TCP fastpath loopback

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The transmission control protocol (TCP) fastpath loopback option is used to achieve better performance for the loopback traffic.

The tcp_fastlo network tunable parameter permits the TCP loopback traffic to reduce the distance for the entire TCP/IP stack (protocol and interface) to achieve better performance.

The application does not require any changes when using this option. When enabled, the TCP loopback traffic is handled similarly to the UNIX domain implementation.

A second option, tcp_fastlo_crosswpar, enables TCP fastpath loopback to work between workload partitions (wpar). The tcp_fastlo option must be enabled for the tcp_fastlo_crosswpar option to function.

To enable the fastpath of the TCP loopback traffic use the no command, by entering:

# no -o tcp_fastlo=1

This option is dynamic and is effective for future TCP connections.

To enable the fastpath of the TCP loopback traffic between workload partitions (wpar), use the no command, by entering:

# no -o tcp_fastlo_crosswpar=1

Note: The two options tcp_fastlo and tcp_fastlo_crosswpar are currently disabled (set to 0) by default. These options is reserved for future AIX releases.

The TCP fastpath loopback traffic is accounted for in separate statistics by the netstat command, when the TCP connection is open. It is not accounted to the loopback interface. However, the TCP fastpath loopback does use the TCP/IP and loopback device to establish and terminate the fast path connections, therefore these packets are accounted for in the normal manner.