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/ip firewall filter
add chain=input connection-state=invalid action=drop comment="Drop Invalid connections"
add chain=input connection-state=established,related,untracked action=accept comment="Allow Established/Related/Untracked connections"
add chain=input protocol=icmp action=accept comment="Allow ICMP"
add chain=input protocol=tcp ports=8291,22 action=accept comment="Allow Winbox and SSH"
add chain=input action=drop comment="Drop everything else"

RouterOS also allows to filter filtering packets before connection tracking and selectively send only specific traffic to connection tracking. This allows us to significantly reduce the load on the CPU and mitigate DOS/DDoS attacks. Configuration of such rules is done in the RAW filtering table.

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FastTrack

IPv4 FastTrack handler is automatically used for marked connections. Use firewall action "fasttrack-connection" to mark connections for FastTrack. Currently, only TCP and UDP connections can be actually FastTracked (even though any connection can be marked for FastTrack). IPv4 FastTrack handler supports NAT (SNAT, DNAT, or both).

Note that not all packets in a connection can be FastTracked, so it is likely to see some packets going through a slow path even though the connection is marked for FastTrack. This is the reason why fasttrack-connection is usually followed by an identical "action=accept" rule. FastTrack packets bypass firewall, connection tracking, simple queues, queue tree with parent=global, IP accounting, IPSec, hotspot universal client, VRF assignment, so it is up to the administrator to make sure FastTrack does not interfere with other configuration.

Requirements

IPv4 FastTrack is active if the following conditions are met:

• no mesh, metarouter interface configuration;
• sniffer, torch, or traffic generator is not running;
• /tool mac-scan is not actively used;
• /tool ip-scan is not actively used;
• FastPath and Route cache is enabled under IP/Settings

Example

For example, for SOHO routers with factory default configuration, you could FastTrack all LAN traffic with this one rule placed at the top of the Firewall Filter. The same configuration accept rule is required:

/ip firewall filter add chain=forward action=fasttrack-connection connection-state=established,related
/ip firewall filter add chain=forward action=accept connection-state=established,related

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