Kernel Configuration

Kernel Configuration

You can change several parameters to customize network behavior for local configurations. The parameters listed below are in the /var/sysgen/master.d/bsd configuration file.For details on reconfiguring the kernel after changing this file, see IRIX Admin: System Configuration and Operation.

Kernel Tunable Options

There are four kernel parameters which directly affect the network performance: tcp_sendspace, tcp_recvspace, udp_sendspace, and udp_recvgrams.

These parameters determine the default amount of buffer space used by TCP (SOCK_STREAM) and UDP (SOCK_DGRAM) sockets. The tcp_sendspace and tcp_recvspace parameters define the initial buffer space allocated to a socket. The udp_sendspace parameter defines the default maximum size of UDP datagrams that can be sent. The udp_recvgrams parameter determines the number of maximally sized UDP datagrams that can be buffered in a UDP socket. The total receive buffer size in bytes for each UDP socket is the product of udp_sendspace and udp_recvgrams. A program can increase or decrease the send buffer and receive buffer sizes for a socket with the SO_SNDBUF and SO_RCVBUF options to the setsockopt(2) system call. Many older TCP implementations have problems with large TCP sendspace/recvspace values. This should be decreased from 60 to 24 in environments where older stations have problems communicating.

For 4.2BSD compatibility, the IRIX system limits its initial TCP sequence numbers to positive numbers.

PC Connectivit y

Many industry-standard personal computers with TCP/IP implementations experience difficulty connecting to Silicon Graphics workstations and servers. This is because of the increased size of the tcp_sendspace and tcp_recvspace variables in the IRIX file /var/sysgen/master.d/bsd.

To allow your personal computers to connect successfully, change the values of the above variables from the default (60 * 1024) to (24 * 1024) and reconfigure the kernel with the lboot command. For more information on reconfiguring these values, see IRIX Admin: System Configuration and Operation.