diff options
Diffstat (limited to 'health/guides/tcp/10s_ipv4_tcp_resets_sent.md')
| -rw-r--r-- | health/guides/tcp/10s_ipv4_tcp_resets_sent.md | 43 |
1 files changed, 0 insertions, 43 deletions
diff --git a/health/guides/tcp/10s_ipv4_tcp_resets_sent.md b/health/guides/tcp/10s_ipv4_tcp_resets_sent.md deleted file mode 100644 index 9a941694e..000000000 --- a/health/guides/tcp/10s_ipv4_tcp_resets_sent.md +++ /dev/null @@ -1,43 +0,0 @@ -### Understand the alert - -TCP reset is an abrupt closure of the session. It causes the resources allocated to the connection to be immediately released and all other information about the connection is erased. - -The Netdata Agent monitors the average number of sent TCP RESETS over the last 10 seconds. This can indicate a port scan or that a service running on the system has crashed. Additionally, it's a result of a high number of sent TCP RESETS. Furthermore, it can also indicate a SYN reset attack. - -### More about TCP Resets - -TCP uses a three-way handshake to establish a reliable connection. The connection is full duplex, and both sides synchronize (SYN) and acknowledge (ACK) each other. The exchange of these four flags -is performed in three steps: SYN, SYN-ACK, and ACK. - -When an unexpected TCP packet arrives at a host, that host usually responds by sending a reset packet back on the same connection. A reset packet is one with no payload and with the RST bit set in the TCP header flags. There are a few circumstances in which a TCP packet might not be expected. The most common cases are: - -1. A TCP packet received on a port that is not open. -2. An aborting connection -3. Half opened connections -4. Time wait assassination -5. Listening endpoint Queue is Full -6. A TCP Buffer Overflow - -Basically, A TCP Reset usually occurs when a system receives data which doesn't agree with its view of the connection. - -When your system cannot establish a connection it will retry by default `net.ipv4.tcp_syn_retries` times. - -### Troubleshoot the alert - -- Use tcpdump to capture the traffic and use Wireshark to inspect the network packets. You must stop the capture after a certain observation period (60s up to 5 minutes). This command will create a dump file which can be interpreted by Wireshark that contains all the TCP packets with RST flag set. - ``` - tcpdump -i any 'tcp[tcpflags] & (tcp-rst) == (tcp-rst)' -s 65535 -w output.pcap - ``` - -- Identify which application sends TCP resets - -1. Check the instances of `RST` events of the TCP protocol. Wireshark also displays the ports on which the two systems tried to establish the TCP connection, (XXXXXX -> XXXXXX). -2. To check which application is using this port, run the following code: - ``` - lsof -i:XXXXXX -P -n - ``` -### Useful resources - -1. [TCP reset explanation](https://www.pico.net/kb/what-is-a-tcp-reset-rst/) -2. [TCP 3-way handshake on wikipedia](https://en.wikipedia.org/wiki/Handshaking) -3. [Read more about Wireshark here](https://www.wireshark.org/)
\ No newline at end of file |