Once I set iptables to reroute a port, how do I undo it?
I've been reading on many sites how to use iptables to reroute one port to another in Linux. For instance, rerouting port 80 to 8080 would look like this...
iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to 8080
My concern is, what if I change my mind? I haven't read anywhere that gives syntax for correcting it. I assume there is a (simple?) way to do it, but I'm too new at Linux to intuitively figure out how to restore port 80 to its original behavior without reinstalling the OS.
Solution 1:
You can use the -D option to iptables to delete rules from your chains. For example
First list the chain you want to remove a rule from, use --line-numbers
sudo iptables -L RH-Firewall-1-INPUT -n --line-numbers
Chain RH-Firewall-1-INPUT (2 references)
num target prot opt source destination
1 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:80
2 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
3 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 255
4 ACCEPT esp -- 0.0.0.0/0 0.0.0.0/0
5 ACCEPT ah -- 0.0.0.0/0 0.0.0.0/0
6 ACCEPT udp -- 0.0.0.0/0 224.0.0.251 udp dpt:5353
7 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:631
8 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:631
9 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
10 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
11 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
To delete line 6
sudo iptables -D RH-Firewall-1-INPUT 6
sudo iptables -L RH-Firewall-1-INPUT -n --line-numbers
Chain RH-Firewall-1-INPUT (2 references)
num target prot opt source destination
1 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:80
2 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0
3 ACCEPT icmp -- 0.0.0.0/0 0.0.0.0/0 icmp type 255
4 ACCEPT esp -- 0.0.0.0/0 0.0.0.0/0
5 ACCEPT ah -- 0.0.0.0/0 0.0.0.0/0
6 ACCEPT udp -- 0.0.0.0/0 0.0.0.0/0 udp dpt:631
7 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 tcp dpt:631
8 ACCEPT all -- 0.0.0.0/0 0.0.0.0/0 state RELATED,ESTABLISHED
9 ACCEPT tcp -- 0.0.0.0/0 0.0.0.0/0 state NEW tcp dpt:22
10 REJECT all -- 0.0.0.0/0 0.0.0.0/0 reject-with icmp-host-prohibited
If you have your iptables configuration saved in a file don't forget to update the file (iptables-save, service iptables save etc.)
Solution 2:
If you are scripting, it's easier to remove by definition:
Example:
To add:
iptables -t nat -A PREROUTING -p tcp --dport 80 -j REDIRECT --to 8080
Notice the -A? it means add.
To remove:
iptables -t nat -D PREROUTING -p tcp --dport 80 -j REDIRECT --to 8080
Notice the -D? it means delete.
Solution 3:
http://linux.die.net/man/8/iptables:
ahem
iptables -L, --list [chain]
List all rules in the selected chain. If no chain is selected, all chains are listed. As every other iptables command, it applies to the specified table (filter is the default), so NAT rules get listed by
iptables -t nat -n -L
Please note that it is often used with the -n option, in order to avoid long reverse DNS lookups. It is legal to specify the -Z (zero) option as well, in which case the chain(s) will be atomically listed and zeroed. The exact output is affected by the other arguments given. The exact rules are suppressed until you use
iptables -L -v
...
iptables -D, --delete chain rule-specification
iptables -D, --delete chain rulenum
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 (starting at 1 for the first rule) or a rule to match.