To the credit of MikroTik engineers, they promptly issue patches fixing newly-discovered bugs. Today, I will explain how to protect your network against known and yet-unknown vulnerabilities in RouterOS.
However, it is not enough just to find a bug – it must be neutralized. The more complex and specific testing rule (further down the list) now only needs to test the first packet of a connection.Īlso, when creating rules, some matching processes performed on a packet will take more CPU than another.Firmware of popular routers often contains errors identified by security researchers on a regular basis. Most packets belonging to an already tested connection will have already had it’s first packet tested against some very specific match parameter and subsequently ‘accepted’ therefore will have a connection type of established (as a result of the connection tracking engine) and therefore if already tested and accepted, all remaining packets of that connection can go into the ‘established and related’ rule. This is why it is wise to create a rule to match for ‘established and related’ packets and place it at the top of the list. In this way, highly popular traffic types will be matched early and reduce CPU usage as it will be matched sooner, rather than later. Naturally, if no firewalling is required at all, using the features of ‘fast-path’ will ensure the packets are forwarded to the correct interface at near wire speed and will avoid being processed by the CPU at all.īut if some firewall rules are required, then there is a basic rule of thumb that the most popular, most frequently matched rules should be higher in the list, compared to the lesser matched rules. This can require a higher processing power than necessary and if the CPU reaches 100%, packet loss will occur. For high packet count traffic, this could mean that all those packets are having to be processed many times before it is matched.
Every new packet is tested against each rule until a match is found.
When creating complex firewall rules on MikroTik routers, especially those with high levels of packet throughput, it is important that any rules are processed in an efficient manner.
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