Warning: If you are logged in via SSH, the following will immediately disconnect the SSH session. Dropping all traffic and specifying what is allowed is the best way to make a secure firewall. Similar to the previous chains, we set the default policy for the INPUT chain to DROP in case something somehow slips by our rules. This is less secure, but is highly compatible with many systems. In this simple example, we will allow all outbound traffic by setting the default policy for the OUTPUT chain to ACCEPT. A secure set of rules for a desktop system, laptop system, cloud server and home/on-prem server would all be very different. However, properly setting up an OUTPUT chain requires information about the intended use of the system. The OUTPUT chain can be a powerful tool for filtering outbound traffic, especially for servers and other devices which do not run web browsers or peer-to-peer tools that need to connect to arbitrary destinations on the internet. For a single machine, however, we simply set the policy of the FORWARD chain to DROP and move on: If you want to set up your machine as a NAT gateway, please look at #Setting up a NAT gateway. We pick these just to match the protocols we want handle with them in the later rules, which are specified with the protocol options, e.g.

The chains can of course have arbitrary names.

Creating necessary chainsįor this basic setup, we will create two user-defined chains that we will use to open up ports in the firewall. Also, rules have an associated runtime cost, so rules should not be reordered solely based upon empirical observations of the byte/packet counters. Of course there is a limit, depending on the logic that is being implemented. Note: Because iptables processes rules in linear order, from top to bottom within a chain, it is advised to put frequently-hit rules near the start of the chain. If there are rules, you may be able to reset the rules by loading a default rule set: Num pkts bytes target prot opt in out source destinationĬhain FORWARD (policy ACCEPT 0 packets, 0 bytes)Ĭhain OUTPUT (policy ACCEPT 82 packets, 8672 bytes) # iptables -nvL -line-numbers Chain INPUT (policy ACCEPT 156 packets, 12541 bytes)

# iptables-save # Generated by iptables-save v1.4.19.1 on Thu Aug 1 19:28:53 2013 To check the current ruleset and verify that there are currently no rules run the following: This article assumes that there are currently no iptables rules set. All stock Arch Linux kernels have iptables support.įirst, install the userland utilities iptables or verify that they are already installed. Note: Your kernel needs to be compiled with iptables support.

Look n stop 防火墙 ipv6 连不通