- FastPath is an ability for the bridge to quickly forward the incoming packet to an egress port, bypassing many processing routines and, therefore, speeding up the process.
- FastTrack or "Fast path for Connection Tracking" is an ability to quickly route packets within the established IPv4 TCP/UDP connections (and someday, hopefully, IPv6 too).
FastPath and VLAN Filtering
- If the connection goes through a bridge, FastPath is required for FastTrack.
- Up to RouterOS 7.1 (including), setting vlan-filtering=yes on a bridge disables FastPath, and, therefore, preventing FastTrack for all the connections going through the bridge.
- Layer 2 Hardware Offloading (L2HW) does NOT care about FastPath. If the switch chip is capable of VLAN filtering (e.g., CRS3xx series), it does that on the hardware level, without invoking software (CPU) at all. For instance, setting vlan-filtering=yes to the hardware-offloaded bridge on CRS317 keeps the wire-speed performance. However, doing the same on CCR1009 decreases the forwarding speed drastically.
- Since Layer 3 Hardware Offloading (L3HW) depends on L2 hardware processing, it does not care about FastPath either. That's why CRS3xx supports hardware Inter-VLAN routing at near to wire speed.
- However, the above statement does not apply for FastTrack HW Offloading. FastTrack HW Offloading requires FastTrack connections in the first place; the latter depends on FastPath, which, in turn, does not support VLAN filtering. In other words, setting vlan-filtering=yes disables FastPath, which, in turn, disables FastTrack and FastTrack offloading.
A Better Tomorrow
Ending this post with good news: We have implemented VLAN filtering support by FastPath, and it will be available for testing soon.
UPDATE: Already available in RouterOS 7.2rc2.