How to Block Bittorrent Traffic with IPtables

How to Block Bittorrent Traffic with IPtables

IPTABLES is a user-space application program that allows a system administrator to configure the tables provided by the Linux kernel firewall (implemented as different Netfilter modules) and the chains and rules it stores.

Setup the IPtables Rules

To block Bittorrent traffic with IPTABLES you can edit /etc/sysconfig/iptables (CentOS) and include the following:

vim /etc/sysconfig/iptables

First you will want to add the chain right above the first rules

:RH-Firewall-1-INPUT - [0:0]

Then add the following above the COMMIT line

# Torrent ALGO Strings using Boyer-Moore
-A RH-Firewall-1-INPUT -m string --algo bm --string "BitTorrent" -j DROP
-A RH-Firewall-1-INPUT -m string --algo bm --string "BitTorrent protocol" -j DROP
-A RH-Firewall-1-INPUT -m string --algo bm --string "peer_id=" -j DROP
-A RH-Firewall-1-INPUT -m string --algo bm --string ".torrent" -j DROP
-A RH-Firewall-1-INPUT -m string --algo bm --string "announce.php?passkey=" -j DROP
-A RH-Firewall-1-INPUT -m string --algo bm --string "torrent" -j DROP
-A RH-Firewall-1-INPUT -m string --algo bm --string "announce" -j DROP
-A RH-Firewall-1-INPUT -m string --algo bm --string "info_hash" -j DROP
-A RH-Firewall-1-INPUT -m string --algo bm --string "/default.ida?" -j DROP
-A RH-Firewall-1-INPUT -m string --algo bm --string ".exe?/c+dir" -j DROP
-A RH-Firewall-1-INPUT -m string --algo bm --string ".exe?/c_tftp" -j DROP

# Torrent Keys
-A RH-Firewall-1-INPUT -m string --string "peer_id" --algo kmp -j DROP
-A RH-Firewall-1-INPUT -m string --string "BitTorrent" --algo kmp -j DROP
-A RH-Firewall-1-INPUT -m string --string "BitTorrent protocol" --algo kmp -j DROP
-A RH-Firewall-1-INPUT -m string --string "bittorrent-announce" --algo kmp -j DROP
-A RH-Firewall-1-INPUT -m string --string "announce.php?passkey=" --algo kmp -j DROP

# Distributed Hash Table (DHT) Keywords
-A RH-Firewall-1-INPUT -m string --string "find_node" --algo kmp -j DROP
-A RH-Firewall-1-INPUT -m string --string "info_hash" --algo kmp -j DROP
-A RH-Firewall-1-INPUT -m string --string "get_peers" --algo kmp -j DROP
-A RH-Firewall-1-INPUT -m string --string "announce" --algo kmp -j DROP
-A RH-Firewall-1-INPUT -m string --string "announce_peers" --algo kmp -j DROP 

Restart IPtables

/etc/init.d/iptables restart

View IPtables/Verify the Rules

iptables -L

Sample Output

...
Chain RH-Firewall-1-INPUT (0 references)
target     prot opt source               destination         
DROP       all  --  anywhere             anywhere            STRING match "BitTorrent" ALGO name bm TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "BitTorrent protocol" ALGO name bm TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "peer_id=" ALGO name bm TO 65535 
DROP       all  --  anywhere             anywhere            STRING match ".torrent" ALGO name bm TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "announce.php?passkey=" ALGO name bm TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "torrent" ALGO name bm TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "announce" ALGO name bm TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "info_hash" ALGO name bm TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "/default.ida?" ALGO name bm TO 65535 
DROP       all  --  anywhere             anywhere            STRING match ".exe?/c+dir" ALGO name bm TO 65535 
DROP       all  --  anywhere             anywhere            STRING match ".exe?/c_tftp" ALGO name bm TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "peer_id" ALGO name kmp TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "BitTorrent" ALGO name kmp TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "BitTorrent protocol" ALGO name kmp TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "bittorrent-announce" ALGO name kmp TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "announce.php?passkey=" ALGO name kmp TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "find_node" ALGO name kmp TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "info_hash" ALGO name kmp TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "get_peers" ALGO name kmp TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "announce" ALGO name kmp TO 65535 
DROP       all  --  anywhere             anywhere            STRING match "announce_peers" ALGO name kmp TO 65535