Iptables command
From DD-WRT Wiki
Contents |
This is an infant page. Clean it up and fill it with content!
I think we should have something about firewall builder on this page, since they're kind of related....
Basic Usage
iptables -[AD] chain rule-specification [options] iptables -[RI] chain rulenum rule-specification [options] iptables -D chain rulenum [options] iptables -[LFZ] [chain] [options] iptables -[NX] chain iptables -E old-chain-name new-chain-name iptables -P chain target [options] iptables -h (print this help information)
Commands
--append -A chain Append to chain --delete -D chain Delete matching rule from chain --delete -D chain rulenum Delete rule rulenum (1 = first) from chain --insert -I chain [rulenum] Insert in chain as rulenum (default 1=first) --replace -R chain rulenum Replace rule rulenum (1 = first) in chain --list -L [chain] List the rules in a chain or all chains --flush -F [chain] Delete all rules in chain or all chains --zero -Z [chain] Zero counters in chain or all chains --new -N chain Create a new user-defined chain --delete-chain -X [chain] Delete a user-defined chain --policy -P chain target Change policy on chain to target --rename-chain -E old-chain new-chain Change chain name, (moving any references)
Options
--proto -p [!] proto protocol: by number or name, eg. `tcp' --source -s [!] address[/mask] source specification --destination -d [!] address[/mask] destination specification --in-interface -i [!] input name[+] network interface name ([+] for wildcard) --jump -j target target for rule (may load target extension) --match -m match extended match (may load extension) --numeric -n numeric output of addresses and ports --out-interface -o [!] output name[+] network interface name ([+] for wildcard) --table -t table table to manipulate (default: `filter') --verbose -v verbose mode --line-numbers print line numbers when listing --exact -x expand numbers (display exact values) --fragment -f match second or further fragments only --modprobe=<command> try to insert modules using this command --set-counters PKTS BYTES set the counter during insert/append --version -V print package version.
Interfaces
When using the -i or -o to define the physical interfaces, remember that by default:
vlan0 is the 4 LAN ports
vlan1 is the WAN port
eth1 is the WIFI
br0 is a bridge connecting the 4 LAN and the WIFI together
Examples
I think examples are the best way to demonstrate the use of iptables.
First I want to view the rules on my INPUT chain, this is the first chain traffic coming into my router will hit.
.# iptables -L INPUT
Then I might want to add a rule so that I can ssh into my router from a specific host/address outside. So I might type the following:
.# iptables -A INPUT -p tcp -s 150.100.whatever.something --dport 22 -j logaccept
So I am saying: Append to the INPUT chain a rule allowing protocol tcp, with a source of <my external IP that i want access from> traffic destined for port 22 on my router, jump to logaccept. I could have used -j ACCEPT which simply jumps to ACCEPT, but in this case I want to log it just to keep track so I use logaccept, which is a chain we have set up for this purpose.
But why doesn't it work?
Now if I type
.# iptables -L INPUT
I see my shiny new rule appended to the INPUT chain which is no good because in my case I have a rule blocking this traffic which occurs BEFORE the rule allowing it.
How do I change it? Simple.
First let's delete the rule we just made
.# iptables -L INPUT --line-numbers
will list the rules with their rule numbers. Let's say our rule is number 11
.# iptables -D INPUT 11
Clearly this Deletes rule number 11 from the input chain.
Now instead of Appending I am going to Insert my rule into the number 1 position.
.# iptables -I INPUT -p tcp -s 150.100.whatever.something --dport 22 -j logaccept
So now rule number 1 is my new rule and the other rules have all shifted down a position.
If I wanted to change the IP address or any other aspect of my ssh rule I could use the -R (Replace) option and simply type in the new rule, ie
.# iptables -R INPUT 1 -p tcp -s 100.100.200.100 --dport 22 -j ACCEPT
This would replace rule number 1 on the INPUT chain with the new rule which has a new source IP address and jumps to ACCEPT instead of logaccept.
One more example: I want to run a mini web server on my router. Let's assume that it is already running on port 8000 and I can access it from the LAN side, but not from the WAN side. With
.# iptables -I INPUT -p tcp -d 192.168.1.1 --dport 8000 -j logaccept
the port 8000 will be opened. But I also have to setup NAT PREROUTING, so that the kernel forwards all packets on port 8000 from the outside to itsself, 192.168.1.1:
.# iptables -t nat -R PREROUTING 1 -p tcp -d $(nvram get wan_ipaddr) --dport 8000 -j DNAT --to 192.168.1.1:8000
--u3gyxap: The very same thing done a bit differently (tested and working), example with port 443 and IP 192.168.1.2
.# iptables -t nat -I PREROUTING -p tcp --dport 443 -j DNAT --to 192.168.1.2:443 .# iptables -I FORWARD -p tcp -d 192.168.1.2 --dport 443 -j ACCEPT
But there's a better way to achieve this: just go to the Port Forwarding page http://192.168.1.1/Forward.asp and forward port 8000/TCP to address 192.168.1.1.
--CaScAdE 11:09, 12 Jul 2006 (CEST) Block/Deny Access to a specific IP
.# iptables -I FORWARD -d 123.456.789.123 -j DROP
Which would DROP all packages to the givin IP. Usefull to block access to whatnot.
External Resources
http://www.iptables.org/documentation/HOWTO//packet-filtering-HOWTO-7.html
http://www.iptables.org/documentation/HOWTO//netfilter-hacking-HOWTO.html