Current File : //usr/share/doc/bpfcc-tools/examples/doc/tcpdrop_example.txt
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 [-4 | -6] [-h]
Trace TCP drops by the kernel
optional arguments:
-4, --ipv4 trace IPv4 family only
-6, --ipv6 trace IPv6 family only
-h, --help show this help message and exit
examples:
./tcpdrop # trace kernel TCP drops
./tcpdrop -4 # trace IPv4 family only
./tcpdrop -6 # trace IPv6 family only
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