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diff --git a/health/guides/tcp/10s_ipv4_tcp_resets_received.md b/health/guides/tcp/10s_ipv4_tcp_resets_received.md deleted file mode 100644 index c17954f2d..000000000 --- a/health/guides/tcp/10s_ipv4_tcp_resets_received.md +++ /dev/null @@ -1,67 +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. - -### 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 - ``` - -- Counter measure on malicious TCP resets - -SYN cookie is a technique used to resist IP address spoofing attacks. In particular, the use of SYN cookies allows a server to avoid dropping connections when the SYN queue fills up. - -Enable SYN cookies in Linux: - - 1. Check if your system has the SYN cookies service enabled. If the value is 1, then the service is enabled, if not proceed to step 2. - ``` - cat /proc/sys/net/ipv4/tcp_syncookies - ``` - - 2. Bump this `net.ipv4.tcp_syncookies=1` value under `/etc/sysctl.conf` - - 3. Apply the configuration - ``` - sysctl -p - ``` - -Enable SYN cookies in FreeBSD: - - 1. Check if your system has the SYN cookies service enabled. If the value is 1, then the service is enabled, if not proceed to step 2. - ``` - sysctl net.inet.tcp.syncookies_only - ``` - - 2. Bump this `net.inet.tcp.syncookies_only=1` value under `/etc/sysctl.conf` - - 3. Apply the configuration - ``` - /etc/rc.d/sysctl reload - ``` - -The use of SYN cookies does not break any protocol specifications, and therefore should be compatible with all TCP implementations. There are, however, a few caveats that take effect when SYN cookies are in use. - -### 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) |