tcp Probes

The tcp probes are described in the following table.

Table 11-66 tcp Probes

Probe	Description
state-change	Fires a TCP session changes its TCP state. Previous state is noted in the tcplsinfo_t * probe argument. The tcpinfo_t * and ipinfo_t * arguments are NULL.
send	Fires when TCP sends a segment (either control or data).
receive	Fires when TCP receives a segment (either control or data).
connect-request	Fires when a TCP active open is initiated by sending an initial SYN segment. The tcpinfo_t * and ipinfo_t * probe arguments represent the TCP and IP headers associated with the initial SYN segment sent.
connect-established	Fires when either of the following occurs: either a TCP active OPEN succeeds - the initial SYN has been sent and a valid SYN,ACK segment has been received in response. TCP enters the ESTABLISHED state, and the tcpinfo_t * and ipinfo_t * probe arguments represent the TCP and IP headers associated with the SYN,ACK segment received; or a simultaneous active OPEN succeeds and a final ACK is received from the peer TCP. TCP has entered the ESTABLISHED state and the tcpinfo_t * and ipinfo_t * probe arguments represent the TCP and IP headers of the final ACK received. The common thread in these cases is that an active-OPEN connection is established at this point, in contrast with tcp:::accept-established which fires on passive connection establishment. In both of the preceding cases, the TCP segment that is presented via the tcpinfo_t * is the segment that triggers the transition to ESTABLISHED - the received SYN,ACK in the first case and the final ACK segment in the second.
connect-refused	A TCP active OPEN connection attempt was refused by the peer - a RST segment was received in acknowledgment of the initial SYN. The tcpinfo_t * and ipinfo_t * probe arguments represent the TCP and IP headers associated with the RST,ACK segment received.
accept-established	A passive open has succeeded - an initial active OPEN initiation SYN has been received, TCP responded with a SYN,ACK and a final ACK has been received. TCP has entered the ESTABLISHED state. The tcpinfo_t * and ipinfo_t * probe arguments represent the TCP and IP headers associated with the final ACK segment received.
accept-refused	An incoming SYN has arrived for a destination port with no listening connection, so the connection initiation request is rejected by sending a RST segment acknowledging the SYN. The tcpinfo_t * and ipinfo_t * probe arguments represent the TCP and IP headers associated with the RST segment sent.

The send and receive probes trace packets on physical interfaces and also packets on loopback interfaces that are processed by tcp. On Oracle Solaris, loopback TCP connections can bypass the TCP layer when transferring data packets - this is a performance feature called tcp fusion; these packets are also traced by the tcp provider.