Iptables manual reference

This iptables is very similar to ipchains by Rusty Russell. The main difference is that the chains INPUT and OUTPUT are only traversed for packets coming into the local host and originating from the local host respectively. Hence every packet only passes through one of the three chains (except loopback traffic, which involves both INPUT and OUTPUT chains); previously a . The iptables service starts before any DNS-related services when a Linux system is booted. This means that firewall rules can only reference numeric IP addresses (for example, ). Domain names (for example, www.doorway.ru) in such rules produce errors. iptables [-t table] -P chain target. iptables [-t table] -E old-chain-name new-chain-name. rule-specification = [matches ] [target] match = -m matchname [per-match-options] target = -j targetname [per-target-options] DESCRIPTION Iptables and ip6tables are used to set up, maintain, and inspect the tables of IPv4 and IPv6 packet filter rules in the Linux kernel. Several .

The set is then referenced in an iptables command as follows: ~]# iptables -A INPUT -m set --set my-block-set src -j DROP If the set is used more than once a saving in configuration time is made. If the set contains many entries a saving in processing time is made. iptables -A INPUT p tcp -s! /24 --destination-port 21 -j DROP. Block outgoing traffic to a port. If you want to forbid outgoing traffic to port 25, this is useful, in the case you are running a Linux firewall for your office, and you want to stop virus from sending emails. iptables -A OUTPUT -m bpf --bytecode '4,48 0 0 9,21 0 1 6,6 0 0 1,6 0 0 0' -j ACCEPT Or instead, you can invoke the nfbpf_compile utility. iptables -A OUTPUT -m bpf --bytecode "`nfbpf_compile RAW 'ip proto 6'`" -j ACCEPT Or use tcpdump -ddd. In that case, generate BPF targeting a device with the same data link type as the xtables match.

27 thg 8, For example, if a user attempts to SSH into your PC/server, iptables will attempt to match the IP address and port to a rule in the input chain. On contemporary Linux systems, the iptables program provides methods for managing the Linux Kernel's Issue the following commands to change this policy. The term iptables is also commonly used to inclusively refer to the kernel-level components. x_tables is the name of the kernel module carrying the shared code.