Some socket options
In fact, both network socket client & server will call a set_common_sockopts function which will set some socket options according to command line options:
void
set_common_sockopts(int s, int af)
{
int x = 1;
if (Sflag) {
if (setsockopt(s, IPPROTO_TCP, TCP_MD5SIG,
&x, sizeof(x)) == -1)
err(1, NULL);
}
if (Dflag) {
if (setsockopt(s, SOL_SOCKET, SO_DEBUG,
&x, sizeof(x)) == -1)
err(1, NULL);
}
if (Tflag != -1) {
if (af == AF_INET && setsockopt(s, IPPROTO_IP,
IP_TOS, &Tflag, sizeof(Tflag)) == -1)
err(1, "set IP ToS");
else if (af == AF_INET6 && setsockopt(s, IPPROTO_IPV6,
IPV6_TCLASS, &Tflag, sizeof(Tflag)) == -1)
err(1, "set IPv6 traffic class");
}
if (Iflag) {
if (setsockopt(s, SOL_SOCKET, SO_RCVBUF,
&Iflag, sizeof(Iflag)) == -1)
err(1, "set TCP receive buffer size");
}
if (Oflag) {
if (setsockopt(s, SOL_SOCKET, SO_SNDBUF,
&Oflag, sizeof(Oflag)) == -1)
err(1, "set TCP send buffer size");
}
if (ttl != -1) {
if (af == AF_INET && setsockopt(s, IPPROTO_IP,
IP_TTL, &ttl, sizeof(ttl)))
err(1, "set IP TTL");
else if (af == AF_INET6 && setsockopt(s, IPPROTO_IPV6,
IPV6_UNICAST_HOPS, &ttl, sizeof(ttl)))
err(1, "set IPv6 unicast hops");
}
if (minttl != -1) {
if (af == AF_INET && setsockopt(s, IPPROTO_IP,
IP_MINTTL, &minttl, sizeof(minttl)))
err(1, "set IP min TTL");
else if (af == AF_INET6 && setsockopt(s, IPPROTO_IPV6,
IPV6_MINHOPCOUNT, &minttl, sizeof(minttl)))
err(1, "set IPv6 min hop count");
}
}
Below is the table which summarize these options:
| Variable | Command option | Socket level & option | Meaning |
| Sflag | -S | IPPROTO_TCP&TCP_MD5SIG | Uses TCP MD5 signatures per RFC 2385 |
| Dflag | -D | SOL_SOCKET&SO_DEBUG | Enables recording of debugging information |
| Tflag | -T | IPPROTO_IP&IP_TOS IPPROTO_IPV6&IPV6_TCLASS | Changes IPv4 TOS value (refer process_tos_opt function) or sets IPv6 traffic class field |
| Iflag | -I length | SOL_SOCKET&SO_RCVBUF | Sets buffer size for input |
| Oflag | -O length | SOL_SOCKET&SO_SNDBUF | Sets buffer size for output |
| ttl | -M ttl | IPPROTO_IP&IP_TTL IPPROTO_IPV6&IPV6_UNICAST_HOPS | Sets the TTL / hop limit of outgoing packets |
| minttl | -m minttl | IPPROTO_IP&IP_MINTTL IPPROTO_IPV6&IPV6_MINHOPCOUNT | Discards packets with a TTL lower than the option value |