you execute the following postrouting command:
# iptables -t nat -A POSTROUTING -o eth1 -s 10.8.0.0/24 -j MASQUERADE
To delete, run the same above commands but replace the “-A” with “-D”
# iptables -t nat -D POSTROUTING -o eth1 -s 10.8.0.0/24 -j MASQUERADE
Another example, run the same commands but replace the “-I” with “-D“. For example:
# iptables -t nat -I POSTROUTING -s 10.8.0.0/24 -j SNAT --to 202.54.1.5
Becomes:
# iptables -t nat -D POSTROUTING -s 10.8.0.0/24 -j SNAT --to 202.54.1.5
OR
# iptables -t nat --delete POSTROUTING -s 10.8.0.0/24 -j SNAT --to 202.54.1.5

Related: Linux Iptables Delete prerouting Rule Command

Conclusion

You learned how to list and remove/delete iptables postrouting rules on Linux server. The above commands works on Debian, Ubuntu, CentOS, RHEL, Fedora and all other Linux distros. The -D or --delete option delete one or more rules from the selected chain. There are two versions of this command, the rule can be specified as a number in the chain (version 1) or a rule to match (version 2) as described above. See iptables man page for more info here and my tutorials for more info:

• Linux: 25 Iptables Netfilter Firewall Examples For New SysAdmins
• CentOS / Redhat Iptables Firewall Configuration Tutorial
• How to setup a UFW firewall on Ubuntu 16.04 LTS server
• How to setup a UFW firewall on Ubuntu 18.04 LTS server
• In-depth tutorial about setting up FirewallD on RHEL 8, CentOS 8, or OpenSUSE 15.1