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Chapter 6Disabling TCP delayed ACK will greatly improve TCP performance,especially when using SAMBA. But this violates RFC1122 guidelines(RFC1122—"Requirements for Internet Hosts – Communication layers"can be found at http://tools.ietf.org/html/rfc1122). You maynot want to disable this feature unless you really have to.RFC 1323 ExtensionsRFC 1323 specifies guidelines (specifically, TCP window scaling) for gaining highTCP/IP performance over large bandwidth*delay paths. This extension is enabled inFreeBSD 7 by default. However, you may want to disable these extensions in somecases to experience network connection stalls.# sysctl net.inet.tcp.rfc1323=0net.inet.tcp.rfc1323: 1 -> 0TCP Listen Queue SizeThe incoming connection queue size is limited to 128 connections by default. This isvery low for busy servers that may need to handle some thousand new connectionsper second. The default value can be changed by modifying the kern.ipc.somaxconn variable:# sysctl kern.ipc.somaxconn=1024kern.ipc.somaxconn: 128 -> 1024TCP Buffer SpaceThe net.inet.tcp.sendspace and net.inet.tcp.recvspace variables control thesend and receive buffer size allowed for any TCP connection.# sysctl net.inet.tcp.sendspace=65536net.inet.tcp.sendspace: 32768 -> 65536The default value for sendspace and recvspace are 32768 and 65536 respectively.It is advised not to increase the default buffer sizes, if you are running a busyserver that is serving many network connections simultaneously. Increasingbuffer sizes will cause more kernel memory usage. In the case of too manyconcurrent connections, your system may end up out of memory, due to inactiveTCP connections. However, if you were serving a server with a few clients andhigh-speed network connectivities, increasing buffer sizes would lead to greatperformance improvements.[ 95 ]