Dynamically configuring the network stack
To change the default network stack parameters, use the sysctl() function or sysctlbyname() function that are declared in the header file sysroot-*-kos/include/sys/sysctl.h from the KasperskyOS SDK. The parameters that can be changed are presented in the table below.
Configurable network stack parameters
Parameter name | Parameter description |
|---|---|
| Maximum time to live (TTL) of sent IP packets. It does not affect the ICMP protocol. |
| If its value is set to |
| MSS value (in bytes) that is applied if only the communicating side failed to provide this value when opening the TCP connection, or if "Path MTU Discovery" mode (RFC 1191) is not enabled. This MSS value is also forwarded to the communicating side when opening a TCP connection. |
| Minimum MSS value, in bytes. |
| If its value is set to |
| Number of times to send test messages (Keep-Alive Probes, or KA) without receiving a response before the TCP connection will be considered closed. If its value is set to |
| TCP connection idle period, after which keep-alive probes begin. This is defined in conditional units, which can be converted into seconds via division by the |
| Time interval between recurring keep-alive probes when no response is received. This is defined in conditional units, which can be converted into seconds via division by the |
| Size of the buffer (in bytes) for data received over the TCP protocol. |
| Size of the buffer (in bytes) for data sent over the TCP protocol. |
| Size of the buffer (in bytes) for data received over the UDP protocol. |
| Size of the buffer (in bytes) for data sent over the UDP protocol. |
MSS configuration example:
static const int mss_max = 1460;
static const int mss_min = 100;
static const char* mss_max_opt_name = "net.inet.tcp.mssdflt";
static const char* mss_min_opt_name = "net.inet.tcp.minmss";
int main(void)
{
...
if ((sysctlbyname(mss_max_opt_name, NULL, NULL, &mss_max, sizeof(mss_max)) != 0) ||
(sysctlbyname(mss_min_opt_name, NULL, NULL, &mss_min, sizeof(mss_min)) != 0))
{
ERROR(START, "Can't set tcp default maximum/minimum MSS value.");
return EXIT_FAILURE;
}
}
