The TCP/IP configuration of SVR4 is similar to the previous two systems, but fewer options are available. In the file /etc/conf/pack.d/ip/space.c two constants can be defined, and the kernel must then be rebuilt and rebooted.
The value of this constant initializes the kernel variable ipforwarding. If 0 (default), IP datagrams are not forwarded. If 1, forwarding is always enabled.
The value of this constant initializes the kernel variable ipsendredirects. If 1 (default), the host will send ICMP redirects when forwarding IP datagrams. If 0, ICMP redirects are not sent.
Many of the variables that we've described in the previous two sections are defined in the kernel, but one must patch the kernel to modify them. For example, there is a variable named tcp_keepidle with a value of 14400.