How To Enable FastTrack - MikroTik Script RouterOS
To mark a connection as fast-tracked new action was implemented "fasttrack-connection" for firewall filter and mangle. Currently, only IPv4 TCP and UDP connections can be fast-tracked and to maintain connection tracking entries some random packets will still be sent to a slow path. This must be taken into consideration when designing firewalls with enabled "fasttrack".
FastTrack handler also supports source and destination NAT, so special exceptions for NATed connections are not required.
Traffic that belongs to a fast-tracked connection travels in FastPath, which means that it will not be visible by other router L3 facilities (firewall, queues, IPsec, IP accounting, VRF assignment, etc).
The easiest way to start using this feature on home routers is to enable "fasttrack" for all established, related connections:
/ip firewall filter
add chain=forward action=fasttrack-connection connection-state=established,related \
add chain=forward action=accept connection-state=established,related \
Notice that the first rule marks established/related connections as fast-tracked, the second rule is still required to accept packets belonging to those connections. The reason for this is that, as was mentioned earlier, some random packets from fast-tracked connections are still sent the slow path way and only UDP and TCP are fast-tracked, but we still want to accept packets for other protocols.
After adding "fasttrack" rule special dummy rule appeared at the top of the list. This is not an actual rule, it is for visual information showing that some of the traffic is traveling FastPath and will not reach other firewall rules.
These rules appear as soon as there is at least one fast-tracked connection tracking entry and will disappear after the last fast-tracked connection times out in the connection table.