| Demonstrations of tcpdrop, the Linux BPF/bcc version. |
| |
| |
| tcpdrop prints details of TCP packets or segments that were dropped by the |
| kernel, including the kernel stack trace that led to the drop: |
| |
| # ./tcpdrop.py |
| TIME PID IP SADDR:SPORT > DADDR:DPORT STATE (FLAGS) |
| 20:49:06 0 4 10.32.119.56:443 > 10.66.65.252:22912 CLOSE (ACK) |
| tcp_drop+0x1 |
| tcp_v4_do_rcv+0x135 |
| tcp_v4_rcv+0x9c7 |
| ip_local_deliver_finish+0x62 |
| ip_local_deliver+0x6f |
| ip_rcv_finish+0x129 |
| ip_rcv+0x28f |
| __netif_receive_skb_core+0x432 |
| __netif_receive_skb+0x18 |
| netif_receive_skb_internal+0x37 |
| napi_gro_receive+0xc5 |
| ena_clean_rx_irq+0x3c3 |
| ena_io_poll+0x33f |
| net_rx_action+0x140 |
| __softirqentry_text_start+0xdf |
| irq_exit+0xb6 |
| do_IRQ+0x82 |
| ret_from_intr+0x0 |
| native_safe_halt+0x6 |
| default_idle+0x20 |
| arch_cpu_idle+0x15 |
| default_idle_call+0x23 |
| do_idle+0x17f |
| cpu_startup_entry+0x73 |
| rest_init+0xae |
| start_kernel+0x4dc |
| x86_64_start_reservations+0x24 |
| x86_64_start_kernel+0x74 |
| secondary_startup_64+0xa5 |
| |
| 20:49:50 12431 4 127.0.0.1:8198 > 127.0.0.1:48280 CLOSE (RST|ACK) |
| tcp_drop+0x1 |
| tcp_v4_do_rcv+0x135 |
| __release_sock+0x88 |
| release_sock+0x30 |
| inet_stream_connect+0x47 |
| SYSC_connect+0x9e |
| sys_connect+0xe |
| do_syscall_64+0x73 |
| entry_SYSCALL_64_after_hwframe+0x3d |
| |
| [...] |
| |
| The last two columns show the state of the TCP session, and the TCP flags. |
| These two examples show packets arriving for a session in the closed state, |
| that were dropped by the kernel. |
| |
| This tool is useful for debugging high rates of drops, which can cause the |
| remote end to do timer-based retransmits, hurting performance. |
| |
| |
| USAGE: |
| |
| # ./tcpdrop.py -h |
| usage: tcpdrop.py [-h] |
| |
| Trace TCP drops by the kernel |
| |
| optional arguments: |
| -h, --help show this help message and exit |
| |
| examples: |
| ./tcpdrop # trace kernel TCP drops |
