12/9/2023 0 Comments Mikrotik basic firewall![]() NAT changes source and destination IPs and ports. Mangling can also change some basic packet properties, such as TTL, DSCP values etc. Mangle has two additional major chains: 'prerouting', which contains packets before destination NAT runs and a routing decision is made, and 'postrouting', which contains all packets after all other chains have been traversed and the router knows where to output the packet. Since the firewall is stateful, you can also use connection states, such as 'new', 'established' and 'related'.įirewall mangling marks packets/connections with markers that are not transmitted over the wire (they are internal to the firewall only), but are used by many other RouterOS portions to make decisions. Some common ones are 'protocol', 'dst-post', 'in-interface' etc. To specify to which exact packets an action should be applied, lots of filters are available. Firewall rules apply actions to packets, the most common ones are 'accept' and 'drop'. The basic idea is that in firewall filtering there are three major chains: 'forward' contains all traffic flowing through the firewall (traffic that is not initiated by the firewall, and doesn't terminate on the firewall), 'input' contains all traffic directly aimed at the firewall and 'output' contains all traffic created by the firewall itself. If you have a rule higher above it that accepts all traffic coming in the WAN interface, or in the forward chain etc. ![]() Of course that rule may not work depending on context. Code: Select all /ip firewall filter add chain=forward in-interface=WAN protocol=tcp dst-port=23 action=drop ![]()
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