TOPIC NETWORKING
TCP Handshake how two machines agree to talk
IN 10 SECONDS
Before sending any data, the client and server exchange three packets (SYN, SYN-ACK, ACK) to synchronize sequence numbers and establish a reliable session.
GOTCHA SYN flood attacks overwhelm servers by sending thousands of SYNs but never sending the final ACKs, exhausting connection queues.
HOW A HANDSHAKE FLOWS
01 Client sends a SYN packet with a random sequence number to initiate connection.
02 Server responds with SYN-ACK, acknowledging the client's SYN and sending its own sequence number.
03 Client sends an ACK packet back. The connection is now established.
POKE IT YOURSELF
netstat -anp | grep SYN_RECV — check for half-open connections (potential SYN flood)
tcpdump -i any tcp[tcpflags] & tcp-syn != 0 — capture raw SYN packets on the wire
Drill this topic →
~60 sec read