TCP Flags
| Flag | Meaning | When set |
|---|---|---|
| SYN | Synchronize | |
| ACK | Acknowledge | |
| FIN | Finish | |
| RST | Reset | |
| PSH | Push | |
| URG | Urgent |
TCP Connection States
| State | Description |
|---|---|
| CLOSED | |
| LISTEN | |
| SYN_SENT | |
| SYN_RECEIVED | |
| ESTABLISHED | |
| FIN_WAIT_1 | |
| FIN_WAIT_2 | |
| TIME_WAIT | |
| CLOSE_WAIT | |
| LAST_ACK |
Key Timers and Durations
| Timer | Default | Purpose |
|---|---|---|
| MSL (Maximum Segment Lifetime) | 30–60s | |
| TIME_WAIT | 2×MSL = 60–120s | |
| TCP keepalive idle | 7200s (2h) | |
| TCP keepalive interval | 75s | |
| TCP keepalive count | 9 probes | |
| Nagle delay | up to 40ms | |
| SYN timeout | ~75s (with retries) |
RTT Latencies (Approximate)
| Path | RTT |
|---|---|
| Loopback (127.0.0.1) | |
| Same host, different process | |
| Same rack (LAN) | |
| Same datacenter | |
| Same region, different AZ | |
| US West → US East | |
| US → Europe | |
| US → Asia |