Fast path is an alternate routing mechanism that provides some advantages over a routing table.
Using fast path provides the following advantages:
How fast path works with NFS-over-UDP
NFS-over-UDP traffic uses fast path only when sending a reply to a request. The reply packet is sent out on the same interface that the request packet came in on. For example, a storage system named toaster uses the toaster-e1 interface to send reply packets in response to NFS-over-UDP requests received on the toaster-e1 interface.
How fast path works with TCP
Data ONTAP can use fast path on every TCP packet transmitted except the very first SYN packet (if Data ONTAP initiates a connection). The interface used to transmit a packet is the same interface the last packet was received on.
For TCP connections, Data ONTAP automatically turns off fast path if it detects that using fast path in a network setup is not optimal.
How fast path affects Telnet sessions and ping
If fast path is enabled and the default router stops working, you might notice that Telnet sessions to your storage system can still be established from a non-local subnet, even though you cannot use the ping utility to communicate with your storage system's interfaces. This happens because the ping utility uses routing table lookups.
Fast path not compatible with asymmetric routing
If fast path is enabled on your storage system in an asymmetric network, the destination MAC address of the response packet will be that of the router that forwarded the incoming packet. However, in asymmetric networks the router forwarding packets to your storage system is not the one forwarding the packets that the storage system sends back. In this case, you must disable fast path.