Each rule consists of two parts - the matcher which matches traffic flow against given conditions and the action which defines what to do with the matched packet. The firewall operates by means of firewall rules. rate at which packets arrive and sequence numbers.interface the packet arrived from or left through.protocol options (ICMP type and code fields, TCP flags, IP options, and MSS).IP addresses (network or list) and address types (broadcast, local, multicast, unicast).MikroTik RouterOS has very powerful firewall implementation with features including: Properly configured firewall plays a key role in efficient and secure network infrastructure deployment. Firewalls are used as a means of preventing or minimizing the security risks inherent in connecting to other networks. Such break-ins may result in private data being stolen and distributed, valuable data being altered or destroyed, or entire hard drives being erased. Whenever different networks are joined together, there is always a threat that someone from outside of your network will break into your LAN. Network firewalls keep outside threats away from sensitive data available inside the network.

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Along with the Network Address Translation (NAT), it serves as a tool for preventing unauthorized access to directly attached networks and the router itself as well as a filter for outgoing traffic. The firewall implements stateful (by utilizing connection tracking) and stateless packet filtering and thereby provides security functions that are used to manage data flow to, from and through the router.

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